Acidification of Oceans May Affect the Brains of Fish

Yesterday's post noted some of the adverse consequences that are likely to arise from acidification of oceans. Another recent study shows that such acidification can influence the behavior of fish because of impacts on their brains; the response of nerve cells can be reversed as acidifying seawater perturbs how a fish regulates acids and bases in its body.

Once "excited," nerve cells need a chemical to calm them down; this function is provided by a compound known as GABA. GABA opens a pore in the cells' outer membrane, allowing ions of chloride and bicarbonate to enter, which quiets the cell. Researchers posed a hypothesis that when a fish's body attempts to maintain chemical balance in the face of rising ocean acidification, chloride and bicarbonate concentrations could become higher inside nerve cells than outside them. If this speculation was correct, when the GABA "gates" opened, chloride and bicarbonate would move out of the cell instead of into it. The result would be that the cell was excited rather than calmed, reversing the nerve's response to a stimulus.

To test the hypothesis, researchers briefly bathed some hatchling reef fish in a chemical that deactivates the ability of GABA to open the pore. Among clownfish raised in a high-carbon dioxide environment, a predator's scent in the water, which is normally repellent, proved an attractant. Until, that is, the researchers immersed these fish for 30 minutes in water heavily spiked with gabazine, which "locks closed the GABA gate." Tests with other fish showed that they turned in the opposite direction from that which was their preference when this system was impaired.

The study can be found at: http://www.nature.com/nclimate/journal/v2/n3/full/nclimate1352.html.