Dietary zinc requirement of juvenile large yellow croaker，Pseudosciaena crocea R.

A growth experiment was conducted to determine the dietary zinc requirement for juvenile large yellow croaker (initial average weight 1.78 ± 0.02 g). Six semi-purified diets were formulated to contain 9.68, 30.63, 48.94, 91.28, 167.49 and 326.81 mg zinc ∕ kg diet, supplied as ZnSO4•H2O. Each diet was randomly assigned to triplicate groups of fish in flow-through system, and each tank was stocked with 40 juvenile fish. Fish were fed twice daily (05：30 and 17：30) to apparent satiation for 8 weeks. The water temperature fluctuated from 26.5 to 29.5°C, salinity from 25‰ to 28‰ and dissolved oxygen was approximately 7 mg l-1 during the experimental period. No significant differences in survival were found among dietary treatments. Specific growth rate (SGR) significantly increased with increasing dietary zinc from 9.7 to 48.9 mg ∕ kg of diet (P<0.05), and then leveled off. Zinc content in the vertebrae, whole body and serum were significantly affected by dietary zinc level (P<0.05). Broken-line analysis showed that the optimum dietary zinc requirement for large yellow croaker juveniles, using SGR and vertebrae zinc saturation as response criteria, was 59.6 and 84.6 mg zinc ∕ kg diet, respectively.