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This study investigated the effect of dietary Zn levels on growth performance, feed utilization, and hematological parameters of juvenile Siberian sturgeon (Acipenser baerii, Brandt 1869). The five semipurified diets were formulated by adding 0, 5, 10, 20, and 40 mg Zn kg -1 diet in the form of zinc sulfate (ZnSO 4 ) to provide the actual dietary value of 14.7, 20.8, 27.3, 37.7, and 46.4 Zn kg -1 diet, respectively. The results showed that dietary Zn elevating level significantly improved the growth and feed utilization of the fish (p \ 0.05), but not the hepatosomatic index (p [ 0.05). Erythrocyte number, hemoglobin concentration, and hematocrit were increased with raising dietary Zn level (p \ 0.05), whereas a regular trend was not observed in blood indices, including MCV, MCH, and MCHC. A significant increase was also found in the leucocyte number followed by their differential counts, except for eosinophil percentage. The broken line regression model indicated optimal dietary Zn level for growth maximization of fish was estimated to be 29.15 mg Zn kg -1 diet. In spite of well correlation with dietary Zn level, no break point was observed to estimate the juvenile Siberian sturgeon requirement based on the erythrocyte numbers.

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This study conducted to evaluate the effect of dietary zinc (Zn) levels on feed utilization, tissue Zn composition and serum enzyme activities of juvenile Siberian sturgeon, Acipenser baerii. Five isoenergetic and isonitrogenous semi‐purified diets were formulated with increasing Zn sulphate (ZnSO4.5H2O) level to provide the actual Zn values of 14.7 (control), 20.8, 27.3, 37.7 and 46.4 mg/kg diet. Each diet was assigned to three groups of 20 experimental Siberian sturgeons with uniform size (initial weight of 26.52 ± 0.94 g) for a period of 8‐week feeding trial. Results showed that growth performance and muscle protein content were significantly increased with increasing dietary Zn level up to 27.3 mg/kg (p < .05), beyond which they remained significantly unchanged (p > .05). Muscle lipid content significantly declined with increasing dietary Zn level. While muscle and serum Zn contents were not significantly changed among treatments (p > .05), liver Zn content tended to rise with increasing dietary Zn supplementation. Alkaline phosphatase, superoxide dismutase and glutathione peroxidase activities were also raised with increasing dietary Zn level. The adequate amount of dietary Zn requirements for the Siberian sturgeon was estimated to be 28.24 mg/kg based on the relative growth rate and 34.60 mg/kg based on the liver Zn content.

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