Effect of dietary vitamin C on the growth performance, antioxidant ability and innate immunity of juvenile yellow catfish ( P elteobagrus fulvidraco R ichardson)

A 12‐week feeding trial was conducted to evaluate the effects of dietary vitamin C on growth performance, antioxidant status and innate immune responses in juvenile yellow catfish, P elteobagrus fulvidraco . Six isonitrogenous and isolipidic diets (44% crude protein and 7% lipid) were formulated to contain six graded dietary vitamin C (ascorbate‐2‐poly‐ phosphate, ROVIMIX ® STAY ‐C ® 35) levels ranging from 1.9 to 316.0 mg kg −1 diet. The results of present study indicated that fish fed the lowest vitamin C diet had lower weight gain ( WG ) and specific growth rate ( SGR ) than those fed the diets supplemented vitamin C. WG and SGR did significantly increase with dietary vitamin C levels increasing from 1.9 to 156.5 mg kg −1 . However, no significant increase was observed with further dietary vitamin C levels increasing from 156.5 to 316 mg kg −1 . Survival, protein efficiency ratio and feed efficiency were not significantly affected by the dietary vitamin C levels. The activities of serum superoxide dismutase, catalase and glutathione peroxidase significantly increased when dietary vitamin C levels increased from 1.9 to 156.5 mg kg −1 , fish fed the lowest vitamin C diet had higher serum malondialdehyde content than those fed the diets supplemented with vitamin C. Fish fed the diet containing 156.5 mg kg −1 vitamin C had the highest lysozyme, total complement activity, phagocytosis index and respiratory burst of head kidney among all treatments. The challenge test with A eromonas hydrophila indicated that lower cumulative survival was observed in fish fed the lowest vitamin C diet. Analysis by broken‐line regression of SGR and lysozyme activity indicated that the dietary vitamin C requirement of juvenile yellow catfish was estimated to be 114.5 and 102.5 mg kg −1 diet, respectively.