Clownfish know how to count For your information

In the warm shallow waters of the Indian and Pacific Oceans, within enormous coral reefs, lives the famous, brilliantly colored clownfish, made famous all over the world thanks to the animated film. Nemo. These fish, of which twenty-eight different species are known, form small colonies and form very strong and complex symbiotic bonds with the anemones that serve as their habitat. The latter protects its hosts from potential enemies thanks to its stinging tentacles, to which clownfish are immune. In return, the latter protects the anemone from potential predators through its territorial behavior. Clownfish have three types of pigment cells that give them their intense orange color but they also have very conspicuous large vertical white bands. Each type has one, two, three, or none at all, which distinguishes it from other types. one of them, Amphiprion ocellarisIt has three vertical ranges and forms small colonies where relationships between individuals are highly hierarchical. So when an individual of the same species gets a little too close to the dominant female, she harasses him relentlessly. Then the question arises: How was the clownfish able to determine whether an individual belonged to its own species or to another species? A team from the Okinawa Institute of Science and Technology, led by Vincent Loudet, studied the question and obtained an absolutely surprising result.

Within the colony, the female dominates, then comes the male, which is a little smaller, and then the juveniles, which are smaller. When the eggs hatch, the fry are taken into the ocean before returning about ten days later. They must then be accepted into the anemone. “Once a young recruit enters the anemone, he never comes out again,” says Vincent Loudet. Therefore, fish from neighboring anemones are unlikely to ever encounter an external congener. In Anemone the question of recognition is raised. In fact, it often happens that two species of clownfish share an anemone, and in this case it is very important that the fish know how to recognize their own species. »

Specialists already suspect that these animals were able to estimate the number of bandanas worn by intruders. But to make sure, the team conducted a series of experiments on 120 individuals of this species Amphiprion ocellaris. First, they place an individual in the aquarium by introducing a clownfish of the same or another species. Second, they released three similar individuals into the aquarium, forming a small colony, by presenting them with a small orange plastic phone with a variable number of vertical white lines that mimicked clownfish of different species. By comparing the relationship between the number of bands and the intensity of clownfish aggression, the researchers realized that the more bands a fish presented or moved, the more it attacked.

This result proves that clownfish are able to evaluate the number of bands on each fish to determine which species it belongs to. “This is an essential ability,” emphasizes Vincent Loudet, “because the social status of the clownfish, and especially its ability to reproduce, depends on its ability to place itself within its hierarchy.”

With global warming and ocean acidification, corals and anemones are bleaching and then dying. Clownfish habitats are set to disappear, putting the species at risk with a social organization that relies too much on its environment.

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