Why Do Fish Swim in Schools?

Why Do Fish Swim in Schools?

There are many reasons why fish swim in a school. The main reason for swimming in schools is for protection. A fish on its own would not stand a chance if they were caught by a predatory fish. If there was a school of them, at least the fish would stand a chance of surviving.

A fish might not be large enough to take on the predatory fish but that fish could not eat the entire school so some would have a chance to escape.

What Does a School of Fish Mean?

This is a group of fish of the same species and sometimes of the same size that appears to act like one organism. When watching a school of fish in your aquarium, it almost looks like a choreographed dance troupe or a military regiment that is well-drilled.

Every fish seems to be able to hold their position relative to the next fish at a constant distance. The school of fish seems to be able to maneuver as if on command. This is especially true if they are trying to escape predators. They seem to move with almost instantaneous movements.

How Do Fish Manage to Swim in a School

Watching a school of fish swim around the aquarium with such precise movements will make you wonder how they manage to do that. How are they communicating with the other fish? They communicate using a combination of using their lateral line and visual contact with the other fish in the vicinity.

The lateral line is a visual organ that is found on their body. The lateral line is susceptible to pressure changes no matter how small the touch in the near vicinity of the fish. This line runs along both sides from the base of the tail to the gill covers. It is what detects water vibrations and currents.

Depending on what the fish closest to them does, whether it is to turn quickly or swim faster, this will be picked up by their lateral line with an immediate response. Each fish will also keep what is called a “private zone’ that helps to protect it from colliding with the other fishes. If one of the other fish gets into that zone, the fish will automatically turn away to avoid any type of physical contact.

Outside of their “private zone” there is another zone called “zone of orientation.” This is where each fish will try to emulate with other fishes in their closest proximity. When the school is moving together, this is when you notice this action.

Why Do Fish Swim in Schools?

Obtain Food

When they attack their prey for food, they form a school to outfox, and outwit their prey which has been proven to be a successful strategy. The Bluefin tuna, when they are swimming in a school for eating, will form a unique shape to make their hunt a success. Swimming in a school and their swimming pattern helps them to catch their prey. Once part of the school has spotted prey, they will telegraph it to the rest of the school so all can get in on the feeding frenzy. With so many eyes on the lookout, they can find their food more effectively.


This is the number one reason that fish swim in schools as there is safety in numbers. They are protecting each other from predatory fish. Also, when they are younger, they have more of a chance to reach maturity when they swim in schools. Sometimes fish will become solitary fish after they mature and will move on from the school. 

Mate and Breed

The salmon will form schools when they are going to their spawning grounds. There are other species that do the same thing.

fish swimming in a school

General Facts About Fish Swimming in Schools

Do All Fish School?

Approximately 80% of fish species live in a school at some point in their lives. Generally, it is the smaller fish that live in schools all their lives. There are some larger fish that also school together.

Fish That Prefer Schools

Some of the freshwater fish that prefer to live in schools includes:

  • Barbs
  • Most Tetras, like phantom or black
  • Danios
  • Loaches such as Kuhli and Clown: They will pine away if not kept in schools of their kind.
  • Weather Loach: They do not need to be in a school.
  • Silver Dollar

When looking at fish to put in your tank make sure that you check and see if they need to be in a school. If they do, then you should get at least four of the same fish. It is a good idea to buy them at the same time. Also, take in the size of your aquarium so you will have enough space for them to swim in a school comfortably.

How Many Fish in a School

How many fish are in a school will depend on the species. There is not a specific number of fish together to make a school. In general, there are hundreds, sometimes even thousands. In the aquarium, if you have schooling fish, to be a comfortable school, there has to be four to six fish. For some fish, like sardines and herring, they can have a billion fish in a school.


  • It seems that older adult marine life fish swim in school than freshwater species.
  • When they are swimming in schools there is constant unrest because they are constantly chasing and nipping at other fish as they try to get close to the center where it is the safest.
  • Not all fish live in schools for protection such as Piranha. They live in schools because they were born into a school. 
  • A Piranha fish will tolerate their brothers and sisters but if a new one, not family, tries to join the school will usually be attacked and killed.
  • In a school of fish, there is no one fish in charge or control.

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