Which small reef fish was reported in 2019 to pass a mirror mark test?

Which small reef fish was reported in 2019 to pass a mirror mark test? The cleaner wrasse, specifically the bluestreak cleaner wrasse, Labroides dimidiatus. In the study, fish were exposed to mirrors and later given a colored mark resembling a parasite on a part of the body they could not normally inspect directly.

The wrasses scraped their bodies against surfaces while viewing the mirror, and they did so more often when the mark was colored and parasite-like. They also checked their reflections before and after scraping. The researchers interpreted this sequence as evidence that the fish recognized the reflected body as its own and used the mirror to locate the mark.

The result remains debated. Gordon Gallup, who developed the mirror test, argued that cleaner wrasses might simply respond to a perceived parasite on another fish rather than demonstrate self-recognition. Follow-up work in 2022 reported additional support, but the episode illustrates why “passed the mark test” is not identical to proving human-like self-awareness.