Anti-predator response in wild and sea-ranched brown trout and their crosses

In this study we compared the anti-predator responses of hatchery-reared brown trout (Salmo trutta) juveniles having sea-ranched or wild origins, or the reciprocal crosses between wild and sea-ranched fish. The experimental fish were exposed to a pike and a heron predator dummy. It was found that juveniles of wild origin differed from those of sea-ranched origin in their response to the predator attacks. Moreover, the wild fish also differed in this regard from the crosses between wild and sea-ranched brown trout. The responses differed mainly in terms of response to the heron dummy and response time to first attack (i.e. duration of initial inactivity when subject to first attack). However, the reciprocal crosses were not intermediate in their response patterns, canonical discriminant analysis revealing that they were closer to the sea-ranched than to the wild fish in this regard. The fish studied were reared under similar hatchery conditions and had a common genetic background, the gene flow from the sea-ranched fish to the wild segment being considerable. Thus, the differences between fish born in the wild and in hatcheries might reflect genetic differences recurrently develop within single-year classes.