Aggression and growth of Atlantic salmon parr. II. Different populations in pure and mixed groups

The aggressive behaviour and growth of different populations of Atlantic salmon parr and the possible effect of fin-clipping on these traits were studied. Each of three 2001 aquaria was stocked with 90 unmarked hatchery parr from one of three different populations (one Swedish, two Norwegian). Three other aquaria were stocked with mixed groups consisting of 30 parr from each population. To enable identification, two of the three groups were alternately fin-clipped (adipose fin or pelvic fins). Significant differences in aggressive activity and growth were found between the populations. The population with the most aggressive parr had the slowest growth in both pure and mixed groups. Parr with cut pelvic fins both performed and received fewer aggressive acts than parr with cut adipose fin or unmarked parr. The results suggest a negative correlation between aggression and growth, and indicate that growth differences between populations to some extent may be mediated by genetically determined differences in behaviour