| Summary: | In order to study aggression and growth of salmon parr of different populations and the possible effect of fin-clipping on these traits hatchery reared parr originating from three populations (2 Norwegian, 1 Swedish) were stocked in three aquaria with 90 unmarked fish in each. Three aquaria were stocked with a mixed group of 30 each of the populations. These fish were fin-clipped (adipose or pelvic fins) in order to enable identification of groups. Observation time was 15 min/day/aquarium, altogether 28 days of observation were made. Total experimental time was 8 weeks. Significant differences in agonistic behaviour as well as in growth (p<0,001) was found between the populations. An effect of fin-clipping could also be detected in this study. At least one fish per aquarium established dominancy for part of the time. Most of the dominants in the mixed groups came from the same population.
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