Variation of agonistic behavior and morphology among juvenile chinook salmon (Oncorhynchus tshawytscha) of hatchery, wild, and hybrid origin under common rearing conditions

Abstract

Hatcheries play an important role in the enhancement of Pacific salmon (genus Oncorhynchus) as a resource, but genetic and phenotypic divergence trom wild populations may occur as a result of founder effects, genetic drift and/or domestication. In this study, agonistic behavior, ability to establish dominance, and morphology were compared among juveniles of chinook salmon (Oncorhynchus tshawytscha) that have experienced five generations of hatchery ranching culture, juveniles derived trom the wild founding stock, and second generation hybrids of the two lines. The parent generation of all lines was cultured in the same hatchery environment as the juveniles tested. Behavioral observations were conducted in replicate artificial stream tanks; hatchery and hybrid fish were significantly more aggressive than wild derived fish. No difference was detected in the ability of fish lines to win dyadic dominance contests. Thin-plate spline analysis was used to characterize morphometric variation; hatchery and wild derived juveniles differed significantly. Canonical discriminant analysis correctly classified 88% of hatchery fish and 90% of wild derived fish. Morphologically, hybrid fish were significantly different trom both hatchery and wild derived fish. These results suggest that the differences observed between lines are genetic in origin although the sources of the divergence were not conclusively identified.