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Fishes Show Individual Personalities in Response to Stress

Trinidadian guppies display complex individual and consistent coping strategies

An essay titled "Fish have complex personalities, research shows" caught my eye this morning because while many people are likely to accept that mammals and perhaps birds display individual personalities, fishes and other animals are often and routinely excluded from the nonhuman animal personality club. In the spirit of informing readers about what's happening in the field called cognitive ethology (the study of animal minds and what's in them), the study with which the above essay is concerned is worth noting because of the care in which the research was conducted.

The essay "Fish have complex personalities, research shows" summarizes a study by Thomas Houslay and his colleagues titled "Testing the stability of behavioural coping style across stress contexts in the Trinidadian guppy," published in the journal Functional Ecology. It's available online so here are some highlights from this very important project: 128 sexually mature guppies (64 males and 64 females) were studied in a 20 × 30 × 20-centimeter tank as they responded to different predator types. The first was a bird strike "that consisted of swinging a counterweighted model heron head into the observation tank such that it struck the water, causing a physical disturbance to the tank, then removing the head immediately." The second was the presence of a cichlid predator. Appropriate control groups were used.

All in all, the results of this detailed study showed "the differences between them [the guppies] 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 fact that the fishes displayed their unique personalities is very important because it shows that while all of the guppies were more cautious in stressful situations, rather than there being a simple spectrum of responses to stress, there were marked individual differences: some attempted to hide, others tried to escape, while some cautiously explored.

In the original research paper the authors write, "Overall, our results provide behavioural evidence in support of the concept of coping styles, but also highlight that the full range of their underlying variation might not be readily captured analytically by a simple, single-axis paradigm, even when considering behaviour alone."

It's important to note that the unique personalities of individual guppies were retained across different contexts and this is a very important discovery that merits more research. For example, the researchers are interested in learning more about the genetics underlying different personality types and also how the different coping strategies are distributed across populations of fishes. To this end they write, "The strong evidence of behavioural change across different stress contexts that we found at the population level, with general shifts towards a 'more shy' behavioural mean, was expected: behaviour is often highly flexible, enabling individuals to react quickly in response to environmental changes ..."

Fishes are far more than merely edible, and in some cases poisoned, protein

The detail with which this study was conducted sets an excellent standard for future research on individual differences in personalities in different species. I learned a lot from reading it and look forward to further research on this fascinating topic. Clearly, fishes are far more than merely edible, and in some cases poisoned, protein.1

Here's a story sent to me by a retired neurologist in Portugal that captures much of what we are learning about fishes in detailed scientific studies (my emphasis):

I'm writing to you to confirm an astonishing fact my wife and I could see many times. We have an house in Ofir-northern Portugal - with a garden and a small lake where we had two small red fishes for years. One day I found one of them on the green, still alive, and I put him back in the lake ... he stayed always at the bottom, unable to swim and resting always on his side. Since then,every time we put food on the watter ,the other fish would'nt eat before going to the bottom of the small lake,gliding himself under the sick fish and taking him to the surface to eat together!

It has been a wonderful experience we could ... and it confirmed my belief that all animals, in diverse degrees, share with humankind conscience and affects.

Please stand by for more on the cognitive and emotional lives of the fascinating animals with whom we share our magnificent planet.

1For more "surprises" on what we know about the very interesting and complex lives of diverse fishes, please see Jonathan Balcombe's book called What a Fish Knows: The Inner Lives of Our Underwater Cousins and his essay called "In praise of fishes" and associated commentaries.

Marc Bekoff’s latest books are Jasper’s Story: Saving Moon Bears (with Jill Robinson); Ignoring Nature No More: The Case for Compassionate Conservation; Why Dogs Hump and Bees Get Depressed: The Fascinating Science of Animal Intelligence, Emotions, Friendship, and Conservation; Rewilding Our Hearts: Building Pathways of Compassion and Coexistence; The Jane Effect: Celebrating Jane Goodall (edited with Dale Peterson); and The Animals’ Agenda: Freedom, Compassion, and Coexistence in the Human Age (with Jessica Pierce). Canine Confidential: Why Dogs Do What They Do will be published in early 2018. Learn more at