EFFECTS OF STOCKING DENSITY ON FOOD-INTAKE, GROWTH-PERFORMANCE AND OXYGEN-CONSUMPTION IN ARCTIC CHARR (SALVELINUS-ALPINUS)

Food intake, growth rates, and rates of oxygen consumption were measured in Arctic charr (Salvelinus alpinus), stocked at low (15 kg.m-3), medium (60 kg.m-3) and high (120 kg.m-3) densities. Growth rates were similar for fish stocked at the medium and high densities, but were markedly depressed at the lowest stocking density. Differences in growth were probably the result of similar differences in food intake. Low levels of food intake were probably also the prime reason for the low oxygen consumption rates recorded in the groups of fish stocked at low density. Stocking density affected the behaviour of the fish, and schooling behaviour was observed in the groups subjected to the medium and high stocking density. No significant correlations were found between initial body size, food intake and growth rates in the groups of fish held at any stocking density. Consequently, social constraints due to the formation of dominance hierarchies may not have been the prime reason for the appetite and growth reduction seen in groups stocked at low density.