Comparison of stress responses in wild and captive winter flounder (Pseudopleuronectes americanus Walbaum) broodstock

Chronic stress is responsible for many problems occurring in fish holding facilities, such as increased susceptibility to disease, reduced growth rate and suppression of the immune response. The goal of this study was to verify if wild winter flounder (Pseudopleuronectes americanus Walbaum) suffer from chronic stress when kept several months in captivity. We hypothesized that winter flounder not subjected to chronic stress in captivity would have similar or higher condition indices and similar stress response compared to fish from the wild. Our results showed that the condition index of winter flounder kept in captivity was higher (1.50) than those from the wild (1.33) even after one year of captivity. The intensity of the acute stress response following short-term exposure to air was similar between wild and captive fish (no significant interaction between the factors 'stress' and 'origin of the fish'). Body water content (an indicator of energy reserves) was lower (76.1%) compared to wild fish (79.8%) after one year of captivity, suggesting that the winter fast had been less energetically demanding in captive fish. These results indicate that no chronic stress was present in captive fish. On the other hand, the mortality during captivity was around 30%, which is high for the aquaculture industry. Further work to address this problem is required.