Abstract:A study was conducted to investigate the effects of dietary zinc levels on growth,blood physiological and biochemical indices and antioxidant ability of juvenile starry flounder -Platichthys stellatus-.Basal diet was prepared using casein-gelatin as the protein source.Zinc (ZnSO4 ·7H2O) was added at graded levels (0,50,100,150,200,and 400 mg/kg diet) to basal diets to formulate six isonitrogenous and isoenergetic purified diets.Triplicate of six treatment groups of juvenile starry flounder (initial weight,62.89±0.51 g) were fed to apparent satiation for 66 d.The results showed that the weight gain rate (WGR ) increased significantly when juvenile starry flounder were fed the diets with 150～400 mg/kg of dietary supplemental zinc (P<0.05).The highest WGR and the lowest feed conversion rate (FCR ) were observed in treatments with 150 mg/kg of dietary supplemental zinc.The number of erythrocytes was significantly higher than the control group when the juveniles were fed the diets with 100～200 mg/kg of dietary supplemental zinc (P<0.05),and the hematocrit and hemoglobin of the control group fed basal diets without zinc were significantly lower than those of other groups with zinc treatment (P<0.05).Contents of serum protein in groups treated with all levels of zinc were comparatively similar (P>0.05).Activity of serum lysozyme (LSZ) in juvenile starry flounder increased significantly with the increasing level of dietary supplemental zinc (P<0.05),but no significant differences were observed among the juveniles fed the diets with equal to or higher than 150 mg/kg of dietary supplemental zinc (P>0.05).The LSZ activity peaked in the treatment with 150 mg/kg of dietary supplemental zinc.Activity of serum CuZn superoxide dismutase (CuZn-SOD) in 0 and 50 mg/kg zinc treatment were significantly lower than those in other groups (P<0.05).The contents of malondialdehyde (MDA) in muscle of juveniles fed with 0 and 50 mg/kg zinc were significantly higher than those in other groups (P<0.05),while the minimum level of MDA was in 150 mg/kg zinc fed group.The optimal dose of dietary supplemental zinc in juvenile starry flounder purified diet was suggested to be 150 mg/kg.
