In the standard mark test, an animal is marked where it cannot see the mark directly and then given a mirror. Touching or trying to remove the mark is scored as evidence that the animal recognises the reflection as itself. It had been passed by great apes, elephants, magpies and dolphins before a 2019 study reported cleaner wrasse doing the same.
The wrasse first attacked the reflection, then performed unusual movements in front of it, then began scraping its throat on the substrate when a coloured mark was present and visible only in the mirror. A larger follow-up from the same laboratory found the response in seventeen of eighteen fish; a replication by an unconnected group has not been published.
The interpretation is contested. Critics argue that a cleaner wrasse inspects marks on bodies for a living, so a brown mark resembling a parasite may trigger scraping without any self-concept, and that mark-directed behaviour may test something narrower than the phrase self-awareness suggests. The findings have prompted a broader argument about whether the mirror test measures what it is assumed to measure.