The effects of hatchery domestication on competitive dominance of juvenile spring Chinook salmon (Oncorhynchus tshawytscha)

We tested the null hypotheses that competitive dominance among juvenile Chinook salmon (Oncorhynchus tshawytscha) in contest and scramble experiments would not be affected by domestication selection after one generation of state-of-the-art hatchery culture. Dyadic challenges of size-matched juvenile fish were conducted after a 6-day acclimation in 113.4 L aquaria. Differences in dominance and frequency of different types of agonistic interactions used were not significantly different in contest (n = 505) or scramble (n = 363) competition experiments (P > 0.05). However, wild origin fish were more aggressive than hatchery origin fish in both types of experiments (P <= 0.05). Furthermore, wild origin fish gained more weight than hatchery origin fish during contest experiments, and hatchery origin fish lost less weight than wild origin fish in scramble experiments (P <= 0.05). Dominant fish, regardless of origin, grew more than subordinate fish in both contest and scramble experiments (P <= 0.05). Our results indicate that aggression, and growth mediated by competition, can be affected by domestication after only one generation of state-of-the-art hatchery culture; however, impacts to competitive dominance appear to be small.