Effects of dietary copper on survival, growth and immune response of juvenile abalone, Haliotis discus hannai Ino

A study was conducted to evaluate the effects of dietary copper (Cu) on the growth, survival, carcass composition and immune responses in juvenile abalone, Haliotis discus hannai. Six semi-purified diets containing graded levels of dietary copper (1.08, 3.76, 6.54, 14.80, 26.84 and 109.41 mg/kg diet) from CuSO4⋅5H2O were fed to juvenile abalone (initial shell length: 17.21 ± 0.04 mm; initial body weight: 0.65 ± 0.00 g) in triplicate groups for 24 weeks in a flow-through system. The results showed that no significant (P > 0.05) differences were found in weight gain rate (WGR, %), daily increment in shell length (DISL, μm/day) and survival among the dietary treatments. However, Cu concentrations in abalone serum, hepatopancreas, muscle and newly grown shell showed a clear increasing trend with the supplementation of dietary Cu, and the concentrations were significantly (P < 0.05) higher in abalone fed dietary Cu ≥ 26.84 mg/kg compared to those fed 1.08 mg Cu/kg. The crude lipid in abalone carcass decreased with increasing dietary Cu and was significantly (P < 0.05) lower in abalone fed dietary Cu ≥ 26.84 mg/kg compared to the rest of the treatments. The activities of copper–zinc superoxide dismutase (CuZn SOD) in the hepatopancreas and serum were significantly increased when supplementation of dietary Cu reached 3.76 mg/kg diet, and 6.54 mg/kg diet provided maximum activity of serum phenoloxidase (PO). There was no significant difference for these enzyme activities when dietary Cu was over those values. The optimum requirement of juvenile abalone for dietary Cu was estimated to be 3–5 mg/kg diet by broken-line regression analysis, based on the activities of CuZn SOD and PO either in abalone hepatopancreas or serum. Deficiency of dietary Cu significantly depressed the immune responses in abalone.