The little fish in the mirror – 02/11/2023 – Reinaldo José Lopes

There was a time when the ability to recognize yourself in a mirror conferred access to a kind of Olympus of animal intelligence. To pass this test, you had to have, at the very least, a relatively large brain; other desirable prerequisites for the vacancy were close evolutionary kinship with humans and, more subjectively, a certain amount of cuteness.

That’s how great apes like chimpanzees and gorillas became first on the list, followed after a few decades by dolphins. Then there were the elephants—OK, big brain, mammals, cute; all right, right? Then came the magpies, a bird related to crows (okay, crows as they are proverbially smart). And, of course, cleaner wrasses (labroides dimidiatus).

Wait, who?

We are talking about a fish about 10 cm long. Sympathetic figure, even, silver and bluish, with a dark stripe that cuts the side of the body from the mouth to the tail. Present in the Indian and Pacific Oceans, the animal’s specialty is to “skincare” fish much larger than itself, removing parasites and pieces of dead tissue from the skin and gills of its “clients”. Excellent deal for both parties: the fish gain a healthier complexion, the cleaner wrasses get a lunch without major headaches.

The mirror test that the little fish passed follows a model established since the first studies with chimpanzees. The animal is sedated and, using ink, the scientists draw an artificial mole on a clearly visible part of the animal’s body. Afterwards, they place a good-sized mirror in a strategic position in the enclosure (or, in this case, the aquarium). If the animal wakes up, looks in the mirror and starts to touch the false spot while examining itself, it is a sign that it knows, somehow, that the reflection on the other side “is him”.

Some researchers tend to put the proverbial ball down on these results. They propose that the reaction to touching the mole does not necessarily signify some kind of self-understanding—”that’s me”—but a simple kinesthetic visual coupling mechanism. Or, in English: the animal is only able to see movements in the mirror and “follow” them mentally.

A new and ingenious study, coordinated by Masanori Kohda, from the University of Osaka City, in Japan, found a way around this by replacing the mirror with photographs —which, as we know, are static, which circumvents the idea of ​​kinesthetic coupling .

In the research, which just appeared in the journal PNAS, Kohda and his colleagues first worked with fish that had already passed the mirror test. These wrasses did not attack photographs of themselves, but they still attacked pictures of strange fish. And, what is even more curious, fish that recognized their own photographs tried to “remove the mole” from the body when the photographs were marked with fake spots.

For the Japanese researchers, the most plausible explanation is that cleaner wrasses are indeed capable of developing a “self-image” in their heads. And they further propose that something like this could be much more common among fish and other vertebrates than we realize.

Therefore, we would not be talking about a select club of animal geniuses, but something that is perhaps a fundamental property of the cognition of many of the branches neighboring ours on the Tree of Life. There is no better mirror than this one.

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