Effects of dietary zinc on growth performance,tissue accumulation and antioxidation of juvenile starry flounder(Platichthys stellatus)

An experiment was conducted to investigate the effects of dietary zinc on growth performance,body composition,tissue zinc accumulation and antioxidation of juvenile starry flounder(Platichthys stellatus)with zinc sulfate(ZnSO₄·7H₂O)as zinc source,by using a purified diet based on casein-gelatin as the protein sources.The basal diet was supplemented with 0,50,100,150,200 and 400 mg zinc per kg diet respectively and juvenile starry flounder［initial weight(62.89±0.51)g］were fed 6 purified diets containing graded levels of zinc(19.95,71.06,118.50,174.00,226.10 and 411.20 mg/kg)respectively for 66-day experimental period.The results showed that weight gain rate(WGR)increased significantly with increasing dietary zinc level(P<0.05),but no significant differences were observed among the juveniles fed the diets with equal to or higher than 174.00 mg/kg of dietary zinc(P>0.05),special growth rate(SGR)and WGR followed the same trend.The fish got the highest WGR,SGR and the lowest feed conversion rate(FCR)in the treatment with 174.00 mg/kg of dietary zinc.No significant differences were observed in whole body composition among dietary treatments(P>0.05),the fat deposition in muscle of zinc supplementation of 0 mg/kg group was significantly higher than those in the other groups(P<0.05).When the juveniles were fed the diet with 411.20 mg/kg of dietary zinc,the zinc accumulation contents in the whole body,vertebrae and muscle were significantly higher than those in the other groups(P<0.05).When the juveniles were fed 118.50-411.20 mg/kg of dietary zinc,the zinc accumulation contents in whole body,vertebrae and serum were significantly higher than 19.95 mg/kg group and 71.06 mg/kg group(P<0.05),however,the liver zinc contents remained comparatively stable among all groups(P>0.05).Serum total antioxidant capacity and superoxide dismutase(SOD)activity increased significantly with increasing dietary zinc level(P<0.05),and then leveled off when the juveniles were fed the diets with equal to or higher than 174.00 mg/kg of dietary zinc.In conclusion,it could improve growth performance and tissue zinc accumulation,and enhance antioxidation function by adding proper dose of zinc in basic diet of juvenile starry flounder.Broken-line regression analysis showed that the optimum dietary zinc requirement for juvenile starry flounder,using WGR as response criteria,was 167.88 mg/kg of dietary zinc.