Basic Course on Aquaculture

8/14/2019 Basic Course on Aquaculture

1/46

Basic Course on Aquaculture

Held at the

Mon Repos Freshwater Aquaculture Demonstration Farm and Training Centre,

Agriculture Road,Mon Repos, East Coast Demerara.

Prepared by:

Tejnarine S. Geer,Senior Fisheries Officer,Aquaculture and Inland FisheriesDepartment of Fisheries

Kamila Singh,Limnologist/Hydrochemist,Department of Fisheries


2/46

2

Topics

I. IntroductionII. Site Selection

III.

Species Selection

IV. Methods of CultureV. Pond Design and Construction

VI. The Aquatic EnvironmentVII. Fertilizing and Liming

VIII. Transporting and Stocking FishIX. Feeds and FeedingX. Fish Health and Disease

XI. Fishing Methods and Fishing GearXII. Post-Harvest Treatment

XIII. MarketingXIV. Record KeepingXV. Tilapia Rearing

XVI. Local InformationXVII. Appendix

XVIII. References


3/46


4/46

4

2. Classifications of Aquaculture:In relation to the salinity of the water where the culture is practiced, aquaculture may beclassified into three divisions:

a.

Freshwater culture: This involves the culture of organisms that live mainly ininland waters with 0.1 parts per thousand (ppt) or less salt content.b. Brackish Water culture: This involves the culture of organisms that live in

water with a salt content between 0.1ppt and full strength seawater.c. Marine or Seawater culture: This involves the culture of organisms that live in

coastal lagoons or in the open sea.This training course focuses on freshwater aquaculture.

In relation to the utilisation of the end product, aquaculture can be classified into:

a) Seed production: The main objective of this type of culture is to produce smallfishes or other organisms, usually called seed, which are stocked into ponds orother culture devices to be grown into adult organisms for market.

b) Grow-Out Production: The main objective of this type of culture is to grow seedstock until the commercial size or weight is achieved.

c) Brooder Production: The main objective of this type of culture is to grow, breedand improve cultured species genetically, so as to improve aquaculture productivity.

3. Types of AquacultureAquaculture can be divided into extensive, semi-intensive or intensive, depending on thefollowing:

- Stocking and fertilization rates- Supplementary feed quality and rates- Level of technology employed- Level of investment and resultant yields

a. Extensive CultureThis is the simplest method of culture, and is characterised by a low stocking rate,use of fertilizer, little or no use of supplementary feed and consequently, arelatively low level of technology. As a result, the level of investment is low, andconsequently, yields are low.Extensive culture is usually practiced over large areas of flooded surface.

b. Semi-intensive CultureThis method of culture is more complicated than the extensive method of culture.The stocking rate used is higher, both feed and fertiliser may be used, andconsequently, the level of technology is higher. The level of investment required ishigher than the extensive method, and as a result, yields are higher.Semi-intensive culture is usually practiced over a smaller area of flooded surface,when compared to extensive culture.


5/46

5

c. Intensive CultureThis method of culture is the most complicated way of growing fish. The stockingrate used is usually very high, and complete feeds are used, instead of a combinationof feed and fertiliser. The level of technology used is high, with automated feeding,aeration and water purification being employed. This requires a high level of

investment, but yields are much higher than the semi-intensive culture method.However, this culture system has a high level of risk associated with it.Intensive culture is usually practiced over relatively small areas of floodedsurface.

In Guyana, the semi-intensive method of culture is recommended.

4. Important Aquaculture SpeciesVery few fish species are suitable for aquaculture. Some of the common aquacultured

species are listed below.

a. The Tilapia GroupTilapia represent 5.6% of the total freshwater fish production and 74.0% of the non-cyprinid fish cultured in freshwater. The main species cultured in the group isOreochromis nilotica, which comprises 75.3% of the total tilapia production, or over 600thousand tons/year.

Tilapia, have a very deep, laterally compressed body, usually with large scales and a doublelateral line. The body colour is generally dark, with even darker bands; often each scale istipped with white; the throat and belly are white. Several hybrids have been developed,

which are red in colour.

Although tilapia can reach 3 kg (6 pounds) commercially they are cultured until 230 g to500g. In all tilapia species males grow larger and faster than females. Tilapia areomnivorous with a marked preference for phytoplankton. They lay a minimum of 2000 eggsper year, and are very good brooders. Tilapia have been distributed from their native Africato all parts of the tropical and sub-tropical world.

Nile Tilapia


6/46

6

b. Chinese Carp GroupChinese carps represent almost 60.7% of the world freshwater fish aquaculture production,or over 8.7 million tons in 1996. This group of fish have a variety of body shape, colour andhabits. The four major species are silver, big head, grass and common carp, all togethercontributing with more than 76% of the total carp aquaculture production. Carps feed on

almost every type of food found in freshwater.

c. OthersThere are many other fishes commercially cultivated in freshwater, brackish water andseawater. In this part of the world, predatory species such as Arapaima (Arapaima gigas)and the American Eel (Anguilla rostrata) are grown. However, predatory species have ahigh feed conversion ratio, usually about 7:1. Nevertheless, they are widely grown, due tothe high market price obtained.

American Eel (Anguilla rostrata) Arapaima (Arapaima gigas)

Some herbivorous fish, such as the Freshwater Pacu (Colossoma macropomum) and theFreshwater Pompano (Piaractus brachypomus) are also grown in this part of the world.Although their market price is lower, they are still widely grown.

Freshwater Pacu Freshwater Pompano (Piaractus brachypomus)(Colossoma macropomum)

Species such as the Lukanani (Cichla ocellaris) and Hassar (Hoplosternum littorale) arevery high priced locally, and have great potential. Hassar has been grown locally, andLukanani may also be grown in the near future.

Lukanani (Cichla ocellaris Hassar (Hoplosternum littorale)


7/46

7

Recently, there has been an interest in Guyana in the culture of the giant freshwaterprawn (Machrobrachium rosenbergii). This species is native to Malaysia, and has beengrown commercially in Mississippi.

II. Site SelectionSite selection is critical for successful aquaculture. Large parts of the planet, andindividual countries, are deemed unsuitable for specific types of aquaculture. Also, manyaquaculture ventures fail due to improper site selection.

The following criteria are to be considered for proper site selection:

a. Land: For successful aquaculture, the land acquired must have some basicattributes. Steeply sloping land is generally deemed unsuitable foraquaculture. On the other hand, a gentle slope is required to facilitateeither irrigation or drainage by gravity. Generally, the slope of the landshould be between 1-1.5.

b. Water: Water is essential for aquaculture. Whereas the land available canbe amended to some extent, water is much more difficult to alter. The site

should have easy access to adequate supplies of either fresh or salt water,or both, if required.At the same time, the site should also have access to another water bodyfor drainage and disposal of used water.

c. Access to Infrastructure: The site should be near to proper roads, as wellas electricity supply, processing facilities and technical assistance(knowledge and trained personnel).


8/46

8

d. Market Analysis and Survey: The site should have easy access to themarket for the product. This also includes access to roads, waterways fortransport, or an airport, if required. A financial analysis of the proposedmarket should be done.

e.

