Mirror, Mirror on the Wall, Who's the Smartest Fish of All?

If you gave a fish a mirror, would it be able to recognize itself? A new study says yes.

Animal sociologist Masanori Kohda of Osaka Metropolitan University in Japan previously had experimented with the mirror test on bluestreak cleaner wrasses. Bluestreak cleaner wrasses are one of the cleaner wrasses located on coral reefs from Eastern Africa and the Red Sea to French Polynesia. The mirror test revealed self awareness through allowing the fish to examine itself in the mirror and then placing a mark on the body to see if the fish would notice.

In a new study, the same fish were able to distinguish their own faces from those of cleaner fish in photographs. This suggested that fish form a mental image in their head, just as humans do.

In the study, ten fish that passed the mirror test were shown a photo of their own face and a photo of a different fish with a cleaner face. Upon seeing the unfamiliar photo the fish became aggressive, but remained non-aggressive at the photo of their own face.

When another eight fish that had spent a week with a mirror but had not previously been marked were shown a photo of their own face with a brown mark on the throat. Six of them began scraping their throats just like the fish that passed the mirror test. However, they did not scrape when shown a photo of another fish with a mark.

Researchers believe the fish learn the skill of identifying themselves by seeing movement in the mirror that matches their own movement. The lab plans to continue testing the cleaner fish and plans to try the photo-recognition method on the three-spined stickleback fish as well.

To read the full study, click here: https://www.pnas.org/doi/full/10.1073/pnas.2208420120