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.”

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:

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.

Source: Manta rays are first fish to recognise themselves in a mirror | New Scientist