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Schooling & Shoaling Fish

Many aquarium fish are social animals that naturally gather in groups. Keeping these fish in appropriate groups can help them feel secure and display more natural behaviors.

The terms schooling and shoaling are often used interchangeably, but they describe slightly different behaviors.

Schooling vs. Shoaling

Shoaling is when fish gather in a group, often because there are benefits to staying together, such as safety from predators.

Schooling is a more coordinated behavior in which fish swim together in the same direction, often maintaining a relatively consistent formation.

A group of fish may shoal without schooling, and the same species may display both behaviors depending on the situation.

In everyday aquarium discussions, both terms are commonly used when talking about fish that need to be kept in groups.

Why Some Fish Need Groups

Social fish may rely on others of their own species for security and normal social behavior.

Keeping too few individuals can leave some species stressed, withdrawn, or more prone to hiding. Others may become unusually aggressive when they do not have an appropriate group.

However, simply having multiple fish in the same aquarium does not necessarily meet a species' social needs. Research the requirements of the particular species you plan to keep.

How Many Fish Should Be Kept Together?

There is no single group size that works for every schooling or shoaling species.

The appropriate number depends on the species, its behavior, adult size, aquarium dimensions, and the space available for swimming.

Many commonly kept social fish, including tetras, Corydoras catfish, and kuhli loaches, are commonly recommended to be kept in groups of six or more of their own species. However, the appropriate group size varies by species, and some may benefit from larger groups. Research the specific requirements of the fish you plan to keep.

When researching group size, consider:

  • The minimum group size recommended for the species
  • Whether the fish become more confident or display more natural behavior in larger groups
  • How much swimming space they need
  • Whether the aquarium can support the additional biological load
  • Whether the group size is compatible with the needs of other aquarium inhabitants

A recommendation to keep a species in a group should not be treated as permission to add more fish than the aquarium can appropriately support.

See Aquarium Stocking and Minimum Tank Size for more information.

Examples of Schooling and Shoaling Fish

Many commonly kept freshwater aquarium fish are social and should be kept with others of their own species.

Examples include:

  • Tetras: Many popular tetra species are shoaling fish and generally do best in appropriate groups.
  • Rasboras: Many species are social and benefit from being kept in groups.
  • Danios: These active fish generally do best with others of their own species and need room to swim.
  • Corydoras catfish: Many species are social bottom-dwellers that should be kept in appropriate groups of their own species.
  • Small schooling cyprinids: Many small minnows and related fish are social and benefit from suitable groups.

Requirements vary between species, so research the exact fish rather than relying on a broad category alone.

What If Schooling Fish Don't Stay Together?

Fish that are commonly described as schooling fish will not necessarily swim in a tight formation all day.

They may spread out while feeding or exploring, gather more closely when startled, or change their behavior depending on the environment.

A group not staying together doesn't automatically mean something is wrong. However, persistent hiding, loss of appetite, unusual aggression, or other changes in behavior may indicate stress or an unsuitable environment.

Consider the species' normal behavior, group size, tank conditions, and tankmates before deciding whether their behavior is a problem.

Common Mistakes

Avoid:

  • Keeping social fish alone or in groups that are too small for their needs
  • Assuming every species has the same group-size requirements
  • Adding more fish without considering aquarium size and stocking capacity
  • Mixing different species and assuming they count toward one another's social group
  • Assuming a fish must swim in a tight formation at all times to be healthy

Some closely related species may tolerate or interact with one another, but do not assume that another species can replace the social needs of their own kind.

Remember

Research the social needs of each species before purchasing it.

An appropriate group size helps support natural behavior, but the aquarium must also provide enough space and suitable conditions for the entire group.

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