Survival of crossbred brown trout under experimental pike predation and stocking in the wild

Unintended domestication in hatchery broodstocks reflects a low success of supportive stocking programs. We crossbred adfluvial hatchery-stock brown trout (Salmo trutta) females with males from two non-native adfluvial hatchery strains and a wild but local resident strain to study survival, growth and behaviour of hybrid offspring alternatives. Experimental predation selected for larger size in wild crosses but not in the original hatchery fish. Non-native hatchery crossing reduced the survival in the predation experiment either directly or due to negatively size-selective predation. Wild crosses evaded the areas where predators were present more often than the pure hatchery origin fish in the predation experiment. Our results support an intrinsic anti-predatory behaviour in wild fish and suggest that crosses with resident fish can produce equally growing offspring that are efficient in predation avoidance. Resident, local, wild populations may be a beneficial source for improving the natural-type fitness in broodstocks affected by domestication without natural reproduction.