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July | August

Feature heading: SustainabilityFeature title: Sustainability - an enduring trend in aquaculture

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Aquaculture will play a

critical role in supplying

the growing demand for

protein by populations

worldwide. According to the FAO

World Agriculture Toward 2015 -30,

consumption of fish will increase 150

to 160 million tonnes, or 19-20kg per

person and aquaculture will be the

critical source of supply as ocean fish

stocks continue to be over fished and

mismanaged.

Obstacles to growthHowever, an obstacle stands in the path

of aquacultures future success.Ineffective fish and crustacean farming

practices result in pollution of the local

environment and disease in the fish popula-

tions. Intensive fish farming currently takes

place in select countries worldwide and is

contributing to a backlash from non profit

organizations, governments and end consum-

ers concerned with aquacultures contribu-

tion to the destabilising and degradation of

local ecosystems.

Unsustainable fish

farming produces

waste water

filled with

fish feces,

f i sh

feed and residues of pesticides and veteri-

nary drugs.

Aquaculture also contributes to envi-

ronmental degradation of 50 percent

of mangrove forests, which serve as

natural coastal protectors from storms.

Aquaculture populations, who require

fresh water to grow, have been given

often-illegal antibiotics and pesticides by

fish farmers.

When residues from the antibiotics and

pesticides are discovered in the fish, the

aquaculture industry cannot sell their prod-

ucts to foreign markets as import bans are

put in place to protect consumers.

Sustainable aquaculture is a trend that

will need to be embraced by the industry or

negative repercussions will follow.

Consumer consciousness worldwide is

already being raised to fear eating con-

taminated fish from fish farms. Activists andgovernments could yet be pushed to limit

the expansion of the industry. Worse yet,

without protection of local ecosystems by

good aquaculture management, there

may not be enough clean water for fish

farming. This would inhibit expansion

of the industry and its ability to meet

the need of a growing population

reliant on fish and crustaceans as a

key source of protein.

Sustainable aquacultureGood management and the correct

application of technology can increase

by Heather Lenz, Buhl er, Uzwil

-

10 | InternatIonal AquAFeed | Juy-augus 09

Sustainability

the sustainability of aquaculture, decrease

the need for chemicals and medicine and

maintain the health and optimal growth of

the fish population.

Aqua feed is a key example of how the

correct application of technology and good

management can decrease the negative

effect of pollution from aqua farming.

The use of unpelleted or poor

quality pelleted fish feed can lead to

inefficient fish growth and uneaten feed

material. Uneaten fish feed becomes

Juy-augus 09 | InternatIonal AquAFeed | 11 -

Sustainability

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Two-stage dryingThe hot and steaming product very

rapidly releases the free surface moisture

to the hot air stream. Once the surface has

been dried, the drying action is limited by

the diffusion rate inside the product, and

the air stream can be reduced.

Such a multi-stage drying process con-

sists of a hot air conveying system and

a fluid-bed dryer, followed by a belt orcounter current dryer.

This process allows very fast, gentle, and

nondeforming drying to the necessary final

moisture content of eight to 10 percent even

of soft and sticky products.

Coating/coolingUsually, the dried extrudates are coated

while still warm directly after the dryer.

During this stage, it is possible to add

fats, flavorings, attractants, colors, and even

powdered ingredients.

Depending on the temperature and the

specific surface area of the extrudates, up

to 12 percent liquids can be absorbed in the

coating drum and the subsequent cooler.

For higher oil quantities up to 40 percent,it is common practice to apply vacuum

coaters/mixers.

One-step in the value chainIn the production of aqua feed, it is

important to ensure the ideal formula-

tion and production. Buhlers technology

and process steps

enable high per-

formance aqua feed

to be produced

by feed millers

worldwide.

But this is just

one step towards

the future sustain-

ability of aquac-ulture. There is

a rising need for

more awareness

and training of

in-farm feed and

water management

strategies for fish

farms in developing

countries.

Leading feed

millers, academics

and other members

of the aquaculture

industry have an

important and

continuing role to

play in transferring

research and good

management prac-

tices to developing

countries to ensure

the advancement of

the entire industry.

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- Juy-augus 09 | InternatIonal AquAFeed | 13

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and continuously optimised on the basis

of commercial and nutritional criteria.

A fine grinding system reduces the raw

component blend to an average particle

size smaller than 250 microns. The blend

is then conveyed pneumatically to the

control sifter.

Control sifting

A sifter especially suitable for processingfinely ground, fatty fish feed formulations is

required to eliminate insoluble substances

such as bones, scales, sand, and fibres, which

might clog die holes smaller than 1.5 -

2mm. Buhler recommends a mesh aperture

smaller than about 70 percent of the die

hole diameter.

Extrusion processThe extrusion process is essentially a

cooking process during which the starch-

containing components are decomposed

and the proteins are denatured.

Together with the other ingredients, a

hydrophil yet water stable matrix is created.

The required heat is added mainly

in the form of direct steam in the

preconditioner. In the extruder, the

mass preheated to about 95C is fur-

ther heated by mechanical processing

so that temperatures of about 120

to 140C are achieved. The patented

Density Control System allows the

steam pressure of the hot dough mass

to be controlled while the mass is still

inside the extruder. This enables the

sinking or floating characteristics to be

controlled across a wide range without

compromising on the cooking degree.

Shaping/cuttingThe die hole geometry is crucial in the

process,as the hot product melt has to be

depressurised,shaped,and cut.Especially

small die holes up to 0.6mm requirean optimised number of

holes and a wear-resistant

die plate.

A correct die selec-

tion achieves high pellet

quality and the right expan-

sion. The cutter speed can be varied

to change the length of the extruded pellets.

Since a considerable volume of moisture is

evaporated at this point, hot air addition and

a good aspiration are needed in order to

prevent condensation and agglomeration of

the products.

fat contents with a good water absorption

rate and high water stability to sink slowly

in saline water.

Fish, such as sturgeons, yellow tail,

and sea bass

can be fed

sinking pellets.

Shrimp pellets

are fast sinking

and retain theirelastic structure

even after hours

in the water.

Steps tosustainableaqua feed

Buhler has

three critical

goals for its aqua

feed production

technology. The

technology must

enable aqua feed

millers to create

a complete diet, which the animal can ingest

and assimilate optimally, maintaining the

animals health.

Extrusion technology should maximise

the conversion rate and the meat qual-

ity while minimizing the costs. Last of all,

Buhler supports good management and

the sustainability of the aqua feed with

technology that reduces the need for

overfeeding.

Blending and mixing, grindingThe raw materials, which account

for over 80 percent of the total

production cost, are formulated

waste in the aquaculture system, pol-

luting the water.

Buhler supplies technology to the aqua feed

industry to decrease the amount of uneaten

feed, maximize the feed conversion rate and

increase the health of the entire fish population

while lowering pollution of water outflow.

The ideal feed for each fish type can be

produced via Buhlers extrusion technology

to maximise feed digestibility and conver-

sion rates while minimising water pollution.

Micro pellets are very small, accurately cut

and for feeding all species whether as float-

ing or sinking. Floating feeds are pellets

with moderate protein and fat content

for feeding warm-water species such as

tilapia and eels. Sinking feed

are pellets with

high protein and

12 | InternatIonal AquAFeed | Juy-augus 09 -

Sustainability

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www.aquafeed.co.ukTHE INTERNATIONALMAGAZINE FOR THE AQUACULTURE FEED INDUSTRY

MemberoftheWorldAquacultureSociety,EuropeanAquacultureSociety,AmericanFeedIndustryAssociationandtheInternationalAquafeedAssociation

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