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Acidification alters fish behavior: higher carbon dioxide in oceans may affect brain chemistry.

A new study may explain how rising carbon dioxide concentrations--and the ocean acidification they induce--can cause changes in the behavior of fish. Like a flipped switch, the normal response of nerve cells can reverse as acidifying seawater perturbs how a fish regulates acids and bases in its body, including the brain.

The findings, published online January 15 in Nature Climate Change, could go a long way toward explaining curious sensory changes observed in fish exposed to acidifying waters, says neurobiologist Andrew Dittman of the National Oceanic and Atmospheric Administration's Northwest Fisheries Science Center in Seattle, who was not affiliated with the study. The scary scent of predators, for example, can suddenly become alluring.

Once excited, nerve cells in the brain need a chemical to calm them down. A compound known as GABA does this by unlocking a "gate" on the cells' outer membrane, allowing ions of chloride and bicarbonate to enter and quiet the cell. Goran Nilsson of the University of Oslo and his colleagues speculated that when a fish's body attempts to maintain chemical balance in the face of changing ocean chemistry, chloride and bicarbonate concentrations could become higher inside nerve cells than outside them.

Later, when GABA gates opened, chloride and bicarbonate would then rush out of the cell instead of into it. That would excite the cell instead of calming it, essentially reversing the nerve's response to a stimulus.

To test the idea, Nilsson's group looked at hatchling reef fish. Among clown fish raised in an environment high in carbon dioxide, a predator's scent in the water--normally repellent--proved an attractant. Until, that is, the researchers immersed these fish for 30 minutes in water heavily spiked with gabazine, a chemical that locks the GABA gate closed. When the fish then reentered carbon dioxide-enriched water, a predator's scent proved repellent, the scientists found.

Fish normally show a preference for turning one direction versus another, the piscine equivalent of a human's left- or right-handedness. In a second experiment using Australian damselfish, Nilsson's group showed that fish in a high-carbon dioxide environment exhibited no turning preference. After a brief bout in gabazine-laced water, however, the fish suddenly demonstrated a marked preference for turning in one direction or the other.

"These are really fascinating results," says Dittman. But scientists need to confirm the idea by looking for actual changes in the cells, he says, not just reversals of sensory-based behavioral changes.


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Author:Raloff, Janet
Publication:Science News
Geographic Code:1USA
Date:Feb 25, 2012
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