When people think of animal intelligence, usually chimpanzees and dolphins spring to mind, not fish. And yet, one of the most charismatic of fish, the Manta Ray, also happens to be the most intelligent of fish, and one of the cleverest animals. Perhaps there is a correlation between their engaging interactions with humans (and each other) and their smarts.
Manta rays have very peculiar brains, for fish.
Manta rays have the largest brains of any fish, up to 10 times larger than a whale shark's and weighing up to 200kg. They also have the largest brain-to-body mass ratio (or how much of their body mass their brain takes up) of all rays. Interestingly, another Nusa Penida resident, the Mola mola, has one of the smallest brain-to-body mass ratios of all fish (a 200kg individual might have a brain weighing 5g)!
The Manta ray brain itself is quite unusual, especially for a fish. It is encased in a system of blood vessels which keeps the brain warmer than the surrounding tissue. This big warm brain seemingly fosters intelligence and some brain parts also suggest well-developed sensory-, cognitive and social behaviour.
The manta ray, a self-aware fish?
Over the years of studying manta ray behavior, Ari Csilla has probably become the world's most prominent specialist on these incredible elasmobranchs. She set up experiments with a mirror to test their self-awareness. Visual self-recognition is considered by humans as a sign of great intelligence. Only a few animals are aware of their existence and can recognize themselves in their own reflection. Inspired by the Mirror Self Recognition( MSR) test, Ari presented two captive Manta rays with a mirror in their tank to monitor their response. Instead of reacting with the normal social cues that the presence of a new individual would generate, the manta passed again and again in front of the mirror making frequent unusual and repetitive movements that suggested contingency checking. In addition, unusual self-directed behaviors were seen when the manta rays were exposed to the mirror. The manta rays not only spent much more time in the area in front of the mirror, but they exposed their belly to the mirror repetitively and even created bubbles somehow, similar to what was observed with dolphins (bottlenose dolphins are one of the few species that passes the MSR self-awareness test.)
Manta rays can change their colour patterns in minutes!
Another breakthrough in understanding manta ray behaviour initiated by Ari Csilla was when she recorded rapid colour changes in the mantas' skin during social interaction and feeding time. This suggests a much more complex communication system between the huge fish than was previously hypothesized. Until recently, natural body colouration was used to distinguish species and ventral spotting to distinguish individuals. After observing captive individuals, Ari described the first evidence of rapid colouration changes in manta rays. Colouration changes were observed most intensely on the dorsal surface and on the head, which occurred within minutes, before feeding and during intense social interactions.
This poses new challenges for conservation efforts as manta ray numbers are partly estimated by compiling numbers of photo-identified individuals. This is mitigated, however, by the fact that individual rays are identified by their ventral markings which seem to change much less if at all. What is for sure is that Dr Ari Csilla's groundbreaking research on manta intelligence and social behaviour is helping support future protection initiatives for these majestic creatures.
Get more in-depth info on Manta ray intelligence and behaviour in Dr Ari's Ted talk and website :