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A comparison of agonistic behaviour between two populations of juvenile coho salmon (Oncorhynchus kisutch) Rosenau, Marvin Leslie


Interpopulation variability in electrophoretically detectable isozyme frequencies, morphology, meristics and migratory behaviour has been demonstrated in many studies for salmonids and these character differences are known to often have an inherited basis. In this study, agonistic behaviours were compared in two British Columbia lower mainland populations of juvenile coho salmon and inherited differences were shown to occur. Using mirror image stimulation techniques, recently emerged laboratory incubated and reared coho juveniles from the study populations were tested for lateral display differences and the Hope Slough coho were found to have an higher activity level than the Nathan Creek fish in two brood years, 1979 and 1980. Additionally, coho of the 1980 experimental group were cross fertilized producing interpopulational "hybrids" and these fish were intermediate to the "pure" fish in lateral display behaviour activity levels. Recently emerged wild juvenile coho were, obtained and brought back to the laboratory and tested with the same mirror image stimulation techniques. Similar interpopulational differences in behaviour were found to occur. Laboratory reared fish were also compared in groups in stream tanks as well as in pairs in isolated aquaria. Hope Slough juvenile coho were found to be relatively more aggressive than Nathan Creek fish. It was felt that these observed differences have an adaptive basis in nature. Therefore, some physical and biological characteristics were measured in the two study watersheds. Potential differences in growth conditions and/or differing densities of predators were postulated as having potential selective effects on the behavioural repertoires of the juvenile coho in the study populations.

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