Atlantic cod actively avoid CO(2) and predator odour, even after long-term CO(2) exposure

INTRODUCTION: The rising atmospheric CO(2) level is continuously driving the dissolution of more CO(2) into the oceans, and some emission scenarios project that the surface waters may reach 1000 μatm by the end of the century. It is not known if fish can detect moderately elevated CO(2) levels, and if they avoid areas with high CO(2). If so, avoidance behaviour to water with high CO(2) could affect movement patterns and migrations of fish in the future. It is also being increasingly recognized that fish behaviour can be altered by exposure to CO(2). Therefore this study investigated how long-term exposure to elevated pCO(2) affects predator avoidance and CO(2) avoidance in juvenile Atlantic cod (Gadus morhua). The fish were exposed to control water or CO(2)-enriched water (1000 μatm) for six weeks before being subjected to tests of behaviour. RESULTS: Despite long term exposure to elevated pCO(2) the cod still strongly avoided the smell of a predator. These data are surprising because several coral reef fish have demonstrated reversal of olfactory responses after CO(2) exposure, turning avoidance of predator cues into preference for predator cues. Fish from both treatment groups also demonstrated strong avoidance of CO(2) when presented with the choice of control or CO(2)-acidified water, indicating that habituation to the CO(2) sensory stimuli is negligible. CONCLUSIONS: As Atlantic cod maintained normal behavioural responses to olfactory cues, they may be tolerant to CO(2)-induced behavioural changes. The results also suggest that despite the long-term exposure to CO(2)-acidified water, the fish still preferred the control water over CO(2)-acidified water. Therefore, in the future, fish may alter their movements and migrations in search of waters with a lower CO(2) content.