Environmental enrichment reduces maladaptive risk-taking behavior in salmon reared for conservation

Hatcheries often produce bold fish that are maladapted to survive in the wild, as absence of predators and selection for fast growth tend to favour risk-taking behaviors. Not surprisingly, losses of hatchery fish through predation can be high immediately after release and this may account for the failure of many ex-situ fish conservation programmes. For supportive-breeding to be useful, it is essential that released fish are able to display natural behaviors. We compared the performance of juvenile Atlantic salmon reared in environmentally-enriched tanks receiving natural prey and subjected to simulated predator attacks with fish reared under standard hatchery conditions while keeping densities constant. No differences were detected between controls and environmentally enriched fish in survival, final size or nutritional status. Yet, changes in rearing conditions had rapid and marked effects on risk-taking behavior. Environmentally enriched fish were 2.1 times less willing, and took significantly longer to leave shelter, than controls within two weeks of enrichment. Thus our study indicates that it is possible through environmental enrichment to modify at least one component of fishes’ behavior known to have clear adaptive implications, i.e. the propensity of hatchery-reared fish to take excessive risks. Ex-situ conservation could therefore benefit from rearing fish in naturalized, structurally complex environments with natural prey to promote the development of more natural behaviors.