Do Hatchery-Reared Southern Pygmy Perch (Nannoperca australis) Develop Effective Survival Behaviour in a Soft-Release...

The captive breeding and release of threatened small-bodied freshwater fish is a common conservation method, yet many of these fish lack the behavioural profile to survive in the wild. Soft-release sites that provide wild-like experiences with minimal threat to survival can improve post-release outcomes. Here, we investigated whether captive-bred first generation Southern pygmy perch (Nannoperca australis) exposed to six months of soft-release experience develop natural behaviour. In laboratory tests, we compared the behaviour of fish from a hatchery, a soft-release site, or the wild in emergence, exploration, habitat choice, predator response, and novel food tests. As predicted, we found that fish from the soft-release site showed similar behavioural responses to wild-caught fish. However, soft-release fish were significantly larger (14.6 mm, 1.6 g advantage) and made greater use of refuge structures (basket ledges). Also, while trends suggested altered anti-predator responses, statistical support was limited, warranting further investigation. We conclude that soft-release experience enhances growth and shelter-seeking behaviour in this species, though further tests in a more natural environment should be undertaken to confirm ecologically important experience-dependent changes in behaviour. We recommend prioritising soft-release programmes that maximise natural foraging opportunities, reduce competition, and provide complex structures to support shelter use. Finally, the overall similarity in behaviour of fish from different environments suggests that, in this species, behaviour appears mostly inherited.