Clownfish count stripes to distinguish friend from foe

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Clownfish count stripes to distinguish friend from foe

Kathryn Knight
Online ISSN: 1477-9145
Print ISSN: 0022-0949

Nemo, the small animated fish, is an icon, snuggled up with his father in an anemone, and Pixar would have you believe that anemonefish life is generally peaceful and tranquil. But the myth belies reality. Anemonefish (also known as clownfish) are feisty little creatures, enthusiastically defending their anemone homes from intruders. And while it is sometimes fine to share with anemonefish of other species, it is never cool to cohabit with intruders of their own species: they always receive the frostiest reception. So how do anemonefish tell members of their own species apart from other stripy fish? According to Kina Hayashi from the Okinawa Institute of Science and Technology, Japan, anemonefish species that live in the same locations tend to have a wide range of stripy patterns – from three vertical white bars to none. Might anemonefish be able to count the number of white bands on other fish's bodies to distinguish friend from foe?

To find out, Hayashi, Noah Locke and Vincent Laudet (both from Okinawa Institute of Science and Technology) raised a school of young Nemos, the common clownfish (Amphiprion ocellaris), from eggs, to ensure that the fish had never set eyes on other species of anemonefish. Once the youngsters were ∼6 months old, Hayashi filmed their reactions to other anemonefish species – including Clarke's anemonefish (A. clarkii), orange skunk clownfish (A. sandaracinos) and saddleback clownfish (A. polymnus) – as well as intruders of their own species, to find out how they responded. Sure enough, the common clownfish gave members of their own species, with three white bands, the hardest time, facing off against 80% of the fish for up to 3 s and even maintaining an 11 s standoff with one fish. In contrast, the intruders of other species had an easier time: the orange skunk clownfish – with no side bars and a white line along its back – got off the lightest and were barely confronted, while the Clarke's clown fish and saddleback clownfish – with two and three white bars, respectively – were mildly bullied. ‘Common clownfish… attacked their own species most frequently’, says Hayashi. But how were the clownfish distinguishing between members of their own species and others?

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