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They’re cute, colourful and … clever? Scientists just discovered that common clownfish can count! Or at least, they can recognise the number of stripes on other fish. And it helps them pick their friends from foes.

Fans of Finding Nemo will know that clownfish take shelter in the arms of a sea anemone. Unlike the gentle animated character, real clownfish fiercely defend their home from intruders. Especially intruders of the same species.

There are 30 species of clownfish and this includes Nemo’s species, the common clownfish. Common clownfish have the famous orange body interrupted by three vertical white stripes, but other clownfish species can have fewer stripes or none at all. A team of researchers asked if common clownfish could tell the difference between all these stripy fish.

First, the researchers painted different numbers of stripes on toy clownfish, and then they put toys and real clownfish into the same tank. They found that the common clownfish chased and bit the toy fish with three white stripes the most. In a second experiment, they found similar results when using real clownfish with different numbers of stripes.

Counting stripes would be helpful to clownfish because each species likes living in different sea anemones. A clownfish’s fiercest competition for a home happens with its own species. All the more need to count stripes and frighten off a fellow Nemo.