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Why do Fish School?

I mentioned in our perch dissection video (which you can check out here), that perch are one of the numerous species fish that travel in schools. In biology, schooling is defined as a behavior in which a group of fish travel in the same direction in coordination. Another term which is used interchangeably is ‘shoaling’ which is technically a broader term that describes when a group of fish stay together for an extended period of time. Now you may be wondering, why do fish school? Because they’re lonely? Not quite. In this article I’ll explain four main reasons behind the schooling behavior of many fish species.

One reason behind schooling is that such behavior in fish increases foraging success. In predatory fish such as the Atlantic bluefin tuna, schooling enables cooperative hunting, where the fish assume a parabolic formation to encircle their prey. For non-predatory fish like the perch, schooling allows increased foraging success as the fish closely monitor each others’ behavior, relaying information about the presence of food: feeding behavior in one fish prompts food searching behavior in other members of the group.

Another advantage fish gain from schooling is reproductive advantages. By living in large schools, fish have easier access to potential mates, and can reproduce with less energy. Additionally, many fish also make migrations during their reproductive cycle, and research shows that fish have increased navigational skills when traveling in groups.

Interestingly, research also shows that a group of fish may travel together because it reduces not only the energy needed to find mates, but also the energy needed to swim– traveling in groups is thought to provide hydrodynamic efficiency. Scientists aren’t really sure how it works, but they hypothesize that it would function similarly to how cyclists draft each other in a peloton.

One final and most important reason [non-predatory] fish travel in groups is because it provides defense against predators. More specifically, there are four anti-predator advantages for smaller fish when traveling in groups. First, when fish travel in groups it confuses the predator, making it harder for them to focus on one individual. Second, schools of fish confuse the lateral line organ (which we talk about in this video) of the predator, which is necessary for the final steps of a planned attack. Third, there is an increased chance in a large group of fish that one of them would spot the predator approaching and alert the rest. Last but not least, research shows that a predator generally eats a smaller number of prey in a larger school than a smaller school, providing incentive for smaller fish to travel in large groups.




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