Dietary vitamin C requirement of juvenile grass carp ( Ctenopharyngodon idella ) and its effects on growth attributes, organ indices, whole‐body composition and biochemical parameters

Vitamin C or ascorbic acid (ASA) is an essential micronutrient for normal growth, antioxidant capacity and immunity of fish. However, appropriate requirements of ASA for Ctenopharyngodon idella, grass carp juveniles (8.46 ± 0.19), remain unknown. For this purpose, a feeding trial of 60 days was conducted in triplicates. Six isolipidic and isoproteic diets containing 0, 25, 50, 100, 200 and 400 mg/kg of ASA were prepared. Results showed a linear increase in growth as ASA supplementation was increased from 0 to 100 mg/kg. However, a further increase in dietary ASA supplementation from 200 to 400 mg/kg resulted in a slight decrease in growth parameters. A similar trend was also recorded for the whole body, proximate composition, antioxidant enzymes and organ indices against ASA supplementation. On the contrary, fish fed with basal diet had higher thiobarbituric acid reactive substances (TBARS) content in the liver and muscles than those fed with ASA supplemented diets. ASA concentration in muscles increased in a dose-dependent manner, while ASA value was the highest in the fish fed with 100 mg/kg ASA concentration. The weight gain (WG%) data were subjected to broken-line regression analysis, and the optimal ASA requirement of grass carp juveniles was estimated to be 67.1667 mg/kg. Taken together, the inclusion of 67.1667 mg/kg of ASA is recommended in the feed of grass carp juveniles for optimum growth performance. We also recommend analysing the effect of ASA in combination with vitamin A and E.