According to science, good guys do not finish last – but good fish just might. The results of a study recently published in the journal Animal Behaviour found that friendlier fish are more likely to end up on the dinner plate than their grouchier neighbors.
Michael Louison, a graduate student at the University of Illinois and a keen angler, spent a week fishing to see if personality traits (specifically, sociability and aggression) affected which individual fish were caught. Before the start of the study, he filled an experimental pond with bluegill (aka bream, brim, and copper nose). Bluegill is not only known for its sociability and tendency to form large groups close to the shore, but for being an easy catch.
For the next five days, Louison and a second angler sat fishing. When a fish was caught, the tracking number was noted and the fish allowed to return to the pond. When the five days were up, they brought the fish they could capture to a laboratory and selected 38 for the next part of the study, roughly half of whom had been caught once or more.
There, they put a random group of six fish in a rectangular tank split in half with a single glass divider. Behind the divider, the researchers placed a test fish. The purpose of the experiment was to test the social curiosity of the six fish by observing how much time they spent next to the divider – the more sociable the fish, the more time it would spend close to the divider.
It turned out that the fish that had been caught during the first stint of the experiment spent more time by the divider and, therefore, were rated as more sociable. The experiment was repeated twice. The results were the same both times.
To measure aggression, the researchers performed a second experiment, which involved placing one fish from the pond in a tank with a test fish.
"In every case, one fish emerged as dominant. It would be hanging out in the center of the tank, with the other fish driven into the corner," Louison explained. "Every time the submissive fish tried to come back into the center, the dominant fish would attack it and drive it back to the side."
But there was no obvious correlation between the aggressive fish and the fish caught in the pond. Aggression, it seems, makes it no more or less likely an individual fish will be caught.
In the wild, these results could have damaging ramifications for the bluegill's social structure.
"Broadly speaking, for animals living in groups, social individuals are really important. They help spot predators, find prey, and transmit information about these things to the rest of the group," Cory Suski, an associate professor and co-author on the study, said in a statement.
The experiment was completed in a lab so it is hard to tell whether bluegills modify their social groups if and when a "friendly" fish is caught. The next step will be to monitor wild populations to check for differences in over-fished versus under-fished ponds.