Cleaner wrasses check their body size in mirror before deciding whether to fight, study finds

A team led by Osaka Metropolitan University has demonstrated that bluebanded cleaner wrasses (Labroides dimidiatus) check their body size in a mirror before choosing to attack fish that are slightly larger or smaller than themselves.

The study, published in Scientific reportssuggests that Bluestreak cleaner wrasses possess certain mental states (e.g., mental body image, norms, intentions, goals), which are elements of private self-consciousness.

The team, consisting of Taiga Kobayashi, a student at OMU’s Graduate School of Science, Specially Appointed Professor Masanori Kohda, Professor Satoshi Awata, and Specially Appointed Researcher Shumpei Sogawa, as well as Professor Redouan Bshary of the University of Neuchâtel in Switzerland, was part of the group that reported last year that the cleaner wrasse could identify photographs of itself as itself, based on its face through automatic mirror recognition.

This time, the cleaner wrasse’s behavior of looking at itself in a mirror installed in an aquarium when necessary indicated the possibility that the fish was using the mirror to compare its own body size to that of other fish and predict the outcome of fights.

“The results showing that fish can use the mirror as a tool may help clarify the similarities between the self-awareness of humans and non-human animals and provide important clues to elucidate how self-awareness evolved,” said doctoral student Kobayashi.