Nico Alioravainen, Jenni M. Prokkola, Alexandre Lemopoulos, Laura Härkönen, Pekka Hyvärinen, Anssi Vainikka

Behaviours that are adaptive in captivity may be maladaptive in the wild and hence compromise after-release survival of hatchery fish. Understanding behavioural differences displayed straight after the release could help improving hatchery protocols and developing behavioural tests for assessing the fitness of fish reared for releases. We characterized the post-release behaviour in two experiments using parr from wild, hatchery and crossed strains of brown trout (Salmo trutta): in small-scale channels and in high and low densities in mesocosm streams. Our results show that hatchery fish were more likely to disperse downstream from the natal stocking site compared to crossbred and wild fish. Small-scale experiment was not sufficient in discovering this ecologically pivotal difference in post-release performance between strains, and individual responses were inconsistent between experiments. Circadian activity patterns were not found to remarkably differ between strains. This detailed empirical evidence of post-release behaviour improves our understanding of the low success of captive-reared fish in the wild. Mixing locally adapted wild fish in the broodstock could rapidly mitigate some of the behavioural effects of hatchery selection.