Deliverables Establishing Environmental Impact Assessment and...

645691 ‐ ECOFISH Project MSCA‐RISE‐2014: Marie Sklodowska‐Curie

Deliverables 2.1 Establishing Environmental Impact Assessment and Habitat Modification

Training design and optimization of aquaponics production systems

Aquaponics is a combination of the words aquaculture (rearing fish) and hydroponics

(growing plants in water without soil) and the eco‐innovative technology behind the concept

(Thorarinsdottir et al., 2015) is the integration of hydroponic plant production into recirculating

aquaculture systems (RAS). Aquaponics is a man‐made ecosystem of plants, fish, bacteria,

sometimes worms and/or other organisms, growing together symbiotically (Thorarinsdottir et al.,

2015).

Aquaponics is also a biointegrated food production system that links recirculating

aquaculture with hydroponic vegetable, flower, and/or herb production (Diver 2006).

Research in aquaponics began in the 1970s, and the integration of aquaculture and the

hydroponic cultivation of plants has been examined repeatedly over the past three decades with a

wide variety of system designs, plant and aquatic animal species, and experimental protocols

(Rakocy and Hargreaves 1993). McMurtry et al. (1993, 1997) created the firstknown closed‐loop

aquaponic system (called an aqua‐vegeculture system) in 1986 that channeled tilapia effluent into

sand‐planted tomato beds.

Recently, the incorporation of recirculated fish with vegetable hydroponics production has

become an interesting model to private sector, aquaculture and environmental scientists (Rakocy

et al., 2006; Bakhsh and Shariff, 2007; Endut et al., 2009).

Classic RAS are designed to rear large quantities of fish in relatively small volumes of water

(Rakocy et al., 2006), thus making water treatment a necessity in order to remove the toxic products

that result from fish waste and unconsumed fish feed. Integrated aquaponic systems control the

accumulation of waste nutrients from fish culture (Rakocy and Hargreaves, 1993) which may lower

overall consumption of water (McMurtry et al., 1997) and produce additional, saleable crops

(Rakocy and Hargreaves, 1993).

Production of multiple crops via the combination of aquaculture and hydroponic

technologies synergizes he economic value of both enterprises (Rupasinghe and Kennedy, 2010).

Adler et al. (2000) have also concluded that the hydroponic system drives potential profitability of

the combined system with major annual returns deriving from plant production. Also, integrated

systems use water more efficiently through the interacting activities of fish and plants. (Endut et al.,

2010). The addition of water to a fish tank to satisfy the oxygen requirements depends on the

oxygen consumption of the fish, the oxygen concentration in the inlet water and the lowest

acceptable concentration in the outlet water (Lekang, 2007).

Aquaculture effluent provides most of the nutrients required by plants if the optimum ratio

between daily feed input and plant growing area is maintained (Rakocy et al. 2004).

The rate of change in nutrient concentration can be influenced by varying the ratio of plants

to fish (Rakocy et al., 2006). Since the soluble nutrients available to the plants in the hydroponic


system do not correlate with the proportions of nutrients assimilated by normally growing plants,

the rates of change in concentration for individual nutrients differ. Thus, suboptimal concentrations

and ratios of nutrients result, reducing the nutritional adequacy of the solution for plants. The

nutrient content of a diet can be manipulated to make the relative proportions of nutrients excreted

by fish more similar to the relative proportions of nutrients assimilated by plants. (Endut et al.,

2009b). With such a diet, there would be an optimal ratio of fish to plants and optimal nutrient

supplementation (Seawright et al., 1998). Several mass balance models have been proposed from

previous studies (Pagand et al., 2000; Papatryphon et al., 2005; Schneider et al., 2005; Mongirdas

and Kusta, 2006), from which the total nitrogen and phosphorus discharges into receiving waters

can be estimated.

No pesticides or antibiotics are used at any stage; therefore, the aquaponic production

system can be regarded as a part of the organic agriculture (Rakocy 1999).

The aim of this review is to create a comprehensive image on the design and the technical

aspects of an integrated aquaponic system.

SYSTEM DESIGN

1. Recirculating Aquaculture Systems (RAS)

Recirculating aquaculture systems are indoor, tank‐based systems in which fish are reared

at high density under controlled environmental conditions.

The proper functioning of a RAS depends on some key factors, such as: mechanical filtration

(solid removal), biofiltration and dissolved gas control.

To maintain good water quality the water has to be filtered to remove solids, ammonia and

CO2. Likewise the dissolved oxygen level, pH and temperature have to be kept at secure levels at all

times (Thorarinsdottir et al., 2015). The RAS technology has been developed in recent years,

especially in relation to sludge handling and biofiltration. The RAS technology development,

together with more stringent environmental requirements and the need to increase profitability,

have led to increased interest in integrated multi‐trophic production methods such as aquaponics

(Dalsgaard et al., 2012).

Generally, recirculating aquaculture systems require continuous wastewater treatment

using a variety of techniques that have traditionally been relatively expensive and require very

skillful personnel to operate (Losordo et al. 1992). The design of the water reuse system, needs to

be efficient, cost effective, and simple to operate (Al‐Hafedh et al., 2008).

2. Mechanical filtration

In order to maintain a good water quality and a good functioning of the system, the removal

of solid waste (fish feces and unconsumed fish feed) is an essential process that must not be

neglected. Not only does waste increases the risk of fish disease and gill damage, but also increase

the ammonia in the water, decrease the oxygen concentration due to higher biochemical oxygen

demand (BOD), reduces the biofilter efficiency by fouling the media with heterotrophic bacteria,

and favors clogging that leads to the formation of anaerobic spots that release hydrogen sulphide,

an extremely toxic gas for both fish and nitrifying bacteria (Thorarinsdottir et al., 2015).


It is important to remove the solids from the water fast, to decrease the retention time of

the solids in the system; in this way reducing the risk that the solids will break into smaller particles

which are more difficult to treat and which consume oxygen. This is why mechanical filtration units

are placed immediately after the rearing tanks and before the biofiltration unit.

The solids removed from the system, in the form of sludge, since it is still rich in nutrients can be

valorized and used in agriculture as a natural fertilizer.

In an aquaponic system, unremoved solids lead to clogged plant roots and grow media,

which in turn increases the oxygen demand of the system, and the risk of generating methane and

hydrogen sulphide.

Mechanical filtration can be accomplished in many ways. Normally filtration methods rely

on gravity (sedimentation, swirl separators/radial flow separators), screening (microscreen (drum)

filter, sand filter and bead filter), oxidation (ozone treatment) or foam fractionation (Thorarinsdottir

et al., 2015).

When choosing a solids filtration method (either passive sedimentation or mechanical) a

good criteria can be the fish rearing intensity of the farm. For a small farm with a low rearing

intensity and low water volume a sedimentation filtration is best suited. As the farm size increases,

stocking densities and feed rates get higher, water volume is higher as well and a mechanical drum

filter is best suited in this case

Some types of mechanical filters include: sedimentation basins, drum‐filters, sand filters,

bead filters, foam fractionator.

Table 1. Comparison of different mechanical filter systems (Thorarinsdottir et al., 2015)

Type Op. water volume (m3/h)

Op. pressure (PSI)

Cost (€) Pros Cons

Clarifier 5 Atmosph. 1000 Maintenance‐free. No electricity, requires only purging the system from sludge.

Low water volume compared to alternatives. Water retention time depends on the particle size to be removed.

Foam fractionator

17‐34 Atmosph. 1200 Maintenance‐free. No electricity, requires only purging the system from sludge.

Low water volume compared to alternatives. Water retention time depends on the particle size to be removed.

Bead filter 1) 10 2) 23 3) 45 4) 68

10 20

1) 3000 2) 8050 3) 12000 4) 20000

Simple operations, limited space for water treatment. Suitable for small or medium farms.

Requires electricity, some maintenance needed, beads may need to be replaced. Water needed for backflush with relative disposal. Number of flushes depend on the solid load.

Sand filter 1) 10 2) 22

30‐50 1) 700 2) 1200

Simple operations, limited space for water treatment.

Requires electricity for pumping, not practical with organic wastes, as


Suitable for small or medium farms.

particles foul on sand making clogs. More frequent backflush.

Drum filter 1) 30 2) 90 3) 140

Atmosph. 1) 5200 2) 7000 3) 9000

Effective for big farms. Water movement is by gravity.

Requires electricity, some maintenance needed, screens need to be periodically replaced. Water needed for backflush with relative disposal.

3. Biofiltration

A key feature of recirculating aquaculture and of integrated aquaponic systems is the

biofiltration component. By recirculating the same water, dangerous toxins accumulate that need

to be removed. This is achieved by biotreating the water, converting the dissolved ammonia, which

is a toxic metabolic product excreted by the fish, into the much less harmless nitrate. Due to the

biofiltration process, realized by beneficial bacteria, RAS are able to avoid the discharge and/or

replenishment of the most part of the technological water, thus huge water savings are obtained. A

healthy and matured biofiltration unit is crucial for a stable and well working RAS (Timmons and

Ebeling, 2010).

In the biofiltration process, three nitrifying bacteria species are responsible for maintaining

optimal water quality parameters. The nitrosomonas converts ammonium into nitrite and the

nitrobacter and nitrospira are converting nitrite into nitrate. It must be mentioned that these

bacteria species are naturally occurring in the environment. They are aerobic autotrophic bacteria,

and most effective in using the ammonium and nitrite as an energy source, process that requires

oxygen and a high surface area to develop on. That is why some of the best biofiltration media used

has a high specific surface area and/or a porous surface (with high water and air retention), such as:

gravel, sand, pumice, plastic materials, and others.

The biofilter is a cylindrical or polyhedral shaped canister or tank that holds the porous

filtration media, the bacteria and the water, which must be well aerated since the nitrification

process is oxygen consuming. The design of a biofilter can be a rudimentary one or a complex

industrial one. Since you can’t actually see the bacteria on the filtration media, the only way to

determine its presence and effectiveness is by constantly monitoring the ammonia, nitrite and

nitrate levels of the technological water.

There are other environmental factors that influence the proper working of a biofilter, such

as: water temperature, pH, dissolved oxygen and salinity.

When first starting a RAS, there is an acclimation period (as long as six weeks), during which the

biofilter becomes effective. The nitrifying bacteria needs time to multiply and colonize the filtration

media in order to be able to efficiently treat the entire volume of water within the system. If fish

are introduced into the system and fed, they will provide the ammonia needed to start the

nitrification process. However the existing bacteria won’t be able to properly treat the water and

lethal toxicity levels can be achieved. That is why it is recommended that the system need to run

without fish for a period, and to speed up the bacteria developing process, another ammonia source

must be added to the system. Also, inoculating the system with technological water and/or filtration


media from an already established system is another way to speed up the acclimation time of the

system.

At the startup of the new system, ammonia levels will increase until the nitrosomonas

bacteria colonizes the system and starts converting ammonia into nitrite. As the ammonia levels

start to decrease, the nitrite levels increase until the nitrobacter/nitrospira bacteria colonizes the

system, converting nitrite into nitrate, and thus decreasing the nitrite levels. The nitrate in the

technological water is relatively harmless to the fish, and when integrating a hydroponic module

with a RAS, the nitrate constitutes the main nitrogen source for the plants, thus removing it from

the system.

The size of the biofiltration unit depends on several factors (Chen et al., 2006), such as:

The temperature;

The dissolved oxygen concentration in the water;

The biofilter’s water exchange;

The salinity of the water;

The fish stocking density and the feeding regime;

The surface area of filtration media;

The protein content of the fish feed.

There are several options when choosing a biofilter, its performance depending on the

technology being used and the characteristics of the filtration media being used. Of which the most

common are:

The trickling filter – this is usually a tower‐like tank or canister filled with different specific

surface media (plastic beads or balls, gravel, pumice, LECA, polyurethane foam). Water is

sprinkled in the upper part of the filter, and, as the name says, trickles down through the

filtration media. This filter type provides a passive aeration and carbon dioxide removal.

The moving bed bioreactors (MBBR) – this filtration unit contains neutrally buoyant filtration

media that are constantly stirred by the aeration process. The aeration also assures the

water is oxygenated and removes the carbon dioxide from the water. The media used in this

type of biofilter is usually composed of plastic balls or other type of plastic product with high

specific area.

The bead filter – this filter it usually is a pressurized cylindrical canister. The media beads

inside are periodically stirred and cleaned to prevent any accumulating waste which is

removed through backwash.

The sand filter – this type of filter, just like the bead filter it usually is a pressurized cylindrical

canister with sand as filtration media. The very high specific area of the sand ensures a very

high nitrification rate.

As it has been stated before, the nitrification process is an oxygen consuming one, beside

the passive aeration occurring in the biofilter, the water needs to be adequately and constantly

aerated (Thorarinsdottir et al., 2015), in order to supply sufficient oxygen to the microbial

community, to the reared fish and even to the plants in the case of an integrated aquaponic system.

4. Hydroponics


The hydroponic technique is the cultivation of plant crops in a soil‐less environment. For the

growing of plants, the aquaponic systems use the design of the hydroponic systems.

The main design of aquaponic systems closely mirrors that of recirculating systems in general, with

the addition of a hydroponic component (Rakocy et al., 2006).

The main components of an integrated aquaponic system are: the rearing tank, the solid

removal units (sump and mechanical filter), the biofiltration unit, the aeration unit, the degassing

unit, the pumps and the hydroponic culture module (Figure 1).

Figure 1. Schematic overview of an integrated aquaponic system (Thorarinsdottir et al., 2015)

Rakocy et al., 2006, considers that there is an optimum arrangement of these components,

as can be seen in Figure 2, thus the solid removal unit and the bio filtration unit must precede the

hydroponic culture module.

Figure 2. Optimum arrangement of aquaponic system components (not to scale)

(Rakocy et al., 2006)


In this way, the effluent from the rearing unit is treated first by removing its suspended and

settable solids, then it is biofiltered by removing as much ammonia and nitrite as possible, finally

reaching the hydroponic culture module, where nutrients (nitrate and other micro and macro

elements) are absorbed by the plants and additional ammonia and nitrite are removed by the

bacteria growing on the surfaces of the hydroponic module and/or the grow media. After passing

through the hydroponic culture module, the water is collected into a sump from where it is returned

to the rearing unit.

The hydroponic units are populated with seedling grown outside the system in soil or in

other types of media (e.g. rockwool, peat moss and coconut coir). The efficiency of hydroponically

grown plant can be found in the physiological adaptation in young plants called “luxury

consumption”. This mechanism, first described in 1974 (Van den Driessche, 1974), states that luxury

consumption is “...the increase in tissue nutrient concentration above the maximum yield, which

does not result in further yield increase.” In other words, when there are excess nutrients available

to seedlings, they can uptake and store them, then mobilize the nutrients to tissues in the future

when needed (Fox et al., 2012).

More than 30 types of vegetables have been raised in integrated systems on an experimental

basis (Rakocy et al. 1992). Lettuce, herbs, and specialty greens (spinach, chives, basil, and

watercress) have low to medium nutritional requirements and are well adapted to aquaponic

systems, whereas fruiting plants (tomatoes, bell peppers, and cucumbers) have a higher nutritional

demand and perform better in a heavily stocked, well‐established aquaponic system (Diver 1996).

Various fish species are presently used in aquaponic systems including Nile tilapia

(Oreochromis niloticus), hybrid tilapia (Oreochromis urolepis hornorum X Oreochromis

mosambicus), koi carp (Cyprinus carpio), hybrid carp (Ctenopharyngodon idella X Aristichthys

nobilis), hybrid striped bass (Morone chrysops X Morone saxatilis), and goldfish (Carassius sp.)

(Selock 2003). Rainbow trout (Oncorhynchus mykiss) (Adler et al. 2000), Australian barramundi

(Lates calcarifer) and Murray cod (Maccullochella peelii peelii), as well as various crustaceans such

as red claw crayfish, (Cherax quadricarinatus) have also been grown in aquaponic systems (Diver

2006).

Different types of hydroponic media have been used for growing crops in aquaponic

systems, including gravel bed ebb and flow systems, aeroponics, nutrient film technique (NFT), rock

wool culture, and sand beds (Gonzales 2002). McMurtry et al. (1990) used sand as a medium for

growing vegetables using aquaculture wastewater, whereas Rakocy and Nair (1987) used floating

rafts.

There are three main aquaponic techniques in use worldwide: media grow beds, deep water

culture (DWC) or floating rafts and the nutrient film technique (NFT) (Thorarinsdottir et al., 2015).

All three of these techniques work well, but a proper mechanical filtration is still needed.

4.1. Media grow beds

This system is mostly used in backyard aquaponic systems and in small scale systems. It is a

solid media‐filled bed system (Thorarinsdottir et al., 2015) filled with light expanded clay aggregate


(LECA) (Figure 3A), pumice (Figure 3B), Growstone (Figure 3C), gravel (Figure 3D), zeolite (Figure 3E)

or expanded shale (Figure 3F).

Figure 3. Different types of growing media

These media provide the plants with a good root fixation substrate, also because of the

porosity (high specific surface area) and a good water and air retention rate, the media provides

extra biofiltration/nitrification and mineralization.

In small scale aquaponic systems that practice a low fish stocking density, the biofilter can

be completely excluded, the nitrification process being realized by the grow bed media.

Also red earthworms (Eisenia fetida) can be added in the grow bed.

These annelids help break down solid waste and excess roots, they supress plant diseases

and provide extra nutrients to the plants through their excrements – vermicompost. Vermicompost

has been shown to enhance plant growth, crop yield, and improve root structure and development

(Pant et al., 2009).

The media grow bed system can be implemented by choosing one of the two flood regimes:

constant (continuous) flow or reciprocating flow (“ebb and flow”).

The constant flow process is simple, just as the name suggests, water flows continuously and

constant into the grow bed through an inlet at one end and fills it until it reaches a certain desired

level, then flows out through an outlet or overflow, usually located at the other end of the grow

bed.

The reciprocating flow process can be achieved by either rigging the influent pump to turn

on and off at specific intervals, or more conveniently, by using a bell siphon (Figure 4) over the

outlet.


Figure 4. Bell siphon schematic (A) and examples of bell siphon (B) (Fox et al., 2010)

Water flows into the grow bed and it fills it up to a specific level, then it drains out almost

completely only to start the process once more. This effect is achieved by narrowing the outlet pipe,

thus creating a suction effect once the water reaches a certain (desired) level.

In the reciprocating flow variant the media and the plant roots get better aeration (Rakocy

et al., 2006), unlike the constant flow variant in which the same media and the roots are always

under the water level. When cultivating a plant with high nutritional requirements, a constant flow

system is recommended, but the reciprocating flow system has a better biofiltration and solid

removal.

Lennard and Leonard (2004 and 2006) have demonstrated in their studies that lettuce has a

greater yield in the constant flow variant and also that it has a better water treatment capability.

Even so the scientific community is divided regarding this matter.

The design of a media grow bed system is quite simple; it is comprised of a rectangular

shaped trough made of plastic or of wood or concrete covered with impermeable lining, plastic

pipes (with valves) and optionally a bell siphon.

This hydroponic module is quite easy to build and depending on the media type that is used,

the cost vary, making it not the cheapest, but also not the most expensive solution.

Maintenance can be difficult if large amounts of solids get through the mechanical filtration

unit and end up in the media, over time clogging the media, the roots and even the piping.

The media grow bed is better suited for plants that bear fruit since the media provides better

fixation for the roots and support for the plant.

The crop yield of the media grow bed system is better than that of the DWC system, which

in turn is better than the NFT system (Lennard and Leonard, 2006).

4.2. Deep water culture (DWC)

Also known as the floating raft system, the deep water culture system is optimal for both

small and large scale production systems.


The design is simple, the hydroponic tanks are large, not too deep, and usually a minimum

of 30cm water depth level is maintained.

The plants grow on polystyrene or plastic sheets that float on the surface of the water,

usually fixed in small plastic net pots.

