Cleaner fish recognize themselves in photos – knowledge

Cleaner fish are something like the hairdressers of the sea. Other fish come into their underwater salons as customers to have parasites eaten from their bodies and mouths. As a reward for this service, the cleaner bites off a piece of his customers from time to time.

So that the customers keep coming back despite the painful bites, cleaner fish proceed tactically. At the next appointment, she treats clients who have particularly mistreated her to a small massage, during which they ride on the clients’ backs. Predatory fish are generally not bitten, because if they should ever bite back, then that was it with the hairdresser. Cleaner fish seem to know that. Even when other fish are watching at work, cleaners hold back and bite less often or not at all. It’s like they don’t want to damage their reputation.

The fish, which are only about ten centimeters in size, can therefore distinguish between their customers and even seem to understand the situation they are in and the relationship they have with them. So it’s hardly surprising that cleaner fish can also recognize themselves in a mirror – and even in photoslike a team led by Masanori Kohda from Osaka Metropolitan University in the journal PNAS describes.

After looking in the mirror, the fish tried to scratch off a parasite

In a first experiment, the biologists working with Kohda attached a brown plastic bump to the neck of cleaner fish in the laboratory, which resembled a parasite. Then they observed the behavior of the animals in an aquarium that had a large mirror on one wall. After seeing themselves in the mirror with the bump, all the animals began rubbing their neck somewhere to get rid of the supposed parasite. “Our results clearly show that cleaner fish recognize themselves in the mirror,” write the study’s authors.

What does that mean? Some behaviorists believe that animals that recognize themselves in a mirror, like humans, perceive themselves as individuals and have an awareness of who they are. In addition to cleaner fish, apes, elephants, dolphins, horses and magpies have also passed the mirror test.

But does that really prove that all these animals have “self-awareness” like humans? People recognize themselves in the mirror because they have an idea of ​​what they look like and compare that mental image to the image they see in the mirror. Is it similar with cleaner fish? Or is there another mechanism behind it, for which self-awareness is not necessary? For example, it would be possible for the fish to match their movements with those of the mirror image.

To find out, the scientists showed their test animals static photos instead of a mirror. In contrast to a mirror image, a comparison of the movements is of course not possible in this case. Each cleaner fish was presented with four different photos, which the researchers held to one side of the tank from the outside: a photo of themselves, one of another cleaner fish, an edited image of a stranger’s cleaner fish with their own face, and one of them edited image with the face of a strange cleaner fish on its own body.

The result was clear: the fish attacked all photos in which a foreign fish face could be seen, regardless of whether it was sitting on their own body or on someone else’s. They obviously saw them as conspecifics who wanted to invade their territory and compete with them for customers. On the other hand, she left photos with her own face alone.

According to the researchers, this means that cleaner fish recognize themselves in these photos – by their faces. This is different from people who also recognize their bodies in pictures and in the mirror. But in order to conclude that the photograph is of themselves, animals, like humans, must have some sort of mental image of what their face looks like, which they then compare to the photograph. According to the researchers, there is no other way to identify yourself in a photo.

What unexpected abilities do these little fish have? Having a mental image of yourself is a gigantic developmental step. Among other things, it is considered a prerequisite for emotions, desires and intentions and as a sign that the small fish – similar to a human being – is probably aware of who it is.

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