The Opah: First warm-blooded fish

Marine biologists discover that the opah, or moonfish belongs to the club of mammals and birds

Photo by: NOAA
Photo by: NOAA

Updated Jul 28, 2015

Researchers from US National Oceanic and Atmospheric Administration (NOAA) have identified the opah, or moonfish as the first fully warm-blooded fish that can adjust its blood temperature independent of the environment.

Tuna and certain sharks have been known for partially warm their body parts such as swimming muscles, brains and eyes in colder depths. In order to protect their hearts they have to limit their time in chilly waters.

However, the unusual design of its gills give opah a distinct advantage over its prey and rivals in deep waters.

Warm blood leaving from the fish’s core heats up the oxygen rich cold blood returning from the surface of its gills. This heat exchange, occuring in a unique spot in its gills, allows the fish’s body to stay in higher temperatures than its environment.

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

"This is a cool innovation by these animals that gives them a competitive edge."

The moonfish is reddish in color with white spots and has bright red fins. It is about the size of a car tire, weighing up to 90 kg. Opah can be found in oceans at depths between 50 and 400 meters

TRTWorld and agencies