First ever fully warm-blooded fish discovered with unique ability to flap fins to generate heat

Researchers have discovered the first ever fully warm-blooded fish which boasts the ability to regulate its own body temperature.

The opah fish, which has been examined in the journal Science, is able to generate heat by flapping its wing-like fins.

This ability leaves the fish with an average body temperature of four to five degrees Celsius - a temperature that is hotter than the water it inhabits.

R esearchers from the US National Oceanic and Atmospheric Administration's (NOAA) National Marine Fisheries Service have said the opah fish is unique in its ability to internally regulate its temperature.

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

"But because it can warm its body, it turns out to be a very active predator that chases down agile prey like squid and can migrate long distances.

"There has never been anything like this seen in a fish’s gills before. This is a cool innovation by these animals that gives them a competitive edge.

"The concept of counter-current heat exchange was invented in fish long before we thought of it,” he said."

The opah fish, weighing in at 90kg, has an oval body shape and, thanks to its unique structure, can remain at the bottom of the ocean hunting for food.

Fish such as some sharks and tuna are able to heat certain parts of their body as they sprawl the depths of the ocean in search of food.

But unlike the opah fish they are at some point forced to return to the surface to warm up.