Behavioural plasticity plays an important role in an organism’s ability to adapt to captive settings but a lack of perceived predation risk during early development in captivity can lead to diminished anti-predator behaviours.. Here, we used Atlantic salmon (Salmo salar) to test whether early developmental exposure to alarm cues (pre-exposure) led to (1) a developmentally plastic response to alarm cue in yearling and (2) an observable change in neural investment. We exposed fry to either a conspecific alarm cue (pre-exposed fish) or control water (non-exposed fish) and measured activity related to anti-predator behaviour such as time spent motionless, number of aggressive acts, and time spent associated with shelter. We found no indication of a developmentally plastic response to early alarm cue exposure but we found that pre-exposed fish developed relatively smaller olfactory bulbs compared to non-exposed fish. Our results demonstrate the importance of and ability to exploit plastic responses in captive-reared Atlantic salmon and highlight the need to link behaviour with neuromorphological changes.

Failure of reintroduction efforts of extirpated populations is thought to be linked to maladaptive behaviors exhibited by captive‐bred individuals in the environment where they are released. Soft‐release conditioning tactics attempt to reduce maladaptive behaviors by providing reintroduced animals an acclimatization period prior to release. We used implanted passive integrated transponder tags and antennae to monitor the spatial and temporal dispersal behavior of captive‐bred Atlantic Salmon Salmo salar that were acclimatized for 6 d prior to release (soft‐release), with fish that were directly released (hard‐release) into East Duffins Creek in Ajax, Ontario, Canada. In total, 232 of the 610 tagged fish (38%) dispersed from the release site. Downstream spatial dispersal did not differ significantly between the hard‐release (32%, n = 98 of 310) and soft‐release fish (30%, n = 91 of 300), but the hard‐release fish were significantly more likely to move upstream (11%) than were the soft‐release fish (3%). Timing of dispersal also significantly differed between the two groups: soft‐release fish were detected dispersing, on average, approximately 15 d earlier than hard‐release fish. These results suggest that soft‐release tactics do affect dispersal behavior, and the findings will be of particular interest to fisheries management agencies that are charged with improving the success for stocking salmonids as part of reintroduction efforts.