Just like the media grow bed troughs, the deep water culture tanks, in this case, have a

simple design; rectangular shape, made of plastic, metal, wood or concrete covered with

impermeable lining, etc. Water flows in the hydroponic module through an inlet at one end and it

flows out through an overflow outlet at the other end of the unit. This way a constant water level is

always maintained and in case of a pump malfunction or power failure, the plants do not die.

The roots of the plant grow directly into the oxygenated water flowing from the fish tanks

with a volumetric exchange rate of approximately 30% per hour. (Thorarinsdottir et al., 2015). If the

solids filtration and removal is not done properly, sludge accumulating at the bottom of the

hydroponic tank and on the roots of the plant blocking oxygen and nutrients uptake.

Crop management involves transplanting the seedlings into the system and harvesting the

plants once they achieve marketable size. This process can be improved by applying a conveyor

movement of the rafts similar to the conveyor production system (CPS) used in the NFT systems.

The seedlings are introduced on floating trays into the system at inlet end of the hydroponic module

and moved along the length of the tank as it grows, reaching the outlet end of the tank when it’s

ready to be harvested.

The DWC system is easiest to build and the least expensive of the three types of aquaponic

systems.

4.3. Nutrient film technique (NFT)

The nutrient film technique system uses long and narrow plastic tubes with a thin layer (film)

of water continuously flowing through them.

An absolute requirement in the case of the NFT systems is a good preliminary mechanical

filtering (Thorarinsdottir et al., 2015). Solids accumulating on the roots must be avoided, not only

because it can inhibit plant growth, but also because it can lead to clogging of the system.

The design of the NFT systems might be more complex than the other two aquaponic

systems, but it certainly is the easiest to manage as long as clogging is avoided. The system uses long

tubes with rectangular or circular section, 10‐15 cm in width or diameter. These tubes have holes

cut into the top part where plants (optionally in plastic pots) are set.

The NFT tubes are placed at a 1% angle, the water entering at the raised end, flowing through

the tube and being gravitationally evacuated at the lowered end. Water is introduced into the NFT

hydroponic modules with a low flow pump, aiming for a 1‐2 L/min flow regime (Thorarinsdottir et

al., 2015). Also these pumps require less energy to recirculate the water into the hydroponic units,

reducing the operational cost.

An absolute advantage of the NFT system over the other two systems is the possibility to

design and build the system vertically, making excellent use of the available growing area.

In order to avoid the oxygen depletion be the plant roots due to the small volume of water flowing

through, the tube must not be longer than 10 m.


NFT systems also have some drawbacks, like the risk of root clogging and the decrease of the

water’s nutrients towards the end of the channel. The first issue can be resolved with a good solid

waste control, whereas the second one can be overcome by implementing a conveyor production

system (CPS) (Figure 5) within the hydroponic modules.

Figure 5. Schematic of a conveyor production system (CPS) (Adler et al., 2003)

The CPS works by introducing the seedlings into the system at the start of the channel, and

as it grows, periodically moving it towards the end, where it is harvested. The CPS not only efficiently

removes the nutrients from the water, and also reduces the sensitivity of plants to imbalances of

mobile nutrients in the wastewater (Adler et al., 2003).

NFT is suitable for a small size plants, such as herbs and salads, but it can also be used to

grow larger plants, such as tomatoes and okra. A great risk of this system is the possibility of a crop

loss in case of a system malfunction or power failure – the roots drying up and the plants dying if

the water input is compromised. That’s why backup solution for power and water flow must be

implements.

The NFT system is very suitable for large scale production systems because of its ease of use

and simple maintenance. The design and building of this type of system requires more work and it

is the most expensive of the three aquaponic systems.

5. Lighting

One important component of the aquaponic system is the lighting equipment needed for

assuring a fast and proper plant development.

There are several options to choose from, such as: fluorescent bulbs, metal halide bulbs. The

lights come in various wave lengths, they cover a certain area and need to be mounted at a certain

height above the plants, depending on plant species. When choosing the lighting solution for an

aquaponic system, a very important aspect also needs to be the acquisition to operating cost ratio.

Basically the more expensive the lighting system acquisition is the less expensive the operation cost

over a longer period of time is.

The lighting operation period during a day can vary depending on the crop that is grown and

the time of year, but usually around 10 hours of light : 14 hours of dark (Lennard and Leonard, 2004).


CONCLUSIONS

An integrated aquaponic production system is a very good way to increase the income of a

fish farm, growing a secondary sustainable marketable product.

All three aquaponic systems have their advantages and disadvantages from multiple point of views;

choosing which one to integrate with a RAS is up to the farmer, depending on the necessities,

maintenance and management capabilities and not the least on the available investment costs.

As general conclusions of this review, the following can be stated:

The media grow bed system has a better plant biomass yield than the deep water culture

(DWC) system, respectively than the nutrient film technique (NFT) system.

The DWC system has better water treatment capabilities than the media grow bed system

respectively, than the NFT system.

The DWC system has lower investment costs than the media grow bed system, respectively

than the NFT system.

The DWC system is easier to build than the media grow bed system, respectively than the

NFT system.

The NFT system is easier to maintain than the DWC system, respectively than the media

grow bed system.

Keeping in mind all of the above, a DWC system is recommended for a starting aquaponic

system.

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Integrated Multi‐Trophic Aquaculture

Integrated multi‐trophic systems general overview and classification

General overview

Over the past decade, integrated multi‐trophic aquaculture (IMTA) has received much

attention as a means of practicing sustainable aquaculture by recycling nutrients through co‐

cultured species from different trophic levels (Chopin et al., 2008). The waste (feed) and by‐products

(faeces and nutrients) from fed species (e.g. finfish) and filtering feeders (e.g. shellfish) become food

for extractive species (e.g. detritivores and seaweed) to reduce farm‐derived organic and nutrient

loading into the environment. Integrated aquaculture has been practiced for centuries in China,

initially through land‐based operations which later expanded to include marine systems (NACA,

1989; Yang et al., 2000). Such integrated culture techniques have recently been incorporated into

scientific based experiments which monitor the feeding and growth of a mixture of species from

different trophic levels. These studies have shown increases in both farm productivity and the

growth rates of co‐cultured species, and a reduction in waste products (e.g. Li et al., 1983; Wang,

2001; Chopin et al., 2008; Hughes and Kelly, 2011).

To avoid or alleviate the negative effects posed by aquafarming, the integrated multi‐trophic

aquaculture (IMTA) is proposed as a potential bio‐mitigation approach. IMTA aims to achieve a

sustainable development of aquaculture and improve the productivity of intensive monoculture

through reusing waste as food resources (Zhang, et al. 2015b). In this integrated system, the

targeted species are cocultivated with others having dissimilar feeding habits in different trophic

levels (Neori et al. 2004). Various species of nutrient absorber, suspended feeder, deposit feeder,

and other organic extractive organism could be considered as the candidates to be co‐cultured with

targeted species (finfish, e.g., red sea bream Pagrus major, Atlantic salmon Salmo salar) in an IMTA

system. Waste released from fish farm could offer food sources for inorganic and organic nutrient

extractive species. For instance (Fig. 1), as particulate organic waste (e.g., fish fecal matter, waste

fish feed) mainly sinks down to sea bottom, the deposit feeders (e.g., Japanese sea cucumber

Apostichopus japonicus, giant California sea cucumber Parastichopus californicus) will ingest it as

food, consequently mitigating the problem of hypoxic bottom water due to increased oxygen

consumption during bacterial decomposition of excessive organic matter.

As another form of aquaculture waste, dissolved nutrients (e.g., phosphorus, nitrogen) cause

eutrophication which increases the risk of harmful algal blooms. Planting nutrient absorbers (e.g.,

seaweeds Gracilaria chilensis, Laminaria japonica, Ulva ohnoi) could minimize this risk through their

competition with phytoplankton for resources, and harvesting macroalgae periodically will speed

up the removal of dissolved nutrients (Buschmann et al. 2008). Meanwhile, as the supplement,

suspension feeders (e.g., mussels Mytilus edulis, M. trossulus, scallops Argopecten irradians,

Chlamys farreri, Platinopectin yessoensis, oyster Crassostrea gigas, arkshell Scapharca broughtonii)

and other organic extractive species (e.g., prawns Fenneropenaeus chinensis, Pandalus platyceros,

abalone Haliotis discus hannai, sea urchin Anthocidaris crassispina, jellyfish Rhopilema esculenta)

are capable of further filtering the phytoplankton as well as the dispersed small particle organic

materials from both fish food and feces in water column.


Fig. 1 Conceptual diagram of the integrated multi‐trophic aquaculture system. Boxes

represent state variables and/or interaction processes. Arrows denote the carbon cycle (brown color) and nutrient cycle (pink color), respectively (Zhang, et al. 2015b).

IMTA has been developed for centuries in China, especially in respect of freshwater

aquaculture, and then expanded to marine systems (Li 1987; Yang et al. 2000, 2004; Zhou et al.

2006; Mao et al. 2009; Li et al. 2014). In the last few decades, many other countries also generate

an interest in IMTA system, for example, Australia, Canada, Chile, France, Japan, New Zealand,

Spain, the United Kingdom (UK), the United States (US), and Turkey (Petrell and Alie 1996; Ridler et

al. 2007; Buschmann et al. 2008; Abreu et al. 2009; Troell et al. 2009; Ren et al. 2012; Yokoyama

2013). A few numerical studies of IMTA have been reported. For example, Ren et al. (2012)

represented a generic IMTA model focusing on finfish‐shellfish‐detritivore‐primary producer

systems; Hadley et al. (2014) developed a numerical model to quantify the remediation of dissolved

nutrients and growth of macroalgae. However, most of these studies did not focus on the design of

extractive organisms in IMTA system based on the hydrodynamic environment. Troell et al. (2009)

has reported that when the direction of long‐line ropes for the extractive organism is not parallel to

that of water current, the scallop culture nets may be wrapped by seaweeds L. japonica with 2‐ to

3‐m length. He also mentioned that the attachment of periphyton had been influenced by current

velocity. In addition, waste diffusion is also proven to be affected by water current in terms of both

direction and velocity (Petrell and Alie 1996; Abreu et al. 2009; Zhang and Kitazawa 2015a).


Therefore, understanding the hydrodynamic environment is important to support decision‐making

on the optimal design of IMTA for mitigating aquatic waste more efficiently.

Monoculture practices do not offer the best use of cultivation units. When one considers the

seawater volume available at a leased site and the volume of water column actually occupied by the

series of salmon cages, it is obvious that a cultivation unit (a site) is not optimized. Developing

integrated aquaculture systems will not only bring increased profitability per cultivation unit

through economic diversification of co‐cultivating several value‐added marine crops, it will also

bring environmental and social sustainability and acceptability (Chopin et al. 2004). Combining fed

aquaculture of finfish with extractive organic aquaculture of shellfish, and extractive inorganic

aquaculture of seaweed provides a balanced ecosystem approach to aquaculture and a cost‐

effective means for reaching effluent regulation compliance by reducing the internalization of the

total environmental costs (Chopin et al. 2001, McVey et al. 2002).

Traditionally, open‐sea fish‐farming methods have focused on the intensive culture of a

single species. An effect of such monospecific cage aquaculture on its surrounding environment is

the output of suspended solids and dissolved nutrients, which in some cases has been shown to

cause environmental degradation (Beveridge 1984, Phillips et al. 1986, Gowen & Bradbury 1987,

Folke & Kautsky 1989, Beveridge et al. 1991, Phillips et al. 1991, Beveridge et al. 1994, Chopin et al.

2001). Salmonid farming in particular has experienced intense scrutiny as a result of the generation

of large amounts of organic wastes in the form of uneaten food, feces, and excretory products,

which may cause localized hypernutrification possibly leading to eutrophication (Gowen et al. 1988,

Folke & Kautsky 1989, Folke & Kautsky 1992). Braaten et al. (1983) estimated that 20% of all food

goes uneaten by cage‐reared salmon, and of what is eaten, 26% is voided as feces. Thus, organic

particulate discharges into the surrounding water column (both direct, via lost food; and indirect,

via feces) constitute a large proportion of the overall losses at salmon aquaculture sites.

Recently, a great amount of emphasis has been placed on the development of more

sustainable marine aquaculture practices worldwide (Folke & Kautsky 1989, Wurts 2000, Chopin et

al. 2001, Troell et al. 2003, Neori et al. 2004), with particular emphasis on the viability of integrated

aquaculture techniques (Kautsky & Folke 1991, Folke & Kautsky 1992, Brzeski & Newkirk 1997, Troell

et al. 1999). Integrated aquaculture, already an established practice in land‐based systems (e.g.,

Gordin et al. 1990, Shpigel et al. 1993a, Shpigel et al. 1993b, Neori et al. 1993, Buschmann et al.

1996a, Buschmann et al. 1996b, Shpigel & Neori 1996, Neori & Shpigel 1999, Neori et al. 2004), has

recently been suggested for use in the marine environment. These techniques involve the addition

of extractive species (those that use food present in the water column and require no human‐

delivered food for growth, such as bivalve molluscs and seaweed, to existing, ‘‘fed’’ (i.e., finfish)

marine aquaculture systems). The system works on the ecologically based premise whereby waste

organic particles and dissolved nutrients from fish cages are taken up and assimilated by species at

lower trophic levels such as bivalves (e.g.,mussels) and seaweed, thus supplying nutritional

enrichment to the extractive species. Such increases in available food and the potential for growth

advantages of bivalves at cage sites has led to worldwide investigations into growth responses of

bivalves in co‐culture with finfish (Wallace 1980, Jones & Iwama 1991, Taylor et al. 1992, Okumusx

&Stirling 1995, Stirling & Okumusx 1995, Cheshuk et al. 2003).


The blue mussel (Mytilus edulis) is a logical candidate for an extractive species in temperate

integrated aquaculture systems. Although M. edulis is one of the dominant intertidal bivalves in

most temperate areas of the northern and southern hemispheres (Seed & Suchanek 1992),

populations also occur sub tidally. Typically, the unique aspects of such subtidal populations include

continuous growth, allowing individuals to attain large sizes in relatively short periods of time (Page

& Hubbard 1987). The ability of subtidal populations to grow rapidly has led to the successful

development of fixed suspended cultivation of the blue mussel worldwide. The preestablishment of

suspended culture, combined with the mussels’ ability to exploit organic food resource from non‐

phytoplankton sources (Widdows et al. 1979, Rodhouse et al. 1984, Page & Hubbard 1987) such as

fish food (Mazzola & Sara´ 2001, Reid et al. 2010, MacDonald et al. 2011) makes the blue mussel a

logical integrated aquaculture candidate species.

In an integrated multi‐trophic aquaculture (IMTA) system, particulate waste normally lost to

the surrounding environment is used by the mussels for growth, hence lessening the overall organic

discharge of the site. In turn, the excess energy received (in the form of farm wastes such as unused

salmon food) is converted to mussel flesh that is then removed as a second market species at

harvest. Furthermore, elevated organic particles generated at salmon aquaculture sites (Cripps

1995) may facilitate year‐round mussel growth during nutrient‐limited winters when many bivalve

species are quiescent and enter a period of zero or negative growth (Widdows et al. 1979). Such

continuous yearly growth, as a function of increased food availability, decreases the grow‐out time

for a commercial crop of mussels, allowing the grower to maximize production and profitability

while lessening environmental impacts.

The availability of organic food particles has been put forward as the single most important

factor determining growth rate of bivalves such as mussels (Seed & Suchanek 1992), and studies

have established the presence of daily increases in suspended solids (Taylor et al. 1992, Lander et

al. submitted) on a year‐round basis (Lander et al. submitted) at salmon farms and they are being

used by bivalves (Lefebvre et al. 2000, Mazzola & Sara´ 2001, Redmond et al. 2010). To date,

investigations addressing bivalve growth rates in integrated culture have yielded varied results.

Although enhanced growth rates have been found in co‐cultured bivalves in several cases (M.

edulis (Wallace 1980), Pacific oyster Crassostrea gigas (Jones&Iwama 1991), and Mytilus

galloprovincialis (Sara´ et al. 2009)), other studies have found no enhancement (Taylor et al. 1992,

Cheshuk et al. 2003, Navarrete‐Mier et al. 2010) or modest enhancement (Farias‐Sanchez 1983,

Taylor et al. 1992, Stirling & Okumusx 1995) of growth in bivalves cultured adjacent to fish cages.

The IMTA model

Biogeochemical fluxes in surrounding water and sediments play an important role in nutrient

cycling and affect internal food supply in farming ecosystems which have been explicitly described

in many modelling studies on shellfish aquaculture (e.g. Bacher et al., 1998; Grant et al., 2007;

Grangeré et al., 2010). As an IMTA operation is much more complex than monoculture, the biomass

and production of each trophic species are difficult to optimise economically through the traditional

technique of trial and error and experimentation. This present study offers a model framework that

considers the influence of natural biogeochemical fluxes over time on the integrated nutritional


pathways between IMTA groups and is designed to predict the optimal stocking biomass at each

trophic level to produce an effective economic yield. The model incorporates hydrodynamic

processes and metabolic energetics of cultured species with an ecological model to design proximal‐

balanced ecological IMTA units (Ren et al. 2012).

Most ecosystem models strive to relate the distribution and fluctuation in abundance and

production of wild living organisms to variations in food conditions, predation and the abiotic

environment (Fransz et al., 1991). Similarly the IMTA model aims to map out interactions between

co‐cultured species and their ecosystem components and predict productive capacity. The impact

of cultured species on the environment in coastal systems can also be quantitatively and objectively

integrated into the model. A few ecosystem models have been developed to assess environmental

impact and carrying capacity of farming systems, but most of the model development has focused

on monoculture of bivalves (e.g. Bacher et al., 1998; Dowd, 2005; Grant et al., 2007). Some

multispecies modelling work has been attempted to study the carrying capacity of a shellfish poly‐

culture system (Duarte et al., 2003). The functioning of poly‐culture differs from an IMTA system

because species from the same trophic level are included in poly‐culture (e.g. oysters and scallops

used in these studies share the same biological and chemical processes which could potentially

impact natural phytoplankton populations). Culturing species at the same trophic level does not

mitigate environmental impacts (Chopin et al., 2008). IMTA practices strive to facilitate nutrient

recycling and optimize co‐culture productivity through bioremediation. To achieve this, biomass

stocking densities of the culture species must be optimized by means of ecosystem models (Ren et

al. 2012).

The main focus of this model is to provide a research tool to fine‐tune the design of field

trials to optimize yields from each trophic level. Model development followed a number of steps.

Firstly, there was developed an IMTA model based on dynamic energy budgets (DEB) for each

trophic grouping within a finfish–shellfish‐detritivore‐primary producer profile. Secondly, to test the

concept and capability of the model, it was parameterized using potential IMTA species namely,

salmon, mussels, sea cucumbers and seaweed. Lastly, IMTA scenario simulations were undertaken

to understand the dynamics and potential ecological benefits of IMTA farming (Ren et al. 2012).

The IMTA model incorporates an ecosystem model (Ren et al., 2010) with DEB sub‐models

for each trophic group within the benthic and pelagic components that interact through carbon and

nitrogen budgets and nutrient cycling (Fig. 2). The dynamics of all biological groups, cultured and

non‐cultured organisms, are described at the population level. For cultured animals, the population

energetics depends on that of individuals. Population dynamics of trophic groups are determined

by culture strategies and natural mortality. Individuals are removed when reaching a harvest size.

Stochastic events may cause additional mortality but are not included in the model. Nutrients,

pelagic organic matter, phytoplankton, zooplankton and carnivores are exchanged between the

farming system and adjacent open waters. This was driven by local hydrodynamic processes where

exchange rates were dependent on advection by water currents and turbulent diffusion (Ren et al.

2012).


