Shy trout grow faster

What is it about?

We observed young trout in individual tanks over and over again and after a while it became clear that individuals behave consistently differently. We released the fish back into the wild and recaptured them at a later date. Contrary to expectations, it were the shyer, more cautious fish that gained the most weight during that time, rather than the bolder, more aggressive individuals.

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Why is it important?

It remains unclear how ‘animal personalities’ make sense from an evolutionary perspective, and little is known about the effects of these differences on fitness in nature. Studies of how variation in behavior affects the performance of animals in the wild can help us understand why personalities persist. Our results provide a challenge to conventional wisdom that fast growth is associated with a more bold lifestyle (‘no pain, no gain’).