The National Oceanic and Atmospheric Administration (NOAA) has confirmed the discovery of the first known warm blooded fish. The moonfish or opah circulates warm blood in the same way that mammals and birds do, this gives the animal a distinct advantage in its environment.

Typically animals that live in the deep ocean are slow moving and set traps for their prey instead of chasing them in order to conserve energy. The opah, which is about the size of a car tire and inhabits the depths of oceans around the world, continuously flaps its fins which sends warm blood through its veins.

The warm blood gives the fish an increased metabolism and makes it one of the few speedy predators in its environment. According to Nicholas Wegner of NOAA Fisheries and lead author of the report in the journal Science, the fish reacts more quickly, sees more sharply and swims faster than other deep sea fish.

“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,” said Wegner in a statement.

The discovery began with a sample of gill tissue collected by study co-author Owyn Snodgrass. Wegner noticed that the gill was different from typical fish. It contained vessels for carrying warm blood into the gills and vessels for carrying cold blood back to the body core.

In engineering the design is referred to as “counter-current heat exchange.” In practice it means that warm blood flowing from the body core helps to heat cold blood flowing back toward the core. According to Wegner the design is similar to a car radiator and helps to conserve heat in an environment where energy is scarce.

“There has never been anything like this seen in a fish’s gills before. This is a cool innovation by these animals that gives them a competitive edge. The concept of counter-current heat exchange was invented in fish long before we thought of it,” said Wegner.

After the initial analysis of the gills, the researchers sampled the body temperatures of Opah caught during a west coast survey. They found the average temperature was about 9 degrees Fahrenheit warmer than the water the fish were caught in. The opah’s body temperature wasn’t as warm as that of typical fish or mammals but is the first fish discovered with a body temperature higher than that of the water it swims in.

Some fish, including sharks and tuna, warm parts of their bodies such as muscles but only for short periods before being forced to return to shallow water to warm up. The opah, by contrast, typically spend their time at depths of 150 to 1,300 feet and do not seem to have a need to warm themselves in shallow water.

“Nature has a way of surprising us with clever strategies where you least expect them. It’s hard to stay warm when you’re surrounded by cold water but the opah has figured it out,” said Wegner.

“Discoveries like this help us understand the role species play in the marine ecosystem, and why we find them where we do. It really demonstrates how much we learn from basic research out on the water, thanks to curious scientists asking good questions about why this fish appeared to be different.” said Francisco Werner, director of the Southwest Fisheries Science Center.

Opah are not typically fished commercially however, that may change. While many fish stocks have been decreasing off the U.S. west coast, the opah actually seem to be increasing in number.