Meet the World’s First Truly Warm-Blooded Fish

Scientists at the National Oceanic and Atmospheric Administration (NOAA) Fisheries have discovered an astonishing information about the opah.

Commonly known as the moonfish, the opah is described as a fish that is about the size of a tire of car, weighs more than 45 kg and thrives in cold deep water.

PHOTO CREDIT: Reef Builders

In a research published in Journal Science, the scientists revealed that the opah is the first fully warm-blooded fish that is capable of regulating the temperature of its whole body.

To generate heat and continually warm its whole body, an opah flaps its large pectoral fin. Moreover, it has thick layers of fat that insulates its heart, pectoral fin muscles, and gills from the surrounding cold environment.

“Before this discovery, I was under the impression [the opah] 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,” said Dr. Wegner, a biologist from NOAA.

In order to establish their claims, the scientists from the NOAA measured the temperature of the various body parts of a freshly caught opah. They also installed thermometers while the fish dived underwater.

The muscles of an opah was proven to be consistently 5C warmer than its surrounding water. On the other hand, the opah’s heart  and head region are about 3C warmer than the water.

They also examined the gills of an opah and found that it contained retia mirabilia, which is the Latin for wonderful net. This intricate tangle of veins and arteries are observed in tuna and sharks, which are known to use the so-called “regional endothermy”. This means that they have the ability to heat some portions of their body.

But the opah is the first fish proven to have the ability to keep its entire body warmer than its environment.

Watch the video below.

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