Zoologger is our weekly column highlighting extraordinary animals – and occasionally other organisms – from around the world

Right way up Getty Images/iStockphoto

Species: Japanese rice fish or the medaka (Oryzias latipes)

Habitat: Rice paddies, marshes, ponds and slow-moving streams in East Asia

Are you good with faces? So is the Japanese rice fish – at least, it is if the faces are the right way up. Just like humans, the tiny fish has no problem recognising faces orientated the usual way, but, again like us, it struggles when they are inverted. The finding indicates that the fish may have developed a unique brain pathway for face recognition, just as humans have.


We have no problem identifying most objects in our environment – say, a chair – no matter what way up they are. But faces are different. It is relatively easy for us to spot the differences between two faces, even if they are physically similar, if we see them in photographs the right way up. But if the images are upside down, telling them apart gets a bit tricky.

“This is because we have a specific brain area for processing faces, and when the face is upside down, we process the image through object processing pathways, and not the face-processing pathways any more,” says Mu-Yun Wang at the University of Tokyo, Japan.

Until now, this face-inversion effect was considered exclusive to mammals as it has only been observed in primates and sheep.

Enter the Japanese rice fish, also known as the medaka (Oryzias latipes), a 3.5-centimetre-long shoaling fish commonly found in rice paddies, marshes, ponds and slow-moving streams in East Asia. These fish are very social, so identifying the right individuals to associate with is important.

Disguise tactics

To work out how medaka fish identify one another, Wang and her colleague Hideaki Takeuchi began by allowing a female to become familiar with a male. Exploiting the fact that females generally mate faster with a familiar male, the pair then employed some disguise tactics. They used semi-transparent films to mask either the face, body or tail of males and observed whether a female could still recognise the familiar male.

They found that only when the face of the male was covered did the female respond in a way that suggested she had failed to recognise the familiar fish.

Learn more at New Scientist Live in London: Discover the world’s most amazing animal

To work out how well the medaka can recognise inverted faces, the researchers then used a prism to invert the face of male fish either vertically or horizontally, and tested how well females dealt with each type of inversion.

Surprisingly, the fish showed the face-inversion effect, says Wang. “They cannot recognise inverted faces, but have no problem with inverted objects,” she says.

This isn’t the first time fish have been shown to recognise each other by their faces, but no one has previously demonstrated that fish are sensitive to the face-inversion effect. The results suggest that the medaka may use a specific brain mechanism to process faces, much like humans and sheep, says Wang.

Evolutionary trade-off

The ability of animals to identify individuals by their faces is important in social species. “Faces are really the ‘business’ end of an animal, where its eyes and teeth are, so it makes sense that animals in general would be interested in faces,” says Michael Sheehan at Cornell University in New York.

But the surprising bit, he says, is that for an increasing number of species, the orientation of the face seems to be crucial. “The information in an upside-down face is the same as the information in a right-side-up face, but our brains and those of other primates, and now fish, have difficulty in understanding social information if images are not in the expected orientation,” says Sheehan.

“It appears that in the process of evolving specialised face-recognition abilities to quickly and accurately extract important information, there has been a trade-off where face-like images in unexpected orientations become especially difficult to process,” he says.

The reason for this trade-off is unclear, but it probably relates to the fact that you rarely see inverted faces, says Sheehan.

To find out more, Wang is searching for the mechanisms involved in the medaka’s face-recognition behaviour. “We are now looking for the genetic background for face processing, as well as how social experience influences the ability to recognise faces,” she says.

Journal reference: eLife, DOI: 10.7554/eLife.24728

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