Fig. 2. Conceptual diagram of the IMTA model illustrating the coupling of ecophysiological

and biogeochemical processes through carbon (C) and nitrogen (N) pathway between the various

compartments. The cultured trophic group comprises fed organisms (finfish), suspended filtering

feeders (shellfish), nutrient extractive organisms (seaweed) and benthic detritivores (sea

cucumber). The pelagic compartment includes phytoplankton, zooplankton, carnivore, dissolved

inorganic nitrogen (DIN), dissolved organic nitrogen (DON), pelagic non‐plankton organic carbon

and pelagic non‐plankton organic nitrogen. DIN consists of ammonia nitrogen (NH4) and nitrate

nitrogen (NO3). The benthic compartment is comprised of carbon sediment and nitrogen sediment

(Ren et al. 2012).

Classification

The most frequently tested organisms are molluscs, which filter organic particles, and

phytoplankton, and macro algae, which have the capability of inorganic nutrient uptake (Granada

et al., 2015).

Seaweeds

Integration of seaweed cultivation to the cultivation of aquatic animals have been

successfully applied to the land‐base system (Rohyani et al., 2015). In the last fifteen years, the

integration of seaweed with marine fish culturing has been examined and studied in Canada, Japan,

Chile, New Zealand, Scotland and the USA. The integration of mussels and oysters as bio‐filters in


fish farming has also been studied in a number of countries, including Australia, USA, Canada,

France, Chile and Spain. Also, the recent offshore relocation of many coastal finfish farms in Turkey

has triggered the interest in IMTA (Granada et al., 2015).

The ability of macro algae to respond to availability of anthropogenic nutrient (nitrogen and

phosphorus) input makes them an efficient instrument for bioremediation (Commission Regulation

(EC) no 710/2009 2009 (Granada et al., 2015). Bio‐filtration by plants, such as algae, is assimilative,

and therefore adds to the assimilative capacity of the environment for nutrients. Plants

photosynthesise new biomass through solar energy and the excess nutrients, particularly C, N and

P. Theoretically, this process recreates an ecosystem, wherein, if properly balanced, plant

autotrophy counts on fish or shrimp and microbial heterotrophy, not only with respect to nutrients

but also oxygen, pH and CO2. Algae, particularly seaweeds, are the most suitable for bio‐filtration

because they probably have the highest productivity of all plants and can be economically cultured.

Integrated multi‐trophic aquaculture research along the Atlantic coast is primarily focused on using

algae (mainly Rhodophyta) with fish (mainly turbot, Scophthalmus maximus, and sea bass,

Dicentrarchus labrax). Much research is being carried out using Gracilaria bursa‐pastoris, Gracilaria

gracilis, Chondrus crispus, Palmaria palmata, Porphyra dioica, Asparagopsis armata, Gracilariopsis

longissima (Rhodophyta), Ulva rotundata and Ulva intestinalis (Chlorophyta) as bio‐filters for use in

IMTA units. Using this knowledge, researchers have begun experimental studies where algae have

been integrated with sea bass and turbot. Recent research on marine IMTA systems in industrialized

nations has mostly been developed using experimental and small‐scale operations, which it is

difficult to extrapolate to larger industrial scale farms. However, some marine IMTA systems,

primarily in Asia (China), have been commercially successful at industrial scales, while experimental

projects are now scaling up towards commercialization in Canada, Chile, the USA and in some

European countries. On the east coast of Canada, in Bay of Fundy, an IMTA combining kelps, such

as Saccharina latissima and Alaria esculenta, with Atlantic salmon and blue mussel, resulted in a

substantial increase of kelps and mussels’ growth rates. In Sungo Bay (China), a company works at

industrial scale, producing the kelp Laminaria japonica with scallop (Chlamys farreri), abalone (H.

discus hannai) and blue mussel (Mytilus edulis) (Granada et al., 2015).

The red algae Gracilaria spp. and the green algae Ulva spp. have been found to be efficient

bio‐filters. Gracilaria spp. have been examined for their usefulness by laboratory (using tank)

outdoor (pond) and field cultivation experiments (Granada et al., 2015).

Ulva spp. have been studied mainly from the viewpoint of the treatment of land‐based

pond/tank effluent, and their usefulness in the coastal IMTA system has not been examined closely

except for a few studies conducted in Japan. An efficient algal‐based integrated mariculture farm

maintains optimal standing stocks of all the cultured organisms, considering the respective

requirements of each for water and nutrients and the respective rates of excretion and uptake of

the important solutes by each of them. This allows the profitable use of each of the culture modules

with minimum waste. Algae, mainly seaweed, have a large market, and just in 2012 about 23.8

million tones valued at US$ 6.4 billion were sold for human consumption, phycocolliods, feed

supplements, agrichemicals, nutraceuticals and pharmaceuticals. Thus, diversifying a culture


system, integrating extractive algal culture with fish or shrimp farming, makes sense not only

ecologically but also from an economical point of view (Granada et al., 2015).

Invertebrates

The reduction of suspended solids and microbial pollution within aquaculture can be

achieved by the use of living organisms. Literature also reveals the potential capability of some

invertebrates to remediate heavy metals, microbial contaminants, hydrocarbons, nutrients and

persistent organic pollutants. Filter‐feeding marine macro invertebrates filter large volumes of

water for their food requirements and exert high efficiency in retaining small particles including

bacteria. Detritus feeder species have also been proposed as a means for recycling the particulate

organic and inorganic nutrient wastes from fish cage farming (Granada et al., 2015).

Polychaetes

The Mediterranean polychaete Sabella spallanzanii showed ability to filter, accumulate and

remove from waste bacterial groups, including human potential pathogens and vibrios. Sabellids are

considered suitable to use in aquaculture farms as bio‐filters, also considering their action in

removing suspended solids in wastewaters to which bacteria can be attached. According to the

Global Marine Aquarium Database, 11 178 of sabellidae polychaetes, also known as fan worms,

were imported from UK between 1991 and 2001 to Indonesia, Philippines, Singapore, Sri Lanka,

USA, Brazil, Cuba and Martinique. Thus, additionally to the bio‐filtering capability of these filter‐

feeding organisms, they are also likely to be traded in the marine aquarium industry (Granada et al.,

2015). The mucus of S. spallanzanii contains a complex of at least ten major and six minor proteins,

one of which displays lysozyme‐like activity. The presence of lysozyme indicates an important

defending role from bacterial attacks, taking into account that these organisms live in eutrophic

environments, like harbours where bacteria, including human pathogens, are abundant. This

antibacterial activity can also be explored from a biotechnological perspective. The use of rag worms

in aquaculture could reduce the production of waste and increase the reproductive fitness of

cultivated animals. The bio‐filtering efficiency of these polychaetes is influenced by the water flow,

the total suspended solids levels, the age‐at‐stocking and density are the factors that also influence

their survival and growth (Granada et al., 2015).

Sponges

During the past few years, it was proposed for the production of sponge biomass to be used

at integrated aquaculture systems and, accordingly, filtering efficiencies and particle uptake in

sponges have been studied. The aim was to understand the energy balance of filtering activity, the

effects of temperature and the uptake of microorganisms and/or particles. Studies have

demonstrated the ability of Demospongiae (Porifera) to unselectively filter organic particles within

a size range 0.1–50 mm, which includes heterotrophic bacteria, heterotrophic eukaryotes,

phytoplankton and detritus, processing the water column within 24 h, and retaining up to 80% of

the suspended particles. The utilisation of bacteria by sponges, as observed for sabellids, also

suggests an applicative role for bioremediation purposes, considering that bacteria are usually

abundant in waters with high amount of organic matter, reaching particularly high densities in areas

subjected to aquaculture activities. Thereby, a large‐scale sponge culture could have a profound

effect on the water quality in the vicinity of fish farms, combining the production of sponges with


remediation of pollution. At the same time, sponge growth is stimulated, making sponge

aquaculture more efficient. Although the idea of integrated sponge/fish aquaculture has been

discussed, it has not been applied on a commercial scale. Studies have been conducted on the

Mediterranean sponges Dysidea avara, Chondrosia reniformis, Chondrilla nucula (Milanese et al.

2003) and Spongia officinalis var. adriatica (Stabili et al. 2006) to assess their potential of filtration

and integration with maricultures. All these species showed great filtering efficiency and higher

growth close to the farm installations (Granada et al., 2015).

Bivalves

Bivalves can be potential bio‐controllers for fish farm effluents and for other eutrophication

sources. Additionally, several authors have found significantly enhanced rates of shellfish, as oysters

and mussels, when co‐cultivated or grown with salmon (Granada et al., 2015).

Integrated multi‐trophic aquaculture in earthen ponds using fish and oyster is not only

feasible but may be profitable (Cunha et al., 2012).

Besides, the effectiveness of the oyster Saccostrea commercialis was tested with positive

results concerning the reduction of total suspended solids, and total N and P. The absorption

efficiency of blue mussels, Mytilus edulis and M. trossulus, on diets of Atlantic salmon particulates

(feed and faeces), with results that support the concept of culturing these organisms in close

proximity to salmon cages in IMTA systems as a process to remediate the solid waste. Moreover,

bivalves are known to bio‐accumulate human pathogens such as Vibrio species, hepatitis A virus,

human sapovirus and adenovirus. Few studies suggest that there is potential for shellfish to act as

reservoirs for finfish pathogens; thus, the integration of shellfish production in fish farms, as in IMTA,

could potentially change the infection dynamics for fish pathogens. It is reasonable to consider that

bivalves can be integrated with fish farming in order to reduce ecological impacts while also having

the potential to develop into a valuable crop for the farmers (Granada et al., 2015).

Filter feeders bivalves are essentially generalist consumers, and it has been demonstrated

that they can exploit organic matter from several sources (autochthonous, allochthonous or

anthropogenic), as a function of its availability. In a conceptual open water integrated aquaculture,

filter feeder bivalves are cultured adjacent to fish floating cages, reducing nutrient loadings by

filtering and assimilating particulate wastes (uneaten food and faeces) as well as phytoplankton. In

this way, bivalves would perform as biological filters. Previous studies have determined that bivalves

can be successfully incorporated into integrated multi‐trophic aquaculture systems, based on the

increased growth displayed and the feeding efficiency on pellet feed and fecal products (Deudero

et al., 2011).

Sea cucumbers

Sea cucumbers are detritus feeders that ingest sediment with organic matter including

detritus of plant and animals, and they are considered important processors of surface sediments

in many coastal marine systems. Therefore, they would be good candidates for co‐culture in IMTA

systems (Granada et al., 2015). The Japanese common sea cucumber Apostichopus japonicas is a

valuable species in many parts of Asia and extensively world traded. This organism showed potential

to be used in integrated multi‐trophic aquaculture systems, being cultured in the water column

below fish cages, with sea urchins in cages, in abalone tanks, and in hanging scallop lantern nets. C.


frondosa exhibit high absorption efficiency (>80%) when challenged with particulate material of

higher organic content, such as salmon food and faeces; therefore, it has a great deal potential to

become an effective organic extractive IMTA species. sea cucumbers may have the potential to

some extent constrain or, in some cases, even reverse the polluting impacts of coastal bivalve

aquaculture (Granada et al., 2015).

Aquaponics, fractionated aquaculture, IAAS (integrated agriculture‐aquaculture systems),

IPUAS (integrated peri‐urban aquaculture systems), and IFAS (integrated fisheries‐aquaculture

systems) may also be considered variations of the IMTA concept (Barrington et al., 2009).

Aquaponics is considered as the most common worldwide IMTA system, generating its main

outputs: raising the efficiency of economic activities by creating additional income using second

crop cultures (vegetables, flowers).

Aquaponics as an integrated multi‐trophic system for water quality control in recirculating

aquaculture systems Ensuring the necessary resources and later on, improving the quality of life by introducing

new products and production methods or improving the existing ones, are characterized as major goals that maintain a continuous upward trend of scientific innovations. Therefore, the need for technical and technological development of several productive sectors in order to increase their productivity and also limit the negative effect manifested on the environment is imperative.

Aquaculture gained popularity among investors, especially in the last decade, mostly due to the possibility of practicing high stocking densities. The technological backgrounds of this intensive aquaculture production are directly related to recirculating aquaculture systems (RAS). Another advantage of RAS implies low water‐use rates, fact that characterizes those intensive production systems in terms of technical and technological performance. According to Masser et al. (1999), the majority of recirculating systems have a daily technological water exchange rate between 5‐10%, with the purpose of preventing ammonia nitrogen, as well as the other nitrogen compounds (nitrites and nitrates), to reach alarming concentrations, but also to re‐establish the quantity of technological water lost due to the processes of evaporation and mechanical filter self‐cleaning (Petrea, 2014A).

Both the implementation of new water treatment methods and improving the existing ones are essential requirements in the development of aquaculture sector (Petrea, 2014A). The uses of high‐end equipment for mechanical, chemical and biological filtration and also the increase of recirculation flow, are generally the proposed technical solutions in order to achieve a more efficient technological water treatment process in RAS (Petrea, 2014A) From applicative point of view, all these solutions have been proved to give positive results, but the profitability of recirculating systems has manifested a downward trend due to the increase of capital costs and especially due to the swift rise of variable costs, especially those related to electricity (Petrea, 2014A).

Therefore, the use of bio and phytoremediation techniques by integrating hydroponics with RAS and synchronizing these two production technologies has the potential to solve the above mentioned deficiencies.

The aim of this present study is to compare the information reported by different authors in their scientific studies regarding the bio and phytoremediation potential of various aquaponics integrated systems, where different combinations of fish to plants species, feeding regimes, fish to plants ratio and aquaponics growing techniques were tested.


The reduction of water exchange rates in RAS, generates a decrease of operational costs.

Thus, it can be stated that a secondary production, consisting of plants, assured by using the nutrients from the technological water, without involving additional costs, improves the profitability potential of a RAS (Timmons, 2002).

Technical and technological factors that influence water treatment capacity of aquaponic integrated systems

The plants biomass has its contribution on water quality optimization process and under a judicious sizing between fish biomass: plants biomass: production of metabolic wastes, they have the potential to replace the biological filtration units.

Also, it is recommended to apply a production management which consists in growing plants in various grow stages during a production cycle, also known as CPS (conveyor production system), in order to ensure the maintenance of a constant nutrients concentration in the RAS (Adler et al., 2003).

The water treatment capacity of an aquaponic system depends mostly by its construction design, aquaponic technique applied and phytoremediation capacity of cultured plant species (Figure 3.).

Figure 3. Technical and technological factors that can influence water treatment capacity of

aquaponic integrated systems

Grabber et al. (2009) mentioned that plants can be grown in aquaponic conditions, on

different types of media, used as biological trickling filter, thus combining the ammonia nitrogen

oxidation process (ANOP) with the absorption of the final products, nitrates. Therefore, the use of


substrate aquaponic technique is recommended especially in case of RAS that have an oversized

production capacity, compared with the size of their biological filtration units.

In contrast to bacterial degradation, nutrient uptake by plants is conditioned by the surface,

fact similar to the relationship between photosynthesis and solar radiation (Grabber et al., 2009).

Therefore, in order to obtain a high nutrients recirculation rate, trickling biofilters must

provide sufficient contact area for plant growth and photosynthesis processes related to them, in

relation to their volume (Grabber et al., 2009).

Water quality in recirculating aquaponics systems

In a recirculating integrated aquaponic system (RAIS), both fish stocking density and plant

culture density must be increased gradually in order to prevent high concentrations of ammonia

and nitrite in the water (Ministry of Foreign Affairs, New Zealand, 2013).

The use of low growing and culture densities, for both fish and plants biomass, generates a

certain fish productivity but, in the end, the production costs proves, to be higher than the total

value of obtained production (Ministry of Foreign Affairs, New Zealand, 2013). Thus, the need of

having high production capacities requires a high managerial input, related to water chemistry

monitoring technology and both fish and plants production planning (Ministry of Foreign Affairs,

New Zealand, 2013).

Rakocy et al. (2006) noted that in a aquaponic system, the concentration of nitrates,

phosphates and sulphates are usually at levels considered more than optimal, compared with the

concentration of potassium and calcium, which are mostly insufficient and must be supplemented

by adding potassium hydroxide and calcium hydroxide. These bases are added in varying amounts

and have as secondary aim, to maintain the optimum pH value.

One of the negative aspects of RAIS is the major deficiencies in various nutrients

concentration, like iron, although in terms of nitrogen concentration, the system is in equilibrium It

should be pointed out that, compared to hydroponic systems, nutrient balance in RAIS is very

different in terms of the concentration of added compounds (Ministry of Foreign Affairs, New

Zealand, 2013; Racoky et al., 2006).

Endut et al. (2009) points out that the process of removing nutrients such as inorganic

nitrogen and phosphate is essential for both industrial water and aquaculture effluents treatment

and also, against eutrophication processes, in order for it to be reused. It is noted that, depending

on the species of plants and fish and also, the growth technology and aquaponic techniques used,

integrated recirculating systems record the following removal rates: BOD5 (47‐65%), total

suspended solids (67‐83%), total nitrogen ammonia (64‐78%) and nitrite (68‐89%) (Endut et al,

2009).

It should be noted that, in a RAIS, the removal rates values are proportional with the

recirculating flow value. Total phosphorus and nitrate removal rates are negatively correlated with

the aquaponic units, inlet flow value and can reach, according to Endut et al. (2009), the following

performances: 43‐53% for total phosphorus and 42‐65% for nitrate. Fish appetite, its metabolism

and also, the feeding regimes applied, are important variables that influence both water quality and

phyto‐bioremediation capacity of a certain recirculating aquaponic integrated system. Cripps and


Kumar (2003) states that depending on the technological conditions, approximately 85% of total

phosphorus inputs and 52‐95% of the nitrogen inputs may be lost through faeces and uneaten food.

Biochemical Oxygen Demand (BOD5)

BOD5 concentration within an RAIS has a tendency to increase during the germination of

plant biomass due to increased concentration of dissolved and suspended solids, generated by this

development stage of the seeds (Nelson, 2004). Also, both uneaten food and fish wastes generated

by the metabolic activity are a major source of organic matter that directly affects the concentration

of BOD5 in the embedded systems (Viadero et al., 2005)

In RAIS, the surface area and plant roots density are major factors that influence BOD5

(Bonzoun et al, 1982). The ratio between plants roots surface and aquaponic unit volume is directly

proportional with BOD5 removal rate. This can be supported by the fact that a greater root surface

offers better opportunities for microorganism development. Graber and Junge (2009) reported

higher removal rates for COD, BOD5, ammonia nitrogen and total phosphorus in aquaponic units

designed with a water column height of 0.27m, compared with those having 0.5 m (Graber and

Junge, 2009).

Total suspended solids (TSS)

The values reported by various authors for total solids concentration in water, within a RAIS,

have a wide variation range Endut et al., 2009; Sikawa et al., 2010; Ghaly, et al., 2005). Endut et al.

(2009) reported a significant influence of the inlet flow value on total suspended solids (TSS)

dynamics. Ghaly and Snow (2008) found as notable the phytoremediation capacity of barley, grown

under aquaponic conditions, in term of TSS removal rate from a recirculating trout production

system effluent.

Different studies have reported a downward tendency of TSS concentration, during the

growth period of plants biomass, in integrated recirculating aquaponic system conditions (Ghaly et

al, 2005). This fact is explained by Ghaly et. al (2005) with the supporting argument that plants

increase their capacity of filtration, at the level of their root area, during their growth cycle.

Dissolved solids within the integrated production system are absorbed by plants as nutrients,

process which is influenced by both plant species, type and culture density (Ghaly et al., 2005). Jiang

and Xinyuan (1999) reported a TSS removal rate of 75%, by using layers of floating submerged and

emerged plants. Lin et. al (2002) reported a higher TSS removal rate, of 90%, by using Paspalum

vaginatum.

Nitrogen

An RAIS can be evaluated in terms of its water treatment capacity by phyto and

bioremediation processes, through a precise nitrogen cycle assessment.

In their research, Ghaly and Snow (2008) revealed a decrease of total ammonia nitrogen

concentration by 75%, within an RAIS, by using biomass trout and barley. Bouzoun et al. (1982)

reported a 34% decrease in the total ammonia nitrogen concentration, after five months, by using

reed hydroponic culture.

