In a series of experiments conducted in Japan, mirror-naïve bluestreak cleaner wrasses (Labroides dimidiatus) frequently attacked photographs of both themselves and strangers; in contrast, after passing the so-called mirror test, aggression against their own photograph and composite photographs of own face/stranger body declined, but aggression remained toward unfamiliar and composite photographs of stranger face/own body; the results suggest that bluestreak cleaner wrasses with mirror self-recognition ability can recognize their own mirror image based on a mental image of their own face, rather than by comparing body movements in the mirror.
Kohda et al. show that bluestreak cleaner wrasses (Labroides dimidiatus) recognize their own mirror image using a mental image of the self-face comparable to humans. Image credit: Masanori Kohda, Osaka Metropolitan University.
“Humans have a mental image of their own face and recognize their mirror reflection via self-face recognition,” said Osaka University researcher Masanori Kohda and colleagues.
“Mental images constitute mental states, which comprise a diverse class including beliefs, emotions, desires and intentions, with the latter linked to a private self-awareness.”
“Demonstrating that nonhuman animals have private self-awareness would require evidence of connected and interacting mental states.”
“Like humans, some animals are capable of mirror self-recognition, implying that they may be aware of the self. However, the mechanisms underlying mirror self-recognition remain unknown and mental images of the self and private self-awareness in nonhuman animals remain controversial topics.”
“The species capable of mirror self-recognition is growing and becoming more diverse, including great apes, Asian elephants, dolphins, horses, magpies, and bluestreak cleaner wrasses.”
In their study, Professor Kohda and co-authors tested the hypothesis that mirror self-recognition ability in bluestreak cleaner wrasses, also known as cleaner fish, is associated with a mental image of the self, in particular the self-face, like in humans.
“Each 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 fish’s body; and a photo of unfamiliar fish’s face on their own body,” they explained.
“Interestingly, the fish did not attack photos with their own faces but did attack those with the faces of unfamiliar fish.”
“Our results indicate that bluestreak cleaner wrasses determined who was in the photograph based on the face in the photo but not the body in the similar way humans do.”
To negate the possibility that the fish considered photographs of themselves as very close companions, the authors conducted a photograph mark-test.
“Fish were presented with a photograph where a parasite-like mark was placed on their throat,” they said.
“Six of the eight individuals that saw the photograph of themselves with a parasite mark were observed to rub their throats to clean it off.”
“While showing those same fish pictures of themselves without parasite marks or of a familiar fish with parasite marks did not cause them to rub their throats.”
“Our study is the first to demonstrate that fish have an internal sense of self,” Professor Kohda said.
“Since the target animal is a fish, this finding suggests that nearly all social vertebrates also have this higher sense of self.”
The findings were publihsed in a paper in the Proceedings of the National Academy of Sciences.
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Masanori Kohda et al. 2023. Cleaner fish recognize self in a mirror via self-face recognition like humans. PNAS 120 (7): e2208420120; doi: 10.1073/pnas.2208420120