Seed Supply: The site should be near the seed supply ideally, to minimizeboth cost and mortality of seed. However, if seed is to be produced on thefarm, then this consideration is minimal.

f. Room for Expansion: The site selected should have room for expansion.As the enterprise grows, several other needs may become evident. Theremay be the need for a hatchery, feed production facility, freezing area, etc.

g. Financial Aspects: Ideally, the site selected should have some financialincentives associated with it, e.g., duty free provisions, tax holidays,subsidies, etc.

h. Climate: The site should have the required temperature, light availability,rainfall, etc.

III. Species SelectionAs mentioned before, several species are suitable for aquaculture, but not every species issuited for every situation. The following should be considered when selecting a speciesfor culture:

- Market demand: A species should only be cultured if it can be sold.- Profitability: The species should fetch a sufficiently high price, so that the

farmer can make a profit.

- Ease of culture: The species should be hardy, resistant to disease, and fastgrowing.

- Supply of seed stock: If the species does not breed readily, there should be areliable supply of juveniles for growout.

- Feeding habits: The species should readily accept artificial feeds.- Legal aspects: In some countries, there are restrictions on the culture of

certain species, for various reasons.


9/46

9

IV. Methods of CultureAquaculture can be practiced using various methods of culture, in a variety of rearingstructures. Some culture methods are used in extensive or semi-intensive types of culture,while others are used in intensive types of culture.

1. Pond CultureA pond is an earthen, or sometimes concrete, impoundment that holds water. Water isadded only to fill the pond or to replace water lost by seepage or evaporation. Sometimesponds are subject to water changes, but this water change does not usually exceed onecomplete change in a 24-hour period.Pond culture is perhaps the simplest way of practicing aquaculture. Most of theaquaculture production in the world is carried out in ponds. Earthen ponds are the mostwidely used structures, mainly due to their relatively low cost. The advantages includelow technology requirements, ease of stocking and harvesting, and less risk from climaticconditions. Pond culture also allows cultured species to utilize natural sources of food.

A major disadvantage is water quality deterioration.Ponds can be used for extensive, semi-intensive or intensive aquaculture. Extensiveponds may be several hectares in size, while semi-intensive ponds usually do not exceedhalf a hectare.

There are several types of ponds:- Watershed Ponds - Inter-tidal Ponds- Excavated Ponds - Beach Ponds- Embankment Ponds - Marsh Ponds

2. Cage CultureCage culture is the practice of rearing fish in cages. It can be applied in existing bodies ofwater that cannot be drained or seined and would otherwise not be suitable foraquaculture. These include lakes, large reservoirs, farm ponds, rivers, cooling waterdischarge canals, estuaries and coastal embayments.Generally speaking, large, deep bodies of water which contain very little nutrients areused for cage culture.Cages have a rigid framework, and a bag suspended below the water surface, in whichthe culture species are retained. The upper surface is provided with flotation devices,which can be manipulated to raise or lower the cage in the water.Cage culture requires the use of complete feeds, which makes it a part of semi-intensiveor intensive culture.

Advantages include:- Flexibility of management- Ease and low cost of harvesting- Close observation of fish feeding response and health- Ease and economical treatment of parasites and diseases- Relatively low capital investment compared to ponds and raceways


10/46

10

Some disadvantages are:- Risk of 1oss from poaching or damage to cages from predators or storms- Less tolerance of fish to poor water quality- Dependence on nutritionally-complete diets- Greater risk of disease outbreaks

3. Pen CulturePens are similar to cages, except that the species is allowed to access the bottom of thewater body.

Pens are generally built in large open waters such as lakes, reservoirs and rivers.However, waters used for pen culture are relatively shallow when compared with cageculture, and usually possess a medium to high level of dissolved nutrients. Fish thereforehave access to natural food. In some cases, supplementary feed is supplied, making penculture suitable for either extensive or semi-intensive aquaculture.

Pen culture is especially characterized by good water exchange, high dissolved oxygenlevel, fast growth rate, low feed conversion ratio (FCR), less disease and better economicreturn. Therefore, pen culture is one of the important strategies for fishery developmentin open waters.

Advantages include:- Flexibility of management- Relatively low capital investment compared to ponds and raceways- Low management costs- Utilization of primary productivity

Disadvantages include:- Difficulty in observing fish feeding response, behavior and health- Difficulty in the treatment of parasites and diseases- Increased chance of fish escape- Difficulty in fish harvesting and recovery

4. Raceway CultureA raceway is a long, narrow rectangular trench in which water is flushed throughcontinuously. The sides and bottom of a raceway may be earthen.

If the land is sloping, a series of raceways can be constructed, linked to each other end toend, one unit flowing into the other, and separated by filters. Oxygen is added to thewater by the splashing action as water exits one cell and drops into the other.

In fish culture, traditional raceways are enclosed channel systems with relatively highrates of moving or flowing water. This high rate of water movement gives racewaysystems distinct advantages over the other culture systems.


11/46

11

Advantages of raceways include:- Higher stocking densities- Improved water quality- Reduced manpower- Ease of feeding, grading and harvesting-

Precise disease treatments- Collection of fish wastes- Less off-flavour

Disadvantages include:- Reliance on electricity or fuel for water flow- Risk of fish mortality due to disease or water quality problems- High level of technology required

Raceways are suited to the intensive type of aquaculture production.

5. Recirculating System CultureIn a recirculating system, the same water is reused, after appropriate physical, biologicalor chemical purification.

Fisheries researchers have used recirculating systems for holding and growing fish formore than three decades. Attempts to advance these systems to commercial scale foodfish production have increased dramatically in the last decade.

Advantages:- Does not require large quantities of land and water.-

A high degree of environmental control- Can be carried out close to market areasDisadvantages:

- Needs a lot of complicated machinery, which can be difficult tomaintain

- Biologically complex- Increased risk of poor water quality- Greater risk of stress and diseases- Common incidence of off-flavor are common- High levels of technical expertise required- High cost

6. Other Culture SystemsTanks made of metal, plastic, or fiberglass are also used in aquaculture. Fish are alsocultured in silos, and species such as oysters may be grown on strings attached to floatingrafts, or even sticks.


12/46

12

V. Pond Design and ConstructionThe design and construction of pond farms depends on several factors, including thespecies reared, the type of culture system (intensive, semi-intensive or extensive) and thewater source. Some general principles will be outlined in this section.

1. PrinciplesAll ponds should be individual units. This means that each pond should have anindividual inlet and outlet, so as to provide for individual irrigation or drainage of eachpond.All ponds should be constructed with a slope towards the outlet, so as to facilitatedrainage. Usually, there should be a difference of 30 cm in depth from the inlet to theoutlet.The sides of a pond should be sloped, usually about 30 degrees, so as to prevent the sidescaving in. The more clay the soil contains, the steeper the possible slope that may beused.

Ponds should be constructed to take advantage of gravity for either irrigation, drainage,or if possible, both.All ponds should contain an inlet, for irrigation, an outlet, for drainage, and an overflow,to remove excess water in a controlled manner.All water entering ponds should be filtered, so as to prevent other unwanted species fromentering the pond.All water leaving the ponds should be filtered, so as to prevent the cultured species fromescaping.