Ammonium is a major source of inorganic nitrogen, absorbed especially by the roots of tall

stemmed plants (Vaillant et al., 2004.). It can be assimilated by microorganisms and turned into

organic matter, or it can be removed via nitrification processes (Ghaly et al., 2005).


In case of RAIS, where zeolite is used for water treatment process, the concentrations of

ammoniacal nitrogen, manganese, zinc and copper records high removal rates, in opposite with

sodium, calcium and potassium (Rafiee et al., 2006). Thus, it should be pointed out that the use of

zeolite in case of applying the substrate aquaponic technique, improves the environmental

conditions for growth and development of plant biomass by facilitating its access to nutrients,

assuring therefore better water treatment performances (Rafiee et al., 2006). Gloger et al. (1995)

assign the ammonium reduction to both plant biomass absorption process and nitrification process

manifested at the level of plant roots surface and culture media. They reported a percentage value

of 9% nitrogen retention, from total amount of nitrogen introduced in the lettuce RAIS, by

administrating the daily feed ratio (Gloger et al., 1995). Mant et al. (2003) obtained a nitrogen

removal rate of 57.7% by using gravel substrate aquaponic technique for growing Salix viminalis.

Ghaly et al. (2005) obtained a 98.1% nitrite removal rate after 21 experimental days by using

barley phytoremediation capacity, in an aquaponic system. Although nitrites have a lower toxicity

rate, compared to ammonia, in RAIS they tend to accumulate on a long term, due to the incomplete

oxidation of bacteria (Poxton et al., 1982; Jo et al., 2000).

Nitrates are essential source of nutrients for plant biomass. Authors have reported values of

nitrate removal rates ranging from 68.8 to 76.7% when using barley plant biomass, growth in

aquaponic conditions (Clarkson and Lane, 1991). Clarkson and Lane (1991) reported an

approximately 10 times reduction of nitrate concentration by using the NFT aquaponic technique

for growing barley in a carp and trout aquaculture production system.

The hydraulic characteristics of an RAIS significantly affect its water treatment

performances. Therefore, an important parameter in this direction is represented by the hydraulic

loading rate (HLR). This statement is supported by several research on this area, as follows: Lin et

al. (2002), Lin et al. (2003) achieving notable results, reporting a nitrate removal rate of 68‐99%,

while Lin et al. (2010) and Schulz et al. (2003) reported an increase of water nitrate levels due to

improper values of applied HLR.

An increase of the aquaponic modules inlet flow generates the occurrence of aerobic

conditions, preventing therefore the denitrification processes from both root surface and growing

media levels (Endut et al., 2009). Also, Dediu et al. (2012) obtained low values of nitrate removal

rates by applying a flow rates value of 16L / min, compared with those obtained for 8L / min, which

were higher.

In case of RAIS, the nitrification process presented at aquaponic units level, lead to a reduced

concentrations of ammonia and also, to higher nitrogen fluctuations (Dediu et al., 2012).

Lennard and Leonard (2006) obtained the best percentage for nitrate retention rate at DWC

(93.2%), comparing with NFT (71.8%) and substrate aquaponic technique (90.9%). It appears that

the NFT technique is the least effective regarding nitrates retention rate, fact confirmed also by

other authors (Wren, 1984). Wren (1984) record a retention rate of 31% for nitrates in variants

where gravel substrate, was used compared to NFT, where the percentage was 20% .

Phosphorus

Except nitrogen, phosphorus is the second important limitative macronutrient, in aquaponic

systems. Phosphorous level records an upward tendency during the plants germination stage, due


to the accumulation of organic matter induced by the presence of both dissolved and suspended

solids (Nelson, 2004). Also, Endut et al. (2009) observed a significant correlation between

phosphorus retention rate and aquaponic modules inlet flow value (Endut et al., 2009). Both

uneaten food and fish faeces represent major sources of phosphorus in RAIS (Endut et al., 2009).

Ghaly et al. (2005) reported a retention rate of phosphorus between 91.8 ‐ 93.6% days by using

barley phytoremediation capacity, in an aquaponic system (Ghaly et al., 2005). A reduction in

phosphorus concentration from 0.3 to 4.4 mg/L was reported by Clarkson and Lane (1991) in an

integrated system, using NFT aquaponic techniques. In general, most authors report a phosphorus

removal rate in RAIS between 10 ‐ 30% (Monneta et al., 2002; Koottatep et al., 1997).

Lennard and Leonard (2006) conducted a comparative study involving the test of all three

main aquaponic techniques (substrate, DWC and NFT), obtaining the best percentage for

phosphorus retention rate in case of using substrate aquaponic technique (52.5%).

It should be noted that high concentrations of calcium in water may cause precipitation of

phosphorus, as dicalcium phosphate (Rakocy et al. 2006).

Dissolved Oxygen (DO)

The values of water dissolved oxygen (DO) directly and indirectly affect the growth

performance of plants biomass and therefore, their phytoremediation capacity, in a RAIS. Goto et

al. (1996) observed a normal development of plant roots at a 2.5 mg/L concentration of DO in water.

A 1,6 mg/L concentration of DO in water has negative effects on growth and development of lettuce

leaves and roots (Yoshida et al., 1997), fact which conducts to lower phytoremediation

performances.

Potassium

Potassium is the third macronutrient, after nitrogen and phosphorus, required in order for a

RAIS to function properly. Seawright et al. (1998) report potassium retention rates between 70‐

75% in case of RAIS.

Mant et al. (2003) reported a potassium retention rate of 24.9% when using gravel substrate

aquaponic technique for growing Salix viminalis. They noted that for determining the retention rate

of potassium, its ability to precipitate in the form of K2S must be taken into consideration (Mant et

al., 2003). Marschner (1998) indicated that high values of potassium concentration generates high

retention rates of this nutrient, fact which can also influence the retention rates of other nutrients,

like magnesium and calcium.

Rakocy et al. (1993) performed a comparative analysis of accumulation rates corresponding

to main nutrients present in a RAIS, obtaining the following relationship: K> N> P> Ca> S>Mg. Quill

et al. (1995) performed a comparative study regarding the need of nutrients supplementation in

both a hydroponic and aquaponic tomatoes systems (Douglas et al., 1985). They found an almost

double phosphorus addition rate for the aquaponic production system, fact that indicates its

possible precipitation (Douglas et al., 1985).

Sodium and Iron

Related to sodium concentration in RAIS water, it should be noted that it must not exceed

50mg/L, a greater value can adversely affect plants potassium and calcium absorption (Douglas et

al., 1985; Rakocy et al., 2006).


Regarding the presence of iron, it must be stated that the hydrated ferric oxide tends to

deposit on RAIS components, fact which explains the low concentration of iron presented in water,

at a certain moment (Seawright et al., 1998). The stability of dissolved iron in water can be increased

by chelating with organic acids such as EDTA, DTPA or EDDHA (Seawright et al., 1998). The iron

derived from the chemical composition of fish food is insufficient for satisfying the growth needs of

plants (Rakocy et al., 2006). Therefore, this situations requires the supplementation of iron

concentration in water by adding chelated iron, which demands the maintaining of pH below the

value of 7 upH, limit which generates the instability of this compound (Rakocy et al., 2006)

Copper and Manganese

The copper concentration in RAIS water has a downward tendency during the production

cycle, fact which indicates its possible precipitation (Seawright et al., 1998). Seawright et al. (1998)

reported a higher net copper concentration in the dissolved solids, compared to its total input in

RAIS, through administrated food.

Manganese concentration in RAIS water indicates a strong downward tendency, associated

also with pH increase (Seawright et al., 1998). Thus, it is recommended that manganese to be used

in its chelate forms, under the conditions of high pH values (Gerber et al., 1985). Seawright et al.

(1998) note a random, but high consumption of manganese, under a lettuce RAIS

Chemical oxygen demand (COD)

In a RAIS, chemical oxygen demand (COD) has an upward tendency during the seeds

germination period, due to the release of enzymes and is in direct correlation with seeds quality

indexes (Ghaly et. al., 2005). During plant growth period, COD concentration of RAIS water register

a significant decrease due to the development of roots filtration capacity and therefore, of the

capacity to absorb the available nutrients (Ghaly et al., 2005). Ghaly et al. (2005) reports COD

decreasing rates between 56‐91%, depending on the type of both fish and plants species. Jiang

Xinyuan (1999) recorded a COD percentage value of 44%, while Gloger et al. (1995) obtained a 54%

in conditions of using lettuce as culture biomass.

Literature review of water chemistry data

The multitude of researches that were made in order to study the performances of

aquaponic systems with different technical and technological characteristics, from both water

treatment and crops productivity aspects, have contributed to the need of centralizing the reported

data, in order to obtain useful correlations (Table 1).

Al‐Hafedh et. al (2008) make a comparative study between three different ratios of fish feed: plant

growing area. Therefore, the highest concentration of phosphorus in water (10.3 mg/L) was

recorded in case of applying the highest ratio (169 g/m2/day), while for the ratio of 113 g/m2/day

and 56 g/m2/day, the phosphorus concentration was 4.9 mg/L, respectively 3.6 mg/L (Al‐Hafedh et.

al, 2008).


Table 1: A literature review of water chemistry data, registered in various aquaponic integrated systems, under different technical and technological conditions

pH

DO

T0 C

Alk

alin

ity

N-N

O2-

N-N

O3-

N-N

H3+

TA

N

Na+

Ca2+

Mg2+

K+

P-PO

4-

S-SO

4

Cl-

Fe3+

Mn2+

Cu2+

Zn2+

B3+

Mo6+

Sour

se

Fish species | Plant species: Leaf lettuce I Nile tilapia (Oreochromis niloticus) Aquaponic technique: DWC Technological conditions: 3 different fish feed to plant growing area ratios of 169, 113 and 56 g/m2/day

Al h

afel

dh e

t al.

2008

7.7 – 8.3

4 – 6.7

28 ND 0.4 – 0.9

5 – 32.4

1 - 2.1

ND ND ND ND 48 10 ND ND ND ND ND ND ND ND

Fish species | Plant species: Romaine lettuce / Nile tilapia (Oreochromis niloticus L.) Aquaponic technique: DWC Technological conditions: Two treatments under different fish densities supplied nutrients at different concentrations

Pan

tane

lla

et.a

l..20

12

ND ND ND ND ND 137 ND ND 17 180 44 106 9 ND ND ND ND ND ND ND ND

Fish species | Plant species: Basil (Ocimum basilicum ‘Genovese’) / Nile tilapia (Oreochromis niloticus L.) Aquaponic technique: DWC Technological conditions: A comparative study regarding vegetable production from aquaponics vs. field conventional production

Rak

ocy

et.a

l.,

2004

7.4 4.2 – 5.6

26.4 - 29.0

96.7 - 155

ND 42 ND 2.2 ND 12 7 45 8 ND ND 2.5 0.8 0.05 0.44 0.19 0.01

Fish species | Plant species: Water spinach (Ipomoea aquatica)/African catfish (Clarias gariepinus) Aquaponic technique: DWC Technological conditions: The evaluation of fish production performance, plant growth and nutrient removal by testing different hydraulic loading rates

End

ut e

t. al

. 20

10 5.6

- 7.3

ND 27.5 - 28.8

ND ND 20 ND ND ND ND ND ND 17 ND ND ND ND ND ND ND ND

Fish species | Plant species: Carp (Cyprinus carpio), grass carp (Ctenopharyngodon idella) and silver carp (Hypophthalmichthys molitrix) /Tomato (Solanum lycopersicum) Aquaponic technique: DWC Perlite substrate Technological conditions: Effects of foliar application of some macro and micro-nutrients

Roo

sta

et.a

l. 20

11 7 -7.7

6.1-6.3

ND 250 1.57 - 1.69

34,6 - 34.9

ND 0.33 ND 34 ND 27 8 ND ND 0.2 ND 0.04 0.37 ND ND


pH

DO

T0 C

Alk

alin

ity

N-N

O2-

N-N

O3-

N-N

H3+

TA

N

Na+

Ca2+

Mg2+

K+

P-PO

4-

S-SO

4

Cl-

Fe3+

Mn2+

Cu2+

Zn2+

B3+

Mo6+

Sour

se

Fish species | Plant species: Okra (Abelmoschus esculentus)/ Nile tilapia (Oreochromis niloticus L.) Aquaponic technique: DWC Technological conditions: An evaluation of UVI aquaponic system production capacity

Rak

ocy

et. a

l 20

04

7.1 ND ND ND 0.95 - 0.1

26 ND 1.58 14 24 6 64 15 6 12 1.3 0.06 0.03 0.34 0.09 0.01

Fish species | Plant species: Nile tilapia (Oreochromis niloticus)/ pak choy (Brassica chinensis) and (COR) coriander (Coriandrum sativum). Aquaponic technique: DWC Technological conditions: A comparative study regarding water quality between an aquaponic integrate system and a recirculating aquaculture system

Sil

va e

t al.,

201

5

ND ND ND ND 0.17 - 0.27

17.81 -15.90

ND 0.10 – 0.13

ND ND ND ND 0.04 - 0.07

ND ND ND ND ND ND ND ND

Fish species | Plant species: Nile tilapia (Oreochromis niloticus)/Tomato (Solanum lycopersicum) Aquaponic technique: DWC Technological conditions: Substrate/ Using different substrates as gravels of 1-3 mm sizes and saw dust mixed, only brick lets of 2-5 cm sizes and only gravels of 1-3 mm sizes in order to estimate their feasibility

Sal

am e

t.al.,

20

14

ND ND ND ND ND ND ND ND 29.99-80.14

ND ND 3.65-5.05

ND 0.23-5.26

ND ND ND ND ND ND ND

Fish species | Plant species: Biculture of Tilapia (Oreochromis niloticus) and crayfish (Procambarus acanthophorus)/ green corn fodder (Zea mays) Aquaponic technique: DWC Technological condition: A comparation of the production of green corn fodder (Zea mays) by using hydroponics and aquaponics techniques

Alf

redo

et a

l.,

2014

6.9– 7.6

3.7 – 5.6

25 - 30

140 0.3 – 3.3

20 - 110

ND ND ND ND ND ND 2.5 - 5


Fish species | Plant species: Tilapia (Oreochromis niloticus) / Tomato (Solanum lycopersicum) Aquaponic technique: Substrate Technological condition: Testing a new concept of aquaponic system in order to improve sustainability and productivity concomitant with lowering environmental emissions K

loas

et

al. ,


pH

DO

T0 C

Alk

alin

ity

N-N

O2-

N-N

O3-

N-N

H3+

TA

N

Na+

Ca2+

Mg2+

K+

P-PO

4-

S-SO

4

Cl-

Fe3+

Mn2+

Cu2+

Zn2+

B3+

Mo6+

Sour

se

5.4 - 7.7

ND 23 - 25

ND 0.09 – 0.78

86 - 168

ND ND 36 - 98

142 - 311

10 -60.8

32.6 - 129

3.2 - 16

99 - 238

41 - 116

0 - 0.46

ND 0 - 2.11

ND ND 0 - 0.52

Fish species | Plant species: Goldfish, (Carassius auratus)/ spinach (Spinaceaoleracea) Aquaponic technique: NFT Technological condition: Testing varied water circulation periods (4, 8, 12, and 24 hrs/day)

She

te e

t al.,

20

13 7.4

- 7.6

5.2 - 5.4

27.1 - 27.8

55.8 - 81.8

0.02 - 0.04

0.23 - 0.28

0.2 - 0.5

ND ND ND ND ND ND ND ND ND ND ND ND ND ND

Fish species | Plant species: Common carp (Cyprinuscarpio), grass carp (Ctenopharyngodon idella), and silver carp (Hypophthalmichthysmolitrix)/ Tomato (Solanum lycopersicum) Aquaponic technique: Perlite substrate Technological condition: The evaluation of the effect of foliar application of some macro and micro-nutrients on plants mineral content

Roo

sta

et a

l.,

2013

7.7 6.1 22.7 ND 1.69 34.6 ND ND ND 34.2 ND 26.7 7.9 ND ND 0.21 ND 0.04 0.37 ND ND

Fish species | Plant species: Atlantic salmon (Salmo salar)/Frillice lettuce (Lactuca sativa var.crispa) Aquaponic technique: NFT Technological condition: Using of unfiltered and filtered technological waste water in aquaponics

Gje

stel

and,

20

13

6.7 - 7.6

ND 17.5 - 17.9

ND ND 1.6-5.6

ND ND 283.6 - 377.7

57.6 - 78.0

38.8 - 50.7

5.56 - 18.6

0,43 - 2.03

0.33 - 0.45

ND 0.014 - 0.04

0.003 -0.022

0.002 -0.144

0.008 -0.012

0.141 - 0.18

0.0021 -0.0138

Fish species | Plant species: African catfish (Clarius gariepinus) / water spinach (Ipomoea aquatica) Aquaponic technique: Gravel substrate Technological condition: Evaluating the effect of flow rate on water quality parameters and plant growth (hidraulic loading rate 0.64; 1.28; 1.92; 2.56; 3.20 L/min)

End

uta

et. a

l. 20

09

7.3 - 7.6

4.1 - 6.7

27.3 -28.7

ND 0.06 - 0.56

6.6 - 18.9

ND

2.34 -10.84

ND ND ND ND 7.5 - 15.9



pH

DO

T0 C

Alk

alin

ity

N-N

O2-

N-N

O3-

N-N

H3+

TA

N

Na+

Ca2+

Mg2+

K+

P-PO

4-

S-SO

4

Cl-

Fe3+

Mn2+

Cu2+

Zn2+

B3+

Mo6+

Sour

se

Fish species | Plant species: Murray cod (Maccullochella peelii peelii)/ Green oak lettuce (Lactuca sativa) Aquaponic technique: Gravel substrate Technological condition: A comparative study between reciprocating flow vs constant flow

Len

nard

et a

l.,

2004

6.8 - 6.9

7.2 - 7.4

21.9 - 22

ND ND 2.6 - 6.3

ND ND ND ND ND ND 0.69 - 0.72


Fish species | Plant species: Murray cod (Maccullochella peelii peelii)/ Green oak lettuce (Lactuca sativa) Aquaponic technique: Gravel substrate, DWC, NFT Technological condition: A comparative study between three different hydroponic sub-systems (gravel bed, floating and nutrient film technique)

Len

nard

et a

l., 2

006

6.7 - 7

7.2 - 7.9

22 ND ND 0.59 - 3.55

ND ND ND ND ND ND 0.61 - 0,7


Fish species | Plant species: Hybrid catfish (Clarias macrocephalus×C. gariepinus)/ lettuce (Lactuca sativa L) Aquaponic technique: Gravel substrate amd sand substrate Technological condition: A comparative study between two different aquaponic substrates, by using both unfilteres and filtered pond water

Sik

awa

et a

l., 2

010

7,1 - 7,4

0.4 - 1.1

28,9 - 30.9

99 - 469

0.01 - 0.17

1.54 - 4.02

ND 2,22 - 2.67

ND 5.05 - 5.3

0.64 - 0.67

10.1 -13.1

0.38 -. 056

ND ND 0.15 - 0.43

0.01 - 0.02

0.02 - 0.03

0.04 - 0.06

ND ND

Fish species | Plant species: Bester sturgeon hybrid beluga (Huso huso) X sterlet (Acipenser ruthenus)/Lettuce (Lactuca sativa L) Aquaponic technique: DWC Technological condition: A comparative study between water chemistry of RAS vs integrated aquaponic system

Ded

iu e

t. al

20

11 7.1

- 8

6.1 - 9

18.3 ND 0.002 17.92

ND 0.4 ND ND ND ND ND ND ND ND ND ND ND ND ND


pH

DO

T0 C

Alk

alin

ity

N-N

O2-

N-N

O3-

N-N

H3+

TA

N

Na+

Ca2+

Mg2+

K+

P-PO

4-

S-SO

4

Cl-

Fe3+

Mn2+

Cu2+

Zn2+

B3+

Mo6+

Sour

se

Fish species | Plant species: Bester sturgeon hybrid beluga (Huso huso) X sterlet (Acipenser ruthenus)/ lettuce (Lactuca sativa L) Aquaponic technique: DWC Technological condition: A evaluation of waste production in an integrated aquaponic system

