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What we did: We explored how low-CO2 water affects the neural physiology and behaviour of the iridescent shark, a species native to high-CO2 waters.
What we found: Fish exposed to low-CO2 water displayed abnormal behaviour in a variety of tests. This was related to the way certain ions (chloride and bicarbonate) distributed across brain cell membranes, which affected the release of an important neurotransmitter, GABA. When we treated these fish with a drug that blocked the suspected membrane ion exchanger, these behaviours were reduced. These results were supported by a series of theoretical calculations.
What this means: The responses observed in this study are consistent with what happens when fish species native to low-CO2 waters are exposed to high-CO2 water, suggesting ion regulation of the fish brain is finely tuned to the prevailing CO2 conditions. This is encouraging because it suggests that fishes may be able to adapt to human-caused increases in environmental CO2.