Variation of agonistic behavior among juvenile Chinook salmon (Oncorhynchus tshawytscha) of hatchery, hybrid, and wild origin

Agonistic behavior and ability to dominate were compared among juveniles from a hatchery stock of Chinook salmon (Oncorhynchus tshawytscha) that has experienced five generations of hatchery culture, juveniles derived from the wild founding stock but produced from parents cultured in the same hatchery environment as the hatchery stock, and second-generation hybrids between the two lines. Equal numbers of parr (18) from equal numbers of families (5) from each fish line (3) were tested, and all lines were raised in a similar hatchery environment. During 20 min of observation in replicate artificial stream tanks, hatchery-derived fish made significantly greater numbers of charges, displays, and nips than wild-derived fish. Hybrids also made significantly greater numbers of charges, displays, and nips than wild-derived fish but significantly fewer displays than hatchery-derived fish. No difference was detected in the ability of fish lines to win dyadic dominance contests. These results suggest that the differences detected are genetic in origin and are consistent with divergence of the hatchery stock from the founding wild stock.