Altered fatty acid compositions in Atlantic salmon (Salmo salar) fed diets containing linseed and rapeseed oils can be partially restored by a subsequent fish oil finishing diet

Abstract

Atlantic salmon post-smolts were fed ten experimental diets containing various blends of two vegetable oils, linseed (LO) and rapeseed oil (RO), and fish oil (FO) in a triangular trial design, for 50 weeks. After sampling, fish previously fed 100% FO, LO and RO were switched to a diet containing 100% FO and grown on for a further 20 weeks. Fatty acid compositions of flesh total lipid were linearly correlated with dietary fatty acid compositions (r = 0.99-1.00, P < 0.0001). Inclusion of vegetable oil at 33% of total oil resulted in a reduction in the concentrations of the highly unsaturated fatty acids, eicosapentaenoate [20:5(n-3)] and docosahexaenoate [22:6(n-3)], to around 70 and 75%, respectively, of the values in fish fed 100% FO. When vegetable oil was included at 100% of total dietary lipid the concentrations of 20:5(n-3) and 22:6(n-3) were reduced to around 30% and 36%, respectively, of the values in fish fed FO. Transfer of fish previously fed 100% vegetable oil to a 100% FO diet for 20 weeks, restored the concentrations of 20:5(n-3) and 22:6(n-3) to around 80% of the value in fish fed 100% FO for 70 weeks. However, concentrations of 18:2(n-6) remained about 1.5-fold higher, compared to fish fed 100% FO, in fish previously fed either 100% LO or RO. This study suggests that RO and LO can be used successfully to culture salmon through the seawater phase of their growth cycle although this will result in reductions in flesh 20:5(n-3) and 22:6(n-3) concentrations that can be partially restored by resuming a diet containing only marine FO for a period prior to harvest.