Scientists at Osaka Metropolitan University in Japan have identified a new and unexpected behavior in cleaner wrasse (Labroides dimidiatus). When shown a mirror, these small reef fish did more than appear to recognize their reflections. They also began interacting with the mirror using a piece of food, suggesting a level of cognitive sophistication not typically associated with fish. The findings indicate that cleaner wrasse may be capable of “contingency testing,” a complex mental process most often observed in highly intelligent marine mammals such as dolphins.

The research team was led by Specially Appointed Researcher Shumpei Sogawa and Specially Appointed Professor Masanori Kohda at the Graduate School of Science. In earlier work, the group demonstrated that cleaner wrasse can identify themselves in photographs.

In the current study, the scientists observed new behaviors during a series of mirror test experiments, a widely used method for evaluating self-recognition and animal cognition. Previous research had already shown that cleaner wrasse respond to their reflections in ways consistent with self-recognition.