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Nemo knows how to count... to protect his territory

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The ability of the clownfish (Amphiprion ocellaris) to count the number of bands helps inform the hierarchy social status of the colony from the threat that awaits it.

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Triple-striped clownfish (Amphiprion ocellaris) may be able to distinguish individuals of their species from other striped species by counting the bars verticals that they have on their sides, say Japanese biologists whose work is published in the Journal of Experimental Biology (New window) (in English).

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Clownfish have a symbiotic relationship with certain species of anemones.< /p>

In the wild, Amphiprion ocellarisis a benevolent host since it allows fish of several species to visit the sea anemones with which it lives in partnership.

There is, however, an exception : fish of its own species which are not part of its colony. The latter are not welcome since they represent a territorial threat that must absolutely be chased away.

This ability to count the number of bands helps inform the colony's social hierarchy of the threat that awaits it, note biologist Kina Hayashi and her colleagues at the Okinawa Institute of Science and Technology.

To understand how clownfish determine the species to which their visitors belong, the Japanese team conducted two experiments with 120 clownfish raised in laboratory.

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Laboratory-raised clownfish.

In the first, she placed different species of fish (bearing different numbers of white bars) in small enclosures inside an aquarium containing a colony of clownfish. They were thus able to observe how often and for how long the fish aggressively stared at the box and circled it.

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In a second experiment, the team presented a colony of clownfish with different plastic discs that had different numbers of stripes in order to measure their level of aggression compared to these models.

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Plastic models used to measure the aggressive behavior of clownfish.

Both experiments found that clownfish attack representatives of their own species much more frequently and aggressively than others.

The frequency and duration of aggressive behavior by clownfish is highest toward fish with three bars like them, while it is lowest with fish with one or two bars, and lowest toward those that have did not have vertical bars.

A quote from Kina Hayashi, Okinawa Institute of Science and Technology

So , according to the researcher, these observations show beyond any doubt that these fish are capable of counting the number of bars on the sides of other fish to establish whether they belong to their species. There are 28 species of clownfish that have between zero and three white bands.

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Clownfish. (Amphiprion Ocellaris)

Amphiprion ocellaris lives in a symbiotic relationship with the sea anemone (Heteractis magnifica) which has tiny tentacles releasing toxic compounds which allow it to immobilize its prey (small invertebrates, fish). However, the clownfish is born with an armor of mucus which, as an adult, is several times thicker than that of other fish, which allows it to live peacefully in colonies among anemones.

A. ocellarisis interesting to study because of their unique symbiotic relationship with sea anemones. Our work, however, shows that we don't know a lot about life in marine ecosystems in general, says Kina Hayashi.

If the clownfish can surprise us with its ability to count bars and maintain strict social hierarchies, one wonders how many remarkable animals and behaviors have yet to be discovered in fragile coral reefs, threatened ecosystems. .

A quote from Kina Hayashi, Okinawa Institute of Science and Technology

Additionally, this work observed a strict hierarchy in clownfish colonies that determines which fish attack the intruder.

In the wild, a colony usually consists of an alpha female, a male, and several juveniles. Social position within the colony is determined by very slight differences in size. Clownfish are not born with three stripes, they get their third and final one when they reach a sufficient size.

This is why the existing alpha uses harsh methods to maintain the status quo, including chasing away members of the colony if they become too big, the researchers explain.

The longest Amphiprion ocellaris reach 11 cm. It is estimated that in the wild, these fish, which inhabit the warm waters of the Indian and Pacific Oceans, from Japan to northern Australia, can live between 6 and 10 years.

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