First Warm-Blooded Fish Species "Opah" Discovered [Video]

Researchers have for the first time discovered a fully warm blooded fish, which has heated blood circulating through its body, similar to birds and mammals.

Opah or moon fish, is about the size of a large car tire and generates heat by rapidly flapping its large pectoral fins.

The silvery fish is known to dwell in low lit, chilly waters hundreds of feet beneath the surface of the ocean.

Typically, fish that inhabit such cold depths are usually said to be sluggish and slow. They prefer to conserve their energy by ambushing their prey rather than chase after them.

The Opah on the other hand, has the ability to constantly flap its fins to generate more body heat which helps to boosts its movement, metabolism and reactions times.

"That warm-blooded advantage turns the opah into a high-performance predator that swims faster, reacts more quickly and sees more sharply," said fisheries biologist Nicholas Wegner, lead author of the paper.

"Before this discovery I was under the impression this was a slow-moving fish, like most other fish in cold environments," Wegner said.

"It turns out to be a very active predator that chases down agile prey like squid and can migrate long distances," he added.

During inspection, Wegner was also intrigued by the fish's unusual design. Blood vessels that were carrying warm blood into the gills were found to be wound around vessels that were carrying cold blood back to the body core after the oxygen from the water had been absorbed.

Since the two blood vessels are so tightly bundled together, the incoming vessels end up warming the outgoing blood vessels.

This process in engineering terms is known as 'counter current heat exchange' and resembles that of a car radiator.

Its nature's response to developing a natural adaptation to heat conservation.

The unique location of heat exchanging process within the gills allows the Opah to maintain an average body temperature of 4C to 5C.

"There has never been anything like this seen in a fish's gills before," Wegner said.

"The concept of counter-current heat exchange was invented in fish long before we thought of it," the authors concluded.