EFFECTS OF KINSHIP ON AGGRESSION AND RNA-CONTENT IN JUVENILE ARCTIC CHARR

The behaviour of juvenile Arctic charr Salvelinus alpinus was studied in groups of four siblings composed of familiar and unfamiliar individ uals or in mixed groups of four where both siblings and unrelated indi viduals were present. The frequency of aggressive acts was significant ly higher in the mixed groups compared to the pure sibling groups and the difference was present at all levels of the hierarchy rank order, based on a dominance index, except the lowest ranked individuals. The difference was significant after but not before feeding, implying that competition with non-kin for a food resource increased the aggression . No significant difference in weight gain was observed between siblin g and mixed groups during the 6 days of the experiment, but the RNA co ntents of lateral musculature in dominant individuals from sibling gro ups were significantly higher than the corresponding fish in the mixed group, suggesting a difference in growth rate when the experiments en ded. No significant difference in RNA content was observed between sub ordinate fish of the two treatments, i.e. siblings v. mixed.