Ocean acidification — one of the consequences of an increasing level of carbon dioxide in the atmosphere — makes rockfish anxious, according to a newly published paper by a neuroscientist at Edmonton's MacEwan University.
"It's actually very similar to a human being anxious at a very basic fundamental level," said Trevor Hamilton. "(The fish are) afraid of any sort of stimuli that could be harmful."
Hamilton and his colleague, biologist Adam Holcombe, were building on previous research that looked at the effect of ocean acidification on reef-dwelling fish. They wanted to find out what might happen to fish that live in areas that experience more upwelling currents, which can change seawater chemistry.
They decided to look at juvenile rockfish, a common species along the Pacific coast.
They kept one group of fish in a tank with normal sea water and put a second group in a tank with sea water at levels of acidification expected in about 100 years. Both tanks were divided into black areas and white areas.
In the normal tank, the fish more or less went about their business swimming freely between the two areas. But in the acidic tank, they tended to huddle in the dark area.
"When the fish moved toward the dark side, that's representative of them being more afraid," said Hamilton.
"We know that because when you give zebrafish, for example, drugs that in humans or other mammals would decrease anxiety, the zebrafish started exploring more."
The scientists were even able to figure out how the feeling of fear was created.
The acidic water stimulated activity in a part of the fish's neural system call the GABA receptor, which humans also have. As the GABA receptor struggled to restore electrochemical balance, it stimulated neural pathways, which created anxiety.
Hamilton noted that the fish calmed down and returned to normal behaviour about 12 days after leaving the acidic tank.
He cautions that his fish were subjected to a sudden shock of more acidic water. In the real world, fish will have many generations to adjust. But, Hamilton said, there's no guarantee they will adapt.
The research could have important implications for predicting fish behaviour as their world slowly changes around them.
"If you've got fish that are more anxious, they're going to have a decreased tendency to leave their safe environment in search of food and in search of potential mates," Hamilton said. "It also has an impact on the whole ecosystem, because other predators will have less potential to go and feed on these fish.
"It even has potential effects on fisheries. If there are more fish that are hiding, it means that less fish may be caught in nets."
Hamilton said his next step will be to find out if fish still fret if they are exposed to a slower climb in acid levels.
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