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Alexandre Meinesz

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

Why do fish form schools?

School of fish — Grouping together can help fish protect themselves, find food and meet mates. © dive.explo360.fr — All rights reserved. Reproduction prohibited without permission.

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.

The shapes schools take

A school of fish fleeing — © dive.explo360.fr — All rights reserved. Reproduction prohibited without permission.

A school’s shape emerges from individual movements and interactions with the environment. It changes with speed, spatial constraints or an approaching predator. Assigning a single purpose to each shape would be too simple.

The vortex

A group can adopt collective rotation, sometimes called a vortex. This form can arise in several contexts. Seeing it is not enough to conclude that the fish are trying to confuse a predator.

The ball

An attack may compress a school into a dense ball. Grouping can dilute individual risk or make a target harder to track, but can also attract predators. Individuals at the centre are not guaranteed protection.

The linear school

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 — All rights reserved. Reproduction prohibited without permission.

The fountain

In a fountain-like response, fish may part around a predator and regroup behind it. This is not an ascent to the surface intended to confuse plankton. The trajectory depends in part on the attack and possible escape routes.

Vision and the lateral line

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 — All rights reserved. Reproduction prohibited without permission.

Three simple rules

Schooling behaviours — Moving closer, aligning and keeping enough distance allow the school to stay organised. © dive.explo360.fr — All rights reserved. Reproduction prohibited without permission.

The simulator uses attraction, alignment and repulsion: approaching, adjusting direction and avoiding collisions. These rules are a simplified model of certain interactions.

Observations show that actual interaction rules vary by species and situation. Apparent alignment can even emerge without an explicit alignment rule. The model helps explore an idea; it does not by itself demonstrate how every school works.

Information spreading

Vision and the lateral line provide information about neighbours and nearby disturbances. A response can spread as other fish react to movement. There is no need to assume a deliberate message or a chemical signal coordinating every turn.

Lateral line communication — One fish’s reaction can quickly influence its neighbours. © dive.explo360.fr — All rights reserved. Reproduction prohibited without permission.

A leader is not always needed

School leader — Each fish adjusts its movement to that of its neighbours: the school can thus coordinate without a permanent leader. © dive.explo360.fr — All rights reserved. Reproduction prohibited without permission.

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 Katz et al. — Inferring the structure and dynamics of interactions in schooling fishpmc.ncbi.nlm.nih.gov Herbert-Read et al. — Inferring the rules of interaction of shoaling fishpmc.ncbi.nlm.nih.gov

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SCHOOLS OF FISH