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Fish Are Friends, and Other Species Similarities

Erik Johnson (‘22) wins a CURA award for his research exploring possible connections between individual personality traits and placement in social hierarchies.

Convict cichlids in a lab fish tank

Would you consider yourself to be timid and submissive, or a bold, domineering type? As deeply social creatures, determining our personality traits can provide great insights into how we understand our own behavior and interact with others. But as it turns out, these personality traits and behaviors aren’t unique to humans—in fact, it’s something we share with our distant ancestors: fish.

In his research titled, “Is social dominance repeatable and inherent? The behavior of social dominance in Convict Cichlids,” recent biology graduate and third place CURA (College Undergraduate Research Award) recipient Erik Johnson (‘22) explores these very behaviors. Specifically, if there is a connection between individual personality traits and placement in social hierarchies. He chose to study convict cichlids—a freshwater fish native to Central America—as the subject because of their easily observable social hierarchies and known patterns of dominant and subordinate behavior.

In the study, Johnson uses a “bold/shy” spectrum to quantify the fish’s personality. “Boldness” is described as the fish’s propensity to explore feed, mate, escape, and perform other activities with confidence; shyness is described as the opposite of boldness. Data is gathered using four different behavioral assays, which test and measure the fish’s time to feed, emerge into new areas, explore novel objects, and interact with a mirror. Fish who are quick to perform these actions receive a higher “boldness” score.

An individual’s size can often be a confounding variable when studying dominance. In order to keep the study’s sole focus on personality, Johnson size matched the fish and separated corresponding pairs into their own tanks. Once paired off, the fish’s dominance or subordination is once again measured by observing behaviors such as “mouth pushes” and chases, or inversely, retreating and hiding.

While previous research has studied a fish’s individual personality and group behavior, Johnson’s study is unique in that it focuses on the crossover between the two topics. Due to our common ancestry, Johnson hopes that the fish can be used as a model system—similar to the way lab rats are often used to provide insights on humans—to make conclusions about individual and group behavior in people as well.

“If [the behaviors] are related, then it’s possible to extrapolate it and say, based on your individual personality, this is how you’ll do in a group setting,” Johnson explains. “For example, when assembling teams within businesses, based on people’s personalities and putting the right personalities together. A team full of alphas is probably going to do worse than a team with one alpha and a lot of betas. This deeper understanding into how personal individual personality affects group decision making and group behavior has a ton of wide implications.”

This isn’t the first time Johnson’s research has focused on fishy functions. In 2020, Johnson published his findings on the connection between behavioral lateralization and morphological asymmetry in the genus Xenophallus umbratilis, a live-bearing prey fish that lives in the same environment as the convict cichlids. The most obvious example of behavioral laterality is handedness, or the tendency to use one hand or the other to perform activities. Behavioral lateralization is what makes someone a righty or a lefty—and this behavior can also be seen in fish, despite their lack of hands.

Fish often display behavioral handedness through their eyes; due to their limited periphery, they have to turn one way or another to see an object. But the male Xenophalus umbratilis is unique in that it also has a modified fin organ that acts as a penis—and the end either tips to the left or the right. Johnson’s research found evidence that the fish’s morphology could be indicative of which way they were going to behave. Left morph males preferred to turn to the left, to view something with their right eye, and vice versa.

“It gives us pretty good evidence that fish are using different sides of their brains for different things,” says Johnson. “You’ve heard about humans having a ‘left-brain’ or ‘right-brain’, where one side specializes in creativity, the other analytical thinking. The idea that we may share this trait with fish could potentially prove that this trait evolved long before we ever thought it did.”

Johnson performed his research under the mentorship of a biology professor whose lab focuses on using model systems of tropical freshwater fish to answer different types of questions about evolution and ecology. His experiences in the lab have been incredibly formative for his career—and as a prospective professor himself, Johnson encourages students to take advantage of the autonomy and opportunities that doing lab research can provide.

“People tend to take initiative by sitting in the front row of their class, by talking with the professor after class, or asking questions during class—it all revolves around class,” Johnson says. “If you can just escape that bubble of thinking college is just your classes, then the world opens up to you—and you can really start learning, experiencing, and growing as a scientist, and as a professional.”

Johnson has been accepted to a PhD program at Kansas State University where he will continue to study evolutionary biology using fish.