Fish can recognise human faces: study

In a first, scientists have discovered that fish are able to distinguish between human faces with a high degree of accuracy - an impressive feat, given this task requires sophisticated visual recognition capabilities.
"Being able to distinguish between a large number of human faces is a surprisingly difficult task, mainly due to the fact that all human faces share the same basic features," said Cait Newport, a research fellow at University of Oxford in the UK.
It has been hypothesised that this task is so difficult that it can only be accomplished by primates, which have a large and complex brain, researchers said.

The fact that the human brain has a specialised region used for recognising human faces suggests that there may be something special about faces themselves.
"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," said Newport.
The researchers, including those from University of Queensland in Australia, found that fish, which lack the sophisticated visual cortex of primates, are nevertheless capable of discriminating one face from up to 44 new faces.

The research provides evidence that fish - vertebrates lacking a major part of the brain called the neocortex - have impressive visual discrimination abilities.

In the study, archerfish - a species of tropical fish well known for its ability to spit jets of water to knock down aerial prey - were presented with two images of human faces and trained to choose one of them using their jets.
The fish were then presented with the learned face and a series of new faces and were able to correctly choose the face they had initially learned to recognise.
They were able to do this task even when more obvious features, such as head shape and colour, were removed from the images.
The fish were highly accurate when selecting the correct face, reaching an average peak performance of 81 per cent in picking the previously learned face from 44 new faces and 86 per cent in second experiment in which facial features such as brightness and colour were standardised.

"We positioned a computer monitor that showed images of human faces above the aquariums and trained them to spit at a particular face," said Newport.
"Once the fish had learned to recognise a face, we then showed them the same face, as well as a series of new ones," she said.
In all cases, the fish continued to spit at the face they had been trained to recognise, proving that they were capable of telling the two apart, researchers said.
Even when we did this with faces that were potentially more difficult because they were in black and white and the head shape was standardised, the fish were still capable of finding the face they were trained to recognise, they said.

The study was published in the journal Scientific Reports.