Imagine a fish the size of your finger passing a test once thought to be the exclusive domain of great apes. It sounds like science fiction, but it’s real—and it’s shaking up everything we thought we knew about animal intelligence. A tiny cleaner wrasse, a fish known for its meticulous grooming habits, has not only recognized itself in a mirror but also used a piece of food to investigate how the mirror works. This isn’t just a quirky behavior; it’s a groundbreaking discovery that challenges our understanding of self-awareness and cognition in the animal kingdom.
The mirror test, a scientific experiment designed to assess self-recognition, has long been considered a benchmark of intelligence. When you fix your smudged eyeliner after catching your reflection, you’re demonstrating self-awareness—you know that smudge doesn’t belong on your face, and the mirror helps you pinpoint exactly where to fix it. For animals, reacting to an out-of-place mark in a mirror is seen as evidence of self-recognition. Great apes, elephants, and dolphins have all passed this test, but until recently, no fish had joined their ranks.
Enter the cleaner wrasse (Labroides dimidiatus), a marine fish that earned its name by cleaning parasites and dead tissue off larger fish. In 2018, it became the first fish to reportedly pass the mirror test. But here’s where it gets controversial: Gordon Gallup, the founder of the mirror mark test, questioned whether the fish were truly recognizing themselves or simply mistaking the marks on their bodies for parasites on other fish. Was this self-awareness or just instinctual behavior?
To address this debate, researchers from Osaka Metropolitan University in Japan and the University of Neuchâtel in Switzerland redesigned the experiment. Instead of introducing the mirror first, they marked the fish before showing them the mirror. And this is the part most people miss: The fish reacted almost immediately, attempting to remove the mark within an average of 82 minutes. This suggests they were already aware of something unusual on their bodies—even before seeing their reflection. But it doesn’t stop there.
After getting accustomed to the mirror, some fish began an unexpected behavior: They picked up small pieces of shrimp from the tank, carried them to the mirror, and dropped them. As the shrimp fell in sync with its reflection, the fish would touch the mirror’s surface with its mouth. Researchers believe this is the fish’s way of testing the mirror’s properties, using an external object to understand how reflections work. This kind of ‘contingency testing’ has been observed in other species, like pigs and corvids, that failed the traditional mark test. Does this mean self-awareness is more widespread than we thought—or are we underestimating the intelligence of animals we’ve long dismissed as ‘simple’?
Biologist Masanori Kohda, involved in both the original and new studies, emphasizes the far-reaching implications of these findings. They could reshape evolutionary theory, redefine our concept of self, and even influence fields like animal welfare, medical research, and AI. The team suggests self-awareness may have evolved as early as 450 million years ago with bony fishes, making it a far more common trait across vertebrates than previously believed.
But here’s the thought-provoking question: If a tiny fish can exhibit behaviors we once thought were exclusive to humans and great apes, what else might animals be capable of? And how should this change the way we treat them? Let us know your thoughts in the comments—this is a conversation that’s just getting started.
