Fish personalities can be surprisingly complex

September 25, 2017, 3:55 p.m.
Photo: Napat/Shutterstock

People don't have a monopoly on personality. Lots of other animals possess individual personalities, too, including tiny tropical fish known as guppies. And according to a new study, there's more depth to guppy personalities than previously thought.

To study the personalities of nonhuman animals, scientists look at consistent behavioral traits that determine how an individual reacts to various situations. In many cases, this means studying how individual animals respond to risk — an approach that has revealed personality differences in creatures ranging from spiders to salamanders to sharks to sheep.

For the new study, published in the journal Functional Ecology, researchers from the University of Exeter examined personality differences in 105 Trinidadian guppies. (The guppy is a small fish native to South America, but it has been widely introduced elsewhere. It's also widely widely studied as a model species in ecology and biology, and widely kept as an ornamental pet.)

The researchers tested whether personality differences could be measured on a "simple spectrum," based on how risk-prone or risk-averse the guppies were. "The idea of a simple spectrum is often put forward to explain the behavior of individuals in species such as the Trinidadian guppy," says lead author Thomas Houslay, an evolutionary biologist at the University of Exeter's Center for Ecology and Conservation, in a statement. "But our research shows that the reality is much more complex."

The study looked at individual guppies' "coping styles," or their personal strategies for handling stress. Houslay and his colleagues created mild stress by transferring individual guppies to an unfamiliar tank, and triggered higher stress by confronting them with models of a predatory bird — a lawn-ornament heron nicknamed "Grim," Houslay tells the Washington Post — or a cichlid fish known as "Big Al." The guppies were never in any real danger, the researchers note, but they didn't know that.

study of personality in guppies A mock-up image showing a Trinidadian guppy (the small fish), a blue acara cichlid and a model of a heron nicknamed 'Grim.' (Photo: University of Exeter)

The sight of predators had an effect on average behavior, Houslay explains — making all of the guppies behave more cautiously overall — but individuals still retained their distinct personalities.

"[W]hen 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," he says. "The differences between them were consistent over time and in different situations. So, while the behavior 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 researchers filmed the guppies' reactions, then used tracking software to automatically extract behavioral data from the recordings. They repeated these experiments many times over a span of weeks, studying the nuances of each guppy's response — including what it did and for how long — to reveal how its personality deals with stress.

"We see quite complex strategies; more complex than we thought," Houslay tells the Post. "The variation isn't just random. There's something more meaningful going on."

Even though these guppies grew up in a laboratory, they've ended up with distinct personalities. That doesn't mean they rival the complexity of a human personality, of course, but it could help shed light on the nature of individuality. The next step, researchers say, is to understand how genetics affect personality, and what role that might play in evolution.

"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," says co-author and University of Exeter biologist Alastair Wilson. "We want to know how personality relates to other facets of life, and to what extent this is driven by genetic — rather than environmental — influences. The goal is really gaining insight into evolutionary processes, how different behavioral strategies might persist as species evolve."

That will be a job for different fish, though. Now that these 105 guppies have unwittingly taught us about their personalities, Houslay tells the Post, they have returned to their home tanks "to live happy lives again."

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