Schools of fish

School of fish — Swimming in a school can help fish protect themselves, find food and meet other fish. © dive.explo360.fr — Tous droits réservés. Reproduction interdite sans autorisation.

Many fish swim together in groups called schools. Almost all of them move in the same direction, as though they were one large group.

Living in a school mainly helps fish protect themselves from predators. When many fish move at once, a predator finds it harder to choose which one to catch. Fish can also spot danger more easily and escape together.

A school can also help fish find food. When one fish discovers a place to feed, others can follow it.

Finally, living in a group makes it easier for males and females to meet and reproduce.

Staying together therefore helps fish protect themselves, feed and reproduce.

To protect themselves

Imagine a predator facing hundreds of fish all changing direction.

It may find it harder to follow a single fish.

Staying in the group can therefore help a fish avoid being caught.

To find food

In a large group, many fish are looking for food.

If some find it, the others can join them.

To meet one another

A school brings together many fish of the same species.

This can also help them find a mate to reproduce.

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

A school can change shape very quickly.

It can become round, stretch out or even turn like a whirlpool.

The fish turn together and form a large whirlpool.

A predator may then have trouble choosing which fish to chase.

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

When danger arrives, some fish move closer together.

The school becomes very compact and looks like a large ball.

Fish can also swim together in a long, stretched-out group.

This shape allows them to travel while staying together.

Linear school — The elongated school: fish move together in the same direction. © dive.explo360.fr — Tous droits réservés. Reproduction interdite sans autorisation.

Sometimes fish swim up and then down together.

Their movement may then look like water in a fountain.

Fish can see the fish swimming around them.

They also have a special sense called the lateral line. It helps them sense water movements around their body.

They can thus tell when a neighbour is approaching or changing direction.

Lateral line and vision — Fish use their eyes and lateral line to follow their neighbours’ movements. © dive.explo360.fr — Tous droits réservés. Reproduction interdite sans autorisation.

Schooling behaviours — Moving closer, following the same direction and keeping a little space allow fish to swim together. © dive.explo360.fr — Tous droits réservés. Reproduction interdite sans autorisation.

Each fish can follow very simple rules:

Move closer if the others are too far away.

Swim in the same direction as its neighbours.

Move away a little if another fish is too close.

This is how fish stay together without bumping into one another.

If a fish sees danger, it may suddenly change direction.

Its neighbour sees or senses this movement and turns too.

Then another fish does the same.

Very quickly, the whole school can change direction.

Lateral line communication — A change of direction can spread very quickly through the whole school. © dive.explo360.fr — Tous droits réservés. Reproduction interdite sans autorisation.

School leader — Each fish follows its neighbours: the school can therefore move without needing a leader. © dive.explo360.fr — Tous droits réservés. Reproduction interdite sans autorisation.

There is not always one!

Each fish mainly pays attention to those nearby.

All these small changes made by each fish allow the whole school to move together.

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Conclusion

A school of fish may seem to work like one large animal, but it consists of many fish reacting to one another.

They watch their neighbours, sense their movements and adjust their direction.

By following a few simple rules, hundreds of fish can thus swim together without bumping into one another.

Sources and references

This section is intended for teachers, parents and educators who wish to check or explore the information in the article further. It is not part of the reading expected of the child.

- 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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