A new study by the National Oceanic and Atmospheric Administration (NOAA) Fisheries has revealed that Opah or moonfish is the first fully warm-blooded or endothermic fish.

In general, fish are cold-blooded or ectothermic, which means they maintain body temperatures as of the surroundings.

However, certain fish like Tuna, Swordfish and some Shark species show warm-blooded adaptations. They raise the temperature of certain organs that aid swimming and catching prey.

Opah is a big fish about two meters long and has a silver body with red fins.

It is capable of keeping its entire body at a higher temperature, by about five degrees, than the surroundings. While it's not as hot as birds and mammals, it certainly outperforms all its relatives.

Opah is swift unlike other bottom dwellers. It flaps its fins to heat its body, speed its metabolism, movement and reaction times.

It is a fast swimmer and dwells at deep waters in chilly and dimly lit waters. Fish dwelling at such depths are usually lazy and use ambush to catch prey and conserve energy.

Research team led by Fisheries biologist Nicholas Wegner of NOAA Fisheries' Southwest Fisheries Science Center in La Jolla, California implanted small thermometers inside the fish and studied opah in the natural habitat.

A consistent higher body temperature was recorded by the implanted thermometers. Also all the body parts including brain, muscles and heart were always kept warm by the fish even at the great depths of the sea.

Wegner added, "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".