Effects of generations in captivity and elevated rearing temperature on Ontario hatchery brook trout (Salvelinus fontinalis) fry quality and survival

With rising environmental temperatures causing concern for the status of freshwater fishes, captive breeding programs may become increasingly important for conservation efforts as well as to support fisheries. Although captive broodstocks provide reliable gamete sources for production stocking, prolonged generations under hatchery conditions can result in changes to fishes as they acclimate to captive settings (domestication) - for example, reduced plasticity due to homogenous captive environments. We assessed the effects of rearing temperature and number of generations spent in captivity on the survival and quality (indicated by lack of malformations) of long-term (F->25) and newly captive (F-1) strains of Ontario hatchery brook trout (Salvelinus fontinalis) with shared genetic history. Elevated temperatures decreased likelihood of survival between the pre-exogenous feed and emergent fry stages and had a greater impact on fry quality (rate of malformations) on F-1 fish compared with F->25 fish, suggesting no reduction in plasticity due to prolonged captivity. However, overall survival between F-1 and F->25 fish was not different. The combined effects of elevated rearing temperatures and number of hatchery generations suggest that (selection) changes due to captivity can occur rapidly even under benign conditions and that additive stressor effects of captivity and temperature have the potential to impact newly established strains.