Predators select against high growth rates and risk-taking behaviour in domestic trout populations.

Domesticated (farm) salmonid fishes display an increased willingness to accept risk while foraging, and achieve high growth rates not observed in nature. Theory predicts that elevated growth rates in domestic salmonids will result in greater risk-taking to access abundant food, but low survival in the presence of predators. In replicated whole-lake experiments, we observed that domestic trout (selected for high growth rates) took greater risks while foraging and grew faster than a wild strain. However, survival consequences for greater growth rates depended upon the predation environment. Domestic trout experienced greater survival when risk was low, but lower survival when risk was high. This suggests that animals with high intrinsic growth rates are selected against in populations with abundant predators, explaining the absence of such phenotypes in nature. This is, to our knowledge, the first large-scale field experiment to directly test this theory and simultaneously quantify the initial invasibility of domestic salmonid strains that escape into the wild from aquaculture operations, and the ecological conditions affecting their survival.