'It's me!' Fish recognizes itself in photographs, say scientists

In this study, relevant experiments were conducted with Labroides dimidiatus, commonly known as a cleaner fish, which are known to be able to recognize themselves in mirrors and regularly attack other unfamiliar cleaner fish who intrude on their territory. 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. Interestingly, the cleaner fish did not attack photos with their own faces but did attack those with the faces of unfamiliar cleaner fish. Together these results indicate that the cleaner fish 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, a photograph mark-test was conducted. Fish were presented with a photograph where a parasite-like mark was placed on their throat. 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 cleaner fish with parasite marks did not cause them to rub their throats.

"This study is the first to demonstrate that fish have an internal sense of self. Since the target animal is a fish, this finding suggests that nearly all social vertebrates also have this higher sense of self," stated Professor Kohda.