Influence of maturity status on the annual cycles of feeding and growth in Arctic charr reared at constant temperature

Temporal changes in feeding and growth of immature (1 +), maturing male (1 +), and mature male and female (3+) Arctic charr were studied by monitoring feed intake and growth of individually-marked fish for over 1 year. The fish were held at a constant temperature (4°C) under conditions of liberal feed supply. Feed intake and growth remained low in the period December-April, with only 20–60% of the fish having fed on each occasion that feed intake was monitored. Feed intake and growth increased markedly during the late spring and summer, but the increases were delayed by approximately 1–2 months in the immature fish compared with their maturing counterparts. Maturing fish decreased feeding during the late summer and by September there had been an almost complete cessation of feeding. This was reflected in changes in fish body weight and condition, both of which declined from August-September onwards. By contrast, the immature fish peaked in weight and condition in September, and weight loss during the autumn tended to be less rapid than observed for the maturing fish. The fish appeared to reduce feeding once a'threshold condition' of 1–4—1–5 had been attained. It is suggested that the fish may become anorexic once there has been replenishment of the energy reserves required for overwintering and, in the case of maturing individuals, for the completion of gonadal growth and Spawning.