Aggression and growth of Atlantic salmon parr. I. Different stocking densities and size groups

The aggressive behaviour and growth of salmon parr under crowded rearing conditions was studied at four different densities. One or several fish per aquarium was dominant, displaying a kind of territorial defence and committing a significant part of the observed aggressive acts. Large subordinate fish were more aggressive than small fish at all densities. The ratio between the number of performed and received aggressive actions was about the same for large and small subordinate fish at the lowest density, but with increasing density this ratio became higher for large parr. Small fish grew slower than large fish at the highest density and suffered generally from a higher mortality. Factors other than aggression also seemed to influence growth, as both the growth rate and number of aggressive acts per fish decreased with increasing density