By Julia Unangst ’20

Science tends to oversimplify the behavior of non-human individuals, but a recent experiment offers evidence that things may be more complicated than previously thought.

When I was ten, my father purchased an aquarium. He proudly set it up in our kitchen, much to my mother’s dismay, and soon bought two clownfish to be the first inhabitants: Nemo and Fin. I spent countless hours peering through the glass watching the two fish swim around in their underwater world. Soon I noticed that Nemo and Fin had distinct personalities. Nemo would constantly pick on Fin, biting and swimming at Fin till Fin would swim away into the nearby coral. Fin had no interest in being social and was content to just lay in the anemone all day. I eagerly told my dad about my findings, but he shrugged them off stating that “fish don’t have personalities.”

My observations were not as uncommon as my father thought. Many people share stories of their fish doing odd things like playing chase or enjoying being “pet”. In recent years, scientists have been trying to make sense of the individual make-up of our non-human friends. Already, there have been numerous studies identifying personality in various species from clownfish to bluebirds. Studying personality has huge implications for understanding how individuals adapt to change. Most recently, a study identified personality in carp gudgeons, a fish no bigger than your thumb.

Although they are quite small, carp gudgeons are relatively sophisticated fish found throughout the lower basins of the Murray-Darling river system in southeastern Australia. This river system is well known for its intermittent water flow as the system cycles through periods of flow and periods of no-flow throughout the year. William D. Coates and colleagues from University of Melbourne used these carp as a study species to examine whether or not freshwater fish of irregular streams exhibit variation in behavior, known to the scientists as a behavioral syndrome. Simply put, behavioral syndrome is just a fancy term for personality. It allows scientists to quantify personality in non-human individuals by testing for correlation of behavioral traits. These traits include boldness, aggressiveness, and sociability. This particular study, described fully in the journal Animal Behavior, examined traits most commonly associated with dispersal behavior: boldness, sociability, and movement.

To do this, researchers constructed an artificial stream and set up video cameras to record fish behavior. Carp gudgeons were collected from the wild and housed in flow-through aquariums. After acclimating to their new surroundings, the carp were placed into the experimental stream to first see if water flow was a cue to disperse. Water flow was found to have little influence on whether or not a carp disperse. What did influence dispersal was personality.

Boldness, sociability, and dispersal movement were all found to be indicative of whether or not an individual carp would disperse (see figure 1 for experimental design in testing these behaviors). For starters, all three traits were repeatable, an important step in quantifying the presence of personality. Repeatability indicates some level of behavioral plasticity, a.k.a changes in an organism’s behavior that follows exposure to stimuli. Some carp were timid and more likely to disperse. Others were more social and tended to group up with others and disperse less. These varying patterns of behavior may result in variation in discrepancy in fitness over time.

Timid carp may have less resource competition than social ones, but they may experience higher rates of predation as they lack safety in numbers. Although this particular study did not look into long term impacts of personality on fitness, the researchers assumed that variation in behavior would lead to disparity in fitness per individual over time.

Studying personality offers some insight into the convoluted lives of our underwater counterparts. We tend to oversimplify the behavior of non-human individuals which unfortunately reduces our ability to understand individual level interactions. Personality may be associated with overall population structure and have some inference with the capacity of a species to persist in a changing world. We need not judge so quickly the minds of those that are not our own.

Coates, W.D., Hale, R., and J.R. Morrongiello. Dispersal decisions and personality in a freshwater fish. , Animal Behaviour (2019),