13/46

13

2. Pond Inlet Structures: These depend on the type of pond that is present, and thewater requirements. Inlets may be simple, such as a PVC pipe with a filter. Inlets mayalso be more complex, with a series of filters, entrance protection, settlement areasand erosion control devices.Inlet structures are built to control the amount of water flowing into the pond at all

times. The need for an inlet varies with the type of water supply. For example, thereis no need for an inlet when water is supplied by rain, surface run-off, groundwater orspring which emerges within the pond, nor for a barrage pond build directly on thestream. There are three main types of inlet structures:

- Pipe inlets- Open gutter inlets- Canal inlets

The following points should be noted:- Place the inlet at the shallow end of the pond- Design its bottom level to be at the same level as the bottom of the

water feeder canal and ideally at least 10 cm above the maximum levelof the water in the pond- Design the inlet structure to be horizontal, with no slope- Try to arrange the structure so that water splashes and mixes as much

as possible when entering the pond- Design the structure to prevent unwanted fish from entering the pond

3. Pond Outlet Structures: Outlet structures are built for two main reasons:- To keep water at a suitable level in the pond- To allow for the complete draining of the pond and harvesting of the

fish whenever necessaryA good outlet should ensure, as far as possible, that:

- The amount of time necessary to drain the pond completely isreasonable

- The flow of the draining water is as uniform as possible to avoiddisturbing the fish excessively

- There is no loss of fish during the draining period- Water can be drained from the top, bottom or intermediate levels of

the pond- Any reasonable excess of water is carried away- The outlet can be reasonably cleaned and serviced- The construction cost and maintenance are relatively low

Outlets have three main elements:- A collecting area on the inside of the pond, from which the water

drains and into which the fish is collected for harvest- The water control itself, including any drain plugs, valves, boards,

screens and gates- A means of getting water to the outside of the pond, such as a pipe, cut

through the wall, and/or an overflow structure.


14/46

14

There are several types of outlets:- Simple cuts through the dam- Simple pipelines and siphons- Sluices- Monks

4. Water Transport Structures: Several different kinds of structures can be used totransport water on a fish farm:- Open Canal: there are various types, including feeder canals, drainage

canals, diversion canals and protection canals. They usually transportwater by gravity

- Aqueducts: these transport water above ground level- Pipelines: these transport water above or under another structure such

as a water canal or an access road- Siphons: these transport water over an obstacle such as a pond dyke


15/46

15

VI. The Aquatic EnvironmentThere are two major types of factors associated with water, biotic factors and abioticfactors. Biotic factors include all the living things associated with water, such asphytoplankton, zooplankton, worms, insect larvae, snails etc. Abiotic factors are the non-

living factors such as light, temperature, salinity, dissolved gasses such as oxygen andcarbon dioxide, and nutrients such as nitrates and phosphates.

The water in which the aquaculture species is farmed has a profound effect on the healthand growth of the species. The water quality may deteriorate considerably over theculture period due to the addition of nutrients via feeding. The major water qualityfactors that affect aquaculture animals are; dissolved oxygen, pH, dissolved nutrients andgasses, temperature and plankton.

1. Dissolved OxygenOxygen is essential to the survival of all animals, and aquacultured animals are no

exception. Air contains approximately 21% oxygen, but the amount present in water isquite low, due to the low solubility of oxygen in water. Oxygen passes from air to waterby diffusion, and the amount present in water can be increased by water circulation due towind, since this exposes more surface water to the atmosphere, thereby increasing therate of diffusion.

In ponds used for aquaculture, the major source of oxygen is photosynthesis byphytoplankton. Phytoplankton are tiny plants that produce the green colour in many fish ponds. Plants containing the green pigment chlorophyll in the presence of light usecarbon dioxide to produce carbohydrate and oxygen:

6CO2 + 6H2O C6H12O6 + 6O2

Since sunlight is essential for photosynthesis, this activity is carried out only indaylight hours. In the night, the phytoplankton carry out only respiration, a process inwhich they use up oxygen and produce carbon dioxide. This means that the dissolvedoxygen levels are lower in the night, and higher during the day. The lowest levels ofoxygen are encountered very early in the morning, just before the sun rises. At this time,the fish farmer should check his ponds, and be prepared to aerate, if necessary.


16/46

16

2. Factors leading to oxygen depletion in pondsOxygen depletion (loss) is the single biggest problem that occurs in fish ponds, especiallywhen the stocking rate is high, and the fish are being fed heavily. The following factorsmay contribute to oxygen loss in ponds:

a. Cloudy or Rainy Weather: Several days of cloudy or rainy weather maylead to a phytoplankton die-off, since photosynthesis stops due to lack ofsunlight. In addition to oxygen not being produced, the dead

phytoplankton will use up oxygen, as they decay.

b. Lack of Nutrients: Nutrients, such as phosphates and nitrates, areessential for the growth of a phytoplankton bloom. If these nutrients arenot available, phytoplankton may not be present to produce oxygen byphotosynthesis. If the fish are being fed, however, this is rarely a problem,since the feed acts as a source of nutrients. Nutrients may also be added byfertilizing fish ponds.


17/46

17

c. Overstocking: The greater the number of fish in a pond, the greater isthe consumption of oxygen as well as the amount of waste productsproduced. The waste products in turn use up oxygen when they decay.For these reasons, farmers are urged to follow the recommended stockingrates for the particular species of fish or shrimp.

d. Blue-green Phytoplankton Scum: A certain type of phytoplankton,called blue-green algae or Cyanophyceae, may form a dense scum on thesurface of the water. This limits photosynthesis to only the top fewcentimeters, since the scum blocks sunlight from penetrating the watercolumn. This means that oxygen levels will be very high in the surfacewaters but lacking in deeper waters. These scum are dangerous since theyprevent fish such as tilapia from accessing surface water as they normallydo when oxygen levels are too low, which can result in total fish kill.

e. Hot Weather: Very hot days with no breeze provide a condition foroxygen depletion. Very warm water, above 32C (90F), holds very littleoxygen. With no breeze, little or no oxygen is added through circulation.In addition, the culture species is more active, requiring more oxygen.Decay processes are also speeded up, thus using more oxygen.

3. Avoiding and Combating Oxygen DepletionIn tropical countries, problems with oxygen depletion occur all year round due to the hightemperatures, and the problem is even greater in brackish water, since oxygen is lesssoluble as salinity increases. By knowing what to look for and what to do, losses can beavoided.

a. Check Pond Water Daily: Dissolved oxygen should be checked inponds at daybreak. In large operations, farmers are advised to purchase adissolved oxygen meter, which quickly and easily gives an accuratedissolved oxygen reading. For smaller operations, the cost of a meter isprohibitive and farmers are advised to use a Secchi disc to monitorphytoplankton levels, which gives a rough guide as to the oxygenproductivity of a pond.

A Secchi disc is a round flat surface on which two alternate quarters arepainted black and the others white:


18/46

18

A rope or a pole is attached to this instrument, andmarked at 10 cm intervals. To take a reading, thedisc is lowered into the water until it just disappears.The following table gives a guide to various Secchidisc readings, and their implications:

Secchi Disc Visibility Comments

Less than 20 cm Pond has too much plankton. There will be problems with lowDO.Water should be exchanged to reduce the amount of plankton.

20 to 30 cm Plankton becoming excessive, but the pond is still in goodcondition.

30 to 45 cm Pond is in good condition.

45 to 60 cm Phytoplankton becoming scarce. Pond should be fertilised.

Less than 60 cm Water is too clear. Pond should be fertilised, using an increasedamount.

