We really need to stop underestimating our fellow creatures. A new study adds a talented tropical fish to the swelling ranks of non-human animals that can tell humans apart. The research was published in the journal Scientific Reports. 

Facial recognition is a vital but complex task—so complex that humans have an entire region in our brains dedicated to it. And because it’s such a sophisticated process, scientists used to assume that we were the only animals that could do it. Then that circle widened a little bit to include other primates. But that circle just keeps growing, and currently includes octopuses, bees, and at least four types of birds. This is, admittedly, kind of strange; with the possible exception of birds, none of these animals have any natural need to tell people apart. 

Nor do fish. And like the cognitive abilities of birds, bees, and cephalopods, fishes’ mental skills have been more or less written off until quite recently. With this fact in mind, a team of researchers from the UK and Australia decided to find out if fish were up to the task. 

One species, the archerfish (Toxotes chatareus), seemed especially well-suited for the experiment. Archerfish are amazing creatures with a super-cool hunting strategy: They wait near the water’s surface for an insect to land on a nearby leaf, then shoot a jet of water at the bug, knocking it into the water. 

Illustration: Pearson Scott Foresman via Wikimedia Commons // Public Domain

Their aim is superb, and their vision acute, which suggests fairly sophisticated mental function. It also makes them great experimental subjects, since they can be trained to choose an object or image by spitting at it. 

The new study consisted of training and two experiments. First, researchers set up a screen above a tank holding a single fish. To see if the fish could tell the difference between two faces, the scientists displayed two faces on the screen, then attempted to train the fish to spit water at only one of them whenever it appeared. The training worked, and quickly, too; within just a few sessions, all the fish had learned to spit at the right face.

Image Credit: Newport et al. 2016.Nature Communications

Then the researchers brought back the same fish and exposed them to lots and lots of faces—44, to be precise. The goal was to see if the fish could still pick out the face they learned in the first round of training. To make it even harder, the researchers then cut all the face images into oval shapes and displayed them in grayscale so the fish couldn’t rely on more obvious cues like face shape or color. 

But the fish didn’t need color or shape. As in their hunting, the archerfish were incredibly accurate when it came to spotting faces. In the first round of 44 faces, the fish subjects averaged 81 percent accuracy. Once the obvious cues were removed they did even better, selecting the right face 86 percent of the time.   

“Fish have a simpler brain than humans and entirely lack the section of the brain that humans use for recognizing faces,” said lead author and Oxford University zoologist Cait Newport in a press statement. “The fact that archerfish can learn this task suggests that complicated brains are not necessarily needed to recognize human faces.”