Like Dolphins, This Tiny Reef Fish Sees and May Be Experimenting With Its Reflection
A small reef fish may be doing something that scientists once thought was reserved for mammals like dolphins and great apes. In a new study, researchers report that cleaner wrasses – tiny tropical fish known to remove parasites from larger fish – not only respond to their reflections in mirrors, but also appear to experience them. When given access to a mirror, some fish dropped pieces of food in front of it and closely followed the movement of the object in the reflection, a behavior that the researchers interpret as a sophisticated form of testing how well the mirror was working.
The results, published in Scientific reportsadds to growing evidence that these fish can recognize and respond to their own thoughts in ways that go beyond simple reactions.
“These findings in cleaner wrasses 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 distributed across a wider range of taxonomic groups, including fishes,” study author Shumpei Sogawa said 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 location it can only see with a mirror. If the animal uses the mirror to inspect or attempt to remove the mark, scientists interpret this as evidence that it recognizes the reflection as itself.
The cleaner wrasses have already attracted attention in past mirror experiments. But in this study, the researchers changed the order of events.
Instead of allowing the fish to become familiar with the mirror first, the team applied parasite-like markings to the wrasse before introducing the mirror. Even fish that had never encountered a mirror before quickly used it to locate and scratch the mark.
In some cases, scratching behavior began within the first hour of exposure to the mirror – much more quickly than in previous experiments where fish had several days to adapt to the mirror before being marked.
Researchers suggest that the fish may have already felt something unusual on their bodies. When the mirror appeared, it provided visual confirmation, triggering an immediate response.
Learn more: Like kindergarten friends, male dolphins who maintain friendships can live longer
Drop shrimp to test thinking
The most unexpected behavior came a few days later. The researchers observed cleaner wrasses picking up small pieces of shrimp from the bottom of the tank and carrying them to the mirror. The fish would release the shrimp and follow its descent along the mirror surface, touching the glass repeatedly while observing the reflected movement.
Rather than reacting to their own bodies, the fish appeared to be testing the behavior of an external object in the reflected space.
The researchers describe this as a “contingency test,” a process by which an animal checks whether movements in the mirror match movements in the real world. Similar behaviors have been reported in dolphins that release air bubbles and observe their movement by 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 very social and rely on complex interactions with other fish while cleaning parasites. This social intelligence can extend to how they process information about themselves.
Researchers caution that passing the mirror test does not automatically prove full self-awareness. But mirror experiments based on wrasse objects 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.
Learn more: Fish pee like us to regulate their bodily fluids – they also poop and fart
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