Fish oil replacement with different vegetable oils in Murray cod: Evidence of an “omega-3 sparing effect” by other dietary fatty acids

Within the context of fish oil replacement in aquaculture, the modification of fillet fatty acid make-up and the maximisation of omega-3 long-chain polyunsaturated fatty acid (n-3 LC-PUFA; namely eicosapentaenoic acid – EPA – 20:5n-3, and docosahexaenoic acid – DHA – 22:6n-3) deposition are attracting increasing interest. The present study investigated these aspects by testing fish oil and four different vegetable oils (selected for their extreme fatty acid composition: palm oil, olive oil, sunflower oil and linseed oil) in a feeding trial consisting of a grow-out and finishing period using juvenile Murray cod. Minimal/no effect on growth performance was recorded. The dietary treatment largely affected the fillet fatty acid make-up, which was to some extent, diluted by the finishing period. The overall fatty acid composition of the alternative oil used (i.e. saturated, monounsaturated and polyunsaturated fatty acids — SFA, MUFA and PUFA, respectively) was found to have a significant effect on the final n-3 LC-PUFA content of cultured fish. It was shown that MUFA, and to a lesser extent SFA, can have a form of “omega-3 sparing effect”, whereby an abundant availability of dietary MUFA and SFA can decrease the catabolism of n-3 LC-PUFA and result in a greater deposition rate of these health-promoting fatty acids into fish fillets.