Effects of diets supplemented with iron citrate on some physiological parameters and on burst swimming velocity in smoltifying hatchery-reared masu salmon (Oncorhynchus masou)

In order to produce hatchery-reared (hatchery) smolt of high quality, we examined the effects of a diet supplemented with iron citrate on the burst swimming velocity (BSV) and on several physiological parameters in smoltifying hatchery-masu salmon, Oncorhynchus masou. Experiments in 2003 and 2004 were performed for about 3 months in spring using 40 or approximately 20,000 fish per treatment group, respectively. Fish were fed control (796 mg iron/kg food), iron-1 (1515 mg/kg) or iron-2 diets (2003 only; 3176 mg/kg) to satiation every day and periodically sampled for analyses. In addition, wild fish were analyzed in both years. The hemoglobin (Hb) concentration, BSV, total iron content in the liver and in stomach food remnants and the ATP content in the liver and white muscle in hatchery controls were significantly lower than those in wild fish (P < 0.05). The iron supplement did not affect fish size, survival ratio and gill Na+,K+-ATPase activity in either year. However, values of the iron-1 group were high compared to those of the control in terms of BSV, of Hb concentration, of total iron content in the liver and in stomach food remnants and of ATP content in the liver and white muscle. Parameter values of fish in the iron-1 group, but not the iron-2 group, were similar to those of wild fish. Simple regression analysis indicated significant correlations between the means of BSV and Hb concentration before burst swimming (P = 0.015) and the means of BSV and ATP content in the white muscle before burst swimming (P = 0.019). In conclusion, BSV and a number of physiological parameters of hatchery-masu salmon were improved by administering the iron-1 diet for about 3 months in spring. The BSV improvement may reflect increased blood Hb concentrations and increased ATP contents in white muscle before burst swimming, respectively.