Effects of dietary vitamin C levels on growth performance, immunity and antioxidant capacity of largemouth bass (Micropterus salmoides) larvae

A 3-week feeding trial was conducted to determine the optimal dietary vitamin C requirement of largemouth bass (Micropterus salmoides) larva (1.2±0.3) mg. Five practical diets were formulated to contain 0 (V0), 200 (V200), 400 (V400), 800 (V800) and 1 600 (V1600) mg/kg vitamin C. Each experimental diet was fed to triplicate groups of fish to apparent satiation seven times a day. At the end of the experiment, the results showed that the final body weight, weight gain rate and specific growth rate increased with the increase of dietary vitamin C level, and then tended to be stable, with the highest values in VC400 group. Weight gain rate (WGR) and specific growth rate (SGR) markedly increased with increasing dietary vitamin C supply and then leveled off while body ASA concentration continued to increase with increasing dietary vitamin C supply. Vitamin C supplementation not only increased antioxidant capacities activity of catalase (CAT), reduced glutathione content (GSH), superoxide dismutase (SOD) and immunocompetence complement C3, complement C4 and lysozyme(LZM) concentration) of the larva, but also decreased lipid peroxidation (malondialdehyde (MAD) concentration) in the body. Broken-line analysis showed that the optimal dietary vitamin C requirement of M. salmoides was 421.2 mg/kg based on WGR. In practical production of largemouth bass larvae, 420 mg/kg of dietary vitamin C should be recommended to maintain normal physiological function.