Can Fish Recognize Themselves in the Mirror?

A new study has found that the cleaner wrasse is capable of self-recognition—but does that mean it is also self-aware?

Alex Jordan via Plos Biology under CC-BY: Redistribution allowed with credit.

When scientists want to determine if an animal is self-aware, they conduct what is known as a “mirror self-recognition test,” in which researchers expose animals to their own reflection, and see if the creatures can figure out that they are looking at an image of themselves. Most species don’t pass the test, but a select few—including chimpanzees, dolphins, elephants and corvids—seem to be able recognize themselves in the mirror. These animals are, incidentally, considered to be quite smart. But as Jake Buehler of National Geographic reports, a new study has found that fish, not typically seen as the brainiest of creatures, may also show signs of self-recognition.

The mirror self-recognition test, first developed by psychologist Gordon Gallup Jr. in 1970, tends to play out in several phases among species that are able to pass it. First, animals are given a chance to get used to the mirror; many respond by trying to attack their reflections, suggesting that they interpret their own image as another animal. But then the test subjects start to act in unusual ways in front of the mirror, as though testing the relationship between their actions and the reflected image, and subsequently use the mirror to explore their bodies. When Gallup applied the test to chimps, for instance, they used mirrors to clean their teeth, pick their noses and examine their genitals. Finally, a colored mark is placed on the animals; if they adjust their bodies to get a better look at the mark in the mirror, or start to poke at the mark while gazing at their reflection, they are deemed as being able to recognize that they are looking at an image of themselves.

Published in the journal PLOS Biology, the new study sought to apply this test to the cleaner wrasse, a little tropical fish that feeds on the ectoparasites and mucus of other fish. Cleaner wrasse are known to be quite clever, as far as fish go; they seem able to keep track of their interactions with more than 100 individual “customers” that come to them for a cleaning, for instance. And according to the study authors, the tiny fish also performed well on the the mirror self-recognition test.

When 10 cleaner wrasse were exposed to a mirror for the first time, they tried to attack it—but that aggression eventually gave way to atypical behaviors, like swimming upside down in front of the mirror, as though the wrasse were starting to figure out that they weren’t looking at another animal. Then the researchers injected a brown gel near the fish’s throats, a spot that they wouldn’t be able to see without the help of a reflective surface. When the wrasse were subsequently exposed to their reflections, they spent relatively long amounts of time in postures that would allow them to observe the color marks in the mirror. They also scraped the marked sides of their bodies on their surroundings—something that many fish do when trying to remove irritants or parasites from their skin.

Crucially, the study authors found that the wrasse didn’t try to scrape their bodies when they were injected with a clear mark, or when they were injected with a colored mark but not presented with a mirror. “It indicates that they understand that the mirror is not something else," Alex Jordan, study co-author and professor of animal behaviour at German’s University of Konstanz, tells the CBC. “It’s not something beyond them. It's not a mirror into another world. But rather, it is reflecting the world that they are already in.”

But other experts aren’t convinced—including Gallup himself. He tells National Geographic’s Buehler that the wrasse, which live and breathe for cleaning ectoparasites on sea creatures, may have spent time gazing at their marks in the mirror because they thought they were looking at parasites on another fish.

“Scraping the throat where the mark is may simply represent an attempt to call the attention of the other fish in the mirror to the presence of an apparent ectoparasite on its throat,” he adds.

Technically, the wrasse passed Gallup’s measure of self-awareness, but the study authors aren’t trying to assert that the fish are actually self-aware. In fact, “self-aware” is a sticky term; chimps may be able to recognize themselves in the mirror, for instance, but that doesn’t mean they while away the hours contemplating the meaning of life. The researchers conclude that the wrasse “undergo a process of self-referencing, in which direct or indirect (e.g., in a mirror reflection) observations of the physical self are perceived as part of one’s own body by the observer but without this involving theory of mind or self-awareness.”

This is turn raises a number of important questions about the utility of the mirror self-recognition test. Is the experiment helpful in determining self-recognition, but not self-awareness? Can passing the mirror test reveal self-awareness in some species, but not in others? How do we even measure self-awareness across diverse species, some of which do not rely on sight or touch as their primary senses? “[T]his ambiguity suggests the mark test needs urgent re-evaluation in the context of comparative cognition studies,” the study authors write.

In addition to highlighting some shortcomings of the mirror self-recognition test, the researchers hope that their study will shine a light on the often underappreciated intelligence of fish.

“A lot of people think fish are vacant animals with three-second memories,” Jordan tells Gizmodo’s Ryan F. Mandelbaum. “But if you educate yourself on what these animals can do, it shouldn’t be surprising that they can do something more complex.”

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