Fish Have Complex Personalities, From Cowardly To Curious


The tiny guppies were tested in response to a (fake) heron and (real) cichlid. University of Exeter

We might think that little fish living in shoals all act as one without much variation between each individual. But now research has shown that tiny fish actually have their own personalities and character traits.

Published in the journal Functional Ecology, a study has revealed that certain fish, known as Trinidadian guppies, have complex differences between them. This variation couldn't be explained by the simple spectrum of behavioral types normally used when discussing the animals. The researchers now hope to explore whether these characteristics have a genetic underpinning.


The team of scientists tested how the guppies responded to a number of stressful situations. First, they simply placed the fish in an unknown environment to see how they would respond. Some of the fish instantly swam for cover and hid, some froze hoping not to be seen, and others swam up and down the side of the tank trying to escape.

The researchers then simulated one of two different predator attacks. Either a terrifying fake heron would descend from the sky and strike the water, or a panel would be lifted to reveal a very much alive predatory cichlid fish, affectionately known as Big Al, on the other side of the glass. Because the guppies were marked, the team was able to see how their responses changed over the period of the experiment.


“The differences between them were consistent over time and in different situations,” explained Dr Tom Houslay, from the University of Exeter, UK, who co-authored the research. “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.”

This, the researchers argue, indicates that there are certain characteristics unique to individual fish, and not wholly determined by the environment in which they find themselves. These differences in “personality” have previously been shown in other animals, from chickadee birds to prawns, but never in guppies.


What the experiments show is that the little fishies, all descended from the same population in Trinidad, and bred and raised in the same environment, all went on to develop different personality traits.  

The researchers now want to test this further by looking at whether or not these seemingly innate differences are heritable. They have begun breeding the fish and will investigate whether mothers pass on their personalities to their offspring, in the hope of finding some form of genetic basis for the variation in behaviors observed.


  • tag
  • fish,

  • genetics,

  • predator,

  • personality,

  • guppies,

  • characteristics,

  • innate,

  • heron,

  • cichlid