Carbon Dioxide Induced Behavioural Alterations in Freshwater Fishes

Behavioural research on complex cognitive processes, such as anxiety, in laboratory rodents has been commonplace in the last century, but there have been relatively few studies on this behaviour in fish.  By adapting reliable rodent paradigms, such as the light/dark test and novel approach test, it is possible to quantify anxiety-like behaviour in fish.  These tests become valuable in combination with exposure to environmental perturbations, such as increased carbon dioxide (CO₂) levels. We have exposed both saltwater and freshwater fish to elevated CO₂ levels that are predicted in the next century and examined their anxiety responses. Californian rockfish (Sebastes diploproa) exposed to ~1125 µatm CO₂ for one week demonstrate increased anxiety relative to controls, whereas pink salmon (Oncorhynchus gorbuscha) reared in freshwater containing ~ 2000 µatm CO₂ show decreased anxiety relative to controls. We have also used pharmacological manipulations of GABA_A­ receptors to alter these responses.  Recently we have also exposed zebrafish (Danio rerio) to various predicted and extreme CO₂ levels and found responses similar to pink salmon in freshwater. This research suggests a common mechanism for freshwater acidification effects that is opposite or completely different from the effects of ocean acidification on saltwater fish.