Title: EXPRESSION OF REGULATORY ENZYME GENES IN RELATION TO LIPID UTILIZATION AND DEPOSITION IN RAINBOW TROUT Authors
Submitted to: Aquaculture America Conference
Publication Type: Abstract Only
Publication Acceptance Date: December 15, 2008
Publication Date: N/A
Technical Abstract: In developing a sustainable diet for piscivorous fish species it will be necessary to not only substantially reduce the current level of fishmeal, but also the level of fish oil. Standard salmonid diets use between 9 and 15% fish oil which functions as a key source of energy and essential fatty acids. While aquaculture is currently using around 50% of the fishmeal produced worldwide it is using greater than 80% of the produced fish oil. In an attempt to replace fish oil studies have been carried out to evaluate the potential of using oils obtained from sustainable sources such as plants. Research has determined that most of the fish oil currently used in salmonid diets can be replaced with plant derived oils without compromising growth performance. However, there is a substantial change in the fatty acid composition of the fillets in fish reared on these diets that generally mimic the fatty acid profile of the dietary lipids. Studies using phase feeding or finishing diets containing fish oil have shown an increase in the level of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in fillets over that of fish fed diets containing only plant oils. In previous studies evaluating the effect of fishmeal and fish oil replacement diets on spawning fish and egg quality, a significant difference was observed in the level of expression of a key enzyme involved in regulating fatty acid biosynthesis. In this experiment expression of the enzyme '6 desaturase was determined to be upregulated in fish fed a diet that had fishmeal and fish oil replaced with plant protein and oil. Furthermore, it was noticed that this upregulation was significantly higher in some families on all diets and that difference even more pronounced when the fish were reared on the formulated plant meal and plant oil replacement diet. To determine the potential level of variation within rainbow trout, thirty-five families of fish were reared for 12 weeks on a diet formulated with plant based fatty acid precursors for the synthesis of EPA and DHA. At the end of the study an average of 25 fish from each family was sampled to determine the deposition of fatty acid in the fish and to evaluate the expression of mRNA for three genes involved in the biosynthetic pathway, namely '6 desaturase, '5 desaturase, elongase, and CoA dehydrogenase.