Scientists at Osaka Metropolitan University have observed cleaner wrasse using mirrors to inspect and remove artificial parasite marks, demonstrating rapid self-recognition. Some fish even performed contingency testing by dropping shrimp near mirrors to study reflections. These behaviors suggest self-awareness in fish may be more common than previously thought.
Researchers led by Shumpei Sogawa and Masanori Kohda at Osaka Metropolitan University in Japan conducted mirror tests on cleaner wrasse, small reef fish known as Labroides dimidiatus. In prior studies, these fish recognized themselves in photographs. The new experiments involved marking the fish with spots mimicking parasites before introducing mirrors for the first time.
The wrasse quickly used the mirrors to locate and attempt to remove the marks. On average, scraping behavior began after 82 minutes, much faster than the 4 to 6 days reported in earlier tests where mirrors were shown first followed by marking. "In this study, the order was reversed, the fish were marked first, then the mirror was introduced for the first time," Dr. Sogawa explained. "The fish were likely aware of something unusual on their body, but they couldn't see it. When the mirror appeared, it immediately provided visual information that matched an existing bodily expectation, hence scraping occurred much faster."
After several days with the mirror, some wrasse engaged in further exploration. They picked up shrimp from the tank floor, released it near the mirror, and observed its movement in the reflection while touching the glass. This 'contingency testing' allowed the fish to compare the shrimp's real path with its mirrored image, similar to behaviors seen in dolphins and manta rays.
The findings indicate that cleaner wrasse perform flexible, self-related processing. "These findings in cleaner wrasse suggest that self-awareness may not have evolved only in the limited number of species that passed the mirror test but may be more widely prevalent across a broader range of taxonomic groups, including fish," Dr. Sogawa stated. Professor Kohda added that such research could influence evolutionary theory, animal welfare, medical studies, and AI development. The study appeared in Scientific Reports in 2025.