Effects of dietary highly unsaturated fatty acid levels on growth,fatty acid profiles,antioxidant activities,mucus immune responses and hepatic lipid metabolism related gene expressions in loach (Misgurnus anguillicaudatus) juveniles

A 9‐week rearing trail was conducted to examine the effects of different dietary highly unsaturated fatty acid (HUFA) levels on the growth performance, fatty acid profiles, antioxidant activities, mucus immune responses and lipid metabolism‐related gene expressions of loach (Misgurnus anguillicaudatus) juveniles. Five test diets supplemented with 0%, 0.32%, 0.64%, 0.96% and 1.28% HUFA were used here. The loaches fed no HUFA diets had the lowest specific growth rate and survival rate. The loaches fed 0.32% HUFA diets had the lowest feed conversion rate and while no significant differences were found among the other four diet groups. Contents of hepatic eicosapentaenoic acid, docosahexaenoic acid and total polyunsaturated fatty acids were significantly increased with incremental dietary HUFA levels. Activities of hepatic superoxide dismutase (SOD), glutathione peroxidase (GPx) and catalase (CAT) in 0% HUFA group were lowest, while malondialdehyde was just the opposite. The lysozyme activity was significantly increased with incremental dietary HUFA levels. However, the activities of alkaline phosphatase and acid phosphatase reached a peak in 0.32% HUFA group. Loaches fed diets with HUFA significantly up‐regulated expressions of SOD, GPx, CAT and two lipid metabolism related genes. In conclusion, the optimal dietary HUFA level for loach juveniles was 0.64%–0.96%.