Dietary copper requirement reevaluation for juvenile grouper, Epinephelus malabaricus, with an organic copper source

To reevaluate the dietary copper (Cu) requirements of grouper, Epinephelus malabaricus, with an organic Cu source, Cu peptide was added to a basal diet at 0, 1, 2, 3, 4, 8 and 12 mg Cu/kg, providing actual dietary values of 0.19, 1.81, 2.55, 3.43, 4.37, 8.99 and 12.81 mg Cu/kg for a total of 7 experimental diets. Each diet was fed to triplicate groups of fish (initial body weight: 21.60 ± 0.08 g) in a recirculating seawater rearing system for 8 wks. Weight gain (WG) was highest (P < 0.05) in fish fed the diet with 2.55 mg Cu/kg, followed by fish fed the diet with 3.43 mg Cu/kg, and lowest in fish fed diets with 0.19, 8.99 and 12.81 mg Cu/kg. Hepatic copper–zinc superoxide dismutase (Cu–Zn SOD) activity was highest in fish fed the diet with 2.55 mg Cu/kg, followed by fish fed diets with 3.43, 8.99, 1.81 and 12.81 mg Cu/kg (in order of decreasing activity), and lowest in fish fed the diet with 0.19 mg Cu/kg. Hepatic thiobarbituric acid-reactive substance (TBARS) value was lowest in fish fed diets with 2.55 and 3.43 mg Cu/kg, followed by fish fed diets with 0.19 and 4.37 mg Cu/kg, and highest in fish fed the diet with 12.81 mg Cu/kg. Analysis by broken-line regression of WG, hepatic Cu–Zn SOD activity and TBARS value, and by linear regression of whole-body Cu retention of the fish indicated that the adequate dietary Cu requirement for grouper determined by Cu-peptide is about 2–3 mg Cu/kg.