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RAFOA
Researching alternatives to fish oil for aquaculture

Salmon, trout, sea bream and sea bass will be fed diets containing various blends of vegetable oils and fish oils with different levels of (n-3) and (n-6) polyunsaturated fatty acids (PUFA). 'Best practices' can then be recommended to the aquaculture industry for substituting fish oils with vegetable oils in fish feeds, thus facilitating continuing aquaculture development independently of the limited supplies of fish oils, without prejudicing the health and welfare or the fish or their health-promoting benefits to the consumer.

Objectives
The objectives of this project are:
1) to feed Atlantic salmon, rainbow trout, sea bream and sea bass diets containing various blends of fish oil and vegetable oils, including linseed oil, rapeseed oil and olive oil, in two trials. Dietary Trial 1 will be with fish aged at least six months younger than market size up to market size to define best candidate oils and blends; the second, using oils and blends so defined, will be with fish grown from first feeding up to market size (Dietary Trial 2)
2) to determine in these trials the feed intake, growth, use of nutrients and energy; classes and fatty acid compositions of flesh lipids and, for salmon and trout, flesh carotenoids; levels and fatty acid compositions of serum lipoproteins; activities of lipoprotein and triacylglycerol lipases in liver, muscle and adipose tissue; activities of selected lipogenic enzymes in liver and muscle; rates of oxidation of polyunsaturated fatty acids (PUFA) and other fatty acids in isolated hepatocytes and in muscle; activities of selected enzymes regulating fatty acid oxidation in liver and muscle; rates of conversion of C18 PUFA to C20 and C22 PUFA in isolated hepatocytes and in vivo
3) to clone and characterise D6 and D5 fatty acid desaturases and to determine their expression, together with the expression of glucose-6-phosphate dehydrogenase and fatty acid synthetase
4) to determine plasma levels of insulin, leptin, cortisol, prostaglandins E and F, and, in trout, voluntary feed intake
5) to determine the potency of commercial vaccines to protect against commercially important disease organisms and the haemolytic capacity of the alternative complement pathway in serum
6) to determine the organoleptic properties of cooked fillets for all species, and smoked fillets for salmon and trout, using taste panels in France, Norway, Spain and the UK
7) to assess sashimi products in Japan
8) to relate the results to non-subjective measurements based on electronic detection of volatile compounds in fillets
9) to determine the stability during ice- and frozen storage of flesh of all the species, and the quality and yield of flesh during the processing of smoked salmon and trout
10) to update the understanding of fatty acid nutrition and metabolism in fish. Also, to provide advice to the industry and the public on 'best practices' for substituting fish oils with vegetable oils in fish feeds, without compromising the health and welfare of the fish, or the health promoting benefits and acceptability of the final product to the consumer and producer.

Progress to Date
The RAFOA programme is proceeding successfully. Detailed recommendations and guidelines for the aquaculture industry for substituting fish oils in aquafeeds for salmon, trout, sea bream and sea bass with blends of sustainable vegetable oils, will be underpinned by advanced understanding of the nutritional biochemistry and physiology of lipids in fish.

Results
Dietary Trial I proceeded smoothly and is now complete. It has established that, in diets containing the normal complement of fish meal, fish oil (FO) can be replaced with rapeseed oil (RO) or linseed oil (LO), completely for Atlantic salmon and rainbow trout, and up to 60% for sea bream and sea bass, in juvenile fish grown on to market size, without compromising the growth of the fish. In addition, 50% of dietary FO can be replaced with olive oil without compromising the growth of the fish.
All species responded metabolically to vegetable oil substitution. These responses included increased desaturation and elongation of PUFA in the liver and increased b-oxidation in the muscle of salmon, although b-oxidation in trout muscle and especially liver was not affected by feeding vegetable oils. No apparent changes occurred in lipoprotein lipase activity or lipogenic capacity in trout fed diets with different dietary oils.
Major advances were made in cloning and characterising genes determining D6 and D5 PUFA desaturations and PUFA elongations in fish. Advances have also been made in expression of cloned desaturase and elongases but a distinct D6 desaturase gene has still to be found in salmon.
Samples of salmon and sea bass have been assessed by taste panels in Scotland, Norway and Spain. The freshness of Atlantic salmon was not affected by inclusion of vegetable oils in diets. Effects on colour were more pronounced in fish fed RO than in fish fed LO but the texture was not affected by inclusion of vegetable oils; however, the firmness decreased with ice storage time.

Classified in HORTICULTURE, FISHERIES AND AQUACULTURE

Scientist responsible for the project

Dr JOHN GORDON BELL
Institute of Aquaculture, University of Stirling
FK9 4LA Stirling
United Kingdom (The) - GB

Phone: +44 1786 467997
Fax: +44 1786 472133
E-mail: g.j.bell@stir.ac.uk

References

Project ID QLRT-1999-30058
Organisation University of Stirling
Area 5.1.2
Start date 01 January 2001
Duration (months) 48
Total cost 5 032 369 €
Total EC contribution   2 600 000 €
Status Completed

The partners

  • Institut Franšais de Recherche pour l'Exploitation de la mer, France - FR
    jrobin@ifremer.fr
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