Water-spitting fish can identify and remember human faces

By squirting streams of water at images on a screen, archerfish show themselves to be quick studies in object recognition study.

WHAT IF THE next time you had to take a test, the teacher asked you to spit at the correct answer?

Don’t laugh. In a recent study, archerfish proved they could identify human faces by squirting a stream of water at the correct image on a screen.

In the wild, archerfish use their spit cannons to knock insects and other prey into the water so they can gulp them down. But in the lab, researchers used food to train these mangrove-loving fish to apply their sharpshooting abilities to an experiment on animal cognition.

Tricks for treats, in other words.

In a recent study, archerfish identified human faces by squirting water at the correct image on a screen.

“Fish are often considered to have short memories or have only enough intelligence to be capable of very basic tasks”, says Cait Newport, a marine biologist at the University of Oxford and lead author of the study. “However, even basic tasks like finding food or mates, or escaping from predators, can require memory and considerable intelligence”.

The new study, for instance, revealed that archerfish could be trained to recognise a three-dimensional rendering of one human face compared with another, different face. What’s more, the fish were able to continue to recognise that image even when the face was rotated by 30, 60, and 90 degrees, from a frontal view to a profile.

While the fish became less accurate at the higher degrees of rotation and took more time to make their decision, Newport says this finding actually reflects the sort of performance seen in humans and other primates.

“The fact that the fish can complete this task at all using human faces is very impressive, considering that fish have no evolutionary need to recognise human faces, and these are a very difficult class of object to discriminate”, says Newport. (Related: Study suggests sheep can recognise human faces).

Not A Question of Intelligence

It will probably come as a shock that an animal as seemingly simple as a fish can be taught to recognise human faces. But it shouldn’t.

“I would have been very, very surprised if they hadn’t been able to do it”, says Vera Schluessel, a zoologist at the University of Bonn in Germany.

While Schluessel was not involved in the new study, she has been studying cognition in cichlids, sharks, and rays for over a decade. And in that time she has always strived to work against the perception that fish are somehow stupid or primitive because they have smaller brains than other animals.

“The fish brain is very different from a mammal brain, but it’s in no way simple”, says Schluessel. (Related: How your dog recognises your emotions).

Just look at the cleaner fish on a coral reef, she says. These animals can discriminate between hundreds or maybe even thousands of other kinds of fish, which they scour for dead skin and parasites. If they can do that, then why shouldn’t an archerfish be able to learn and remember the face of a human?

Like archerfish, pigeons and bees have also been shown to recognise human faces, even when distorted by rotation. How well they do so varies by species and experimental setup, but the fact that all of these animals can identify novel objects without possessing a neocortex like mammals should tell us that brain size and shape aren’t universal indicators of know-how.

There are ten species of archerfish and all of them spit "arrows" of water into the air to hunt small prey—including the banded archerfish seen here at the Oklahoma City Zoo.

“The big question for scientists isn’t whether or not fish are intelligent”, says Newport; “it is whether they perform complex tasks the same way animals with larger brains do, or whether they have found simpler solutions to the similar tasks”.

This paper suggests that these fish “are using similar mechanisms to primates”, she says.

Life in Three Dimensions

Perhaps there’s another reason why the archerfish proved a quick study when it comes to rotated objects. Unlike flightless animals like humans, fish have evolved to move easily about an aquatic world of three dimensions.

This means these animals are constantly approaching and being approached by objects at all angles, so it makes perfect sense that the archerfish should be able to figure out that an object is the same even when it’s turned a bit, says Schluessel.

Even though she wasn’t surprised by the new study’s findings, Schluessel called the work really valuable, not only for the way it adds to scientific knowledge, but also for how it might make non-scientists think about these misunderstood animals.

The fact that the archerfish can identify human faces as opposed to, say, squares and circles seems like something we can more easily relate to, says Schluessel.

“I just think it’s a nice study because it shows people that fish can really do a lot of things that most people wouldn’t think they could do”.

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