Abstract

The territorial and competitive behaviours of hatchery-reared brown trout stocked in a semi-natural stream channel were studied over 15-day periods with and without the presence of wild conspecifics. Individual fish were ranked as dominant and subordinate fish based on their ability to successfully forage and grow within their group (n=6). The results show that hatchery-reared trout are competitively inferior to previously resident wild trout. One dominant wild fish was more aggressive, maintained home stations closer to the food resource, foraged at a higher rate and exhibited a higher growth rate than later introduced hatchery-reared trout. As a consequence of competition, mortality rates were high in hatchery fish and surviving individuals were in very poor condition at the end of the study. When stocked in an empty habitat, hatchery-reared trout quickly form a social structure similar to that of wild fish and with similar differences in territorial behaviour between individuals. A comparison of dominant wild and hatchery-reared individuals between trials reveals that fish of wild origin forage and grow at a higher rate, but perform less frequent aggressive acts than hatchery-reared ones. The attacks by wild trout seemed, however, to be much more powerful and authoritative. We conclude that the ability of hatchery-reared trout to colonise natural habitats after release is influenced by the presence of wild fish

Published in

Rapport / Sveriges lantbruksuniversitet, Vattenbruksinstitutionen
2003, number: 38
Publisher: Vattenbruksinstitutionen, SLU

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