Schooling Fish

Few aquarium scenes are more enjoyable than a group of fish swimming in unison, changing directions in an instant, yet never colliding with each other. How are they able to swim in unison? Why do some fish swim alone while others prefer schools? Not everything is known about schooling behavior, but here is what experts know about schools of fish.

Why do fish swim in schools?
First and foremost, schools protect fish from enemies. It's the same rule our mothers taught us, always stay in a group because there is safety in numbers. Predators find it easier to chase down and gobble up a fish swimming all alone, than trying to cut out a single fish from a huge group. The same holds true in reverse. Fish can better defend their territory in a group. Bullies will think twice about facing an angry school of fifty fish.

It is also believed that swimming close together reduces friction and allows fish to conserve energy when swimming. When dinner time comes, food is easier to find as a group. Having fifty sets of eyes and noses gives the school a better chance of finding food. Last but not least, when fish spawn a school ensures that at least some eggs will elude predators due to the sheer numbers produced in a large group.

How do they swim so close without colliding?
A complex combination of senses allows fish to achieve those smooth schooling movements we marvel at. At one time it was believed a leader in the school directed their movements. However, it is now known that each fish responds to the movements of the other fish, as well as stimuli such as pheromones. If one fish moves in a different direction all the others sense it and move accordingly.

Eye placement on the sides of the head allow the fish to readily see what is next to them and move accordingly. However, sight is not the only factor used in schooling. Fish are able to establish their placement and direction in a school by using hearing, lateral line, sight, and even the sense of smell.

Do all fish school?
Even though eighty percent of all fish school at some point in their lives, some fish live solitary lives. As a rule smaller fish are more likely to live out their lives in schools, although some large fish will school together.

Furthermore, not all fish that school do so for protection in numbers. In fact some of the fiercest fish in the world live in schools. Piranha fish live in large schools that they are born into. Although they tolerate their brothers and sisters, a new piranha attempting to join the school later is usually attacked and killed.

How many fish make a school?
There is no magic number, but in the wild schools are generally large, often numbering in the hundreds or thousands. In captivity, schooling fish need to have at least four to six to create a comfortable school.

Which fish prefer schools?
Quite a few popular freshwater fish prefer to live in schools. Barbs, Danios, and most Tetras should all be kept in schools. Loaches such as the Clown and Kuhli loach often will pine away if they are not kept in a school of their own kind. Even larger fish such as the Silver Dollar prefer to live in a school.

It's a good idea to check with your LFS (local fish shop), or consult a library for information before choosing a new fish. If the fish you are considering prefers to live in a school you should plan on purchasing at least four of the same species.