Narrow size regime among individuals favors rapid growth in Arctic char (Salvelinus alpinus) juveniles

We studied whether social environment in the form of different body size re gimes in rearing groups affects the growth of juvenile Arctic char (Salveli nus alpinus) in hatchery conditions. Young-of-the-year Arctic char were div ided into groups of three different compositions (a wide, a bimodal, and a narrow size-frequency distribution) in which individuals would be subjected to different dominance and competitive relationships. After a 9-month grow th period the fish in the narrow size distribution had grown the fastest in both length and weight. Also, total biomass gains were highest for fish or iginating from the narrow size distribution treatment. The adjusted mean bi omasses for wide, bimodal, and narrow size regime treatments were 5400, 500 0, and 5900 g, respectively. Our results give support to the hypothesis tha t individuals in size-sorted groups should show enhanced growth compared wi th individuals originating from a wider size-frequency distribution where m ore aggressive interactions are to be expected.