The combined effects of stocking density and sustained exercise on the behaviour and food intake – growth relationship of individually tagged juvenile Arctic charr (Salvelinus alpinus L.) were examined. Both food intake and growth (weight gain) were significantly lower in fish stocked at the high density (initial biomass ~47 kg∙m−3) than in fish stocked at the low density (initial biomass ~23 kg∙m−3). When the charr stocked at low densities were subjected to sustained exercise, they showed higher growth rates than fish reared in standing water (control). In contrast, exercise did not give rise to improved growth performance in fish stocked at high densities. The growth – food intake ratio (food utilization) differed markedly between control and exercised fish. Irrespective of stocking density, food utilization was significantly better in exercising fish than in fish reared in standing water. The differences in food intake, growth, and food utilization are discussed in relation to the changes in behaviour and social interactions induced by forcing the fish to swim against a water current.
