Sustainability - An Enduring Trend In Aquaculture

July | August Feature heading: Sustainability Feature title: Sustainability - an enduring trend in aquaculture International Aquafeed is published five times a year by Perendale Publishers Ltd of the United Kingdom. All data is published in good faith, based on information received, and while every care is taken to prevent inaccuracies, the publishers accept no liability for any errors or omissions or for the consequences of action taken on the basis of information published. ©Copyright 2009 Perendale Publishers Ltd. All rights reserved. No part of this publication may be reproduced in any form or by any means without prior permission of the copyright owner. Printed by Perendale Publishers Ltd. ISSN: 1464-0058

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Sustainability

Sustainability

by Heather Lenz, Buhler, Uzwil

A

quaculture 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 growth However, an obstacle stands in the path of aquaculture’s future success. Ineffective fish and crustacean farming practices result in pollution of the local environment and disease in the fish populations. Intensive fish farming currently takes place in select countries worldwide and is contributing to a backlash from non profit organizations, governments and end consumers concerned with aquaculture’s contribution to the destabilising and degradation of local ecosystems. Unsustainable fish farming produces waste water filled with fish feces, fish

feed and residues of pesticides and veterinary drugs. Aquaculture also contributes to environmental 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 products 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 contaminated fish from fish farms. Activists and governments 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 aquaculture Good management and the correct application of technology can increase 10 | InternatIonal AquAFeed | July-august 09

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

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Sustainability waste in the aquaculture system, polluting the water. Buhler supplies technology to the aqua feed industry to decrease the amount of uneaten

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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 their elastic structure even after hours in the water.

Steps to sustainable aqua feed

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 Buhler’s extrusion technology to maximise feed digestibility and conversion rates while minimising water pollution. Micro pellets are very small, accurately cut and for feeding all species whether as floating 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

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 animal’s health. Extrusion technology should maximise the conversion rate and the meat quality 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, grinding The raw materials, which account for over 80 percent of the total production cost, are formulated

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 processing finely 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 process The extrusion process is essentially a cooking process during which the starchcontaining 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 95°C is further heated by mechanical processing so that temperatures of about 120 to 140°C 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/cutting The 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 require an optimised number of holes and a wear-resistant die plate. A correct die selection achieves high pellet quality and the right expansion.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.

Two-stage drying The 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 consists of a hot air conveying system and a fluid-bed dryer, followed by a belt or counter 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/cooling Usually, 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 chain In the production of aqua feed, it is important to ensure the ideal formulation and production. Buhler’s technology

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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 practices to developing countries to ensure the advancement of the entire industry.

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and process steps enable high performance aqua feed to be produced by feed millers worldwide. But this is just one step towards the future sustainability of aquaculture. There is a rising need for more awareness and training of in-farm feed and water management strategies for fish farms in developing countries.

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