Fish Can Recognize Human Faces

A team of researchers from the University of Oxford and the University of Queensland has proven that fish are capable of distinguishing one human face from the next. The study, recently published in the journal Scientific Reports, is the first of its kind.

How did scientists test the fish?

The study set out to disprove the theory that only animals with advanced intelligence could practice facial recognition. Led by Dr. Cait Newport from the University of Oxford, the team tested its theory using archerfish, a tropical species found primarily in the mangroves and estuaries of Australia and southeast Asia. The team chose archerfish specifically for their ability to spit jets of compressed water. The fish use this skill in the wild to shoot down insects and other small terrestrial prey. For the initial tests, scientists presented the fish with images of two different human faces. Researchers projected the images on a computer monitor suspended above the aquarium.

The researchers used food conditioning to teach the fish to choose one of the faces over the other one, and to mark their selection by spitting at it. Once conditioned, scientists showed the fish the familiar face again, along with a series of new faces. Incredibly, the fish were able to identify the learned face with startling accuracy, showing an 81 percent success rate even when presented with a group of up to 44 new faces. The researchers made the task harder by presenting all the faces in black and white, and by standardizing their head shape. In this instance, the fish demonstrated an 86 percent success rate.

Ramifications of the study

The accuracy of their results stunned Newport and her peers. Recognizing human faces is a difficult task, which scientists previously only thought possible for animals with complex brains. Unlike primates and some species of birds, which until now were the only animals scientists had shown capable of recognizing faces, fish lack a neocortex. This most recently evolved part of the human brain is responsible for sensory perceptions and language. As such, scientists thought facial recognition would be impossible. But now, Newport says, “there is increasing research showing that fish are capable of doing a lot more than previously thought.”

That archerfish have no evolutionary need to recognize human faces further surprised the scientists. However, Newport hypothesizes that the fish could be adapting the pattern-recognition ability that they use in the wild to detect their prey. Newport also found that Picasso triggerfish could differentiate between black and white discs. This means that archerfish aren’t the only fish species with unexpected levels of visual cognition. It’s possible that other fish species may be similarly capable, and that they use their pattern and color-recognition skills to return to favored breeding sites in the wild.

If this is the case, coral-bleaching disasters like the one currently threatening the Great Barrier Reef could affect fishes’ ability to recognize their surroundings. Newport warns, “these guys [the fish] are looking at colors and patterns and textures. And if all of that is bleached…we don’t know if they’re still going to be able to find their territories, their homes. We don’t know how that will affect how they detect predators or potential prey.” Despite these new questions, Newport says that the results so far prove that while fish may have relatively simple brains, they are perfectly evolved for their specific needs.

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