Ded

iu e

t.al.,

201

1

7.6 - 7.3

6.3 - 6.4

ND ND ND

32.52 -34.52

ND 0.39 - 0.43

ND ND ND ND ND ND ND ND ND ND ND ND ND

Fish species | Plant species: Tilapia/Aubergines and Perch, Tomatoes, Cucumbers Aquaponic technique: Light-expanded clay aggregate (LECA) Technological condition: A evaluation of waste production in an integrated aquaponic system

Gra

ber

et. a

l., 2

009 6.8

- 7.8 7 - 7.4

2.6 - 4.8 6.7 - 7.5

ND ND

0.08 - 0.57 0.01 - 0.18

1.9 – 42 12.1 - 95

ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND

Fish species | Plant species: Red Tilapia (Oreochromis sp.) and Lettuce (Lactuca sativa var. longifolia Aquaponic technique Zeolite substrate Technological condition a evaluation of water chemistry in an integrated aquaponic system

Raf

iee

et

al. ,

2006

6.3 ND ND ND ND ND ND 2.87 ND 27.0 3.7 5.78 8.3 ND ND ND 0.04 ND 0.05 ND ND

Fish species | Plant species: Tilapia (Oreochromis niloticus), strawberry Aquaponic technique: NFT Technological condition: A evaluation of water chemistry in an integrated aquaponic system, by using two fish stocking densities

Vil

larr

oe e

t. al

.201

1 6.1 - 7.2

22 21.7 - 21.9

ND 0.12 - 2.06

32.63-44.57

ND ND 64.6 - 96.9

21.6 - 36.3

3.89 - 6.11

9.52 – 15.9

ND 9.73 - 11.2

23.8 -34.4

ND ND ND ND ND ND


pH

DO

T0 C

Alk

alin

ity

N-N

O2-

N-N

O3-

N-N

H3+

TA

N

Na+

Ca2+

Mg2+

K+

P-PO

4-

S-SO

4

Cl-

Fe3+

Mn2+

Cu2+

Zn2+

B3+

Mo6+

Sour

se

Fish species | Plant species: Stellate Sturgeon (Acipenser stellatus), Spinach–Matador variety Aquaponic technique: LECA substrate Technological condition: The evaluation of water chemistry and vegetable production in an integrate aquaponic system, where 3 crops culture densities were applied

Pet

rea

et.a

l. 20

14

7.7 7.3 19.4 52.9 0.18 39.74

ND ND ND 102 30.4 28.2 2.7 ND 26.4 0.65 0.54 ND ND ND ND

Fish species | Plant species: Rainbow trout (Oncorhynchus mykiss), Nores variety spinach (Spinacia oleracea Aquaponic technique: DWC Technological condition The evaluation of water chemistry and vegetable production in an integrate aquaponic system, where 3 crops culture densities were applied

Pet

rea

et.a

l. 20

13

6.9 7.5 16.8 200 0.05 21.52

ND ND ND 90.4 30 9.42 1.2 ND 27.7 0.37 0.48 ND ND ND ND


In the same study, similar results were recorded for potassium concentration in water, which

varied from 47.5 mg/L to 31.4 mg/L and 19 mg/L, by applying the feeding regimes of 169 g/m2/day,

113 g/m2/day and 56 g/m2/day (Al‐Hafedh et. al, 2008).

By analyzing the obtained results, Al‐Hafedh et. al, (2008) concluded that there is a direct

correlation between phosphorus and potassium concentration in water and the ratio of fish feed:

plant growing area.

Endut et. al (2010) tested the use of different hydraulic loading rates (HLR) for an water

spinach african catfish aquaponic system.

The concentration of nitrogen nitrite varied from 0.19 mg/L to 0.14 mg/L, 0.11 mg/L, 0.09

mg/L, 0.06 mg/L for HLR of 0.64 m/day, 1.28 m/day, 1.92 m/day, 2.56 m/day and 3.2 m/day (Endut

et. al, 2010). In case of nitrogen nitrate, the highest concentration (9.7 mg/L) was recorded for a

HLR of 3.2 m/day, while the lowest value (5.4 mg/L) was registered for a HLR of 1.28 m/day (Endut

et. al, 2010). Phosphorus had the same evolution like nitrogen nitrate by registering the highest

value (7.9 mg/L) in case of HLR – 3.2 m/day and the lowest value (6.3 mg/L), for a HLR of 1.28 m/day

(Endut et. al, 2010). Therefore, Endut et. al (2010) proved that the changes in concentration of

different nutrients in aquaponic systems, differ because of the disparity between the relative

proportions of available nutrients generated by fish and nutrients uptake by plants. Also, he

mentioned that, the HLR is an important parameter for determining the phytoremediation capacity

of an RAIS (Endut et. al, 2010).

In another study Endut et. al. (2009) evaluated the effect of flow rate on plants

phytoremediation capacity in a RAIS. Therefore he recorded the highest phosphorus removal rate

(50%) for a 0.8 L/min flow rate (Endut et. al, 2009). A flow rate of 1.6 L/min generated the highest

nitrogen nitrate removal rate (64.9%), while at 4 L/min is recorded the highest nitrogen nitrite

removal rate (89.5%) and TAN removal rate – 78.3% (Endut et. al, 2009).

Silva et. al (2015) demonstrated that an RAIS of Nile tilapia – pak choy had better water

treatment performance, compared with a similar system of Nile tilapia – coriander. Therefore, the

study concluded that pak choy phytoremediation capacity by using dynamic root floating technique

could allow the reduction of investment costs in an RAIS (Silva et. al, 2015).

Shete et. al (2013) experimented various water circulation periods (4, 8, 12 and 24 hrs/day)

in an goldfish – spinach aquaponic system, by using nutrient film technique (NFT). The highest

nitrogen nitrate concentration in water (0.28 mg/L) was recorded for the experimental variants with

12 and 24 hrs/day water circulation (Shete et. al, 2013). In case of nitrogen nitrite and ammonia

concentration in water, the highest concentration (0.3 mg/L for ammonia and 0.04 mg/L N‐NO2)

were recorded for the experimental variants where a 4 hrs/day water circulation period was applied

(Shete et. al, 2013). The study showed that the water circulation period has a direct effect on water

quality parameters in a RAIS (Shete et. al, 2013).

Lennard and Leonard (2004) make a comparative study between two hydraulic regimes, as

follows: constant flow and reciprocating flow (ebb and flow). The nitrate and phosphate

concentrations in water, in case of constant flow (11.8 mg/L – nitrate and 3.87 mg/L – phosphate),

are lower than in reciprocating flow (13.3 mg/L – nitrate and 4.04 mg/L – phosphate), fact that


shows a better plant phytoremediation capacity at constant flow hydraulic regime (Lennard and

Leonard, 2004).

In a bester sturgeon hybrid – lettuce RAIS, Dediu et. al (2012) registered higher values for

retained nitrogen (1.13 g/m2/day), in case of using a low flow rate, corresponding to a hydraulic

retention time (HRT) of 5.4 min, compared with a high flow rate (HRT=2.7 min), where retained

nitrogen value was 1.05 g/m2/day.

Petrea et. al (2013B) tested three plants densities a (59, 48, 39 plants/m2) in a rainbow trout

– spinach RAIS. He registered TAN removal rate of 1.24 mg/L/day for the highest plants culture

density, followed by 1.09 mg/L/day and 0.71 mg/L/day for the variant with 48 plants/m2,

respectively 39 plants/m2 (Petrea et. al, 2013B). The nitrate removal rate, registered a value of 16.4

mg/L/day, 12.5 mg/L/day and 8.23 mg/L/day for the variants with 59, 48, 39 plants/m2 (Petrea et.

al, 2013‐B). As a conclusion, Petrea et. al (2013‐B) mentioned that the phytoremediation capacity

on a aquaponic module is in a direct correlation with plants culture density. In the same experiment,

Petrea et. al (2014‐D) registered the highest phosphorus and calcium removal rates (3.83 mg/day –

phosphorus and 3.9 mg/day – calcium) in the experimental variant with 59 plants/m2, while for the

other two variants (48 and 39 plants/m2), the phosphorus and calcium removal rates were lower

(3.04 mg/day – phosphorus and 2.69 mg/day – calcium, respectively 2.18 mg/day – phosphorus and

1.95 mg/day – calcium).

Petrea et. al (2014C) tested three plants density (59, 48, 39 plants/m2) in a stellate sturgeon

– spinach RAIS, by using light expanded clay aggregate (LECA) aquaponic technique (Petrea et. al,

2014C). He registered TAN removal rate of 0.3 g/m2/day for the highest plants culture density,

followed by 0.37 g/m2/day and 0.31 g/m2/day for the variant with 48 plants/m2, respectively 39

plants/m2 (Petrea et. al, 2014C). The nitrogen nitrate removal rate, registered a value of 13.4

g/m2/day, 11.97 g/m2/day and 11.49 g/m2/day for the variants with 59, 48, 39 plants/m2 (Petrea et.

al, 2014C).

CONCLUSIONS

Although aquaculture has proved its contribution in food security and poverty alleviation,

the global aquatic environment pollution due to the waste released has also attracted considerable

public concerns. In this scenario, IMTA is proposed as one of the bio‐mitigation options to avoid or

alleviate the negative change caused by aquaculture waste. However, effective implementation of

IMTA requires a more elaborate consideration of its design (Zhang, et al. 2015b).

Mussel growth has been calculated in a variety of ways such as measuring changes in size

distribution of a common population (Bayne & Worrall 1980, Kautsky 1982, Page & Hubbard 1987,

Stirling & Okumusx 1995, Cheshuk et al. 2003) or, alternatively, by measuring individually marked

or caged individuals (Kautsky 1982, Page & Hubbard, 1987, Dolmer 1998). Successive measurements

of marked or caged mussels can provide valuable records of the effect of size, season, and

environmental condition on growth (Page & Hubbard 1987).

Although growth in M. edulis has been attributed to a variety of factors, including site

characteristics and season (Mallet & Carver 1989, Mallet & Carver 1993), genetics (Mallet et al.


1986), water temperature (Page & Hubbard 1987), depth (Rodhouse et al. 1984), salinity (Kautsky

1982, Kautsky et al. 1990, Westerbom et al. 2002), density (Seed 1968, Kautsky 1982), and

chlorophyll concentration (Page & Hubbard 1987, Page & Ricard 1990, Thorarindo¨ ttir 1996), it is

indeed the quantity and quality of the food supply that has been cited on several occasions

(Fre´chette & Bourget 1987, Seed & Suchanek 1992, Øie et al. 2002) to be the single most important

factor in determining growth in this species.

There may be examples when additional particulates released from salmon farms may not

result in enhanced growth of mussels. This could occur in environments that already have high levels

of natural seston or where supplemented concentrations from the farms exceed levels where

pseudofeces production will begin in mussels. In a comparable study in Tasmania, no enhanced

growth was found in the Tasmanian blue mussel (Mytilus planulatus) at a single salmon aquaculture

site during a 14‐mo period as a result of a combination of factors, including high ambient seston

concentrations that were consistently above the pseudofeces threshold, thereby limiting ingestion

of fish farm generated particles from ‘‘ingestive competition’’ between waste and natural

particulate matter (Cheshuk et al. 2003). In a Chilean study Troell and Norberg (1998) recorded

pulses of organic matter that increased suspended solid concentrations 3‐ to 30‐fold. They

concluded that ambient levels of seston already exceeded pseudofeces production levels, and these

short‐term pulses would not influence mussel growth in this situation. Combined bivalve–finfish

culture may, therefore, be best suited in coastal systems with low ambient seston concentrations.

Based on the diversity of studies designed to evaluate bivalve growth in several different

species around finfish farms in a great variety of different environments and oceanographic

conditions, it is not surprising that inconsistencies in growth rates have been observed. Cheshuk et

al. (2003) cited location of the experimental mussels in relation to the salmon site as a factor limiting

mussel growth in Tasmania. In their study, mussels were located between 70 m and 100 m from the

salmon, which was likely outside the zone of salmon‐produced particulate food sources. Navarrete‐

Mier et al. (2010) did not observe significant growth during a 3‐mo period in oysters or mussels held

between 0mand 1,800mfrom the fish farms. Others have recognized the importance of shellfish

placement and have found significant growth rates of bivalve species in the proximity of finfish

farms, but there has not necessarily been a consistent trend of reduced growth with increasing

distance from the farm (Perharda et al. 2007, Sara´ et al. 2009, Handa et al. in press).

Although studies have estimated organic enrichment up to 500 m from salmon cages (Brzeski

& Newkirk 1997), most studies measuring horizontal displacement suggest that 99% of all

particulates settle within 50–60 m of fish cages (Gowen & Bradbury 1987, Coyne et al. 1994).

In summary, mussels grown adjacent to salmon cages had faster shell growth than mussels

held 200m or 500 m away from the cages and those held at reference locations outside the direct

influence of salmon farms. Mussels held at salmon cages continued to grow in the winter months

and maintained a greater meat weight and CI than mussels held 200 m away or at a reference site.

Establishing the relationships between distance from the cages and mussel growth rates will have

implications for mussel growers with respect to a reduction in time to harvest, and a faster turnover

time per crop compared with customary mussel culture techniques. The current commercial salmon

aquaculture infrastructure can be adapted to fit mussel raft culture as existing ropes and mooring


systems can be used, decreasing the initial startup investment. The fact that mussels experience

growth during winter periods at salmon sites in the Bay of Fundy further validates this approach to

establish integrated mussel–salmon aquaculture because mussels can be harvested well into late

fall and (at least) early winter (Lander et al. 2012).

Although this study represents a positive first step, the implementation of IMTA systems

requires extensive experimentation into the varied intra‐ and interspecies interactions, and intersite

differences, as well as processes governing the co‐culture of multiple trophic levels to maximize

nutrient use, total product yield, and bioremediative potential of the overall system (Lander et al.

2012).

The primary motivation to develop the IMTA model was to provide a quantitative tool for

the development and management of IMTA practices through mapping energetic pathways

between trophic groups and their environment. Application can assist designing IMTA practices to

maximize resource utilization and minimize environmental impacts (Ren et al. 2012).

This revision of literature helped to identify several limiting factors regarding water

treatment capacity of various aquaponic systems. Therefore, there were identified both technical

and technological factors, that directly influence the phyto and bioremediation capacity of a certain

aquaponic integrated system.

Among the technological factors, the most commonly encountered were the ratios between

fish stocking density: plants culture density and fish feed: plant growing area. Also, the biochemical

composition of administrated fish diets and therefore, the water nutrient load level are important

factors that directly influence the phyto and bioremediation capacity of aquaponic integrated

systems.

The technical factors are firstly represented by the type of aquaponic technique that is

applied (DWC, NFT or culture substrate). In case of culture substrate technique, significant water

treatment differences were registered when using different types of substrates (gravel, LECA, sand

or zeolite), or by using different hydraulic regimes (continuous flow or flood and drain). The

aquaponic module inlet flow, characterized by both hydraulic retention time (HRT) and hydraulic

loading rate (HLR) was demonstrated as having a significant effect on phyto and bioremediation

capacity of aquaponic integrated systems.

Beside both technical and technological factors mentioned above, the management of

production has a key role on assuring a constant water nutrient load throughout the entire

production cycle. Thus, the literature recommends a conveyor production system management in

order to obtain a higher percentage of nutrient recovery at plants biomass level and also, better

water treatment performances.

The present literature overview had demonstrated that in order to use a RAIS phyto and

bioremediation capacity at its maximum potential, different technical, technological and production

management factors must be taken into consideration.

In the future, it is recommended that research should be made in order to study the

correlation between microbiological activity at aquaponic modules level and phyto and

bioremediation capacity of RAIS


The feasibility of a modelling approach for general management in the aquaculture industry

hinges on the flexibility of a model for various species and portability between farming systems.

Because the IMTA concept is very flexible, it can be applied to open water, land‐based, marine and

freshwater systems (Chopin et al., 2008) and therefore the choice of secondary organisms should

be based on their commercial value as well as bio mitigation potential in the local farm environment.

Practically, culture feasibility, economic value and social potential are primary consideration for

both principal and secondary species (see Chopin et al., 2008). Up to date, there have been different

mixed‐species aquaculture systems in study and in operation worldwide (Barrington et al., 2009).

Through the lack of predictive modelling tools, both experimental and commercial‐scale operations

have been dependent on field trials and results remains semi‐quantitative (see Neori et al., 2004;

Chopin et al., 2008). Some effort has been made to model salmonid solid and soluble nutrient

loading for co‐culture trials of seaweeds and mussels in salmon farms (Angel and Freeman, 2009).

The authors have recognized the need to develop flexible models that can simulate co‐culture

interactions and the effects of IMTA systems on water quality inside and around the farm. We

believe that the present model accommodates this flexibility. The development of energetic sub‐

models that are specific to a trophic group is based on DEB theory that species share the

commonality in physiology and hence follow the same energetic pathways across species (Kooijman,

2000). In addition, the temperature effect on the rate processes of all biological groups follows a

single Arrhenius relationship. The model is transferable to other IMTA systems with species

combination of finfish–shellfish‐detritivore‐primary producer for optimizing yields and reducing

farm‐derived wastes. Adjustments lie in the parameterization for local environmental processes and

hydrodynamic properties (Ren et al. 2012).

The capability of the model has been examined through IMTA scenario simulations for both

fish and mussel farms where crop species of different cohorts were all seeded at the same time.

Although this assumption was somewhat arbitrary, the model outputs have helped us understand

system behaviours of the IMTA scenarios. Generally, the model could generate reasonable

outcomes on the required biomass of each trophic level for the prescribed IMTA system. The model

outcomes have shown that IMTA practices would considerably reduce environmental impacts.

Simulations have also illustrated some of the difficulties in optimizing production and

bioremediation on an IMTA farm. One of the important features is that the consumption rate of sea

cucumbers mismatched the mussel bio deposition rate during the simulation period, particularly

during the first few months of the simulation. The bio deposition rate showed clear seasonal

variation, while the sea cucumber consumption generally showed an increasing trend (Ren et al.

2012). This mismatch resulted from the difference in physiological characteristics: mussel bio

deposition rate depends on food supplies and temperature (e.g. Hawkins et al., 1999), while the

consumption of sea cucumber is largely affected by temperature (e.g. Yang et al., 2005). Although

the biomass of sea cucumbers could be increased to match mussel bio deposition rate initially, this

would cause less food availability and starvation during some periods, particularly in winter months

when bio deposition rate is low. This disagreement between consumption and bio deposition would

cause low reduction efficiency where a large fraction of the bio deposition remains in the system.

The optimization between consumption and bio deposition rates could be achieved through


manipulations of stocking density, seeding time and harvesting frequencies, but any proposals for

culture operations should be economically practicable and cost‐effective. Therefore, acceptable

levels of reduction efficiency would account for feasibility and profitability of culture operations.

For the salmon farm, however, the bio deposition rate matched reasonably well with the

consumption rate of sea cucumbers, reflecting little variation of reduction efficiency. This result is

very promising for the development of fish‐based IMTA practices, as it is feasible to achieve

acceptable levels of consumption rate and reduction efficiency without additional costs resulting

from multiple stocking density and harvesting operations. Because finfish aquaculture can cause

much higher environmental impacts than shellfish farming (see Hatcher et al., 1994; Buschmann et

al., 2006), the co‐culture of sea cucumbers would have promising mitigation potential.