From this table, it is seen that a desired Secchi disc reading is between 30 to 45 cm.NOTE: Turbidity occurs when the water is muddy. For the Secchi Disc readings to be ofuse, the transparency should be due to plankton.


19/46

19

b. Check Phytoplankton Blooms: A healthy bloom in ponds is indicatedby a green colour, similar to the colour of vegetation. A change in colourfrom green to brown indicates that the bloom is dying, and is oftenassociated with a sour smell.As mentioned before, blue-green algae often form scums on the surface of

ponds, sometimes with bubbles of gas. These can cause fish to suffocatewhen they surface due to the inevitable low oxygen levels that occur in thelower waters.

c. Adjust Feeding Rates: In ponds with no artificial aeration, feeding ratesshould be lowered during very hot, still weather; in the event that there isan undesirable plankton bloom; or if the culture species is not eating theration that they are being fed. If a floating feed is used, it is easy to see ifall the feed is being eaten. With a sinking feed, it is advisable to checkfeed boxes before every feeding.

d.

Water Exchange: Whenever the water quality seems to be deteriorating,it is advisable to exchange water in a pond. It is best to always removewater from the bottom of a pond since that is where the water quality isthe worst. Clean water is then added to replace the dead water that hasbeen removed. Always remove water first, before adding new water to apond.

e. Mechanical Aeration: The quickest method for combating low dissolvedoxygen is by using a system to expose a large surface area of water to theair. Commercial aerators are available, some of which use electricity, butmay be too expensive for small farmers. A water pump, fitted with adevice for spraying water in the air at the discharge end has been found tobe effective.

4. pHThe pH of a liquid refers to its acidity or alkalinity, and is measured on a scale from 0 to14. Substances that have a pH below 7 are said to be acidic, while those above 7 are saidto be alkaline. A pH of 7 is neutral, that is, neither acidic nor alkaline. Pure water has apH of 7.

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14Increasing Neutral IncreasingAcidity Alkalinity

The pH values of natural waters vary considerably depending on the soil type and theamount of organic matter present. Dark coloured water is often acidic, due to humic acidthat is dissolved in it. Water found in regions where a lot of pagasse is present is alsoacidic. On the other hand, water found in limestone regions may be slightly alkaline.


20/46

20

The desirable pH range for freshwater fish culture is between 6.5 and 9.0. Low production occurs below 6.5 and above 9.0. In a fishpond with phytoplankton, the pHfluctuates, increasing during the day and decreasing at night, similar to the change indissolved oxygen. However these changes are not large enough to cause problems. Theacid death point is 4 and the alkaline death point is 11, meaning that fish can die below 4

pH units and above 11 pH units. If a farmer wants to carry out aquaculture in an areawhere the pH is below 6.5, liming may be done, but this will incur an extra cost, whichwill have to be considered.

The pH of water has an effect on the availability of some nutrients and the toxicity ofsome compounds. For example, ammonia becomes more toxic with increasing pH levels.

5. Dissolved Nutrients and GassesMany substances are found dissolved in natural waters, and some of these are of particular importance in fishponds. Some, such as phosphate and nitrate, are fertilizers

that enable phytoplankton to bloom. Others, such as nitrite, and the gasses ammonia andhydrogen sulphide, are poisonous when present in certain lethal amounts. The levels ofthese substances increase with increased stocking and feeding rates, but whenrecommended stocking and feeding rates are followed, and good water qualitymanagement is carried out, they are rarely a problem.

6. TemperatureWater temperature is an important consideration in aquaculture, since it affects thegrowth and reproduction of culture species. Fish grow faster when temperatures arewarmer. In temperate countries, where there are warm and cold seasons, the growth period for fish is generally limited to the warm months, and reproduction for somespecies only occurs when the water temperature reaches a certain minimum value. InGuyana, however, water temperatures are warm all year round, and the species grown arenot affected by varying temperatures. Growth and reproduction for these tropical speciesare year-round activities.

7. PlanktonPlankton refers to living material that is found floating in water. There are two majortypes; phytoplankton and zooplankton. Phytoplankton are tiny plants and zooplanktonare tiny animals.

a. PhytoplanktonAs described before, the major function of phytoplankton (also known as algae) is theproduction of oxygen during photosynthesis, which is used by the farmed fish or shrimp.It is also a natural food source for some fish, e.g. tilapia and some Chinese carps.Phytoplankton can be divided into several groups, including green, blue-green, brownand red algae.


21/46

21

- Clorophyceae: These are the green algae, and cause waters to appearolive green in colour. They are the most important group both in termsof oxygen production and as a food source.

- Cyanophyceae: These are the blue-green algae and may cause watersto appear blue-green or bright green in colour. They are the mostdangerous type of algae to fish and are found when the water ispolluted with a lot of organic matter. They form scums as describedbefore and also produce harmful substances.

b. ZooplanktonThese tiny animals usually feed on phytoplankton and are very important as a food sourcefor the larval stages of most fish and shrimp. There are three major types that areimportant in aquaculture.


22/46

22

- Cladocera: These are a type of crustacean and are commonly calledwater fleas due to their resemblance to fleas.

- Copepoda: These are another type of crustacean and are almostcylindrical in shape. Although some are useful as food, others are parasites on fishes, e.g., Argulus, or Fish Louse, which occurs ontilapia reared in brackish water.


23/46

23

- Rotifera: These zooplankton are closely related to a group of animalscalled flatworms and are very important as a food source for the firstlarval stage of fish.


24/46

24

VII. Fertilizing and Liming1. What are Fertilizers

Fertilizers are natural (organic) or man-made (inorganic) substances that are used inaquaculture to increase the production of the natural food organisms to be eaten by the

fish. Fertilizers supply various nutrients in different amounts. Therefore, differentfertilizers have different uses, and are to be used in different amounts.

2. What is a Liming AgentA liming agent is a substance, either natural or man-made, that is used to reduce acidity,and therefore increase pH, in a culture system.

3. Reasons for FertilizingFertilizers are added to ponds to improve the level of nutrients present in the water. These

nutrients assist the growth of plankton, which may be used by the fish.

Also, by improving the amount of plankton, fertilizers enable the correct stocking rate tobe maintained, since adequate plankton produce oxygen for the fish.

4. Inorganic FertilizerInorganic fertilizers are man-made, and usually supply high amounts of one particularnutrient. Examples are Urea and ammonium nitrate, which supply nitrogen, and triple orsimple super-phosphate, which supply phosphorus.

5. Organic FertilizerOrganic fertilizers are usually occur naturally, and supply a variety of nutrients in varyingamounts. Examples are animal manure, crop residues and compost.

6. RatesFertilizer rates vary widely, and depend on the species to be grown, the soil and watertype. The rates are important to achieve the desired water condition. If the watercondition is suitable, then fertilization is not necessary. Fertilizer is added at thebeginning of a culture cycle, to get the pond ready for the introduction of the fish. Oncethe fish are introduced, fertilizer is added to maintain the appropriate water condition, ifnecessary.

7. Methods of ApplicationFertilizers should be uniformly applied over the whole pond surface, or distributed inspecific places carefully selected to get a uniform distribution by the water current or thewaves.


25/46

25

In the case of inorganic fertilizers, they may be dissolved in water, which is then broadcastover the pond surface.

In the case of organic fertilizer, they may be placed in bags and submerged into the ponds, atthe windward side. Holes should be made in the bag, to allow the nutrients to seep out into

the water.

