2024-02-01 20:42:27
The little fish Nemo, protagonist of the animated film of the same name, and all the ‘colleagues’ of the clownfish family also have another gift, in addition to that of inspiring tenderness and thrilling the public with their underwater adventures. These are unexpected mathematical abilities. According to a team of researchers who have studied them in depth, “they know how to count” and by paying attention to the number of stripes of those who appear before them they are able to distinguish friends from enemies and intruders.
Nemo is an icon and has entered the imagination of the little ones, curled up with his dad in a sea anemone. With this initial idyllic scenario, Pixar could lead the viewer to believe that the life of the clownfish is peaceful and tranquil. But this myth is contradicted by reality. Clownfish (or anemonefish) are feisty little creatures, eagerly defending their anemone homes from intruders. And even if sometimes it’s okay to share them with some anemone fish of other species, they don’t find it nice to coexist with those they consider the ‘intruders’ par excellence, the fish of their own species. These always receive the coldest welcome. But scientists have wondered: How do clownfish distinguish members of their species from other striped fish? According to Kina Hayashi of the Japanese Okinawa Institute of Science and Technology and colleagues, specimens of Amphiprion ocellaris – this is the scientific name of the common clownfish – would be able to count the number of white bands on the bodies of other fish.
The scientists explain how they arrived at this conclusion in the ‘Journal of Experimental Biology’. To discover the mathematical talent of the little fish in question, Hayashi, Noah Locke and Vincent Laudet raised a school of young ‘Nemo’ fish from the eggs to ensure they never set their sights on other species of clownfish. Once the hatchlings were about 6 months old, Hayashi filmed their reactions to other clownfish species, including the Clark’s clownfish (A. clarkii), the orange skunk clownfish (A. sandaracinos), and the orange clownfish (A. sandaracinos). sella (A. polymnus), as well as intruders of their own species.
As expected, the common clownfish put members of its own species, with three white bands, in the most trouble by tackling them and maintaining a stalemate. By contrast, it went easier on intruders of other species: the orange skunk clownfish – without sidebars and with a white line along its back – was barely confronted, while Clark’s clownfish and clownfish saddle – with 2 and 3 white bars, respectively – were only slightly ‘bullied’.
In a second experiment the team then isolated small schools (of 3) of juvenile common clownfish in individual tanks and filmed the reactions to a plain orange fish model or to models painted with one, two or three white bands, keeping a count how often the fish chased or attacked the intruder. Clownfish paid little attention to the plain orange pattern, occasionally becoming interested in and chasing the single-stripe pattern, while sharply increasing pressure on the 3-stripe patterns. They didn’t like sharing space with three-barred strangers they looked alike.
And the two-line patterns also ended up in the crosshairs, probably, Hayashi hypothesizes, because during development common clownfish initially form only two white stripes, at about 11 days of age, and acquire the third only 3 days later. The suspicion is therefore that they can also see the fish with two white bars as competitors to be chased away. Consequently, however, all this also suggests that the Nemo people know how to discriminate based on the number of white stripes on the sides, they know how to count them, and this allows them to defend their home from intruders who might try to evict them, paying less attention to the fish of other species that have little interest in establishing themselves in their anemone residence.
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