There’s something impressive about a school of fish. Hundreds of fish seem to dance in unison, with no leader. But why do they school?
Several anti-predator functions have been suggested. One study showed that shoaling reduces the amount of power spent swimming by reducing wasted sideways motion. Another shows that schools allow for more efficient foraging by allowing fish to closely follow each others’ behavior.
Why do fish school?
When you see fish swimming in a tight cluster, gleaming as they shimmer in the water, chances are they are part of a school. This is not a coincidence. In nature, fish school for safety, to feed and even for spawning.
Schooling allows small species and young fish to protect themselves from predators because it is difficult for a hungry fish to pick out one individual. Schooling also improves a fish’s foraging success because one fish can relay information to others about the presence of food. In addition, schools help a fish swim more efficiently by drafting (swimming in the wake) of those ahead.
Fish use a variety of senses to communicate with one another and make the smooth, synchronized movements we recognize as a school. They rely on the sight of their neighbors, a system of organs called the lateral line that runs down the side of their body, and vibration.
In a home aquarium, schooling is natural and can make your fish tank feel more like the ocean or a freshwater lake. However, it is important to carefully match the type of fish with its habitat and environment. For example, a peaceful community fish should be kept with other peaceful fish and not aggressive or territorial fish. Keeping fish in their natural environment is the best way to ensure they are happy, healthy and well-matched.
How do fish stay together?
Anyone who has ever seen a wildlife documentary or Disney’s Finding Nemo imagines fish as either loners or traveling in dense schools. But the schooling behaviors seen in these creatures aren’t just an act of nature; they have a genetic basis, a fact recently confirmed by two separate studies.
Both studies showed that the schooling behavior in sticklebacks and tuna is linked to genetic structures that are only found in these species when they’re in a school. Researchers also found that the behavior is not just a learned response to predators; the fish appear to travel at two distinct gears or speeds when in a school, with one speed useful for moving slowly around and conserving energy, and another much faster speed that would be helpful for escaping from predators in a flash.
The schooling behavior is also an example of ‘emergence,’ a phenomenon in which there are properties that the group (in this case, the fish) possesses but that individual members do not have. The school’s direction is determined by a complex interplay of visual cues—including the way that the fish are positioned relative to other schoolmates—and sensory information that’s transmitted through their bodies, including their skin and lateral line.
The synchronized movement of the fish also reduces friction in the water, which helps them save energy, and it makes it easier for them to find food as a group than on their own. Scientists aren’t quite sure how they do this, but it seems to involve a combination of sight, hearing, and a feeling of motion that’s transmitted through the lateral line.
What are the benefits of schooling?
In the wild, schooling provides protection from predators by making it harder for a single fish to stand out. When many of the same fish move together and act almost as one, it’s hard for a hungry predator to pick out its prey. In addition, swimming close to others reduces friction and conserves energy. And when it’s time for dinner, the group approach allows a lot of eyes and noses to scan the water for food—and one hungry fish can’t steal all the food.
Schools also improve foraging success: a single fish can encircle its prey, and the movement of feeding fish can prompt searches by nearby individuals. In captivity, a large school can provide safety and comfort by appearing as a single creature that’s difficult for a predator to attack.
Finally, studies have shown that schooling fish are less stressed than lone individuals—and reduced stress means more energy available for growth and reproduction. But the benefits of schooling go even further. A 2016 study found that the synchronized movements of a school can create two distinct gears or speeds, one slow and steady for cruising around and conserving energy, and another more rapid speed that would allow the group to escape from a predator in a flash. This research used state-of-the-art technology to conduct some of the most thorough tests yet of the hydrodynamic efficiency of schooling. The results are a game changer for schooling fish biologists—and could help in developing robots that explore the ocean floor.
What are the disadvantages of schooling?
Schooling can be a disadvantage for some fish. For example, a fish that is the only one in a large school may be more vulnerable to predators because it is harder for them to defend themselves. Also, schooling can affect the water chemistry of a tank and cause it to become unstable. This can be particularly problematic for smaller tanks that are not equipped with a sufficient mechanical filter.
However, there are some benefits to schooling that outweigh the disadvantages. For one, it can help to protect fish from predators. Schools of fish can act as a deterrent to larger predators by confusing them with their movement and making it difficult for them to strike. Schooling can also make it easier for fish to find food and mates. Additionally, schools can improve the hydrodynamics of individual fish by reducing friction and allowing them to conserve energy while swimming.
Another benefit of schooling is that it can help fish recognize other members of their species. This is because many fish species release pheromones that allow other fish to detect their presence. Pheromones can also be used to signal to other fish that they are in a safe territory or that a mate is nearby. In addition, fish that are in a school can communicate with each other through body language. This can be useful when a fish is stressed or injured.
