Cortisol stress response of juvenile winter flounder ( Pseudopleuronectes americanus, Walbaum) to predators

Abstract

Wild stocks of winter flounder ( Pseudopleuronectes americanus) in the Northwestern Atlantic have been depleted to an extent that has warranted increasingly stronger fishing regulations in the last decade. As a means to strengthen the wild populations of winter flounder and to avoid further fishing restrictions, the rearing of juvenile fish in hatcheries for release in coastal waters has been viewed as a possibility. Many fishery biologists have concern that hatchery-reared fish are not behaviorally and/or physiologically equipped to survive in the wild due to a lack of predator interaction and conditioning. This study aimed to determine whether hatchery-reared juvenile winter flounder exhibited a stress response, as evidenced by an increase in whole-body cortisol concentrations, to cohabitation with potential predators. The green crab ( Carcinus maenas) and sand shrimp ( Crangon septemspinosa) have been implicated as sources of juvenile flounder mortality in laboratory and field studies and therefore were chosen as invertebrate predators. In addition, the summer flounder ( Paralichthys dentatus) was selected as a predator because of its co-existence with young winter flounder in estuaries during early summer. Juvenile fish ( n = 12) were exposed to predators for 24 h in an arena. Results from radioimmunoassay indicate that juvenile winter flounder initiate a cortisol response to sand shrimp and summer flounder cohabitation, whereas the presence of a green crab does not elicit such a response. The ability of a fish to detect and react to a predator is vital for survival to a reproductive size. This study demonstrates that a hatchery-reared juvenile winter flounder can mount a stress response in the presence of predators.