VIII. Compost1. What is composting

Composting involves the intensive decomposition by micro-organisms of organicmaterials, generally under controlled conditions. This process makes it possible to utilizea wide range of cheap wastes, residues and natural vegetation for the production of aclean, dry material rich in organic matter and primary nutrients. This material is called

compost.

2. Reasons for use of CompostCompost may be used in fishponds as an organic fertilizer. In drained ponds, compost isspread over the bottom area and mixed with the upper soil layer before refilling. Later,compost can be regularly applied to the pond to fertilize the water, with the greatadvantage that it does not increase the demand for dissolved oxygen as much as otherorganic fertilizers. For this reason, compost is particularly suitable for applying to nurseryponds.

Compost can also be used directly as a low-cost feed for a number of fish species, such ascatfish and Nile tilapia, in simple fish farming systems.

3. Making CompostA simple method of preparing compost in tropical rural areas from various materials suchas tree leaves, grass, household wastes, rice husks, straw and animal manure, is thefollowing:

(a) Mark the corners of a square area 1.5 m x 1.5 m with poles about 1.5 m above groundlevel.(b) Within this area, build a first layer of coarse material about 25 cm high. Cut the rest ofthe material into small pieces.(c) Add a second layer of 5 to 10 cm made of low C/N material, preferably animalmanure. Moisten as necessary.(d) Build up your heap until it is about 1.5 m high by adding more layers. Alternate 20-cm layers made of high C/N material with 10-cm layers made of low C/N material. If youdo not have enough animal manure, sprinkle some nitrogen fertilizer on top of each highC/N layer. Moisten each layer so that it is damp but not soggy.


26/46

26

(e) If it does not rain, you may need to sprinkle water on top of the heap every three days.(f) Turn over your pile after ten to 14 days. Check its heat production and moistureregularly.(g) Your compost should be ready after another ten to 15 days.

Note: you can protect the composting heap from sun and excessive rain by covering itwith plenty of straw and by rounding off the top of the heap.


27/46

27

IX. Transporting and Stocking Fish1. Transporting Fish

The development of the aquaculture has made it necessary to transport fish from oneplace to another. This movement of fish may be inside the farm, between farms in the

neighbourhood, or even between countries or continents.

Fish should be able to be transported at any growth stage in their life, in such conditionsso that they do not suffer lethal stress, while at the same time being economical. It is possible to transport fishes and have total survival, using large amounts of space andwater. However, this may not be economical. There must be a balance betweentransporting as many fish as possible, using as little water and space as possible.

As fish are placed for long periods in the same small amount of water for transport, thewater quality starts to deteriorate. Dissolved oxygen content is reduced, carbon dioxidecontent increases, and other toxic compounds such as ammonia and nitrite increase.

An easy way of overcoming this problem is to change the water frequently duringtransport. However, this may not be possible at all times. Therefore, there are somesimple rules and devices, which enable fish survival during transport.

a. Preparation of Fish Before TransportFish for transport should be captured and held in a separate area 24 hours before beingtransported. This will reduce the stress during transport, since the fish will be easilyrecaptured. The fish will also become accustomed to a new environment outside of thepond.Fish should not be fed for 24 hours before transport. This will enable them to empty theirintestines before being transported, so that they do not foul the water during transport.It is also possible to use chemicals to reduce fish metabolic rate during transport. Thesechemicals are applied to the water before transport. However, these chemicals areexpensive, and some of them are not safe to use with food fish.

b. Water Quality for TransportWater for fish transport should be clean, and well water or rainwater should be used.Pond or canal water will deteriorate faster, stressing the fish. Room temperature watercan be used. However, adding a small amount of ice, to reduce water temperature, willaid in the survival of the fish.

c. Stocking Rate for TransportThe amount of fish to be transported in a fixed volume of water depends on the species,the size of the fish, and whether or not aeration is supplied. Advice on specific stockingrates can be obtained from technical personnel.


28/46

28

d. Methods of TransportA simple way of transporting small amounts of fish, without aeration, is by the use of aplastic bag, partially filled with water. These vary widely in size, shape, and capacity. Fortransporting aquarium fishes the usual capacity is about one or two litres, while forcommercial purposes is widely used a 40 litres double plastic bag.

A double plastic bag is recommended to use for transporting small fishes, fry, larvae orfingerlings as well as breeders when the total amount is small. A quarter of the bag isfilled with water, and the remaining three-quarters filled with pure oxygen. The top of theplastic bag is then secured with a rubber band. Using this method, fish can remain alivefor 24 hours.

Another way of transporting fish is by theuse of rigid containers. Containers areusually metal or plastic, and are fitted witha portable aeration device. These

containers have proven to be very efficientand reliable for transporting fish locally

2. Stocking FishesWhen the transported fish arrive at their destination, they should not be placed into thenew water body immediately.

If plastic bags were used for transport, the bags must be put into the water in which thefish will be placed, for at least 15 to 30 minutes to allow the water in the bag to attain thesame temperature as the water outside the bag. Failure to this may cause thermal shock tothe fish, and may cause death.

If containers were used, then some water from the intended destination of the fish shouldbe slowly added to the container, to equalise the temperature. At the end of 15 minutes,the water in the container should have approximately the same temperature as the waterinto which the fish will be placed. Only then should the fish be removed from thecontainer and placed into the new water.


29/46

29

X. Feeds and FeedingVery careful attention should be paid to fish feeds and feeding. In semi-intensivesystems, feed usually accounts for 60-75% of the total running costs of a fish crop.

If fish are fed properly, then they will be less susceptible to disease. Appropriate use of agood feed will improve growth rates, reduce crop time, and result in larger fish.

1. Types of FeedThere are three types of food used in fishponds:

- Natural food- Supplementary feeds- Complete feeds.a. Natural food: This is found naturally in the pond. It may include

detritus, bacteria, plankton, worms, insects, snails, aquatic plants and

fish. Their abundance greatly depends on water quality. Liming andfertilization, in particular organic fertilization, can help to provide agood supply of natural food for the fish. Natural food is very importantin the extensive system of aquaculture.

b. Supplementary feeds: These are feeds that are regularly distributed tothe fish in the pond, and which contain many, but not all, the nutrientsrequired for growth. . They usually consist of cheap materials locallyavailable such as terrestrial plants, kitchen wastes or agricultural by- products. Supplementary feeds are important in the semi-intensivesystem of aquaculture.

c. Complete feeds: These are feeds that are regularly distributed to thefish in the pond. They are made from a mixture of carefully selectedingredients to provide all the nutrients necessary for the fish to growwell. They must be made in a form which the fish find easy to eat anddigest. These feeds are quite difficult to make on the farm and areusually quite expensive to buy. Complete feeds are important in theintensive system of aquaculture.

