AKIPRESS.COM - The scientists have found the first known example of a fish with warm blood.

The large circular fish is called an opah, or sometimes a moonfish, and researchers have determined that it can keep its internal temperature 5 degrees Celsius warmer than its environment.

"We were shocked," said Heidi Dewar, a fisheries research biologist at the National Oceanic and Atmospheric Administration who worked on the study published in Science. "How often do you get to find something that no other fish has? It is a once-in-a-lifetime opportunity."

There are other fish in the sea capable of elevating the temperature of specific parts of their bodies. For example, some families of tuna and sharks are able to warm their aerobic swimming muscles. Billfish, including sailfish and marlin, are able to warm their eye and brain region.

However, until now, no fish had ever been discovered that can warm its entire body.

The opah spends most of its time hundreds of feet beneath the ocean surface where the water is cold and little light penetrates. Previous research suggested that even at these depths it was able to warm the areas around its mouth and brain. But scientists weren't sure how until a few years ago when NOAA gill specialist Nicholas Wegner got some opah gills into the lab.

"He was just poking around like nerdy scientists do, and he found this amazing structure," Dewar said.