Dietary iron (Fe) requirement of coho salmon (Oncorhynchus kisutch) alevins assessed using growth, whole body and hepatic Fe concentrations and hepatic antioxidant enzymes activities

In this study, the effects of different dietary iron levels on the growth performance, body composition and antioxidant responses were investigated in the coho salmon Oncorhynchus kisutch alevins. Six experimental diets were formulated to contain graded levels (23.7, 46.4, 59.8, 77.3, 101.7 and 127.7 mg/kg) of iron provided as FeSO4 center dot 7H(2)O. Each diet was fed to triplicate groups of coho salmon alevins with initial mean weight of 0.35 +/- 0.02 g in a flow-through rearing system for 84 days. The results showed that there was no significant difference in survival among dietary treatments. Specific growth rate (SGR) increased significantly (p < 0.05) while feed conversion rate (FCR) decreased significantly (p < 0.05) with increasing dietary iron level from 23.7 up to 101.7 mg/kg. Whole body moisture and ash showed no significant differences among dietary treatments. Fish fed the diet with 127.7 mg/kg had the significantly highest whole body protein and lipid levels (p < 0.05). Whole body and hepatic iron concentrations increased with increasing dietary iron levels (p < 0.05). However, hepatic iron concentrations were decreased when the dietary iron was higher than 77.3 mg/kg treatment. Fish fed the diet with 77.3 mg/kg had the significantly highest activities of catalase (CAT) and total superoxide dismutase (T-SOD) but the lowest malondialdehyde (MDA) activity in liver (p < 0.05). Based on the SGR, iron concentrations in the whole body and liver and CAT, T-SOD and MDA activities in liver, the optimal dietary iron requirements for coho salmon alevins were 101.7, 79.3, 75.7, 90.8, 83.6 and 68.9 mg/kg respectively.