Researchers in Scientific Reports are claiming the first non-human instance of an animal possessing some mental states (e.g., mental body image, standards, intentions, goals), which are elements of private self-awareness.

They show that Labroides dimidiatus (bluestreak cleaner wrasse) checked their body size in a mirror before choosing whether to attack fish that were slightly larger or smaller than themselves. 

The authors say the cleaner wrasse’s behavior of going to look in the mirror installed in a tank when necessary indicated the possibility that the fish were using the mirror to check their own body size against that of other fish and predict the outcome of fights.


Labroides dimidiatus (bluestreak cleaner wrasse) on the right, with its mirror image on the left. Credit: Osaka Metropolitan University

“The results that fish can use the mirror as a tool can help clarify the similarities between human and non-human animal self-awareness and provide important clues to elucidate how self-awareness has evolved,” says doctoral candidate Taiga Kobayashi of Osaka Metropolitan University. Last year, the group, including Specially Appointed Professor Masanori Kohda, Professor Satoshi Awata, and Specially Appointed Researcher Shumpei Sogawa, and Professor Redouan Bshary of Switzerland’s University of Neuchâtel, claimed that cleaner wrasse could identify photographs of itself based on its face through mirror self-recognition.