2. Reasons for Feeding FishFish should be fed for the following reasons:

- Natural foods may not be enough to give the required growth rate- More fish may need to be stocked in the pond than the natural food

will support- Larger fish may be required, in a short amount of time- It may be uneconomical to rely on natural food


30/46

30

There are several occasions on which it is advantageous or even compulsory to stopfeeding the fish:

- When the water temperature is too low or too high- When dissolved oxygen content is low-

On the day you manure is applied to the pond- If a disease epidemic appears in the pond

3. Methods of Applying Artificial FeedsThere are several methods of artificial feeding:

- Broadcasting: feed is evenly distributed over the surface of the water- Hand-feeding: feed is distributed by hand, in specific parts of the rearing area- Automated (Demand) Feeder: feed is released by way of a trigger mechanism

which is activated by the fish- Select Feeding: Feed is distributed using a boat, etc., at specific parts of the

rearing area- Feeding Trays: Feed is placed in trays, which may be submerged or floating- Feeding Frames: feed is placed in floating frames, which prevent floating

feeds from dispersing

4. Types of Artificial FeedsThere are several types of artificial feeds:

- Mash (powder)- Cakes- Pellets- Green Feeds

5. Advantages and Disadvantages of Artificial FeedsThere are several advantages of artificial feeds:

- When properly made, they can provide the correct balance of nutrients needed- They are usually easily available to the farmer- The cultured species usually grows very quickly- They are easily stored for relatively long periods

There are several disadvantages of artificial feeds:- They are usually expensive- Unsuitable for some species- May pollute the water- May lead to allergic reactions if not properly made- May lead to pathogen virulence- May be lacking in completeness


31/46

31

6. Feeding RatesThe feeding rate describes the amount of feed that is applied to a particular area, over aperiod of time.Different fish species are grown using different feeding rates. Feeding rates are usuallygiven to farmers in the form of a chart, showing the amount of feed to be applied each

day.Sometimes, feeding is done according to the weight of the fishAt other times, fish are fed as much as they can eat. This is called ad lib feeding.

7. Basic Feeding PrinciplesThe following are some basic feeding principles:- Underfeeding leads to a loss in fish productivity, while overfeeding is

uneconomical, and also leads to poor water quality and production losses- The feed conversion ratio (FCR) is very important. It can range from 1.45:1 to50:1

- More feed is required in warm water than in cooler water


32/46

32

XI. Fish Health and DiseaseIt is important to ensure that fish grown on aquaculture farms are healthy and free fromdisease. Around the world, disease has caused the collapse of several important aquacultureenterprises, such as the shrimp industries in China and Ecuador.

Fish diseases may cause severe losses on fish farms through:- Reduced fish growth and production- Increased feeding cost caused by lack of appetite and waste of uneaten feed- Increased vulnerability to predation- Increased susceptibility to low water quality- Death of fish.

1. Characteristics of Healthy Fisha.

ReflexesThe following four reflex actions indicate healthy fish:

- Escape reflex: Fishes are usually not easy to catch. They escape at any minorshadow or movement in or near the water. If the fish is slow to escape, then it isprobably sick.

- Fight reflex: When a fish is caught, it tries to defend itself by vigorousmovements of the tail and fins. If the fish rests quietly and makes little attempt toescape, it is probably sick.

- Tail Reflex: The tail of a healthy, captured fish remains strongly arched orexhibits a rapid back and forth movement. A fish which does not move its tail inthis manner, or allows the tail to hang flaccidly, is probably sick.

- Eye Reflex: A healthy fish, when captured and lying on its side, turns its eye soas to keep it in the position it would normally be if the fish was upright. If thefish keeps it eye pointing upward while lying on its side, then it is probably sick.

b. External Characteristics of Healthy Fish- Bright, wet and normally pigmented skin- Flat and firm scales- Red, wet gills which are covered with a slight layer of mucous- Firm and elastic muscles- Anus closed and normally coloured- Clear, transparent and slightly protruded eyes- Characteristic fish-like smell- No nodules, parasites or ulcerated on the skin- No excessive mucus


33/46

33

c. Internal Characteristics of Healthy FishGenerally speaking, no fluid, gas or parasites should be evident inside the fish.

2. Types of Fish DiseasesOne of the simplest ways of grouping fish diseases is as follows:

- Infectious and invasive diseases- Nutritional diseases- Environmental diseases

a. Infectious DiseasesInfectious diseases are caused by external or internal invasion of the fish body by diseasecausing organisms. Bacteria, fungi, viruses and parasites like protozoa are the most common

agents of infectious diseases. Rapid death of many fish is usually a sign of an infectiousdisease.

b. Nutritional DiseasesNutritional diseases are caused by too much or too little of a particular nutrient, and areusually indicative of improper feeding practices.

Excessive feeding, or feed that contains too much fat cause the following problems:

- Obesity with fatty deposits on internal organs, especially on the liver- Water retention in tissues due to kidney failure- Problems with the gills extracting oxygen from water

The other group of important nutritional diseases is related to the lack of vitamins andminerals in the diet.The lack of vitamins and minerals can cause a variety of problems, such as reduced growthrate, gill corrosion, eye opacity, skin problems, fluid retention, etc.

All these nutritional problems are due mostly to improperly balanced feed, as well as feeddegradation caused by feed being stored for too long a period before use.

c. Environmental DiseasesStrictly speaking, environmental diseases are not really diseases. Rather, they are related tounsuitable conditions in the environment in which fish live. They are usually grouped intofour classes:


34/46

34

a) Asphyxia: This is due to low dissolved oxygen level in the water, and usuallyoccurs in the early morning.

b) Traumatisms: The traumatisms are skin lesions caused by poor handling incapturing, stocking or general handling. This may lead to other disease

conditions, such as infections.

c) Bubble Illness: This usually occurs in fry and small fishes. It results from too rapidtransfer of fish from one water condition to another.

d) Poisoning: Poisoning is due to the presence of harmful substances in the water.These may be pesticides, oil, household waste, etc. It is important to keep thepond and its surroundings clean to avoid this problem.

3. Fish Defence Against Infectiona. Mucus: Mucus (slime layer) is the first physical barrier that inhibits entry

of disease organisms from the environment into the fish. It is also achemical barrier, containing enzymes and antibodies that can kill invadingdisease organisms.

b. Scales and Skin: Scales and skin function as a physical barrier that protects the fish. These are injured most commonly by handling, roughsurfaces of tanks or cages and by fighting caused by overcrowding orreproductive behavior. Parasite infestations can also result in damage togills, skin, fins, and loss of scales.

c. Inflammation: Inflammation is a natural immune response by the cells toa foreign protein, such as bacterium, virus, parasite, fungus, or toxin.Inflammation is characterized by swelling, redness, and loss of function. Itis a protective response, an attempt by the body to wall off and destroy theinvader.

d. Antibodies: Unlike inflammation and other nonspecific forms ofprotection, antibodies are compounds formed by the body to fight specificforeign proteins or organisms. The first exposure results in the formationof antibodies by the fish that will help protect it from future infection bythe same organism.


35/46

35

4. Preventing diseases through good managementThe following points are important, and should be carefully followed:

- Ensure good water quality: sufficient supply, with adequate dissolved oxygenconcentration and free of pollution

- Keep the pond environment healthy, e.g., control pond silt, control unwantedplants

- Keep a healthy balance of phytoplankton and zooplankton and exchange water ifneeded.

- If necessary, use mechanical aeration.- Disinfect the pond regularly, using simple methods such as allowing the pond to

dry after each crop.

- Keep the fish in good condition, e.g., control stocking density, by placing onlythe recommended amount of fish in each pond.

- Keep different sizes or sexes separate if necessary to control fighting. Woundscan become inflamed, leading to disease problems.

