Effects of dietary inorganic copper on growth performance and immune responses of juvenile beluga, Huso huso

A 12-week feeding trial was conducted to evaluate the optimum dietary inorganic copper (copper sulphate) in juvenile beluga, Huso huso. Eight semi-purified diets containing 1.1 (Cu-1.0), 3.5 (Cu-4.0), 7.1 (Cu-7.0), 9.7 (Cu-10), 13.1 (Cu-13), 25.1 (Cu-25), 49.9 (Cu-50) and 195 (Cu-195) mg Cu kg(-1) diet in the form of CuSO4 center dot 5H(2)O were fed to fish of initial body weight 8.49 +/- 0.32 g and length 11.85 +/- 0.66 cm (mean +/- SD) in triplicate groups in a flow-through system. Weight gain (WG) of fish fed Cu-10 and Cu-13 diets was significantly higher than that of fish fed Cu-1.0, Cu-4.0, Cu-25, Cu-50 and Cu-195 diets (P < 0.05). Whole-body and muscle crude protein increased with dietary Cu up to the supplementation level of 13.1 mg kg(-1) diet and then decreased. Whole-body lipid content was negatively correlated, while whole-body ash was positively correlated with dietary copper concentration. Hepatic copper zinc superoxide dismutase activity of fish fed Cu-10 and Cu-13 diets was significantly higher than that of fish fed Cu-1.0, Cu-4.0 and Cu-195 diets. Hepatic thiobarbituric acid-reactive substances of fish fed Cu-13 diet was significantly lower than those of fish fed the other diets except for that of fish fed Cu-10 diet. Aspartate aminotransferase, alanine aminotransferase and copper accumulation in tissues increased with dietary copper. Broken-line analysis of WO suggested that the optimum dietary Cu level was 10.3 mg Cu kg(-1) diet. Therefore, these results may indicate that the optimum dietary Cu levels could be greater than 10.3 mg Cu kg(-1) diet but less than 13.1 mg Cu kg(-1) diet in juvenile beluga, when copper sulphate is used as the dietary source of inorganic copper.