Manta rays, which have the largest brains out of all fish, have been caught on video observing their reflections in a manner that appears to suggest that they are self-aware. Manta rays exuded no social behaviour towards a mirror image, which is what has led researchers to conclude that they have passed the mirror test of being self-aware, which only a few animals have passed to date.

The experiment was conducted by Csilla Ari of the University of South Florida in Tampa when she observed and filmed two giant mantras in a tank with and without a mirror inside. According to Ari's analysis of the behaviour, when the mirror was placed inside the tank, the rays moved their fins a lot more and blew bubbles, which implied that they were aware of their reflection.

"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," said Ari. Critics, however, believe that the mirror test can not be used as a litmus test for self awareness in all animals.

"This new discovery is incredibly important...It shows that we really need to expand the range of animals we study," said Marc Bekoff of the University of Colorado in Boulder, according to a report in the New Scientist. "It would be nice if someone could do neuroimaging while these animals are doing something in response to seeing a reflection."

Other critics have said that the rays circling in front of the mirror and moving more than usual when the mirror was placed in the tank could simply be a sign of curiosity. "Humans, chimpanzees and orangutans are the only species for which there is compelling, reproducible evidence for mirror self-recognition," said Gordon Gallup Jr of the University at Albany in New York.