Replacement of fish oil with rapeseed oil in diets of Atlantic salmon (Salmo salar) affects tissue lipid compositions and hepatocyte fatty acid metabolism

Duplicate groups of Atlantic salmon post-smelts were fed five practical-typ e diets in which the added lipid was 100% fish oil [FO; 0% rapeseed oil (0% RO)], 90% FO + 10% RO (10% RO), 75% FO + 25% RO (25% RO), 50% FO + 50% RO (50% RO) or 100% RO, for a period of 17 wk. There were no effects of diet o n growth rate or feed conversion nor were any histopathological lesions fou nd in liver, heart, muscle or kidney. The greatest accumulation of muscle l ipid was in fish fed 0% RO, which corresponded to significantly lower muscl e protein in this group. The highest lipid levels in liver were found in fi sh fed 100% RO. Fatty acid compositions of muscle lipid correlated with RO inclusion in that the proportions of 18:1(n-9), 18:2(n-6) and 18:3(n-3) all increased with increasing dietary RO (r = 0.98-1.00, P < 0.013). The conce ntrations of eicosapentaenoic acid [20:5(n-3)] and docosahexaenoic acid [22 :6(n-3)] in muscle lipid were significantly reduced (P < 0.05), along with total saturated fatty acids, with increasing dietary RO, Diet-induced chang es in liver fatty acid compositions were broadly similar to those in muscle . Hepatic fatty acid desaturation and elongation activities, measured using [1(-14)C] 18:3(n-3), were increased with increasing dietary RO. Limited su pplies of marine fish oils require that substitutes be found if growth in a quaculture is to be maintained such that fish health and product quality ar e not compromised. Thus, RO can be used successfully as a substitute for fi sh oil in the culture of Atlantic salmon in sea water although at levels of RO > 50% of dietary lipid, substantial reductions occur in muscle 20:5(n-3 ), 22:6(n-3) acid the (n-3)/(n-6) polyunsaturated fatty acid (PUFA) ratio, which will result in reduced availability of the (n-3) highly unsaturated f atty acids that are beneficial for human health.