Very few non-human animals are known to pass the mirror test, an experiment that is designed to prove self-awareness by seeing if a creature recognizes itself in a mirror. Most of the great apes can pass it, including chimpanzees, bonobos and orangutans. Elephants and several cetaceans (bottlenose dolphins, orcas) have passed. More obscurely, magpies have demonstrated self-awareness through the test too.
It's a short list. But now, apparently, the first fish can be included in the exclusive group, reports New Scientist. In a surprising development, manta rays — large, harmless filter feeders related to other rays and sharks — have demonstrated that they recognize themselves in the mirror.
Mantas might seem like unlikely animals to exhibit such intelligent behavior, but they actually have the largest brains among fish. Like whales, they breach for unknown reasons, and they often demonstrate genuine curiosity.
For the study, lead author Csilla Ari of the University of South Florida filmed giant manta rays inside a tank with and without a mirror. The mantas' behavior was then recorded to see whether it changed in ways that indicated self-awareness. Sure enough, when the mantas swam in front of the mirror, they became preoccupied with themselves, blowing bubbles and flapping their fins. This conduct is not common social behavior for mantas, meaning that it's unlikely they were simply reacting as if their reflection was another manta ray.
“The behavioral responses strongly imply the ability for self-awareness, especially considering that similar, or analogous, behavioral responses are considered proof of self-awareness in great apes,” said Ari.
Of course, interpreting the meaning behind manta ray behavior requires a larger leap of reasoning than interpreting, say, primate behavior. Primate behavior is more recognizable; it shares more in common with our own behavior. The meaning behind bubble blowing and fin flapping is more difficult to parse. While the experiment does seem to demonstrate that mantas react to their reflections differently than they do when interacting with other mantas, some are skeptical about whether this indicates self-awareness.
“Humans, chimpanzees and orangutans are the only species for which there is compelling, reproducible evidence for mirror self-recognition,” claimed Gordon G. Gallup Jr. of the University at Albany, New York, who originally developed the mirror test.
More research will probably need to be done to eliminate other possible explanations for the mantas' mirror behavior before self-awareness can be definitively proven, but the study does at least raise the level of expectation for what other animals are capable of.
“This new discovery is incredibly important,” said Marc Bekoff, of the University of Colorado in Boulder. “It shows that we really need to expand the range of animals we study.”