Competitive differences between newly emerged offspring of captive-reared and wild coho salmon

We investigated competition among newly emerged fry from captive-reared and wild female coho salmon Oncorhynchus kisutch by conducting dominance chall enges and growth and survival experiments in laboratory stream channels. Ne wly emerged fry from captive-reared females won a significant majority (72. 7%) of dyadic dominance challenges against fry from wild females. In a grow th and survival experiment conducted from emergence to 30 d postemergence. fewer captive brood fry died of apparent starvation when food was limited t han wild fry. further suggesting a competitive advantage for the captive br ood fry. All fry used in the study were paternal half-sibs, so observed dif ferences between captive brood and wild fry were attributed to the maternal parent. We hypothesize that fry coloration resulting from differences in e gg color between wild and captive-reared females may have influenced the ob served competitive asymmetries. If so, such differences might be ameliorate d by changes in husbandry practices such as providing more natural diets.