The mathematical abilities and intelligence of the anemonefish can be greatly underestimated
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When the Pixar cartoon film, Finding Nemo, came out in 2003, was a sensation, and suggested to viewers that its colorful stars were kind and peaceful beings. Except they’re not: they’re actually energetic little fish who vigorously compete for and zealously defend their anemone homes from others of their own kind. Which raises the question: how do anemonefish distinguish members of their own species from other striped fish living in the neighborhood?
Kina Hayashi, a Research Fellow at the Okinawa Institute of Science and Technology, noticed that anemonefish species that live in the same locations tend to have different stripe patterns – from three vertical white bars to nothing. Can these fish really do it? counting the number of white bands on other fish to identify and distinguish friend from foe?
To find out, Dr Hayashi and collaborators raised a school of 120 common clownfish, Amphiprion ocellaris, from eggs and in isolation from all other clownfish species. When the juveniles reached about six months of age, Dr Hayashi and collaborators exposed them to other species of clownfish with distinctive stripe patterns that differed from their own, including Clarke’s anemonefish, A. clarkiiorange skunk clownfish, A. Sandaracinoand saddleback clownfish, A. polymnus (all photos in this piece) — as well as individuals of their own species, and filmed their reactions.
Dr Hayashi and collaborators quickly discovered that their cute little Nemos were aggressive little monsters: they tackled 80% of the other three-striped common clownfish in about 3 seconds, with a showdown that lasts 11 seconds.
“The common clownfish… are the most likely to attack their own species,” Dr Hayashi said.
In contrast, other anemonefishes face less territorial aggression: the orange skunk clownfish, with a white stripe on the top of their body, is (mostly) left alone, while the Clarke’s clownfish, with three white bar, and saddleback clownfish, with two. white patches, are weakly bullied.
To find out whether the number of stripes rather than their specific shapes or placements triggered the tiny Nemos’s territorial aggression, Dr Hayashi and collaborators made orange-shaped model fish with one, two or three bars, presented them in groups consisting of three young anemonefish in individual tanks and filmed their reactions.
As predicted by Dr Hayashi and collaborators, the young anemonefish showed little interest in the plain orange model and only occasionally courted the model with a white bar. The two-barred model, however, received more bullying. Plus, anemonefish have repeatedly shown that they actually do no such as sharing their space in the three-barred model.
But since the common anemonefish has three stripes, why are they bullying the two-bar model? Bad math skills? Bad eyesight? childhood trauma? Maybe not. Dr Hayashi suggested that the clownfish’s aggression in the two-bar model fish may be related to their development: the typical clownfish initially has two white bars around 11 days before acquiring a third bar three days later . So they may think of two-barred fish as younger interlopers driven from their home by the anemone, whereas fish with fewer (or no) bars are obviously different species and therefore, are unlikely to steal their anemone host.
“We concluded that A. ocellaris use the number of white bars as a cue to recognize and attack only competitors that can use the same host,” concluded Dr Hayashi and collaborators. “We consider this an important behavior for efficient defense of hosts.”
This study, which adds detail to previous work (below), has several limitations. For example, young Nemos have only seen members of their own species, so it is difficult to know whether their aggressive behavior is innate or learned because of their childhood. But it is useful to point out that previous studies have found that anemonefishes use their marks to distinguish each other as individuals as well as other species.
“Amphiprion ocellaris therefore fish with bar patterns can be recognized as competitors and often attack and repel them to defend their host anemone,” explained Dr Hayashi and collaborators in their study. “The previous study indicates that white bars may be an important color pattern for identifying competitors for territory in anemonefish.”
Source:
Kina Hayashi, Noah JM Locke and Vincent Laudet (2024). Counting Nemo: anemonefish Amphiprion ocellaris identify the species by the number of white bars, Journal of Experimental Biology 227(2):jeb246357 | doi:10.1242/jeb.246357
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