- Ensure good food supply. Make certain that the feed is not spoilt or deteriorated.- Handle the fish properly, especially during harvesting and sorting/grading. Use

fishing gear with mesh size appropriate to the size of fish.

- Care for your fish during storage and transport.- Prevent the entry of disease organisms from outside the farm, by controlling

wild fish by using filters and screens. Regularly remove them from canals andponds.

- Disinfect all fish stocks imported from outside as eggs, juveniles or adults.- If a disease breaks out on the farm, remove dead or dying fish from the ponds as

quickly as possible, at least daily.

- Disinfect fishing gear regularly, by soaking in bleach.- A simple disinfecting bath for fish can be made using common salt in a 3%

solution for 5 minutes


36/46

36

XII. Fishing Methods and Fishing GearThe objective of using fishing gear in aquaculture is to obtain aquaculture products fromtheir natural environment, in an efficient manner.

1.

Classification of Fishing GearFishing gear can be classified as:

a. Destructive Fishing Gear: These gear are designed to obtainaquaculture products to supply a market in which the product isnot required to be alive

b. Non-destructive Fishing Gear: These gear are designed toobtain aquaculture products to supply a market in which theproduct is required to be alive for.

Fishing Gear can also be classified as:

a. Passive Gear: Passive fishing gear are gear that capture fish byallowing the fish to move toward the gear to be captured.

b. Active Gear: Active fishing gear are gear that capture fish bymoving toward the fish.

2. Commonly Used Fishing GearFishing gear commonly used on fish farms tend to have very small mesh sizes. This is toensure that fish and shrimp are not gilled, or physically harmed, during capture andhandling. Rather, the aquacultured species are physically restrained.

This is necessary since aquacultured species are usually handled several times before theyare ready for market. If they are not handled with care during the culture cycle, mortalitywill result, which will reduce the profit margin.

The most commonly used fishing gear are hand nets of various sizes, cast nets of variousmesh sizes, fish stretchers and seines of various mesh sizes.

a. Hand Nets: Hand nets with long handles are frequently used catch andhandle fry or fingerlings. They usually have very small mesh sizes, andcan even be made of some types of cloth.


37/46

37

b. Fish Stretchers: These are used to transport and handle very large fish,usually broodstock, within the farm. Fish stretchers are usually made ofstrong canvas, and have a cover with a wooden beam to protect the fishfrom sunlight, and thereby reduce handling stress.

c. Seines: A seine is a type of gill net. Seines are an active fishing gear,made of various types of net material, to give the desired mesh sizesuitable to the size of fish being handled. Seines are made to suit the widthand depth of the pond, to facilitate easy use. A seine is comprised of thefollowing parts:

- Net Material: This is the part that actually restrains the fish. It is attached to thevarious ropes of the seine using twine.

- Head Rope: The head rope has floats attached to it, to keep the top part of theseine above water.

- Foot Rope: The foot rope has lead attached to it, so as to allow the seine to dragthe bottom of the pond.


38/46

38

- Lead and Floats: Floats are required to keep the top part of the seine abovewater, while lead is required to allow the bottom part of the seine to drag thepond bottom.

d. Cast Net: The cast net is an active fishing gear, operated by a single person. They work very well in shallow water, but are less effective indeeper waters. A cast net is composed of two main parts:

- The net, formed by several triangular patches of net joined together in the shapeof a cone. This ends in a bag at the border of the net

-

The rope, one end of which is attached to the net, and the other part, which isheld by the fisherman.

While cast nets are often used to sample fish, it should be noted that since bigger fishescan swim faster than smaller ones, cast nets tend to capture the small and medium fishes.This may give a slightly incorrect picture of the fish in the pond.


39/46

39

XIII. Post-Harvest TreatmentProcessing is required because most fishery products have a high water content, as wellas high protein, which make them prone to rapid spoilage.

The following are the common methods of processing:a. Drying: Water is removed from the fish, and heat is transferred inwards.This slows down microbial and enzymatic activity. Drying is influencedby the air temperature, relative humidity, air velocity, water content of thefish, and thickness of the fish.

b. Smoking: This results in drying, as well as flavouring of the fish. Cookingmay also occur, except if cold smoked.

c. Salting: This prevents of drastically slows down bacterial action, and iscommonly used in combination with drying or smoking. The objective is

to get 6-10% salt in the tissue, and 35-45% water content in the fish. Thisis influenced by the fat content of the fish, the thickness of the flesh, thefreshness of the fish and the temperature of the environment.

d. Freezing: The objective is to reduce temperature in the fish to point wheremicrobial and enzymatic activity slows down or stops. The rate of freezingis important, to prevent tissue damage.

XIV. MarketingMarketing of the aquaculture product is an important aspect of the entire culture cycle. Itis in the interest of the farmer to know for what market he is producing the product for,even before starting culture. It is also important to supply the market on a regular basis,so as to maintain a reliable outlet for the product.

1. Local MarketProducing for the local market is far more easy than producing for the export market. It isrecommended that farmers start out producing for the local market, and then move up tothe export market once all the systems are in place.The information below relates to Red Tilapia.

a. Size: A minimum size of 170g, or 6 ounces, is suitable for thelocal market. Large fish usually sell for a higher price.

b. Quantity: There is no minimum quantity to be attained forsupply to the local market.

c. Price: Tilapia retail for approximately $120 per pound for smalland medium sized fish. Larger fish usually sell for a higher price.


40/46

40

d. Where to Sell It: Tilapia can be sold at any of the local marketsaround the country. The New Guyana Marketing Corporation isalso willing to purchase tilapia for $110 per pound.

2.

Overseas MarketProducing for the overseas market is more difficult than producing for the local market.While numerous aquaculture farmers have sold fish and shrimp on the local market, nonehave supplied the export market on a regular basis.

Before entering into a production system that will supply aquaculture produce to theexport market, it is recommended that a supply contract be obtained from the purchaser.This contract should outline the parameters of the product, the quantity to be supplied,and a price guarantee.

The information below relates to Red Tilapia.

a.

Size: A minimum size of 500g, or 18 ounces, is required for theexport market.

b. Quantity: A minimum quantity of 5,000 pounds per week isrequired for supplying the export market.

c. Price: The price offered for tilapia to supply the export market isapproximately $120 per pound, for whole fish.

XV. Record KeepingOnly by keeping accurate records can it be determined if a profit is being made, and howmuch of a profit. Records also allow us comparisons to be made of yields of variouscrops, so as to find out if progress is being made, and if improvements are continuing.

Record keeping does not have to be a complicated business. Once a few basic factors arerecorded, many conclusions can be derived. The most important ones to be noted arepresented below.

1. Stocking DataThis refers to the type of species being cultured, how much has been placed into thepond, and what date they were placed into the pond.

2. Feeding DataThis refers to the type of feed supplied to the fish, and the amount of feed supplied on adaily basis.


41/46

41

3. Sampling DataAt fixed times during the culture cycle, fish should be caught, weighed and returned tothe pond, so as to observe how fast they are growing, and to observe the general health ofthe fish.

4.

Mortality DataThis refers to the amount of dead fish, and the weight of the dead fish.

5. Harvest DataThis refers to the total amount of fish harvested and the individual weight of each fish.

6. Marketing DataThis refers to the amount of fish sold, the quantities sold to each buyer, and the pricecharged.

From the data taken above, the following can be determined:

a.

