A small species of fish, the cleaner wrasse, has repeatedly passed tests designed to measure self-awareness—a cognitive ability once believed to be exclusive to larger, more complex animals like apes, elephants, and dolphins. Recent experiments conducted by researchers at Osaka Metropolitan University in Japan and the University of Neuchâtel in Switzerland have strengthened the case for fish intelligence, suggesting that self-recognition may be far more widespread in the animal kingdom than previously assumed.
The Mirror Test and Why It Matters
The standard test, called the mirror mark test, involves placing a visible mark on an animal’s body and observing its reaction when presented with a mirror. If an animal recognizes the mark as being on itself rather than on another individual, it will attempt to remove it, indicating self-awareness. This test is significant because the ability to recognize oneself in a mirror is often linked to higher-order cognitive functions, such as theory of mind—understanding that others have independent thoughts and feelings.
Initial Skepticism and Improved Experimentation
The cleaner wrasse first passed this test in 2018, but skepticism lingered. Some, including the mirror test’s originator, evolutionary psychologist Gordon Gallup, suggested the fish might simply be reacting to the mark as if it were a parasite on another fish, given their natural cleaning behavior. To address this concern, researchers reversed the experimental procedure. Instead of habituating the fish to a mirror then applying a mark, they marked the fish first and then introduced the mirror. The fish quickly located and attempted to remove the mark upon seeing their reflection, suggesting they were aware of something unusual on their own bodies before the mirror provided visual confirmation.
Beyond Recognition: Mirror Tool Use
The experiments went further. After becoming familiar with the mirror, some cleaner wrasses began picking up small pieces of shrimp and dropping them near the reflection. The fish then closely observed how the shrimp appeared in the mirror, touching the glass surface as if exploring how the reflected images work. This behavior, termed “contingency testing,” has been observed in species that fail the mirror mark test, like pigs and manta rays, and suggests a deeper understanding of the mirror’s properties.
Evolutionary Implications and Broader Impact
These findings are prompting a reassessment of evolutionary theory. The cleaner wrasse’s success suggests self-awareness may have evolved much earlier than previously thought—potentially as far back as 450 million years, with the emergence of bony fishes. This has implications not only for academic understanding of animal cognition but also for practical fields such as animal welfare, medical research, and even the development of artificial intelligence. The researchers argue that the findings could influence how we treat animals and how we approach building more sophisticated AI systems.
“Our results suggest that self-awareness evolved at a minimum with the bony fishes…and is likely widespread across vertebrates,” conclude the study authors.
In conclusion, the cleaner wrasse’s demonstrated intelligence challenges long-held assumptions about animal cognition. The fish’s ability to recognize itself and explore the properties of a mirror highlights the potential for complex mental capabilities in species previously considered less intelligent.
