Dr.John B’s Newsletter

Few animals are able to recognize themselves in the mirror, but this does not necessarily make them more intelligent. Find out why.

In 2018, a study was published indicating that, for the first time, a fish had passed the mirror test, an experiment in which it recognized itself in a reflected image. It was a cleaner wrasse (Labroides dimidiatus), a fish between 10 and 14 cm in length that lives in reefs and feeds on parasites and dead tissues on the skin of other marine animals. However, it wasn't truly the first instance, as some manta rays had also passed the test in 2016.

The significance of the news was that this tiny fish had passed a test that numerous animals considered more intelligent have failed, such as dogs, cats, several species of apes, and birds considered among the smartest, like parrots and crows. The ability to recognize oneself in the mirror is not necessarily relevant when assessing the intelligence of a species.

The mirror test was designed by psychologist Gordon Gallup in 1970 to determine whether an animal can recognize itself in its reflection. It involves putting the animal to sleep and marking a part of its body that it cannot normally see, such as the face, with an odorless dye or gel. Next, a mirror is placed in front of the animal. If, upon seeing the mark, the animal repeatedly examines it on its own body—not on the reflection—it is interpreted as a sign of self-recognition, indicating that the animal realizes the individual in the reflection is itself and that there is something unusual on its body.

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