Development of the novel IMTA model is not without difficulties and shortcomings. Some

knowledge gaps have been detected, one of which is the lack of comprehensive physiological

information for potential co‐culture species in New Zealand. Although this would have contributed

some uncertainties in the parameterization of the DEB sub‐models, model simulations may not have

been greatly compromised. The variation of parameter values may not be considerable between

related functional species and hence borrowing parameter values is common in bioenergetics

modelling studies. For example, a model for sockeye salmon could successfully predict the

behaviour of Coho salmon and Chinook salmon (e.g. Stewart and Ibarra, 1991). Similarly, other

studies have shown that rainbow trout metabolism was an adequate substitute for chinook salmon

metabolism (Madenjian et al., 2004). In addition, some limited information indicates that

physiological rates of sea cucumber (A. mollis) are similar to those of S. japonicus and the rates of

seaweed (E. radiata) are close to the parameter values used in the model (NIWA unpublished data).

Nonetheless, the model has contributed to understanding the dynamics of IMTA systems and

provided a quantitative tool for designing and managing IMTA practices (Ren et al. 2012).

The advantages of integrated multi‐trophic aquaculture are multiple and it relates to the

transformation of the by‐products, the flexibility of the concept, environmental sustainability and

economic efficiency.

The wastes from one species become into inputs (fertilizers, food and energy) for another

(Barrington et al., 2009). IMTA systems can be land‐based or open‐water systems, marine or

freshwater systems, and may comprise several species combinations (Barrington et al., 2009). IMTA

may create a balanced system for environmental sustainability of earthen ponds while increasing

their profitability and social acceptability (Cunha et al., 2011).

IMTA is the only practical remediation approach with a prospect for additional farm

revenues by adding commercial crops, while all other bio‐mitigation approaches have generally

involved only additional costs to the producer (Granada et al., 2015).

In conclusion, the development of IMTA practices, the balanced ecosystem approach, is

bound to play a major role worldwide in sustainable expansions of aquaculture (Soto, 2009). An

IMTA ecosystem model is a useful tool for gauging optimal stocking scenarios based on the

predicted amounts of farm‐derived wastes. The model structure is flexible for application to

different IMTA operations. Further improvement of the model would rely on comprehensive

physiological information of trophic species collected from specially designed experiments that


provide data suitable for modelling requirements. The predictive accuracy of the model presented

here will be enhanced with feedback from monitored commercial IMTA farms that are likely to grow

in number as pressure for space increases and environmental accountable becomes more acute

across the world (Ren et al. 2012).

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Improving fish health

Due to the continued decrease of wild fish captures and to the increased fish requirements,

aquaculture became the fastest growing food‐producing sector worldwide. Although aquaculture

has continued to develop, is facing a number of problems due to diseases and other health issues

causing big economic losses and undermining the sustainability of the aquaculture industry.

Mainly, fish are growth in intensive systems, so they are frequently exposed to a range of

stressors such as handling, poor water quality, food and feeding regimes, high stocking density,

grading, starvation, diseases and parasite infestation, vaccinations, methods of slaughter, fasting,

loading and transport and so on.

Therefore, the recent expansion of intensive aquaculture practices led to a strong interest in

understanding various diseases of fish, and the way of they can be treated or prevented. It has been

demonstrated extensively that the occurrence of diseases in farmed fish is due to several factors

related to the technology of growing and the variation of environmental conditions.

Lately, there is a real concern of authorities, scientists, and consumers regarding animal

health and welfare, both terrestrial and aquatic. However, the concept of animal welfare is difficult

to define, because it is used in many different ways by people with a different background (Edward

2012). According to Appleby et al 1997 and Duncan et al 1997, it refers to the quality of life or state

of well‐being, i.e. the physical and mental state of the animal in relation to the enviroment.

Although fish welfare and health are quite appropriate, an approach based only on the

health of fish is unrealistic disregarding all components welfare. For example, poor welfare

condition in the growing system can affect the health status of fish and favors spreading disease and

implicit a bad welfare state.

For aquaculture, the term of "health" is often correlated with disease absence. In the last

years, aquaculture sector had awarded a big importance on the prevention diseases. Disease in

aquaculture has become a primary constraint, impeding both economic and social development in

many countries. This situation can be attributed to a variety of multifaceted and highly

interconnected factors, such as (Fish State 2010):

the increased globalization of trade in live aquatic animals and their products;

the intensification of aquaculture through the translocation of broodstock, post larvae, fry,

and fingerlings;


the introduction of new species for aquaculture and fisheries enhancement;

the development and expansion of the ornamental fish trade;

the enhancement of marine and coastal areas through stocking aquatic animals raised in

hatcheries;

unanticipated negative interactions between cultured and wild fish populations;

poor or effective biosecurity measures;

slow awareness on emerging diseases;

the misunderstanding and misuse of specific pathogen‐free (SPF) stocks (e.g. shrimp);

climate change, and

all other human‐mediated movements of aquaculture commodities.

Stress in farmed fish has an important significance to both welfare and productivity as it has

been linked to a reduction in growth, abnormal behavior, and immunodepression (Wedemeyer,

1996; Ashley, 2007). The “stress” term is defined as all non‐specific reactions triggered by the body

when it goes from a normal physiological state to one abnormal. The stress response is considered

an adaptive mechanism that allows the fish body to perceive and react to stressors for maintaining

normal physiological balance. If the intensity of stress factors is pronounced or lasts too long

hemostatic response is reduced, favoring deterioration of vital signs, physiological response

mechanisms are compromised, leading to the occurrence of the disease and even fish mortality

(appear loss of appetite, impaired growth and muscle wasting, immunosuppression and suppressed

reproduction).

As a response to the action of stressors factors, the fish body suffers a series of physiological

and biochemical changes in order to face the stress factors. If the action is short, stress is acute and

allows the body fish respond to stressors and to return to a normal physiologically state, while if the

action is in the long term appears more severe effects of chronic stress. So, under conditions of

stress, the body of the fish emits immediate responses recognized as primary, secondary and

tertiary responses (Figure 1).

The primary response is the perception of an altered state of the central nervous system and

the release of the stress hormones, cortisol and catecholamines (adrenaline and epinephrine) into

the bloodstream by the endocrine system (Randall & Perry 1992). Secondary responses occur as a

consequence of the release stress hormones, causing changes in the blood and tissue chemistry,

e.g. an increase of plasma glucose. In tertiary response appear behavior modification, the slowdown

in growth and development, metabolic activity, reproductive capacity, impaired immune function

and decrease resistance to disease, however claiming the being with decreased survival rate

(Schreck et al 1997; Pickering A.D 1998; Conte FS et al 2004). The primary stress‐induced hormone

produced and released is represented by cortisol which can suppress the immune system and lead

to fish mortality (Huntingford FA et al 2006).

Some authors (Barton, 2002; Ortuno et al 2002), studied the blood corticosteroid levels as

ban indicators of stress because the extreme sensitivity of the hypothalamic–pituitary‐interrenal

(HPI) axis. Prolonged stress conducted to activation of HPI axis, continuously or for prolonged

periods, resulting in a chronically extended stress response. According to Wenderlaar‐Bonga, 1997,

cortisol represents the main glucocorticoid in fish and the end‐product of the HPI axis activation.


Elevation of corticosteroid plasma levels is one of the most evolutionary conserved stress responses

and it is commonly used as an indicator of the degree of stress experienced. Also, behavioral

modification appears, like reduction of feed appetite, changes in levels of activity and swimming

performance.

Figure 1. Primary, secondary and tertiary responses.

According to FAWC, 1996 ensuring the welfare of fish biomass can be done by respecting the

rights of fish, known as the ”five freedoms” (Table 1).

Table 1. The five Freedoms of Animal welfare (FAWC, 1996) and the indicators used to assess welfare

impairment

Five freedoms of animal welfare Indicators

Freedom from hunger and thirst Feed intake, growth rate, condition factor

Freedom from discomfort Physical damage, fin condition, cataracts, lesions, immune responses (e.g. lysozyme activity, respiratory burst, phagocytic activity)

Freedom from pain, injury or disease Environmental monitoring: water quality monitoring, ammonia, pH, carbon dioxide, suspended solids) Target sampling of fish: gill condition, checking for parasite infestation

Freedom to express normal behavior Abnormal behavior: swimming and feeding behavior, distribution of the fish within a system (e.g. clumping around inflows),responses of fish to an approaching farmer

Freedom from fear and distress Measuring primary and secondary stress response: plasma cortisol, glucose, lactate, muscular activity.


According to Iwama et al 2006, fishes are exposed to stressors in nature as well as in artificial

conditions such as in aquaculture or in the laboratory. In intensive rearing fish are exposed to a

regime of acute and chronic stressors, which have adverse effects on growth, reproduction,

immunocompetence, and flesh quality (Barton et al 1987; Maule et al 1989; Shreck et al 2001).

These stressors, which are peculiar to fish in aquaculture range from chemical, biological, physical

and procedural. The most common way that induced stress in fish are represented by the daily

management operation (Table 2).

Table 2. Stressors common in intensive aquaculture according to Field Survey (2007)

Stressors Occurrence

(%)

Chemical stressors

Poor water quality (Low DO., improper pH) 20

Pollution‐ intentional pollution: efficient, wastes, sewage;‐accidental pollution: spills: insecticide, pesticide

10

Diet composition imbalance diet 10

Nitrogenous and other metabolic wastes (i.e accumulation of ammonia or nitrite)35

Biological stressors

Stocking density / over crowding 5

Social dominance 1

Micro organisms–pathogenic and nonpathogenic 2

Macro organisms‐internal and external parasites 2

Physical stressors

Temperature 1

Light 1

Sounds 0

Dissolved Gases 1

Procedural stressors

Handling 3

Transportation 5

Sorting/Grading 3

Disease Treatments 1

Generally, in fish farming, fish health and welfare are dependent on a good management

which depends on the knowledge of the echo‐technological requirements of the growth species.

Also, it is important and necessary early detection of the abnormal situation which may occur in fish

growth in order to remove them or to limit their action.

As we mention before on fish health can action chemical, biological, physical and procedural

stressors.

Chemical and physiological stressors.

Between the main chemical stressors, a big importance is attributed to chemical conditions

of the water and fish diet.

Water quality. Water quality parameters are unavoidable in fish health assessment,

considering its influence on health condition, productivity and fish behavior, described in papers by

Svobodova et al (1993), MacIntyre (2008) and Dulić et al. (2010). Because fish are in constant

interaction with their environment through the gills and skin, therefore, maintaining a good water

quality is crucial for their health and welfare (Bianca, 2009).


Fish biomass, from both the natural environment and growth in other systems, can be

affected by a number of physical and chemical agents. If these factors registered abnormal values

can determinate physiological and metabolic disturbance, becoming harmful for fish health (Table

3).

Table 3. Effects of the main physicochemical parameters of water on fish health

Parameter Effects on fish health References

pH Low Fish produce an increased amount of mucus on the skin and on the inner side of the gill covers.

Zdenka Svobodova et al 1993

High Damage to fish tissues, especially the gills, and hemorrhages may occur in the gills and on the lower part of the body.

Temperature When the temperature is changing suddenly fish can die, showing symptoms of paralysis of the respiratory and cardiac muscles.


Suboptimal temperature

The decrease of basal metabolism, metabolic activity, oxygen consumption, respiratory rate, Gills absorption and penetration of toxins, pathological risks.

Zdenka Svobodova et al 1993 Munteanuand Bogatu, 2003

Supra‐ optimal temperature

High metabolism, a decrease of metabolic activity, a higher oxygen consumption, respiratory rate and gills absorption and penetration of toxins.

Dissolved oxygen

Oxygen deficiency

Fish asphyxiation, loose appetite, a very pale skin colour, congestion of the cyanotic blood in the gills, adherence of the gill lamellae, and small haemorrhages in the front of the ocular cavity and in the skin of the gill covers., collect near the water surface, gasp for air (cyprinids), gather at the inflow to ponds where the oxygen levels are higher, fail to react to irritation, lose their ability to escape capture and ultimately die.


Oxygen excess Gills of such affected fish have a conspicous light red color and the ends of the gill lamellae fray, can apperar bubble gas disease


Ammonia Slight restlessness, and increased respiration; the fish congregate close to the water surface, their restlessness increases with rapid movements and respiration becomes irregular; then follows a stage of intense activity, they lose their balance, leap out of the water, and their muscles twitch in spasms; affected fish lie on their side and spasmodically open wide their mouths and gill opercula; finally, they lose their balance, leap out of the water, and their muscles twitch in spasms. Affected fish lies on their side and spasmodically open wide their mouths and gill opercula. The gills are heavily congested and contain a considerable amount of mucus; fish exposed to high ammonia concentrations may have slight to severe bleeding of the gills. Intense mucus production can be observed on the inner side of the gill opercula, mainly at the posterior end. The organs inside the body cavity are congested and parenchymatous and show dystrophic changes.


Water with a bad quality not necessarily lead to fish mortality, but can lead to a weak

utilization of food, being directly responsible for fish health and survival. Poor water quality can

cause allocation of energy for secondary physiological processes, nonessential (growth,

reproduction) in the primary process, essential (metabolism or resistance function). The sublethal


effects of poor water quality are also commonly associated with the increase in disease

susceptibility. That's why maintaining a good water quality it is important for raising fish in order to

maintain a good health.

According to Relic et al., 2010, the level of fish welfare in one environment is considered

satisfactory if the values of the water quality parameters do not deviate from optimal. Also,

according to a review published in the OIE`s Animal Welfare, failure to provide the ideal

environment result in stress, distress, impaired health and mortality (Håstein T, Scarfe AD, and Lund

VL. 2005).

In table 4 is presented the water quality criteria for Aquaculture (after Meade, 1991; Piper

et al. 1982; Lawson, 1995). Influence of physical and chemical parameters is different on the species

of fish, but a particular importance is attributed to water temperature, the concentration of

dissolved oxygen, as well as the amount of free ammonia, e.g. nitrogen compounds, which are toxic

to fish.

Table 4. Water quality criteria for aquaculture, according to Meade, 1991; Piper et al 1982; Lawson,

1995

Parameter Concentration (mg/L)

Alkalinity (as CaCO3) 50–300

Aluminum (Al) <0.01

Ammonia (NH3‐N unionized) <0.0125 (Salmonids)

Ammonia (TAN) Cool‐water fish <1.0

Ammonia (TAN) Warm‐water fish <3.0

Calcium (Ca) 4–160

Carbon Dioxide (CO2)

Tolerant Species (tilapia) <60

Sensitive Species (salmonids) <20

Chlorine (Cl) <0.003

Hardness, Total (as CaCO3) >100

Hydrogen cyanide (HCN) <0.005

Hydrogen sulfide (H2S) <0.002

Iron (Fe) <0.15

Lead (Pb) <0.02

Magnesium (Mg) <15

Manganese (Mn) <0.01

Mercury (Hg) <0.02

Nitrogen (N2) <110% total gas pressure

<103 % as nitrogen gas

Nitrite (NO2) <1, 0.1 in soft water

Nitrate (NO3) 0–400 or higher

Nickel (Ni) <0.1

Oxygen Dissolved (DO) >5

Ozone (O3) <0.005

pH 6.5–8.5

Phosphorous (P) 0.01–3.0

Potassium (K) <5

Salinity depends on salt or fresh species

Sulfate (SO4) <50

Total dissolved solids (TDS) <400 (site specific and species specific; use as a rough guideline)

Total suspended solids (TSS) <80


Temperature, represent one of the essential factors of the environment of aquatic life that

influence the development of critical processes of fish. Fish are poikilothermic organisms, whose

temperature is approximately equal to that of the environment where they live. Also, a big attention

must be accorded when the water temperature increase, to the concentration of oxygen dissolved

because the oxygen dissolved capacity is inversely proportional to temperature.

Temperature increase may influence hormonal control of growth through the stress

hormone cortisol. There are few studies who suggest that continuous exposure to an elevated

temperature can make the fish sterile and/or sexually incompetent (Strüssmann et al 1998; Majhi

et al 2009) and even causes swimming disability (MacNutt et al 2004). Water temperature also has

a great influence on the disease appearance. According to Roberts 1975, increasing temperature

grow the potential of infectiousness of many pathogens and the toxicity of many dissolved

contaminants (Wedemeyer, 1996).

Thermal stress appears when water temperature exceeds the optimal physiological of the

species, this initiating changes that disturb normal physiological functions, resulting in depletion of

energy the body's response to stress or even appear of morality. Additional costs due to metabolic

response to thermal stress as a consequence, have impaired growth and immune system defenses.

Thermal stress is responsible for compartmental disturbance, consisting of sudden movements of

fish, lose their equilibrium in swimming, refuse food and appear digestive disorders.

The indirect effect of temperature on fish health is manifested by:

Conditioning water quality parameter values at which the fish are very sensitive, such as

oxygen content, dissociated ammonia, lethal doses of toxins, etc.

Stimulate multiplication of bio‐aggressors.

Oxygen Dissolved (DO) represents one of the most important parameters from aquaculture.

The necessary quantity of oxygen depends on fish species, fish size, feeding intensity, water

temperature, pH, and salinity. In the management of intensive systems, it is important to maintain

an optimal concentration of DO.

Maintaining fish at the interval limits of admissibility, lead to low growth performance and

as a secondary consequence appearance of diseases. Low concentration of DO can become a lethal

factor for fish even when the deficit lasts even for short periods (some minutes). In low

concentration of DO fish shows anorexia gets crowded in places where the current is stronger,

breath at the water surface, they tend to leave the unfavorable environment. Major pathological

changes that occur in the fish body affected by oxygen deficiency in the water are skin

discolorations, congestion to the cyanosis of the gills, erosion of gills, and the appearance of small

bleeding in the anterior chamber of the eye on the fish skin (Munteanu G 2003). Also, a high

concentration of DO in water can lead to fish paralysis.

Oxygen requirements of fish vary depending on the species, carp being less exigent regarding

the optimum concentration of DO from water, a value between 6‐8 mg/L is considered optimal;

when this concentration is under the value of 1.5‐2 mg/L then appear hypoxia signs.

Ammonia is a toxic substance for fish. In aquaculture systems ammonia is present due to

metabolic products, uneaten food and other organic substances found in the aerobic decomposition

process.


Ammonia is very toxic for fish being acceptable in the maximum concentration of 0,05 mg/l

for carp. For fish, unionized ammonia is toxic respiratory and nervous, and can easily enter in

tissue barriers. This it goes through the gill epithelium in the blood and has a harmful action on the

nervous system of fish. A short exposition of high concentration of ammonia can cause an increase

in gill ventilation, messy and fast swimming, lose of balance, or even fish mortality.

Between the main physicochemical parameters of water, a big importance is accorded to

water pollution with heavy metals. The progress of industries has led to increased emission of

pollutants into ecosystems (Saleh et al 2010). Water pollution with heavy metals can cause

poisoning, diseases and even death for fish and the absorption and the accumulation of different

biological tissues on pollutants are different.

The most common heavy metals in aquaculture systems are copper, cadmium, lead and zinc.

Accumulation of these metals in fish can have a serious consequence: affects organs, causing loss

of equilibrium, increased opercular movement, irregular vertical movements, finally leading to

death.

Nutritional factors. After physicochemical parameter of water, food is the most important

factor, determining the production costs and the profitability of fish farming and environmental

impacts.

As the intensive aquaculture development takes place, besides providing environmental

conditions for fish growth, a very important technological aspect it is the achievement of a good

feeding management. In aquaculture, nutrition is a decisive branch because food represents

between 40% and 70% of production costs. Nutrition is actually a branch of physiology that

comprises a set of processes: food ingestion, absorption, digestion, nutrient metabolism, excretion

and elimination of feces.

The optimization of growth performance of fishes and feed efficiency depends on the

quantity of food delivered, feeding method and feeding frequency, quality and composition of the

diet. Fish must receive adequate quantities of feed, which mainly depend on depending on size, age,

and species or in function of the rearing systems. The use of species‐appropriate feeding techniques

can limit heterogeneous growth within a group of fish and thus the need for frequent grading

(Brannas et al 2003). Excessive feeding must be avoided in order to prevent water quality

deterioration.

Also, fish food must provide their necessary nutrients and energy for growth and for

essential physiological processes. Nutritional deficiency signs usually appear gradually, and it is

difficult to detect clear signs in the early stages (Bureau D.P., and C.Y. Cho, 1999).

