Effect of vitamin C on growth,immunity and anti-ammonia-nitrite stress ability in juvenile black carp(Mylopharyngodon piceus)

Studies were conducted to investigate the effects of dietary vitamin C(VC)on growth,immunity and anti-ammonia-nitrite stress ability in juvenile black carp,Mylopharyngodon piceus(initial average weight 7.27±0.40 g).Six iso-nitrogenous and iso-energetic diets were formulated to supply at dosages of 0(control),16.3,33.9,69.1,137.8 and 277.5 mg/kg vitamin C diet,respectively.After feeding 8 weeks,according to specific growth rate,three group of 0,69.1 and 277.5 mg/kg of black carp were subjected to an ammonia-nitrite stress(20 mg/L)for 24 h.Results indicated that the effective vitamin C content for maximum growth is about 63.0 mg/kg.The vitamin VC levels in liver,muscle and serum were in positive correlation with VC content in diet,and no significant differences were observed among fish fed the diets with equal to or higher than 137.8 mg/kg of vitamin VC.No significant differences in total superoxide dismutase(T-SOD)and malondialdehyde(MDA)were observed among dietary treatments.But VC could significantly increase the catalase(CAT)and glutathione peroxidase(GSH-px)activity(P0.05).With the VC content increased,CAT increased at first and then decreased.Glutathione(GSH)and Na+/K+-ATPase(NKA)increased when VC concentration in diets were increased,cortisol(COR)were decreased at first and then increased.After ammonia-nitrite stress,each group of the VC concentration in liver,T-SOD,CAT,GSH-px activity and GSH content in serum and gill NKA activity decreased,serum VC level,COR and MDA content increased.The T-SOD,CAT and NKA activity,GSH,MDA and COR content significantly changed before and after ammonia-nitrite stress.Liver vitamin C concentration in fishes fed VC diets significantly decreased after stress,however,there are no significant changes in CAT,NKA activity and GSH,cortisol content compared with control group.T-SOD activity in 69.1 mg/kg vitamin C diet had no significant change before and after stress,but GSH-px activity and MDA content had significantly changed.In 277.5 mg/kg vitamin C group,GSH-px activity and MDA content had no significant change except T-SOD activity and serum VC level.All the results indicated that the effective vitamin C requirement of juvenile black carp for optimal growth might be 63.0 mg/kg diet.Fish have been stressed when put in ammonia-nitrite,and VC concentration in diet could improve immunity and anti-ammonia-nitrtie stress ability of black carp.