Abstract
Ocean acidification, the decrease in ocean pH caused by anthropogenic emission of carbon dioxide, can cause behavioural disturbances in marine teleost species. We investigated whether AB-strain zebrafish (Danio rerio) show similar behavioural disturbances in the presence of elevated CO2, because this model species could open up a toolbox to investigate the physiological and neurological mechanisms of CO2 exposure. We found no effect of elevated CO2 (~1600 μatm) on the behaviour of zebrafish in the open field test, indicating that zebrafish are largely insensitive to this elevated CO2 level. In the detour test of lateralization, however, zebrafish exposed to elevated CO2 swam more often to the right, whereas individuals exposed to control CO2 (~400 μatm) had no preference for left or right. This may indicate that some behaviours of some freshwater fishes can be altered by elevated CO2 levels. Given that elevated CO2 levels often occur in recirculating aquaculture and aquarium systems, we recommend that dissolved CO2 levels are measured and, if necessary, the aquarium water should be aerated, in order to exclude CO2 level as a confounding factor in experiments.
Highlights
Anthropogenic emissions of carbon dioxide are acidifying the world’s water bodies
We investigated whether AB-strain zebrafish (Danio rerio) show similar behavioural disturbances in the presence of elevated CO2, because this model species could open up a toolbox to investigate the physiological and neurological mechanisms of CO2 exposure
We found no effect of elevated CO2 (~1600 μatm) on the behaviour of zebrafish in the open field test, indicating that zebrafish are largely insensitive to this elevated CO2 level
Summary
Anthropogenic emissions of carbon dioxide are acidifying the world’s water bodies. It has been estimated that ocean pH has already dropped 0.1 pH unit since the onset of the industrial revolution, and a further decrease in ocean pH of 0.2–0.3 pH units is expected by the end of the century (Haugan and Drange, 1996; Rhein et al, 2013). Fish take up bicarbonate ions (HCO3−) into the gill cells and extrude chloride ions (Cl−) into the water (Brauner and Baker, 2009) This alters the plasma ion concentrations, which in turn can affect the electrochemical gradients over the cell membranes. To investigate whether elevated CO2 can affect the GABA system of a freshwater fish species, we exposed adult zebrafish (Danio rerio) to control (~400 μatm) or elevated CO2. The natural habitat of the zebrafish consists of slow-moving pools and rice paddies, with reported pH as low as 5.9 and as high as 8.1 (Engeszer et al, 2007), environments where pCO2 can reach high levels If this species familiar with high CO2 concentrations is affected, this will probably be the case for many more freshwater fish. We explored whether any behavioural disturbances could be reversed by treatment with the specific GABAA receptor antagonist, gabazine
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