Fish feed must be balanced in protein, fat, carbohydrates, vitamins, and minerals. In fact,

feed quality represents an important aspect of fish health (Lim and Webster, 2001). The studies

from the last `50 in fish nutrition emphasize the importance of proteins, amino acids, minerals but

also the requirement of energy. Fish should be fed a high quality diet that meets their nutritional

requirements depending on the species, age, and size and production function (Table 5).

According to Santosh P. Lall 2000, nutritional status is considered one of the important

factors that determine the ability of fish to resist diseases Outbreaks of fish diseases commonly

occur when fish are stressed due to a variety of factors including poor nutrition. Administration of


improper feed for fish (qualitative and quantitative), mostly increases the susceptibility of fish to

infectious diseases. Feeding errors associated with unbalanced compositions or contamination with

toxic substances, causing nutritional diseases, compromise immune function and skeletal

deformities appear (Lall and Lewis‐Mccrea 2007).

Feeding errors, which can have serious consequences on fish health, consisting of the

administration of feed with:

Feed with a high content of lipids or carbohydrates, lead to fish overweight, due to the

abnormal deposing of lipids on viscera and dorsal muscles;

Deficiency of elements indispensable for growth (vitamins, minerals salts and amino acids)

lead to anemia, atrophy or necrosis of organ tissues, body deformities;

Toxic products, which comes from the feed spoilage and influence negatively nutrition

efficiency; the most spread are mycotoxin which causes serious pathological diseases.

Table 5. Dietary protein and energy levels resulting in highest growth rates in various fish species (%

of dry diet) according to Tacon (1990), De Silva and Anderson (1995); Hassan et al. (1996)

Biological stressors.

Stocking density. In intensive aquaculture fish are grown in high stocking densities, suffering

a variety of welfare problems such as fin erosion, physical injuries, skeletal deformities, increasing

susceptibility to disease and mortality.

In aquaculture, stocking density represents the concentration at which fish are stocked into

a system (Cristea et al 2002). In intensive systems, growing fish in high densities represents a way

to optimize productivity and profitability of commercial fish farms (North et al 2006). It is important

a careful evaluation of all the risks involved in choosing high stocking densities because the practice

of inadequate densities can affect fish leading to negative consequences on long‐term. It has been

proven that rearing fish at inappropriate stocking densities may impair the growth and reduce fish

immunity.

Mainly, in the calculation of optimal stocking density for a production system, it is important

to take into consideration the carrying capacity of the holding environment and the spatial and

behavioral needs of the species. Carrying capacity refers to the maximum number of fish that an

environment can support through oxygen supply and removal of metabolic waste and will be

determined by, amongst other things, the oxygen consumption rate of the fish and their response

to metabolic waste products such as CO2 and ammonia (Ellis 2001).

Species Crude dietary protein (%)

Gross dietary energy(kj/g)

Rainbow trout (Oncorhynchus mykiss) 40‐45 19.1‐20.8

African catfish (Clarias gariepinus) 40‐45 18.6

Asian catfish (Clarias batrachus) 30‐35 17.2

Channel catfish (Ictalurus punctatus) 35‐40 11.5‐16.9

Common carp (Cyprinus carpio) 31‐40.6 12.8‐22.7

Grass carp (Ctehopharyngodon idella) fry 41‐43 ‐

Grass carp (Ctehopharyngodon idella) fingerling 23‐28 ‐


The mechanisms by which stocking density affects the growth and feed efficiency are

controversial. Most authors affirm that the high stocking density represents a stressful factor for

fish (Fagerlund et al 1981; Pickering et al 1987; Vijayan et al 1988; Docan et al 2011) and, as a result

of the physiological stress‐induced effects are responsible for the adverse effects on the growth

performance. But, there are situations, when is recommended to grow fish in high densities, mainly

because aggressive behaviors is diminished (Wedemeyer GA. 1997).

Usually, stress response in fish is evaluated by measuring levels of biochemical,

hematological parameters in the blood, as well as growth and feeding parameters. Under the action

of stress‐density was observed increases in hematocrit, hemoglobin concentration and the number

of red blood cells, suggesting a strategy to increase the ability to transport oxygen in the blood

during exhausting periods of metabolically.

Many authors (Vijayan and Moon, 1992; Biron and Benefey1994; Trenzado et al 2003)

reported at fish which is grown in high densities, a temporary increase of blood glucose or of cortisol.

Ruane et al 2003 observed at carp an increase of cortisol values at high stocking densities (2.6 kg l−1

min). Also, Wei Dai et al., 2011, observed a decreased of African catfish welfare at densities between

35 kg m‐3 and 65 kg m‐3 treatments.

Another consequence of practicing of high stocking density is the deterioration of water

quality. Theoretically, increasing stocking density leads to degradation of water quality due to

respiration and metabolic processes of many fish per water volume (Björnsson and Ólafsdóttir,

2006, Ellis et al 2002).

High stocking densities favor transmission and propagation of specific pathogens. The

majority of disease agents are present in soil and water and under normal condition fish are

protected by their natural defense mechanisms. When the stocking densities are too high, their

natural disease defense can be affected, reducing the organism capacity to protect against disease.

Fish disease prevention it is obtained assuring a good water quality management, nutrition, and

sanitation.

However, it is not obvious how stocking density affects growth performance of fish. At high

densities energy demands of fish increase and require that fish to cope with metabolic adjustments,

such as changes of gluconeogenic and glycolytic activities.

Social dominance. Besides the interaction of fish with the chemical and physical factors, fish

are in a permanent interaction with each other. These interactions are reflected in fish behavior and

include social dominance, aggression, hierarchy, and competition (Wedemeyer G. 1996). Both in the

wild and in controlled growth conditions, fish are in a permanent competition for food, space, and

if these requirements are not unaccomplished can lead to serious consequences.

Intraspecific aggression is generally recognized as being common in many fish species. In fish

groups stocked at low rearing densities, occurs formation of dominant hierarchies; a hierarchy can

be defined as a serious of dominant groups, composed of fish which is on the top of hierarchy,

followed by a number of subdominants.

Aggressive behavior is used by fish in order to establish their territory and can lead to

physical injuries. The aggressive behavior can be minimized by applying a good technological


management, such as choosing the suitable stocking densities or an increasing number of feeding

satiation per day, graded and sorting fish to appropriate size classes or species.

Disease. Stressful conditions such as high stocking density, poor water quality, and

aggressive interactions could predispose cultured fish to the high incidence of diseases and

parasites. Defining “disease state” involves both natural causes and human activities induced by

anthropic activities (Figure 2). A biotope which can provide normal development of natural defense

mechanisms is interposed in the way of pathogenic organisms or optional pathogenic with big

changes of annihilation.

Figure 2. Scheme of general etiology inducing potential natural causes and induced, and their

interaction in the outbreak of disease at fish, according to Kinkelin P. et al 1985)

In the recent years, many efforts were made by scientific and researchers to understand the

epizootiology of fish diseases and to find treatments, vaccines or some measure to reduce their

incidence. Control of many serious infectious diseases has been achieved through new medicines

and vaccines, with real success in cases of bacterial diseases.

Lately, several vaccines were developed, which are quite efficient for bacterial fish

pathogens, but the success against virus disease has been more limited. Besides the fact that

appearance of the disease in a farm affects the fish health, it also leads to water quality

Aquatic environment Physical factors : Physical properties of water

(temperatrure, turbidity, pH, etc) Radiation Trauma

Chemical factors: Chemical properties of water (acidity.

alkalinity, gas solvit, nitrogenous substances, toxic substances)

Feed

Bio aggressors (Viruses, bacteria, fungi, algae, animal parasites)

Pollution ‐Techonogical management (density, feeding intensity, manipulation, handling, transportation, treatments)

Biological p

opulatio

ns, clim

atic, natu

ral causes

Technology (Transferring fish which carriers bio‐aggressors

carriers, bad biosecurity)

Fish Function of: Relation (skeletal, muscles, nervous system) Nutrition (digestion, circulation, respiration, excretion) Reproduction Alarm and defense (stress, immunity)

DISEASE


deterioration, reducing fish growth, implicit the decrease of the productivity and the acceptability

of fish on the market.

However, fish disease eradication remains a current problem, so it is permanently necessary

to found new solutions.

MEASURE TO IMPROVE FISH HEALTH

For a good health condition of fish raised in aquaculture, it is essential to remove stress

factors by adopting good management strategies, according to requirements of the fish species.

Strategies to reduce disease susceptibility, minimize stress responses, and avoid aggression are very

important. Stressors that appear insignificant may have cumulative and long‐term effects on fish

health (Schreck, 2000).

According to Whay 2007, there are 3 suggested stages in the process of improving the welfare

of farmed fish:

1) assessment of welfare;

2) identification of risk factors;

3) interventions in response to the risk factors.

It is very important developing a health management plan, for all fish farms, representing a

critical part of a successful aquaculture business. Maintaining fish as healthy as possible means a

careful isolation of pathogens already present, and/or minimizing the spread of pathogens within

or between farms. Also, it is important a permanently monitoring of fish for disease signs, visible

lesions and to analyze their behavior. Fish which shows signs of disease must be moved to

quarantine or discarded to protect the entire fish population.

Fish should be kept at reasonable densities, depending on of the fish species, size, number,

type of rearing unit and water quality/availability. The optimum stocking density must take into

consideration the requirements of fish for space, their social behavior, feeding, production and

health state. According to Broom 1986, 1991, maintaining a good physiological, immunological and

behavioral function means that fish organism function well biologically, with a low‐stress level,

adequate growth, reproduction, and health.

Also, feed quality represents an important aspect of fish health. In the last years, researchers'

concerns about improving the health of fish brought into attention using natural immunostimulants,

like prebiotics, probiotics or some medicinal plants.

The first application of probiotics occurred in 1986, to test their ability to increase the growth

of fish. Later, probiotics were used to improve water quality and control of bacterial infections,

implicit fish health. It is widely accepted that probiotics can improve immunity and level of nutrition

of fish culture by strengthening and restoring the natural balance of the body and,consequently, the

fish become more resistant to infectious diseases. From the literature, resulted that probiotics

administered at fish can be divided into a dominant group of Gram + bacteria (Lactobacillus species

(LAB), Bacillus and sour) and the group of Gram ‐ (several strains of Aeromonas, Vibrio,

Pseudomonas and Enterobacteriaceae). All these bacteria vary greatly in how they action, including

the ability to stimulate the immune system and therefore each probiotic, differ from one another

by their functional role (Boyle şi al 2006; Pineiro şi Stanton, 2007). However, the use of probiotic


must be made in controlled condition for maximum efficacy. This aspect supposes the knowing of

the right feed formulation, ensuring that the environment is clean and safe for fish stocks and that

general disease prevention mechanisms are in place.

In order to replace the use of antibiotics in aquaculture, a special attention has been accorded

on adding plants in fish feed. Plants were widely used in human and veterinary medicine, knowing

their beneficial effects on health. Among their effects may be mentioned immunostimulatory

effects, immunomodulatory, bio, antioxidant, antimicrobial, stimulating effects on enzymatic

equipment (Das et al 2002, Ji et al 2007).

Also, an important advantage of the use of prebiotics, probiotics, and plants in aquaculture is

that there are natural substances, without risk on fish health, human or environmental.

Lately, there are increasing demand for improved aquatic animal biosecurity.The concept of

biosecurity is relatively new in aquaculture, simple to understand, but sometimes can be difficult to

put into practice. In aquaculture, biosecurity refers to the concept of applying appropriate measures

to reduce the profitability of a biological organism or agent spreading to an individual, population

or ecosystem, and to mitigate the adverse impact that may result (Subasinghe et al 2006).

According to Roy P. E. Yanong, 2003, the goal of “biosecurity” is maintaining the “security”

of a facility with respect to “biological” organisms, specifically “pathogens” (disease‐causing

organisms) that can result in infectious disease (parasites, bacteria, viruses, and fungi). Biosecurity

involves following strict management protocols to prevent specific pathogens from entering a

system or reducing the numbers.

Usually, successful fish health management is correlated with the prevention of disease

rather than treatment, disease outbreaks being a significant cause of the economic losses in

aquaculture.

Prophylactic occurrence of diseases in aquaculture systems can be counteracted by applying

strict measures:

quarantined of fish about 2 weeks prior to transfer thereof to the rearing systems;

ensuring an optimal feeding in terms of quality (nutritional components of the feed must be

balanced and to ensure nutritional requirements) and quantity (poorly feed rations result in

slowing or stopping the fish growth and decreased immune response against factors and

pathogens)

taking frequent water samples (chemical, microbiological) and monitoring physical and

chemical parameters;

taking frequent fish samples for monitoring growth parameters;

cleaning and disinfection of rearing units, auxiliary spaces, access roads, work equipment /

work tools, equipment, laboratory equipment;

a special attention must be awarded to space where the feed is stored, so the feed does not

suffer biochemical degradation or contamination with some chemical substances, pests,

rodents; ensure proper storage (in a cool, dry location) and usage (follow manufacturers

recommendations/expiration date) of manufactured feeds to prevent loss of nutrients and

buildup of pathogens or toxins;


acclimatization, ventilation and maintain optimal temperatures of air and water at spaces

where are located the growth systems;

implementation of effective measures for preventing and counteracting stress factors on

fish (light intensity, noise, frequent and improper handling of fish);

limiting access of foreign persons and animals of any kind;

maintaining proper sanitization disinfection strategies.

Rearing fish in aquaculture systems suppose numerous welfare challenges.

The development, implementation, and management of appropriate production practices

and facilities to ensure the well‐being of growing numbers of farmed fish are critical, as significant

concerns with stress responses, water and environmental quality, stocking densities, disease and

parasites, selective breeding, genetic selection and transgenic manipulation, nutrition and feed,

external impacts, crowding, handling, netting and grading, transport, and stunning and slaughter

contribute to decreased welfare. A good stocking density should take into consideration space,

behaviour, feeding, production, health and normal biological expressions of the fish in culture.

Mainly, the requirements for management of the health status of fish consisting exclude any

possibility of entering of pathogens within the farming system, mandatory application of preventive

measures on infectious and parasitic diseases, conducting effective treatments and energetic at the

onset of diseases, respect for hygiene all process steps, mainly feeding and maintenance of optimal

environmental conditions, particularly those on the organic load and ammonia and nitrite content.

In the event of disease outbreak, mortalities should be removed immediately.

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Environmental Impact Assessment and Habitat Modification

Fish is considered a food with a high nutritional value, providing an important source of

protein and a wide variety of vitamins (such as D and B2‐riboflavin), minerals (iron, zinc, iodine,

magnesium, and potassium) and poly‐unsaturated omega‐3 fatty acids. According to FAO, Fisheries

& Aquaculture Department, 2014, in 2010, fish accounted 16.7% of the global population’s intake

of animal protein and 6.5 % of all protein consumed. Taking into consideration that world’s

population keeps growing during next decades and global life standards, respectively animal protein

need rises, fish demand will certainly growth. Because the wild fish captures are already exploited

at maximum level, a large part of those new demands must be satisfied through aquaculture activity.

As a result, aquaculture has generated a great interest from the international scientific community,

supplying the concerns regarding the increase of sustainability and profitability by different

methods.

Aquaculture represents the farming of aquatic organisms including fish, mollusks,

crustaceans and aquatic plants. According to the Food and Agriculture Organizations (FAO),

aquaculture is the fastest growing animal food sector in the world. (FAO, Fisheries & Aquaculture


Department, 2014). In present, aquaculture supplies an estimated 49% of all fish that is consumed

by humans globally (FAO, Fisheries & Aquaculture Department, 2014) and is expected to contribute

to more than half of the global fish consumption till 2030 (NACA/FAO, 2000).

Although aquaculture has many benefits (providing food and ensuring jobs for humans) a big

concern which is facing it is represented by its environmental impact and water quality degradation.

If this sector is not well managed we may experiencing some unreasonable phenomena such as: the

random discharge of aquaculture waste water, the abuse of medical medicines, and the escaping of

aquatic animals, (Guangjun et al., 2010), which have seriously influences on the environment.

A. Situation of Aquaculture in the world and European Union (EU). World food fish

aquaculture production expanded at an average annual rate of 6.2% in the period 2000–2012,

slower than in the periods 1980–1990 (10.8 %) and 1990–2000 (9.5 %). Between 1980 and 2012,

world aquaculture production registered a slight increase with an average rate of 8.6 % per year. A

record growth was reported for 2012 registering almost 90.4 million tonnes, including 66.6 million

tonnes of food fish and 23.8 million tonnes of aquatic algae, being estimated for 2013 a production

of 70.5 million and 26.1 million tonnes, respectively (Figure 1). (FAO, Fisheries & Aquaculture

Department, 2014). World per capita apparent fish consumption increased from an average of 9.9

kg in the 1960s to 17.0 kg in the 2000s and 18.9 kg in 2010, with preliminary estimates for 2012

pointing towards further growth to 19.2 kg. (FAO, Fisheries & Aquaculture Department, 2014).

Figure 1. World capture fisheries and aquaculture production (FAO, Fisheries & Aquaculture Department, 2014)

Principally, the species that dominate world aquaculture are aquatic plants, shellfish,

herbivorous fish and omnivorous fish. Also, a rapid increase is obvious for marine aquaculture of


carnivorous species, especially salmon and shrimp and other marine finfish (FAO, Fisheries &

Aquaculture Department 2014). The most widespread type of aquaculture in the world is

represented by the farming of tilapias (in 2014, was expected to produce 4.5 mmt), followed by

Catfish (was expected to produce 2.1 mmt for 2014) and Pangasius (was expected to produce 2.1

mmt for 2014) (The Global magazine for farmed seafood, Volume 17, Issue 6, November/December

2014).

The global distribution of aquaculture production in all regions and countries with different

levels of economic development remains unbalanced. Asia dominates this production, accounting

for 88.39% of world aquaculture production in 2012, this being determined by the significant

contribution of China. (FAO, Fisheries & Aquaculture Department 2014).

Compared to world aquaculture production, which continues to rise, European aquaculture

is in a period of stagnation. EU contributions to world aquaculture production has been decreasing

significantly over time in both volume and value terms, representing only 1.9% and 3.5% of world

production in 2012. According to Eurostat, aquaculture production by the European Union Member

States was approximately 1.25 million tonnes of live weight in 2012, almost the same as in 2011.

This represented a decline in aquaculture production of about 11% after the relative peak of 2000.

(Eurostat, 2014).

Mainly, the most valuable species produces in EU are Atlantic salmon, oysters, sea bream,

sea bass and trout. The main species produced in freshwater is represented by trout.

Also, carp is another important species mostly produced in Eastern Europe, where the main

producer is Poland covering 39% in terms of total value. (FAO, Fisheries & Aquaculture Department,

2014).

The three largest aquaculture producers among EU Member States were Spain, the United

Kingdom and France, which together accounted for more than half (54%) of the EU aquaculture

production in 2012. (Eurostat, 2014).

Aquaculture production systems. Aquaculture systems can be classified in extensive, semi‐

intensive, intensive, or highly or superintensive depending upon the number of organisms grown

per volume of water and the water source and supply. Extensive aquaculture is practised without

feed or fertilizer inputs. In semi‐intensive aquaculture fertilizers can be added to increase the

natural productivity and the water quality can be improved using additional aeration. In intensive

aquaculture high densities are practised using aeration, full feed and chemical supplements in order

to promote the health of organism grown. In principal, freshwater aquaculture is practiced either in

fish ponds, pens, cages or, on a limited scale, in rice paddies, in high flow‐through tanks or in

recirculating aquaculture systems (RAS), brackish aquaculture is done mainly in fish ponds located

in coastal areas and marine culture employs either fish cages or substrates for mollusks and

seaweeds such as stakes, ropes, and rafts. (FAO, Aquaculture Systems and Practices: a Selected

Review, 1989).

