Fish May Be Self-Aware, New Study Finds

The new study suggests that some fish can recognize themselves in photographs, challenging our existing assumptions about these animals.

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Bluestreak cleaner wrasse. Credit: François Libert

Some fish have the ability to recognize their own reflection in photographs and reflective surfaces, a new study suggests, signifying that self-awareness may be more common among animals than previously believed.

“It is believed widely that the animals that have larger brains will be more intelligent than animals of the small brain,” such as fish, says animal sociologist Masanori Kohda. It may be time to rethink that assumption, Kohda says.

Previous research by scientists from Japan’s Osaka Metropolitan University (OMU), used something called the mirror test MSR, which has been used to test cognitive abilities in animals for decades. 

Scientists showed cleaner fish (Labroides dimidiatus) their own reflections in a mirror, allowing the animals to familiarize themselves with the image. They then anesthetized the small fish and placed a small brown mark on their throat. When the fish woke up, scientists placed them in front of a mirror again and observed them to see if the animals recognized and tried to touch the new mark. In total, 94 percent - or 17 out of the 18 fish - tried to rub the spot off.

In this new study, cleaner fish also appeared to recognize themselves in photographs. When shown photographs of their fellow fish with marks drawn on their throats they did not try to rub the mark off. What’s more, they acted aggressively towards photographs of unknown cleaner fish, but not towards their own. The study’s findings, published in the Proceedings of the National Academy of Sciences, suggest the fish are capable of forming a mental image of their own face, the same way humans identify themselves.

"Humans are also capable of having a mental image of the self-face, which is considered an example of private self-awareness," the scientists wrote. "We demonstrate that combining mirror test experiments with photographs has enormous potential to further our understanding of the evolution of cognitive processes and private self-awareness across nonhuman animals."

So far self-awareness has only been found in humans and a few other species like dolphins, elephants, and several great apes. This new study is adding to the growing body of research challenging the traditional hierarchies of animal intelligence that have long dominated our perception of animals.

“I think it’s truly remarkable that they can do this,” says primatologist Frans de Waal of Emory University in Atlanta who was not involved in the research. “I think it’s an incredible study.”

Jonathan Balcombe, a biologist with a Ph.D. in ethology, the study of animal behavior has described the new study as “robust and quite brilliant,” according to Science News. People shouldn’t be surprised that fish could be self-aware given that they have already been shown to have complex behavior including tool use, planning and collaboration, he said. “It’s time we stopped thinking of fishes as somehow lesser members of the vertebrate pantheon.”

There are 33,000 species of fish and what many of them are capable of is absolutely mind-blowing. Listen to the Species Unite podcast episode with Jonathan Balcombe to learn more about these fascinating creatures.

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