Culture timeb. Survival percentagec. Growth rated. Feed Conversion Ration (FCR).e. Cost of Productionf. Profit

It is only when all the costs are taken into consideration, and subtracted from the income,then will it be possible to find out if your aquaculture farm is profitable.

XVI. Tilapia RearingThe tilapia is an ideal species for aquaculture, due to its production of many offspring,hardiness, resistance to disease, ability to live in either fresh or brackish water, and theability to eat either formulated or natural feeds.

1. Pond ConstructionPonds for tilapia rearing should be constructed in a place where there the soil has at least35% clay, to prevent water loss by seepage. The pond should be near an adequate supplyof either fresh or brackish water, and in a place where water can be easily put into it, andtaken out of it. The water used in the ponds should have a pH of between 6.5 and 9.0,since acidity reduces growth rate in tilapia.

A pond depth of at least 5 ft (1.4m) is required to hold 3.5 ft (1.1m) of water at the inletside and 4.5 ft (1.4 m) of water at the outlet side.The sides of the pond should slope at a 30-degree angle, and the bottom graded towardsthe outlet, to allow for drainage.


42/46

42

2. Stocking RateIn the production ponds, tilapias are stocked at 1 fish for every 3 square feet, or 3 fish persquare meter. This works out to 14,530 tilapia per acre, or 20,000 tilapia per hectare.In the brood pond, tilapias are stocked at 1 fish for every 5 square feet (2 fish per squaremeter). In the fingerling pond, tilapia are stocked at 1 fry per square foot.

3. FertilizingFor freshwater ponds, the following rate is recommended:

- 500 pounds cow manure per acre per month- 50 pounds TSP per acre per month

4. FeedingIf sinking pellet feed is used, a feed box is required. This feed box can be constructed ofwood, and should be 3 feet long, 2 feet wide and 6 inches deep. It should be suspended 6-12 inches below the water surface. Each pond must have at least two feed boxes, andabout 8 feed boxes are required per acre.

The recommended feeding rate in a growout pond is usually at 5% of the body weight ofthe fish per day.Feed should be placed in the feed box, and feeding should be done two times daily. Thefirst feeding should be done between 8:00 hrs and 9:00 hrs, and the second between 15:00hrs and 18:00 hrs.

5. BreedingTilapia will breed naturally in the brood pond. In the brood pond, the stocking ratio is 1male to 3 females. The adult male is usually longer and darker than the female, and has anarrowly pointed vent or genital opening. The female is shorter, lighter in colour, and hasa broad vent.The male prepares a circular depression in the pond bottom, and then encourages thefemale to lay her eggs in it. He then fertilizes the eggs and the female then takes theminto her mouth and keeps them until after they hatch.Each female can produce about 450 eggs per breeding cycle. Each female can achieveabout 6 cycles per year, giving a total of 2,700 eggs per year.


43/46

43

6. Pond ManagementThe water level in the pond must be kept constant. Therefore, water should be added toreplace that lost by seepage or evaporation.The feedbox in the pond can be used as an indicator of the pond water level. Fish shouldnot be overfed, since this can cause the water in the pond to become polluted, and resultin an unhealthy environment for the fish.Feed boxes must be taken out of the pond once per week, cleaned and left to dry in thesun, to disinfect them. Ponds should only be fertilized if there is a need to do so.Fertilizing should only be done on sunny days. All water entering and leaving the pond

must be filtered.Because tilapia breed readily in the growout ponds, usually before reaching the desiredmarket size, and females are usually much smaller than males, all-male culture isrecommended. There are three main ways of doing this; hand sexing of fingerlings, theuse of male hormones (sex reversal), and the use of super-males for breeding, whichproduce only males.

7. Growth rateThe growth rate obtained depends on the feed used, and whether or not only males aregrown, or both males and females are grown in the same pond. If tilapias are fed ricebran, a size of 8 ounces (227 g) can be achieved after 6 months. If Broiler Starter is used,

then a size of 8 12 ounces (341g) can be achieved after 5 months. If Tilapia floatingpellet is used, a size of 1 pound (2.2 kg) can be achieved after 6 months.

8. Record keepingRecords must be kept on all aspects of production. These records include the amount ofmoney spent, the type and quantity of feed used, and other important aspects of pondmanagement. This is to enable farmers to calculate their profit, at the end of a crop.


44/46

44

XVII. Local InformationBased on trials conducted at the Mon Repos Freshwater Aquaculture DemonstrationFarm and Training Centre, the following data has been obtained with respect to theculture of Red Tilapia in ponds.

All the trials were conducted with hand sexed male tilapia.

1. Tilapia Grower Feed, Sinking Pellet (28% protein, locally produced)

After 6 months in the growing pond (total seven months), 93% survival was obtained.The average weight was 255g (9 oz), and 70% of the population was over 227 g (8 oz),while 7% was over 340 g (12 oz).The FCR was 2.14:1Cost of Feed: $23 per pound Selling Price for Fish: $120 per pound

2. Tilapia Floating Pellet (33% protein, imported from Trinidad)After 5 months in the growing pond (total six and one half months), 78% survival wasobtained. The average weight was 374 g (13.2 oz). The amount of fish over 454 g (onepound) was 22%.The FCR was 1.82:1Cost of Feed: $35 per pound Selling Price for Fish: $120 per pound


After 4 months in the growing pond (total five months), the average weight was 274.8 g(9.7 oz). Survival percentage was 80%.The FCR was 2.2:1Cost of Feed: $26 per pound Selling Price for Fish: $120 per pound

4. Tilapia Floating Pellet (33% protein, imported from Trinidad)

After 6 months in the growing pond (total seven and one half months), the survivalpercentage was 98.2%. The average weight was 512.7 g (18.1 oz), with 72% of the fishover one pound.The FCR was 1.81:1Cost of Feed: $35 per pound Selling Price for Fish: $120 per pound


After 6 months in the growing pond (total seven and one half months), the survivalpercentage was 80%. The average weight was 403.5 g (14.2 oz), with 35% of the fishover one pound.The FCR was 2.53:1Cost of Feed: $26 per pound Selling Price for Fish: $120 per pound


45/46

45

XVIII. Appendix


46/46

XIX. References1. Annual Report of the Mon Repos Freshwater Aquaculture Demonstration Farm and

Training Centre. 2001-2002.

2.

FAO Training Series. Simple Methods for Aquaculture. Pond Construction forFreshwater Fish Culture. 20/1: Building Earthen Ponds.

3. FAO Training Series. Simple Methods for Aquaculture. Management for FreshwaterFish Culture. 21/1: Ponds and Water Practices

4. FAO Training Series. Simple Methods for Aquaculture. Management for FreshwaterFish Culture. 21/2: Fish Stocks and Farm Management.

5. Fonticiella, D; Monteagudo, A. 2000. Manual on Basic Aquaculture.6.

National Development Strategy for Guyana (Shared Development through aParticipatory Economy), Chapter 13 Fisheries Policy, 1997-2002. Ministry of

Finance, Government of Guyana.

7. The State of World Fisheries and Aquaculture. 2000. Food and AgricultureOrganization of the United Nations.

8. Van Gorder, S.D. 2000. Small Scale Aquaculture.9. Avault, J.W. 1998. Fundamentals of Aquaculture.

Basic Course on Aquaculture

Documents

Transcript of Basic Course on Aquaculture