Neuromorphological and behavioural effects of early developmental exposure to alarm cue on captive-reared Atlantic salmon (Salmo salar)

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.