2009/782 Impact of fish oil replacement on the expression of antioxidant genes and genes involved in the synthesis of omega-3 long chain polyunsaturated fatty acids in Yellowtail Kingfish

By Nathan Rout-Pitt

Fish flesh contains high levels of omega-3 long chain polyunsaturated fatty acids (n-3 LCPUFA) such as eicosapentaenoic (EPA) and docosahexaenoic acid (DHA) are beneficial for human health to help brain and neural development, decrease the risk of cardiovascular disease and help various other aspects of human lives. EPA and DHA can be synthesised via the LCPUFA synthesis pathway in fish from α-linolenic acid (ALA) which is abundant is some plant oils which are totally devoid of n-3 LCPUFA. Captured fish are currently used as a source of fish oil to feed fish in aquaculture, but capture fisheries are currently at their limit and using captured fish stocks as aquaculture feed is unsustainable and therefore alternative lipid sources to replace fish oil are required to allow the aquaculture industry to continue growing.

This research investigated dietary fish oil replacement with plant or terrestrial animal oils and its impact on the seafood product quality of Yellowtail Kingfish (Seriola lalandi), an important aquaculture species in South Australia. It investigated how this replacement affected the expression of the fatty acid synthesis genes ∆6 fatty acyl desaturase (∆6 fads) and fatty acyl elongase (elovl), and the antioxidant genes peroxiredoxin 1 and 4 (Prx1 and 4) and glutathione peroxidase 1 and 4 (GPx1 and 4).
It was found that fish oil substitution with canola oil and poultry oil did not significantly change the expression of the fads or elovl genes. The antioxidant genes also showed no significant changes in gene expression except for GPx1 which showed an increased expression in fish fed the canola oil-based diet compared to fish fed the fish oil-based diet. Based on these results, and the results of the hepatosomatic indices, it is proposed that GPx1 expression may be up-regulated in fish fed the canola oil-based diet due to increased immune system activity as a result of the relatively high concentration of omega-6 fatty acids in their flesh.