​London, June 7 (IANS) Despite having a much simpler and smaller brain than that of primates, fish have the remarkable ability to distinguish between human faces, new research has found.

“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 first author Cait Newport from Oxford University.

“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,” Newport noted.

To test this idea, the researchers 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.

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 perform 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 the first experiment (picking the previously learned face from 44 new faces) and 86 per cent in the second experiment (in which facial features such as brightness and colour were standardised).

The study was published in the journal Scientific Reports.

“Once the fish had learned to recognize a face, we then showed them the same face, as well as a series of new ones. In all cases, the fish continued to spit at the face they had been trained to recognize, proving that they were capable of telling the two apart,” Newport said.

“The fact that archerfish can learn this task suggests that complicated brains are not necessarily needed to recognise human faces,” Newport noted.​