World's first warm blooded fish tastes like tuna

 Image by: NOAA / REUTERS

The Guardian reports that scientists have found that the opah generates heat by constantly flapping its fins and has developed an internal “heat exchange” system within its gills to conserve the warmth.


Scientists at the National Oceanic and Atmospheric Administration discovered the opah’s unusual internal system after analysing samples of gill tissue from fish captured off the west coast of the US, the Guardian reports.

“Before this discovery I was under the impression this was a slow-moving fish, like most other fish in cold environments,” said NOAA marine biologist Nicholas Wegner, who led the research.

Because it can warm its body, it turns out to be a very active predator Marine biologist Nicholas Wegner “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.

According to Reuters, the opah, also known as a moonfish, the creature is about the size of a tyre.

The fish has blood vessels in its gills that carry warm blood from the body's core.

These vessels wrap around other vessels near the gills, where the fish breathes, bringing in oxygenated, cold blood.

Opah fish live in the deep ocean where predators tend to ambush prey rather than chase it.

Some other fish, like tuna and some sharks, can warm up some certain parts of their bodies and muscles to boost swimming performance in the cold depths, but their internal organs quickly get cold, forcing them to rise to shallow waters in order to warm up.

With red fins that are constantly flapping, the opah fish stays warm even when the water gets colder, speeding its metabolism and maintaining a quick reaction reflex.

In addition to the network of warming blood vessels, the opah fish have fatty tissue around the gills, heart and muscle tissue to insulate itself and stay warm.

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

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

According to Chef's Resources, it tastes a bit like tuna - though the top loin is more sweet and lean, suitable for Sashimi.

While it isn't generally a commercially targeted species, it is normally bycatch - caught in fisheries more dedicated to tuna or mahi mahi, it is listed as a 'good alternative' in Hawaii.

Unfortunately, mercury can be a concern.