Effects of dietary astaxanthin on the growth, innate immunity and antioxidant defence system ofParamisgurnus dabryanus

The effects of astaxanthin supplementationon the growth, innate immunity and antioxidant defence system of loach (Paramisgurnus dabryanus) were investigated in this study. A total of 450 fish (initial average weights of 3.00 +/- 0.10 g) were fed five diets with graded levels of astaxanthin (0.00, 50.00, 100.00, 150.00 and 200.00 mg/kg) for 56 days. The results showed that astaxanthin supplementation significantly stimulated the growth (FBW, WG, FER, HSI), innate immunity (AKP activity in the hepatopancreas, intestinal tract, muscle and skin and LZM activity in the hepatopancreas, intestinal tract and skin), antioxidant ability (T-SOD, GSH-PX and CAT activities and T-AOC, GSH and MDA contents in the hepatopancreas, intestinal tract, muscle and skin) of loach. Moreover, dietary astaxanthin supplementation significantly up-regulated the relative mRNA levels ofNrf2andMaf, and down-regulated the relative mRNA level ofKeap1in the hepatopancreas when the supplementation levels of astaxanthin were 50-200 mg/kg. In conclusion, the diets with 100-151.06 mg/kg astaxanthin supplementation were optimal for loach, which based on the growth, immunity and antioxidant-related indicators, and the astaxanthin supplementation regulated the antioxidant ability partially referring to Keap1-Nrf2 signallings.