Bold claim: a tiny fish may possess self-awareness, not just instinct. And this is the part most people miss: the test setup and what it reveals about animal intelligence are more nuanced than they seem. Here’s a clearer, expanded rewrite that preserves the core facts while making them accessible to newcomers.
A minuscule fish has demonstrated a surprisingly high level of intelligence in mirror tests. In these experiments, the animal must recognize itself in a reflection and, intriguingly, sometimes use a piece of food to probe how the mirror works. Mirror mark tests are a standard tool scientists use to explore self-recognition in animals. When an animal notices a mark on its body in a mirror and behaviorally responds as if adjusting or investigating it, researchers take this as evidence that the animal understands the reflection is about itself.
The idea behind the test is simple in theory: if a creature responds to a mark on its own body that is visible only via the mirror, it suggests a level of self-awareness. Humans typically do this by applying makeup or noticing a smudge on our own face in the mirror and correcting it. For many animals, passing the test is taken as a marker of intelligence comparable to certain aspects of human cognition. Species such as chimpanzees, elephants, and dolphins have been cited as having passed these mirror tests, which has contributed to the view that self-awareness exists across evolutionary lines beyond humans.
The cleaner wrasse, a finger-sized tropical fish, earned its name by cleaning parasites and dead tissue off larger fish. It made headlines in 2018 when researchers reported that it passed the mirror self-recognition test. Given its cleaning behavior, scientists reasoned that if it detected a parasite-like mark on its own body, the wrasse might use a mirror to inspect and “freshen up.” However, this finding was contested. Gordon Gallup, the psychologist who originated the mirror test, suggested that the wrasse might simply be mistaking marks on its body for parasites on other fish rather than showing true self-recognition.
A new study from Osaka Metropolitan University in Japan and the University of Neuchâtel in Switzerland revisited the experiment with a modified approach to probe self-awareness more deeply. Clarifying the previous setup, researcher Shumpei Sogawa explains that earlier studies typically let the fish view a mirror for days, after which a mark was added. In the new study, researchers did the opposite: they marked the fish first, then introduced the mirror for the first time. The idea was that the fish would already sense something unusual on its body; when the mirror appeared, it could immediately receive visual information that matched this expectation, leading to quicker reactions—scraping off the imagined parasite much faster than before.
The results were striking: on average, the fish tried to rub off the altered area within about 82 minutes after the mirror was shown. This rapid response suggests a level of self-awareness that existed before the fish had even seen a mirror for the first time in the experiment.
As the study progressed, a subset of fish displayed a further intriguing behavior after they had become accustomed to the mirror. They would take a small piece of shrimp from the tank bottom, carry it to the mirror, and drop it. The shrimp and the reflected image moved in sync, and the fish began touching the mirror with its mouth in close coordination with the reflected shrimp. The researchers interpret this as the fish using an external object to probe the mirror’s properties, a form of “contingency testing”—an exploratory behavior aimed at understanding how the mirror works.
This kind of tool use and contingency testing has been observed in other species that did not pass the standard mark-based mirror test, including pigs, rhesus monkeys, manta rays, and various corvids. The broader takeaway is that self-awareness and sophisticated mirror-related cognition may not be limited to the great apes. Masanori Kohda, a biologist involved in both the current work and earlier cleaner wrasse studies, notes that these findings could influence multiple fields—from evolutionary theory and concepts of self to practical considerations in animal welfare, medical research, and even AI studies.
The researchers conclude that self-awareness, once thought to be the exclusive domain of great apes, might have arisen in a wider array of animals, possibly across vertebrates. They suggest that self-recognition could have emerged at least as far back as bony fishes, about 450 million years ago, indicating a much broader distribution of this cognitive skill than previously recognized.
The study detailing these findings was published in Scientific Reports, contributing to ongoing debates about the origins and scope of self-awareness in the animal kingdom. If you’re curious about the broader implications, consider how such cognitive traits could affect how we design enrichment, welfare standards, and even how we model intelligence in non-human minds.
