A Fish Just Passed a Test of Self-awareness by Recognizing Itself in a Mirror

Labroides dimidiatus
A cleaner wrasse fish. Karelj/CC

A little fish just passed a classic scientific test of self-awareness by recognizing itself in a mirror, scientists have announced. The cleaner wrasse fish, which measures around 10cm in length, was recorded attempting to remove a mark that had been placed on its forehead while looking in a mirror—seemingly realizing it was looking at a reflection of itself and understanding something was wrong. While the study has not yet been published, it could have implications for our understanding of cognition in other animals.

The mirror self-recognition test is a hallmark of animal intelligence. As of yet, only a relatively small group of animals have passed it. These include apes, elephants, dolphins and crows. However, Masanori Kohda, from Osaka City University in Japan, and colleagues are considering whether the test itself is flawed and that other animals we traditionally think of as having limited cognitive abilities are actually far more intelligent than we think.

To find out if fish could pass the test, they constructed an experiment where cleaner wrasses were placed in view of a mirror. Initially, they reacted territorially, as if their reflection were another fish. However, over the course of several days, their behavior began to change. Instead of warning off their reflection, they began to act differently, approaching it at different angles or from upside-down. These unusual responses continued up until around day 10 when they stopped reacting.

Next, the scientists attached a colored tag to the fish and they found the fish attempting to remove it—but only in the presence of the mirror.

The researchers say this means the cleaner wrasse has passed the mirror self-recognition test—and that "this remarkable finding presents a challenge to our interpretation of the mark test." It means, they say, that either fish are self-aware, that the test is flawed or that the fish behavior has emerged as a result of a cognitive process that is not self-recognition.

The research has not been peer-reviewed yet, so has not been scrutinized by other scientists. "The results we present here will by their nature lead to controversy and dispute, and we welcome this discussion," the researchers wrote.

"Cleaner wrasses show behavioral responses that fulfill the criteria of the mark test, but as this result does not mean they are self-aware, a question naturally arises. Can passing the mark test be taken as evidence of self-awareness in one taxon but not another?

"Based on our findings, we therefore advocate for a reappraisal of the interpretation of the mark test, and conclude that many more species may be able to pass the test when it is applied in a manner that is sympathetic to their natural biology."