A non-invasive assay for monitoring stress responses: A comparison between wild and captive-reared rainbowfish (Melanoteania duboulayi)

The stress response of wild and captive reared rainbowfish (Melanoteania duboulayi) following chasing by a simulated predator was examined. Cortisol release rate was monitored using a flow through system by measuring water borne hormone levels. Tests using known cortisol concentrations revealed that the technique yielded 95% of the cortisol present in the water. Cortisol release rates increased several fold in both populations after being chased but peaked at different time periods. Wild fish showed a typical stress response with release rate rising to (2.29 ± 0.22 ng g− 1 h− 1) 2 h after exposure followed by rapid recovery. The captive-reared population by contrast showed an atypical response with cortisol release rate peaking 4 h post exposure but reaching only half the level of the wild fish (1.19 ± 0.11 ng g− 1 h− 1). The implications for the release of hatchery-reared fish for stock enhancement are discussed.