CO2 ‘sends fishes nerves haywire’

Rising carbon dioxide emissions threaten the survival of some fish species by sending their central nervous systems haywire.

Researchers from the Centre of Excellence for Coral Reef Studies and James Cook University say concentrations of carbon dioxide are predicted to reach between 700 and 900 microatmospheres before the end of the century, interfering with the fishes’ ability to hear, smell, turn and evade predators.

“It is now pretty clear that they sustain significant disruption to their central nervous system, which is likely to impair their chances of survival,” Professor Phillip Munday said yesterday.

“We’ve found that elevated carbon dioxide in the oceans can directly interfere with fish neurotransmitter functions, which poses a direct and previously unknown threat to sea life.”

The team examined how baby clown and damsel fish and their predators dealt with water enriched by carbon dioxide.

While the predators were slightly affected, the baby fish suffered to a much greater degree.

“They found it harder to locate a reef to settle on or detect the warning smell of a predator fish,” Professor Munday said in a statement.

The team looked more closely and found the hearing of the fish was affected as well as its smell.

Then they started to lose their natural instinct to turn left and right.

“All this led us to suspect it wasn’t simply damage to their individual senses that was going on but rather that higher levels of carbon dioxide were affecting their whole central nervous system.”

The team concluded that high levels of carbon dioxide stimulates a receptor in the fishes’ brains called GABA-A.

As a result, the receptor’s function is reversed and some nerve signals become over-excited.

Professor Munday said 2.3 billion tonnes of carbon dioxide emissions dissolve into the ocean each year.

“We’ve now established it isn’t simply the acidification of the oceans that is causing disruption, as is the case with shellfish and plankton with chalky skeletons, but the actual dissolved carbon dioxide itself is damaging the fishes’ central nervous systems,” he said.

The fish most affected are expected to be those with high oxygen consumption.

This suggests some species are affected by carbon dioxide more than others and may also have implications for species sought by fishing industries.

The research has been published in the journal Climate Science.