Fish can recognise human faces

The last fish you set free may not forget you, according to a new study – for the first time, researchers have shown fish can recognise human faces.

A research team conducted a series of tests on archerfish (Toxotes chatareus), a tropical species found in India, Australia and the Philippines, and found the species was adept at distinguishing between people’s faces.

The findings, published this week in the journal Scientific Reports, may contribute to a wider understanding of how the ability to recognise human faces has evolved over time. 

The ability to recognise human faces is a particularly impressive one, because most people’s characteristics are actually quite similar and we need to pick up on very subtle differences in order to tell each other apart.

How we recognise human faces has been debated by experts, many of whom point to the neocortex – a part of the brain concerned with hearing and sight. Others suggest that face recognition is a behaviour we learn throughout life to help us perform socially, among other benefits.

It’s not just humans that can recognise faces. Pigeons, for example, can not only tell between rotated images of human faces, but also categorise them based on expression and gender, placing them up there with primates in terms of face recognition.

In these tests, though, exists the possibility that these animals may have adapted this skill after years of co-habitation with humans. Besides, pigeons have a neocortex.

Cait Newport, a zoologist at Oxford University and lead author of the paper, says it was once thought that only primates, with their complex brains, could manage to recognise human faces: “To test this idea, we wanted to determine if another animal with a smaller and simpler brain, and with no evolutionary need to recognise human faces, was still able to do so.”

Archerfish are interesting animals to study, says the team, which included researchers from the University of Queensland and Oxford University, because of their particular need for strong visual ability. They spit water at insects, knocking them into the water, and feed on them, so their aim must be dead on.

Using food rewards, fish were trained to spit their water jets at one of two faces, presented to them at the same time.

Once they learnt to associate a food reward with a particular face, they were tested to single it out among a group of new faces.

Fish chose their “reward face” from among 44 colour images, and among 18 black and white images, with a strike rate of more than 80%.

The researchers say it is impossible to tell whether archerfish use the same visual information as humans when discriminating between faces. But, they write, their work “that some aspects of the facial recognition task can be learnt, even in the absence of a neocortex.”