Cleaner wrasse are small reef fish that clean parasites from larger marine animals. New research shows that these fish exhibit unexpectedly complex behavior when they see their own reflection in a mirror, a trait often associated with advanced cognition.
A recent study from Osaka Metropolitan University, published in Scientific Reports, found that cleaner wrasse (Labroides dimidiatus) used mirrors to inspect marks placed on their bodies. The fish also engaged in contingency testing, a form of exploratory behavior typically observed in mammals such as dolphins.
A Rapid Response
Scientists often use the mirror test to assess whether animals recognize their own reflection. Traditionally, researchers first allow animals to become accustomed to a mirror before placing a visible mark on their body. If the animal uses the mirror to check or try to remove the mark, scientists see this as a sign of self-recognition.
In this experiment, the researchers changed the usual order. They first placed a mark resembling a parasite on the fish and then introduced the mirror.
Wrasse that had never encountered a mirror before quickly used it to try to remove the mark. On average, the fish began responding to the mark within 82 minutes, a much faster reaction than the four to six days reported in previous studies. This rapid response suggests that the fish were able to combine internal bodily cues with visual information from the mirror.
“In this study, the order was reversed,” said lead researcher Shumpei Sogawa. “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.”
Testing Other Objects
After several days with the mirror, researchers noticed another behavior in some of the fish. The wrasse picked up small pieces of shrimp from the tank floor, carried them to the mirror, and released them while watching the reflection.
As the shrimp pieces fell, the fish followed their movement in the mirror, repeatedly touching the glass as they watched the reflected motion.
Researchers interpreted this as contingency testing, a behavior where an animal evaluates how objects behave in a mirrored space. Rather than just reacting to their own reflection, the fish seemed to be testing how the mirror represented other objects. Similar exploratory behaviors have been documented in manta rays and dolphins, which release bubbles and observe their reflections.
Interpreting Self-Recognition
These findings support the idea that cleaner wrasse demonstrate flexible behaviors when interacting with mirrors, going beyond simple confusion or learned responses.
Even with these results, the mirror test is still debated in animal cognition research. Some scientists say passing the test does not always demonstrate human-like self-awareness, but does show an ability to combine sensory information in complex ways. The authors suggest that mirror-based self-recognition might be more common in different species than once believed.
“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,” Sogawa said.
The study shows that even small reef fish can use mirrors in ways that go beyond simple reflexes. This challenges old ideas about fish intelligence and adds to evidence that advanced cognitive ability is not limited to mammals and birds. If more species show these behaviors, scientists may need to rethink how animal intelligence is measured and understood.
Austin Burgess is a writer and researcher with a background in sales, marketing, and data analytics. He holds a Master of Business Administration, a Bachelor of Science in Business Administration, and a Data Analytics certification. His work combines analytical training with a focus on emerging science, aerospace, and astronomical research.