Increased Temperatures Turn Fish into Daredevils

A temperature increase of a few degrees can cause a change in fish personalities, making them more aggressive and bold. If global temperatures continue to rise, this may have important implications for fish survival.

As the world grows warmer, some fish may stop acting like themselves. With a small rise in temperature, a new study found, some fish become more daring and more aggressive than they would otherwise be. The finding suggests that climate change could put fish in peril in unexpected ways.

"The fact that big effects on behavior were happening over the course of just a couple degrees surprised me," said Peter Biro, a fish ecologist and evolutionary biologist at the University of New South Wales in Sydney, Australia. "I would have never expected that from the things I had read in the literature."

Biro stumbled on the discovery by accident. He was working with damselfish in an indoor lab that naturally got warmer over the course of a day. His original goal was to study personality traits in the fish.


But as the lab heated up every day, he noticed some fish becoming more active, aggressive and bold.

To figure out what was behind their personality transformations, Biro and colleagues put 30 young damselfish in individual aquaria. All fish were the same size and the same age, and the researchers gave them as much food as they wanted so that hunger wouldn't affect their behavior. Then came the personality tests.

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