As every schoolchild knows, just because all the other kids are doing something, that doesn’t mean you should do it, too. On the other hand, if the other kids are avoiding something that looks like it might be dangerous, it might be a good idea to stay away. According to new research, these are lessons that even the rainbow trout knows by heart.

In a study from the University of Liverpool in the U.K., researchers found that bold, risk-taking fish can become more cautious after observing the behavior of shyer fish, but shy fish do not become bolder after watching other fish take risks.

Fish have personalities, which are characterized primarily by their willingness to take risks. Aggressive daredevils fall on the bold end of the spectrum, while timid and cautious fish are considered shy. The study, published in the journal Proceedings of the Royal Society B, tested whether bold fish can become shyer and vice versa.

“Our study shows that fish are significantly affected by watching other fish, and they’re able to learn from others,” said Liverpool animal biologist Lynne Sneddon, an author of the paper. They found that the personalities of bold fish were more consistently flexible, suggesting that bold fish may be better equipped to adapt to changes, including climate change.

Researchers determined how bold or shy each fish was by measuring how long it took the fish to approach a Lego piece that was dropped into its tank—bold fish approach the Lego sooner than shy fish do. After establishing the personalities of the fish, the researchers had them observe other fish as they reacted to the Lego pieces and to red mosquito larvae, unfamiliar prey.

Then, the researchers retested the original fish. They found the bold fish that observed shy fish became more cautious, taking longer to touch the Lego, while bold fish that observed other bold fish did not change their behavior. The researchers suggest that when the bold fish observed fish that were more cautious, they received cues that the environment might be dangerous.

However, shy fish watching bold fish did not become bolder, Sneddon said.

“Shy fish appear to compare their relative competitive ability to others, so when observing a bold demonstrator, they may perceive their competitive ability is lower and remain shy,” she said.

But shy fish did become bolder after watching other shy fish, possibly because they realized that increased boldness might help them to be competitive, she added.

Whereas shy fish seem to make decisions based on their own competitive ability, the bold animals are more sensitive to observations about the relative risk of the environment, Sneddon said. This sensitivity may mean that bold fish have a survival advantage in the face of environmental changes, such as climate change, Sneddon suggested. She is currently conducting a study on the effects of temperature change on fish that may confirm this hypothesis.

Originally published December 15, 2006


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