Way of life · Behaviour

SCHOOLS OF FISH

A school of fish is a group of fish swimming together with coordinated movements. The school can change direction or shape very quickly without all the fish colliding. To achieve this, each fish watches and senses what the fish around it are doing.

By DIVE.EXPLO360.FR · 11/08/2026

Fish mainly form schools to protect themselves from predators. By swimming together and coordinating their movements, they increase their chances of survival. To stay close to one another, they use their vision and their lateral line, a sensory organ that detects water movements.

When facing a predator, the school offers two advantages. The confusion effect makes it difficult to choose a prey among all the moving fish. The dilution effect reduces each fish’s risk of being caught, because that risk is shared among many individuals. The group can also detect danger more quickly.

Living in a school can also make food easier to find: when one fish discovers a food source, others can benefit from that discovery. However, they sometimes have to share the same resources.

Finally, groups make reproduction easier, because fish have more chances of finding a mate.

Schooling is therefore a collective strategy that supports protection, feeding and reproduction, although it also has some drawbacks, such as competition for food.

Protection

In a large school, a predator must choose its prey from many moving fish.

The group’s changes of direction can also confuse the predator and make a target harder to follow.

Searching for food

Having many fish can make it easier to discover a food source.

If some fish find food, others can react to their behaviour and join the area.

Reproduction

A school brings together many fish of the same species.

This can make it easier for mates to meet, particularly during certain breeding periods.

A school of fish fleeing — © dive.explo360.fr — Tous droits réservés. Reproduction interdite sans autorisation.

Fish do not always swim in the same way.

Depending on the situation, a school can stretch out, tighten up or change shape completely.

The fish turn together and form a kind of whirlpool.

During an attack, these many moving fish can make it harder for a predator to choose its prey.

Vortex — The vortex: fish turn together as if in a whirlpool. © dive.explo360.fr — Tous droits réservés. Reproduction interdite sans autorisation.

When threatened, some fish move very close together.

The school then becomes a compact mass resembling a ball.

Fish can swim in a long, stretched-out formation.

This arrangement is particularly suited to travelling and searching for food.

Linear school — The linear school: fish move together in an elongated formation. © dive.explo360.fr — Tous droits réservés. Reproduction interdite sans autorisation.

Fish can swim up and then down along paths resembling the movement of water in a fountain.

In the article, this formation is particularly associated with searching for small prey.

Fish use their eyes to see their neighbours and follow their movements.

They also have a sensory system called the lateral line. It allows them to detect movements and vibrations in the water.

These two systems help them react very quickly.

Lateral line and vision — Vision and the lateral line help fish detect their neighbours’ movements. © dive.explo360.fr — Tous droits réservés. Reproduction interdite sans autorisation.

Schooling behaviours — Moving closer, aligning and keeping enough distance allow the school to stay organised. © dive.explo360.fr — Tous droits réservés. Reproduction interdite sans autorisation.

To stay in the school, each fish can follow three main rules:

Attraction: stay near the group.

Alignment: swim in a similar direction to its neighbours.

Repulsion: do not get too close, to avoid collisions.

With these simple rules, the whole group can stay organised.

A fish can detect a neighbour speeding up or suddenly changing direction.

It can then change its own movement.

This reaction can be detected by other fish and spread quickly through the school.

Lateral line communication — One fish’s reaction can quickly influence its neighbours. © dive.explo360.fr — Tous droits réservés. Reproduction interdite sans autorisation.

School leader — Each fish adjusts its movement to that of its neighbours: the school can thus coordinate without a permanent leader. © dive.explo360.fr — Tous droits réservés. Reproduction interdite sans autorisation.

Contrary to what we might think, a school does not always have one fish deciding the direction.

Each individual mainly reacts to the fish nearby.

If several fish detect danger and turn, their neighbours may follow. The change of direction then spreads through the group.

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Conclusion

A school of fish is an organised group capable of quickly changing its shape and direction.

Vision and the lateral line allow fish to follow their neighbours. By staying close, aligning and avoiding collisions, they can move together.

This group life can help them protect themselves, find food and reproduce.

Sources

- Pitcher, T. J., & Parrish, J. K. (1993). "Functions of shoaling behaviour in teleosts". *Behaviour of Teleost Fishes*, 363-439.link.springer.com - Couzin, I. D., & Krause, J. (2003). "Self-organization and collective behavior in vertebrates". *Advances in the Study of Behavior*, 32, 1-75.citeseerx.ist.psu.edu - Sumpter, D. J. (2006). "The principles of collective animal behavior". *Philosophical Transactions of the Royal Society B: Biological Sciences*, 361(1465), 5-22.pubmed.ncbi.nlm.nih.gov - Breder, C. M. (1967). "Studies on social groupings in fishes". *Bulletin of the American Museum of Natural History*, 134(4), 329-360.digitallibrary.amnh.org - Partridge, B. L. (1982). "The structure and function of fish schools". *Scientific American*, 246(6), 114-123.www.jstor.org - Herbert-Read, J. E. (2016). "Understanding how animal groups achieve coordinated movement". Journal of Experimental Biology.journals.biologists.com

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