One Fish, Two Fish, Red Fish, Smart Blue Fish

cleaner wrasse
A cleaner wrasse interacts with its reflection in a mirror placed on the outside of the aquarium glass. ALEX JORDAN

One of my favorite super-specific categories of animal videos to watch when I'm in procrastination mode is Pets Looking in Mirrors. Seriously, Google it. There are confused cats, dogs totally losing it, and even birds admiring their beaks with the self-admiration of Narcissus. It's an awesome way to waste work hours. And now, there's a new animal to add to the list of reflection-curious critters: fish.

To be fair, it's just one specific species that scientists have determined to be aware of their image. According to a study publishing today in the open-access journal PLOS Biology, researchers report the cleaner wrasse (Labroides dimidiatus) responds to its own reflection and even attempts to remove marks on its body during something called a mirror test.


The Mirror Test

Developed in the 1970s, the mirror test is considered the gold standard for determining self-awareness and involves marking an animal with an odorless dye and then observing whether the animal becomes aware of the mark (i.e. turns to get a better look at it, pokes at the spot on its body or in the reflection, etc.) when faced with a mirror. While the cleaner wrasse may not have the appendages to indicate awareness as animatedly as animals like chimpanzees and elephants, they do appear to recognize their own reflections.

"Appear" is the operative word here. The study's researchers from the Max Planck Institute for Ornithology (MPIO) in Germany and Osaka City University (OCU)in Japan are clear that the results are open to interpretation.


"The behaviours we observe leave little doubt that this fish behaviourally fulfils all criteria of the mirror test as originally laid out," senior author Alex Jordan said in a statement. "What is less clear is whether these behaviours should be considered as evidence that fish are self-aware — even though in the past these same behaviours have been interpreted as self-awareness in so many other animals."

So how exactly did the researchers get fish to take part in a test of any kind? Probably with a lot of patience. The cleaner wrasse may have been good contenders for the experiment because they have a habit of scouring other fish for parasites, so they seem to have a capacity for observation. To test how that attentiveness might translate to their own bodies, researchers placed colored marks on the fish in areas the subjects could only see in reflection. If a fish touched or investigated the mark in any way, it "passed" the test and researchers considered it a demonstration that the animal perceived its own reflected image.

If you're wondering how in the world a fish could touch or investigate anything with a complete lack of limbs, consider the fact that those terms were used rather loosely in the study. If the fish scraped their bodies on hard surfaces after viewing themselves in the mirror, the scientists considered those scrapes attempts to remove the markings.

And that's not an unreasonable consideration given that the fish never tried to scrape off transparent marks when a mirror was present, and they never appeared to get rid of the colored marks when no mirror was present, which suggests their self-scraping was in response to the visual cue of their reflected image. To further back that theory up: Unmarked fish that interacted with marked fish across a clear divider didn't try to remove anything from their own bodies, and they didn't try to remove marks placed on the mirror itself (which you might expect, given their natural inclination to seek out environmental parasites).


Still Skeptical?

But if you're still skeptical that fish can actually recognize themselves, the study's authors don't really blame you, but they beg to differ. "Depending on your position, you might reject the interpretation that these behaviours in a fish satisfy passing the test at all," Jordan said. "But on what objective basis can you do this when the behaviours they show are so functionally similar to those of other species that have passed the test?"

Anticipating some controversy, the editors of PLOS Biology recruited an expert to provide additional commentary on the study. Professor Frans de Waal, a leading primatologist at Emory University who has studied mirror self-recognition in mammals, said that self-awareness in animals likely isn't an all-or-nothing issue.


"What if self-awareness develops like an onion, building layer upon layer, rather than appearing all at once?" he asked. "To explore self-awareness further, we should stop looking at responses to the mirror as its litmus test. Only with a richer theory of the self and a larger test battery will we be able to determine all of the various levels of self-awareness, including where exactly fish fit in."