Dietary copper requirements of postlarval coho salmon (Oncorhynchus kisutch)

A 12-week feeding trial was performed to determine the dietary copper (Cu) requirement of postlarval coho salmon (Oncorhynchus kisutch). The postlarvae were reared on six experimental diets containing either 0.4, 1.9, 3.8, 5.6, 7.6 or 9.1 mg Cu/kg, provided as copper sulphate pentahydrate (CuSO4 center dot 5H(2)O). The highest specific growth rate (SGR) and condition factor (CF) were observed in fish fed with 5.6 mg Cu/kg diet, which was significantly higher (p < .05) than the 0.4 mg Cu/kg treatment. Feed conversion ratio (FCR) showed an inverse trend with SGR. Whole-body lipid was significantly increased (p < .05) with dietary Cu concentration up to 5.6 mg/kg and decreased thereafter. Fish fed with 9.1 mg Cu/kg diet exhibited the highest Cu concentrations in vertebrae and whole body. The total hepatic superoxide dismutase (T-SOD) and catalase (CAT) activities were positively affected by the dietary Cu concentration up to 5.6 and 7.6 mg/kg respectively. The lowest hepatic malondialdehyde (MDA) content was found in 5.6 mg/kg treatment. Hepatic lipoprotein lipase (LPL) and hepatic lipase (HL) contents significantly decreased (p < .05) with increasing Cu level up to 5.6 mg/kg and then levelled off. Analyses based on the SGR, Cu concentrations in whole body and vertebrae, the optimal dietary Cu requirements for postlarval coho salmon were estimated to be 5.1, 5.5 and 5.2 mg/kg respectively.