Fish That Can Recognise Themselves in Mirrors: The Surprising Science of Self-Awareness

For decades, scientists believed that recognising oneself in a mirror was a rare ability limited to highly intelligent animals such as great apes, dolphins and elephants. Fish were rarely considered capable of such complex thinking. That assumption changed when researchers observed an unexpected behaviour in a small tropical species known as the cleaner wrasse. Faced with a mirror, these fish appeared to inspect marks placed on their own bodies, suggesting they recognised the reflection as themselves rather than another fish. The findings sparked intense scientific debate, challenging long-held ideas about animal intelligence and raising fascinating questions about how different species perceive the world around them.

Fish That Can Recognise Themselves in Mirrors

What Is the Mirror Test ?

The mirror test was first developed in 1970 by psychologist Gordon Gallup Jr. It is designed to assess whether an animal can recognise its own reflection.

In the test, researchers place a small, harmless mark on an animal in a spot it cannot normally see. If the animal notices the mark in the mirror and tries to remove or inspect it, scientists consider this evidence of self-recognition.

For many years, only a handful of mammals and birds consistently passed the test. Fish were not expected to come close.

The Cleaner Wrasse That Surprised Scientists

The cleaner wrasse, a brightly coloured reef fish found in the Indo-Pacific, changed that perception. These fish are well known for removing parasites from larger fish, giving them an exceptional ability to notice tiny details on skin and scales.

In a landmark study, cleaner wrasse initially reacted aggressively to their reflections, treating them as rivals. After repeated exposure, their behaviour changed. When researchers placed a coloured mark on their bodies, the fish repeatedly examined themselves in the mirror before attempting to scrape the mark off against rocks or the seabed.

This behaviour resembled the responses seen in animals that had previously passed the mirror test.

Why the Discovery Is Still Debated

Although the cleaner wrasse's behaviour impressed many researchers, not everyone agrees that it proves true self-awareness.

Some scientists argue the fish may simply associate the reflection with information about their own body without actually understanding that it is themselves. Others believe the mirror test may not measure intelligence equally across different species.