Dietary vitamin C requirement and its effects on tissue antioxidant capacity of juvenile largemouth bass, Micropterus salmoides

Abstract An eight week feeding trial was conducted to determine the optimal dietary ascorbic acid (ASA) requirement of juvenile largemouth bass (6.67 ± 0.03 g). Six practical diets were formulated to contain 17.5 (the basal diet), 54.6, 84.3, 179, 335 and 1042 mg ASA equivalent per kg diet supplied as l -ascorbyl-2-monophosphate. Each experimental diet was fed to triplicate groups of fish to apparent satiation two times a day. At the end of the experiment, observed signs of ASA deficiency included anorexia, poor survival and growth, lordosis and skin darkening along with sluggish behavior and exophthalmia. Survival and feed conversion ratio (FCR) were inferior in fish fed the basal diet to those of fish fed ASA-supplemented diets. Weight gain (WG), specific growth rate (SGR) and liver ASA concentration markedly increased with increasing dietary vitamin C supply and then leveled off. Lipid accumulation in the mesenterium and liver was reduced in response to vitamin C supplement. ASA supplementation not only increased antioxidant capacities of the liver (activity of catalase (CAT), reduced glutathione content (GSH) and total antioxidant capacity (T-AOC)) and muscle (activities of CAT and superoxide dismutase, GSH and T-AOC), but also exerted a sparing effect on vitamin E utilization in the plasma and liver, thereby decreasing lipid peroxidation (malondialdehyde concentration) in the plasma as well as the liver. Broken-line analysis showed that the optimal dietary ASA requirement of largemouth bass was 109.5, 102.6 and 147.8 mg/kg based on WG, SGR and liver ASA storage, respectively. In a practical production of largemouth bass, 148 mg/kg of dietary ASA should be recommended to maintain normal physiological function as a result of lots of stressors.