Pond aquaculture. Pond aquaculture represented the oldest fish farming activity and

involves maintaining the environmental conditions at the same level of the technological

requirements of fishes. In this systems fish are raised at low densities, mainly because of lack of


additional feeding, fish feeding on aquatic animals reared strictly resulting from natural productivity

and due to the difficulty to control water quality. Usually, in order to improve natural food are

applied organic and inorganic fertilisers, which contribute to developing natural developing micro

and macro flora, food that will support fish populations or other aquatic animals. Higher production

can be obtained in condition of supplementary feeding and higher stocking densities, but this

supposes water aeration. According to SRAC (Publication No. 163/1997) in a pond without aeration

it can be obtain from 226 kg to 680 kg of fish per 0.40 ha. Instead, in a pond with aeration it can be

obtained around 1133 kg to 1814 kg of fish per 0.40 ha. To increase the profitability of these systems

is indicated to combine both fertilizer and supplementary feeding.

Between the main disadvantages of these systems we emphasize: require large volumes of

water, large land/pond area, due to the use of organic and inorganic fertilisers may cause

eutrophication of the waters, incapacity to guarantee the safety of the product to consumer,

because ponds systems are open‐air there is always a risk of water contamination. But, according

to Verdegem & Bosma (2009) if this systems succeed a better optimization of water consumption

and feed management they could triple production without increasing freshwater usage. That's

why, to increase the economic efficiency of this systems it`s crucial to optimize water consumption,

a good solution being the integration into other production systems and also applying of a

production management focused on sustainability.

Aquaculture in Raceway. Raceway, also known as a flow‐through system, represents

enclosed systems which are based on the continuous water flowing through the culture tanks.

Because in these systems water enters at one end and flows through the raceway in a plug flow

manner, the best water quality exist only at the head of the tank, were the water enters, and then

deteriorates along the axis of the raceway toward the outlet (Timmons and Ebeling, 2013). In

comparison with the ponds these systems have several advantages, as: higher stocking densities,

improved water quality, feeding and harvesting are done more easily, less off flavour and an easier

way to control disease problems. Fish metabolites are carried out with the effluent, while settleable

particulate wastes can be collected by settling or less frequently by other means of filtration.

Optionally, this type of systems can be integrated into agricultural production, a fraction of

the waste process water used in the irrigation of different agricultural areas.

Between the main environmental concerns of these systems we mention eutrophication as

a main consequence of increased nutrient loadings (faecal and uneaten food waste), the use of

chemicals to control parasites and disease. Also, a big disadvantage of raceways is related to the

needs of constant flows of water with a high quality.

Cages and Pens. Cages are boxes shaped enclosure which floats, is suspended, or sits on the

bottom of a larger water body. Usually, the cages size varied from 1.0 m3 to 1,000 m3. Usually, pens

are much larger and serve as enclosures to hold organism for grown. In pens organism have free

access to the bottom within the enclosed area. Growing and production of farmed aquatic

organisms in caged enclosures has been a relatively recent aquaculture innovation. Primarily, these

systems have been associated with the culture of salmonids, but due to the rapid expansion of

aquaculture in the last 20 years this sector has grown very rapidly. Generally, cage culture are

suitable for the growing of carnivorous species with a high economic value (Atlantic salmon, Coho


salmon and Chinook salmon Japanese amberjack, red seabream, yellow croaker, European seabass,

gilthead seabream, cobia, rainbow trout, Mandarin fish) (A.Tacon et al., 2007).

The main advantages of cage culture are associated with the use of existing water and the

fact that doesn`t require land ownership, the related capital costs being quite low making this

technology the most economical culture. Also, a big advantages it`s represented by the possibility

to move into optimal rearing environments and sheltered areas. Between the disadvantages of the

system we mention the fact that these systems are permanently exposed to foul weather conditions

making impossible the controlling of physical‐chemical water and also the environmental impact on

water quality generated by these systems. Also, cage cultures are vulnerable to poaching and

vandalism and to higher risks of fish escaping. (Sugiura et al., 2000, Tacon A. et al., 2007).

Aquaculture in recirculating systems (RAS). Recirculating Aquaculture Systems are used for

fish farming or other aquatic organisms by reusing the water in the production by mechanical,

biological chemical filtration sterilization, oxygenation and other treatment steps. That's why RAS

systems represent an alternative to pond aquaculture due to low water consumption (Verdegem et

al., 2006) better opportunities for waste management and recycling of nutrients (Piedrahita, 2003)

and due to the easy way to control the spread of disease (Summerfelt et al., 2009; Tal et al., 2009).

RAS are intensive production systems than most other types of traditional aquaculture systems

(Timmons and Ebeling, 2013) and are the most compatible with environmental sustainability

(Martins et al., 2010), due to the production of small quantities of wastes and of water reuse.

However, the main disadvantages of these systems are high capital and operational costs and

requirements for very careful operational management. That's why this type of systems are justified

only for growing high value species such as sturgeon, pike, perch, eel, catfish, tilapia, etc.

B. Impacts of aquaculture on environment. Due to rapid expansion and to continued

pressure on natural water resources, energy and feed, aquaculture can produce different impacts

on the environment. Aquaculture can exert both positive impact and negative on the environment.

Usually, the quality and quantity of waste from aquaculture as well as the environmental impacts

of aquaculture vary with farmed species, the management practices used and location of the

production system but also on feed quality and management (feed composition, feed ration and

feeding method). (Preston et al., 1997; Wang et al., 2005; Podemski C.L. and Blanchfield P.J., 2006).

In table 1 is presented the main environmental impacts of aquaculture depending on the

culture system (extensive, semi‐intensive and intensive) and the benefits for producers, after Pullin

(1993) modified by Bardach E. (1997). Among the major effects of aquaculture on the environment

in this paper we refer to:

Effluent discharges;

Effects of other discharges from aquaculture (e.g. fertilizers, chemicals and medicines);

Escapes from fish farms and potential effects on wild populations.

Effluent discharges

Aquaculture effluents contain dissolved and suspended solids that have biochemical oxygen

demand (BOD), ammonia and nutrients phosphorus (P) and nitrogen (N) that are derived from fish

excretion, faeces, and uneaten feed, and specific organic or inorganic compounds (i.e.


therapeutants). (Figure 2). Between all these components a special attention is directed towards

nitrogen and phosphorus which are considered the main pollutants of intensive aquaculture

(Hakanson et al., 1998). These components are a real source of pollution and if they are developed

at high level can cause of eutrophication (González et al., 2008), resulting in occurrence of the

harmful algal blooms (Pearl, 1997; Goldburg R. et al.,1997) and the depletion of oxygen due to the

increase of microbial activities (Diaz, 2008).

Figure 2. Suspended particle in an aquaculture system (after John S. Lucas, Paul C. Southgate, 2012)

It is obviously that feeding is the main source of waste output from aquaculture, due to the

high amounts in fishmeal (FM) which is rich in P. In fact, Ackefors, 1999 said that the content of

phosphorus and nitrogen in the feed and the feed conversion rates are of importance in assessing

environmental impacts of aquaculture. According to Jackson et al., 2003 and Schneider et al., 2005

only 20% to the cultured organism is retained as biomass, while the rest is incorporated into the

water column or sediment. Moreover, Pierhadrita, (2003) says that nitrogen and phosphorus

retention range between 10‐49% and 17‐40% respectively, while from faeces N and P is released

from 3.6% to 35% and 15% to 70% respectively. Lastly, dissolved N and P excretions range from 37%

to 70% respectively. Nowadays, modern aquaculture is based mostly on feeding of manufactured

feeds (extruded pellets) reducing the phosphorus excretion. For example, in a diet for salmon, with

40% protein, 30% lipids, 13% carbohydrate and a energy content of 19.2 MJ kg‐1, the nitrogen

content is around 7%, aspect which makes possible to use fat for energy (instead of protein) and

excreted of smaller volumes of nitrogen compounds (Pillay, 2004). That`s why it is very important

to known the ingredients from the feeds and to balance these nutrient in order to improve the

nutritional quality. Cho et al., (1991), says that the goal of aquaculture is to produce feed very well

suited to the nutritional needs of the fish so that the maximum growth can be achieved with

minimum waste, particularly phosphorus and nitrogen. So, a way to reduce P waste produced by


aquaculture is to replace the fish meal (FM) with FM substitutes that contain lower P (Youssouf A.

et al., 2012) without affecting the growth performance of fish. A possible alternative protein sources

include animal proteins from rendering or slaughter, plant protein concentrates and novel proteins

such as algae, yeast, dried distillers grains with soluble (DDGS) and insect meal (Ayoola A., 2010).

Besides feed composition, others factor responsible for pollution effluent from aquaculture

are the type of the culture systems and the practised stocking densities. In general, the effluent

resulting from aquaculture raceway is more polluted in comparison with ponds effluent and cages

and pens, mainly because water passes quickly through raceways and dissolved and suspended

matter are flushed out. Generally, wastes emitted from cages and raceways are quickly diluted but

also can generate changes in sediment structure and function (Beveridge M. et al., 1997). On the

other hand effluent from RAS systems it is around 10% (daily water exchange) of total system

volume per day, but RAS produce a concentrated waste.

Another important issue which will receive increasing attention is the practiced stocking

densities. High stocking densities suppose the concentration of many organisms in a low water

volume, increasing the waste productions and thus increasing the concentration of phosphorus and

nitrogen compounds from water. Also, not all fish species have similar metabolism having different

capacities to process energy and nutrients, and that`s why choosing the suitable species for growth

and the suitable grown system can be a good solution to protect the environment. Also, as a

measure to reduce nutrient wastes, aquaculture effluents should be monitored and managed, to

avoid or reduce any negative environmental impacts (Manoochehri et al,. 2010).

Table 1. Developing country Aquaculture Systems: Environmental Impact and Benefits for Producers, after Pullin 1993, modified by Bardach E, 1997.

Culture System Environmental Impact Benefits

EXTENSIVE

Seaweed culture May occupy formerly pristine reefs; rough weather losses; market competition; conflicts/failures, social disruption.

Income; empolyment, foreign change.

Coastal bivalve culture (mussels, oysters, clams, cockles)

Public health risks and consumer resistance (microbial diseases, red tides, industrial pollution; rough weather losses; seed shortages; market competition especially for export produce; failures, social disruption.

Income; emplyment, foreign change; directly improved nutrition.

Coastal fishponds (mullets, milkfish, shrimps, tilapias)

Destruction of ecosystems, especially mangroves; increasingly non‐competitive with more intensive systems; nonsustainable with high population growth; conflicts/failures, social disruption.

Income; empolyment, foreign change; directly improved nutrition.

Pen and cage culture in eutrophic waters and/or rich benthos (carps, catfish, milkfish tilapias)

Exclusion of traditional fishermen; navigational hazards; conflicts, social disruption; management difficulties; wood consumption.

Income; empolyment; improved nutrition

SEMI‐INTENSIVE

Fresh‐ and brackishwater pond (shrimps and prawns, carps, catfish, milkfish, mullets, tilapias)

Freshwater: health risks to farm workers from waterborne diseases. Brackishwater: salinization/acidification of soils/aquifers. Both: market competition, especially for export

Income; empolyment, foreign change (shrimp and prawns); directly improved nutrition


produce; feed and fertilizer availability/prices; conflicts/failures, social disruption.

Integrated agriculture‐aquaculture (rice‐fish; livestock/poultry‐fish; vegetables ‐ fish and all combinations of these)

As freshwater above, plus possible consumer resistance to excreta‐fed produce; competition from other users of inputs such as livestock excreta and cereal brans; toxic substances in livestock feeds (e.g., heavy metals) may accumulate in pond sediments and fish; pesticides may accumulate in fish.

Income; empolyment; directly improved nutrition; synergistic interactions between crop, livestock, vegetable and fish components; recycling of on‐farm residues and other cheap resources.

Sewage‐fish culture (waste treatment ponds; latrine wastes and septage used as pond inputs; fish cages in wastewater channels)

Possible health risks to farm workers, fish processors and consumers; consumer resistance to produce.

Income; empolyment, foreign change; directly improved nutrition; waste disposal liabilities turned into productive assets.

Cage and pen culture, especially in eutrophic waters or on rich benthos (carps, catfish, milkfish, tilapias)

As extensive cage and pen Systems above. Income; empolyment; improved nutrition

INTENSIVE

Freshwater, brackishwater and marine ponds (shrimps; fish, especially carnivores ‐ catfish, snakeheads, groupers, sea bass, etc.)

Effluents/drainage high in BOD and suspended solids; market competition, especially for export product; conflicts/failures, social disruption.

Income; empolyment, foreign change.

Freshwater, brackishwater and marine cage and pen culture (finfish, especially carnivores ‐groupers, sea bass, etc. ‐ but also some omnivores such as common carp)

Accumulation of anoxic sediments below cages due to fecal and waste feed build‐up; market competition, especially for export produce; conflicts/failures, social disruption; consumption of wood and other materials.

Income; employment, foreign change (high‐princed carnivores); a little emplyment.

Other ‐ raceways, silos, tanks, etc.

Effluents/drainage high in BOD and suspended solids; many location‐specific problems.

Income; empolyment, foreign change; a litlle empolyment.

Effects of other discharges from aquaculture (e.g. fertilizers, chemicals and medicines).

Besides the wastes, aquaculture effluents may contain chemicals (fertilizers, disinfectants

and chemotherapeutants pesticides, antibiotics). Usually, fertilizers are used in aquaculture ponds,

in order to increase the primary productivity by stimulating the phytoplankton growth. For that, a

very important aspect is to establish the needed doses. These doses may be determined only from

the knowledge of the chemical composition of the water and the physical‐chemical characteristics

of its bottom. Generally, in aquaculture are used organic fertilizers or inorganic fertilizers, or a

combination of both. Inorganic fertilizers are inorganic compound which contain nitrogen,

phosphorus and potassium. However, fertilizers whether they are artificial or organic, can cause

serious problems if they contaminate water or are added in excess, contributing to the deterioration

of water quality and implicit to discharged effluents.

In modern aquaculture, especially in high‐stocking density aquaculture, to prevent diseases,

eliminate harmful biota, disinfect and restrain polluted and damaged water, multiple chemicals and

medicines are used (Okomoda V., 2011). (Table 2). In the lasts years the use of antibiotics has grown,

even their use remains still controversial.


Table 2. Chemicals commonly used in European Aquaculture after Fernandes et al., 2006.

Chemicals in use Different compounds Examples

Antibiotics

Oxytetracycline, Florfenicol, Amoxicillin, potentiated sulphonamides, Flumequine, Oxolinic acid

Chemicals associated with structural materials

Stabilisers Pigments Antioxidants UV absorbants

Flame retardantsFungicides Disinfectants

Antifoulants on solid surfaces and on net and rope structures (i.e. cages)

Soil and water treatments

Alum EDTA Gypsum

LimeZeolite

Flocculants to reduce turbidity in ponds To remove ammonia

Fertilisers

Organic and inorganic

To enhance production of natural food in ponds

Disinfectants

Chloramine T Formalin Hypochlorite

IodophoresOzonation Quaternary ammonium compounds

To maintain hygieneTo treat disease (little or no use in extensive systems)

Antibacterial agents

Β‐lactams Nitrofurans Macrolides Phenicols

4‐QuinolonesRifampicin Sulphonamides Tetracyclines

Prophylactic use

Therapeutants other than antibacterials

Acriflavine Copper compounds Dimetridazole/Metronidazole Formalin Glutaraldehyde Hydrogen peroxide

LevamisoleMalachite green Methylene blue Noclosamide Potassium permanganate Trifluralin (Treflan)

Antifungal agents Against Ectoparasites Protozoan infections Very specific and limited use, in general

Pesticides

Ammonia Azinphos ethyl (Gusathion) Carbaryl (Sevin) Dichlorvos Ivermectin (Ivomec) Nicotine (tobacco dust)

OrganophosphatesOrganotin compounds Rotenone (derris root) Saponin (tea seed meal) Trichlorfon (Neguvon, Dipteres

Control predators and snails in ponds Control ectoparasitic crustacean infections in finfish culture

Herbicides/ Algaecides Copper compounds (Aquatrine) Very limited use in marine aquaculture

Feed additives

Astaxanthin Butylated Hydroxyanisole Butylated hydroxytoluene Canthaxantin Carotenoids

EthoxyquinFeeding attractants Immunostimulants Vitamin C (ascorbic acid) Vitamin E

Artificial and natural pigments Vaccines andimmunostimulants Mould inhibitors and antioxidants

Anaesthetics

Benzocaine Metomidate 2‐phenoxyethanol

QuinaldineTricaine methanesulphonate

To assist immobilisation of brood animals during egg and milt stripping Treatment purposes/ transport


Generally, the antibiotics are incorporated in fish pellets and due to uneaten feed go straight

into water and bottom. Also, they can enter in water through faeces and by urine excretion. In fact,

there are researches who indicates the approximately 70‐80% of the drug ends up in the

environment. (Samuelsen, Torsvik and Erik, 1992; Lalumera et al., 2004). Mainly, in aquaculture

antibiotics are used for therapeutic purposes and as prophylactic agents (Zheng et al., 2012), the

most frequent fish infections treated with antibiotics are skin ulcers, diarrhoea and blood sepsis

(FAO, 2005).

Although their use is carefully indicated, there are cases when their discharge into the

aquatic environment can lead to serious damages, due to the fact that they came in direct contact

with water and soil. (Boxall, 2004). These risks are associated with the direct toxic effects (on benthic

micro and meiofauna, algae, plankton and other aquatic organisms) and more subtle effects

including potential modification of bacterial communities (and the promotion of antibiotic resistant

organisms) (Marine Strategy Framework Directive, 2015). However, the use of antibiotics in

aquaculture remains still difficult, because they must be administered directly into the water, and

that's why should be taken into account a number of considerations such as environmental

integrity, the safety of fish and the aquatic products intended for human consumption.

Escapes from fish farms and potential effects on wild populations, represent another big issues of

aquaculture, with detrimental effects on the environment. According to a report published by The

Scottish Association for Marine Science and Napier University Scottish Executive Central Research

Unit in 2002, escapees from fish farms may interbreed with wild population resulting in losses of

genetic variability, including loss of naturally selected adaptations, thus leading to reduced fitness

and performance. Also, escaping of fish from farms can be responsible for the spreading diseases

and others pathogens. It is necessary for a better understand the relationships between disease and

both as a means of preventing environmental economically serious disease outbreaks and indirectly

promoting the need for better environmental management. (Pullin et al., 1993). In cases of cages,

pens or other systems which release the untreated effluent directly into water the possibility of

transmitting diseases to wild fish stocks is quite high. The main way of introducing diseases is the

transfer of infected farmed juveniles to these systems, or through infected food equipment, and

through water streams (Ruiz et al., 2000, Murray et al., 2005, Salma et al., 2011).

CONCLUSIONS

Aquaculture represents the sector with an important economic activity being situated on top

of the food production industry. Increasing customer demand for aquaculture products, together

with increasing environmental and also the costs associated with land and water, will determinate

the producers to develop their technological facilities or to implement new solutions in order to

Hormones

Growth hormone (GH)17 a‐methyltestosterone Oestradiol 17b

Ovulation‐inducing drugs Serotonine

Control and induce ovulation Teleost sex control measures


assure the practice of high stocking densities and to meet the market demands, while taking into

consideration environmental protection.

In order to protect environment, aquaculture activities must be conducted sustainably, with

minimal impact on environment. In fact, the aquaculture industry is already working on this

requirement, which in many countries has reached an impasse. In conclusion, to develop a

sustainable growth of aquaculture is needed to be profitability, economic development and to

practice a good waste management. There are many measures which can be taking in order to

reduce the environmental impact of aquaculture, as: reducing as much as possible food losses, the

adoption of management strategies of discharged effluents, like the utilization of the recirculating

systems or systems with low or zero water exchange, the revalorization of the wastes by integrating

in hydroponic systems for plants production or for composting for garden applications. Also, it is

important to ensure sustainable sourcing of feed, to avoid escapes by adopting technical standards,

to minimise biodiversity impacts and to reduce the impact of chemicals and medicine use,

particularly antibiotics.

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