Study suggests that fish can recognise themselves in mirror

Labroides dimidiatus
Labroides dimidiatus – the species of cleaner fish used for the study. Credit: Karelj, Wikimedia Commons

It is a well-known fact that not all animals have the ability to instantly recognize themselves in the mirror! However, a few animals can recognize themselves, such as the great apes, dolphins, Asian elephants, Eurasian magpies, and of course humans! A species of fish with the ability to recognize itself in the mirror is commonly known as the cleaner fish.


Cleaner fish are found in the Indian Ocean and the Pacific Ocean near coral reefs. These fish exist as “cleaning stations” for other fish (known as hosts). Cleaner fish are fish which “clean” the dead skin and parasites from other fish. This interaction is of benefit for cleaner fish, which get a meal, as well as for the other fish species, which are freed from parasites. Such a type of interaction is known as mutualism. Remarkably, cleaner fish also manage to clean large predatory fish which might prey on them.


Recently, a group of scientists in Japan found that cleaner fish might have the ability to identify themselves in photographs! It was already known that cleaner fish could recognize themselves in mirrors and would attack unknown cleaner fish. So, the team wanted to test whether the same was seen in the case of photos as well!


To test their theory, the team of scientists showed four types of photos to the cleaner fish. Two types of pictures included a photo of themselves and a photo of an unknown cleaner fish. The third type of picture was a photo of an unknown cleaner fish with the fish’s own face edited onto it. The fourth type of photo included its own body but with the face of an unknown cleaner fish.


They found that cleaner fish attacked only those photographs which did not have their own faces. This result was similar to the ability of humans to recognize each other based on their faces and not by their bodies. Through this study, scientists could determine that all fish have a sense of self. Rather, this sense of self exists in all social animals which have a backbone or are evolutionarily advanced in comparison to fish.


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