Manta ray hears the dinner bell Norbert Wu/Minden Pictures/FLPA

Looking good. Giant manta rays have been filmed checking out their reflections in a way that suggests they are self-aware.

Only a small number of animals, mostly primates, have passed the mirror test, widely used as a tentative test of self-awareness.

“This new discovery is incredibly important,” says Marc Bekoff, of the University of Colorado in Boulder. “It shows that we really need to expand the range of animals we study.”

But not everyone is convinced that the new study proves conclusively that manta rays, which have the largest brains of any fish, can do this – or indeed, that the mirror test itself is an appropriate measure of self-awareness.

Csilla Ari, of the University of South Florida in Tampa, filmed two giant manta rays in a tank, with and without a mirror inside.The fish changed their behaviour in a way that suggested that they recognised the reflections as themselves as opposed to another manta ray.

They did not show signs of social interaction with the image, which is what you would expect if they perceived it to be another individual. Instead, the rays repeatedly moved their fins and circled in front of the mirror (click on image below to see one in action). This suggests they could see whether their reflection moved when they moved. The frequency of these movements was much higher when the mirror was in the tank than when it was not.

The rays also blew bubbles in front of the mirror, behaviour that Ari had not observed in the rays before.

“The behavioural responses strongly imply the ability for self-awareness, especially considering that similar, or analogous, behavioural responses are considered proof of self-awareness in great apes,” Ari says.

Diana Reiss, of Hunter College in New York, says that it is interesting that manta rays did not show social behaviour towards the mirror image, as fish usually do. But she says it is unclear whether the rays actually recognise themselves in the mirror.

Curious behaviour

Gordon G. Gallup Jr, of the University at Albany, New York, who originally developed the mirror test, is also sceptical. The unusual movements in front of the mirror might have merely been a sign of curiosity or exploratory behaviour, he says.

Other studies have suggested that dolphins, elephants, monkeys and magpies, and even a robot, can recognise themselves in the mirror. But Gallup says these were usually conducted on just one or two animals and the results were not reproducible.

“Humans, chimpanzees and orangutans are the only species for which there is compelling, reproducible evidence for mirror self-recognition,” he says. This implies that self-awareness may be limited to humans and some great apes.

But Bekoff says that the mirror test may not be the litmus test for self-awareness in all animals. It is a visual measure, so it might not work in species that navigate their worlds primarily using senses other than vision. Such species may fail the mirror test, but they may still be self-aware, Bekoff says.

He thinks it is time to raise the bar on the way we study self-awareness in animals, including manta rays.

“It would be nice if someone could do neuroimaging while these animals are doing something in response to seeing a reflection,” he says.

Journal reference: Journal of Ethology, DOI: 10.1007/s10164-016-0462-z

Read more: Hey! good looking