How do fish know who they are? © Dan Bright

How do fish know who they are?

Fish can recognise members of the same species and tell if other fish are siblings, but they probably can’t identify themselves.

Asked by: Kate Harris, Torquay, Devon

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Fish can’t see themselves, and so presumably don’t know what they look like. But they’re still able to recognise other members of their own species and join them in a shoal.

Smell is an important sense for fish. Many species release potent pheromones, which tell other fish not only if they belong to the same species but also if they’re siblings.

Recent studies of zebrafish, the lab rats of the fish world, have also shown that some fish may spot their own species by the way they move. When a zebrafish is shown a computer screen with a black dot moving in bursts, characteristic of a zebrafish’s swimming style, it will follow the dot for hours. Even fish brought up in isolation will trail after the dot, suggesting that this behaviour is innate in zebrafish, and possibly in other species too.

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