Trinidadian guppy
A mock-up image showing a Trinidadian guppy (the small fish), a blue acara cichlid and a model of a heron. University of Exeter

Fish have complex personality differences, according to new research from the University of Exeter. Scientists found there were significant differences in behaviour between individual guppy fish when they were placed in different situations.

The researchers looked at whether differences between individual fish could be measured on a "simple spectrum" of how risk-averse or risk-prone the guppies were. However, they found that the variations between individuals were too complicated to be described in such terms.

"The idea of a simple spectrum is often put forward to explain the behaviour of individuals in species such as the Trinidadian guppy," said Dr Tom Houslay, from the Centre for Ecology and Conservation (CEC) at the University of Exeter.

"But our research shows that the reality is much more complex. For example, when placed into an unfamiliar environment, we found guppies have various strategies for coping with this stressful situation – many attempt to hide, others try to escape, some explore cautiously, and so on.

"The differences between them were consistent over time and in different situations. So, while the behaviour of all the guppies changed depending on the situation – for example, all becoming more cautious in more stressful situations – the relative differences between individuals remained intact."

The study, published in the journal Functional Ecology, looked at the "coping styles" of guppies in situations designed to cause varying levels of stress.

To induce mild stress, the researchers transferred fish to an unfamiliar tank, while higher stress was caused by simulating an attack by predators using models of predatory fish or birds.

The addition of the fake predators affected the "average behaviour" of the guppies by making them more cautious overall. However, individuals still retained their distinct personalities, according to the researchers.

"We are interested in why these various personalities exist, and the next phase of our research will look at the genetics underlying personality and associated traits", said Alastair Wilson, also from the CEC at Exeter.

"The goal is really gaining insight into evolutionary processes; how different behavioural strategies might persist as species evolve."