A research group led by Masanori Kohda, a Specially Appointed Professor at the Graduate School of Science, Osaka Metropolitan University, has announced that they have demonstrated for the first time in the world that fish can self‐recognize themselves in a photograph. The experiments have also shown that the fish recognize their face. The researchers demonstrated that fish have an internal sense of self and anticipate their work to advance the study of animal cognition. The results were published in PNAS, Proceedings of the National Academy of Sciences.
Humans recognize themselves in the mirror and at the same time can recognize themselves in facial photographs, which is thought to be because humans have a mental picture of their own face. Apart from humans, it has been confirmed that chimpanzees and other primates, elephants, dolphins and corvids can recognize their reflection in a mirror as themselves (mirror self‐recognition).
The research group has recently demonstrated that this mirror self‐recognition is also present in cleaner fish. They also revealed in 2015 that the African freshwater pulcher, which live in families, recognize their companions by their facial patterns.
In the present study, the research group conducted experiments with the cleaner fish to identify how animals recognize their mirror image as themselves. The presence of different pattern variations on the faces of the cleaner fish also varied from individual to individual, and it was possible that individuals were identified by these variations. They therefore conducted an experiment to verify whether the cleaner fish could recognize their faces as their own.
Each cleaner fish was presented with four photographs: a photo of themselves; a photo of an unfamiliar cleaner; a photo of their own face on an unfamiliar cleaner's body; and a photo of unfamiliar cleaner's face on their own body. Each photograph was presented for five minutes to 10 cleaner fish that were capable of mirror‐image self‐recognition.
In doing so, before mirror self‐recognition (before the mirror was presented), the fish attacked both their own full‐body photo and a full‐body photo of an unknown individual an average of about 20 times.
However, after mirror self‐recognition, they rarely attacked their own full‐body pictures and attacked the full‐body pictures of unknown individuals on average about 20 times. Furthermore, they rarely attacked composite photographs of their own face and the body of an unknown individual but attacked composite photographs of the unknown individual's face and their own body on average about 20 times.
At this stage, to negate the possibility that the fish considered photographs of themselves as very close companions, a photograph mark‐test was conducted with a full‐body photograph. The fish were presented with a photograph where a parasite‐like mark was placed on their throat. Cleaner fish have a habit of feeding on parasites on the bodies of other fish and are sensitive to the presence of parasites on their own bodies. It has also been observed that mirror‐image self‐aware cleaners will rub the marked area against the floor or other surface when presented with a marked photograph of themselves.
The results showed that when presented with a marked photograph of themselves, six out of eight individuals tried to rub their throats to remove the mark, whereas this behavior did not occur with an unmarked photograph of themselves or a marked photograph of a familiar individual. This proved that the cleaner fish accomplish self‐recognition based on their face.
It is likely that self‐recognition is similarly possible in fish species with well‐developed social skills. The researchers will continue to verify the existence of consciousness, which fish were previously thought not to have.
"I believe that, since the days of Descartes, we have been very mistaken about our sense of self," explained Kohda. "We believe this experiment shows that animals can also think and that they have a sense of self and a mind."
Journal Information
Publication: Proceedings of the National Academy of Sciences (PNAS)
Title: Cleaner fish recognize self in a mirror via self‐face recognition like humans
DOI: 10.1073/pnas.2208420120
This article has been translated by JST with permission from The Science News Ltd. (https://sci-news.co.jp/). Unauthorized reproduction of the article and photographs is prohibited.