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A small reef fish may be doing something scientists once thought was limited to mammals like dolphins and great apes. In a new study, researchers report that cleaner wrasse — tiny tropical fish known for removing parasites from larger fish — not only respond to their reflections in mirrors, but appear to experiment with them.
When given access to a mirror, some fish dropped bits of food in front of it and closely tracked how the object moved in the reflection, a behavior researchers interpret as a sophisticated form of testing how the mirror works. The findings, published in Scientific Reports, add to growing evidence that these fish can recognize and respond to their own reflections in ways that go beyond simple reactions. “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,” said study author Shumpei Sogawa in a press release. Self-Recognition in Animals The mirror test is a classic experiment used to probe animal cognition. In its standard form, researchers place a visible mark on an animal’s body in a spot it can only see with a mirror. If the animal uses the mirror to inspect or try to remove the mark, scientists interpret that as evidence that it recognizes the reflection as itself. Cleaner wrasses have already attracted attention in past mirror experiments. But in this study, researchers changed the order of events. Instead of allowing the fish to become familiar with the mirror first, the team applied parasite-like marks to the wrasse before introducing the mirror. Even the fish that had never encountered a mirror before quickly used it to locate and scrape off the mark. In some cases, scraping behavior began within the first hour of mirror exposure — far faster than in earlier experiments where fish had days to adjust to the mirror before being marked. The researchers suggest the fish may have already sensed something unusual on their bodies. When the mirror appeared, it provided visual confirmation, triggering an immediate response. Read More: Like Kindergarten Buddies, Male Dolphins That Keep Friendships Can Live Longer Dropping Shrimp to Test the Reflection The most unexpected behavior came days later. Researchers observed some cleaner wrasse picking up small pieces of shrimp from the tank floor and carrying them toward the mirror. The fish would release the shrimp and follow its descent along the mirror’s surface, repeatedly touching the glass while watching the reflected movement. Rather than responding to their own bodies, the fish appeared to be testing how an external object behaved in reflected space. Researchers describe this as “contingency testing” — a process in which an animal checks whether movements in the mirror correspond to movements in the real world. Similar behaviors have been reported in dolphins that release air bubbles and watch how they move in reflection. Rethinking Fish Intelligence The idea that fish might engage in mirror-based exploration challenges long-held assumptions about the limits of animal cognition. Cleaner wrasses are highly social and rely on complex interactions with other fish while cleaning parasites. That social intelligence may extend into how they process information about themselves. The researchers caution that passing the mirror test does not automatically prove full self-awareness. But the wrasse’s object-based mirror experiments suggest flexible, context-dependent processing rather than simple conditioning. If similar behaviors are confirmed in other species, it could reshape how scientists think about the evolution of self-recognition. Read More: Fish Pee Like Us to Regulate Their Bodily Fluids – They Also Poop and Fart Article Sources Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article: This article references information from a recent study published in Scientific Reports: Rapid self-recognition ability in the cleaner fish
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