Meet the World’s First Fully Warm-Blooded Fish Discovered by NOAA

by Terresa Monroe-Hamilton | May 16, 2015 11:45 am

NOAA Fisheries has discovered the Opah[1], or Moonfish, that is the first fully warm-blooded fish that circulates heated blood throughout its body much like mammals and birds, giving it a competitive advantage in the cold ocean depths. It’s supposedly the size of an automobile tire and revs its metabolism and heats its blood by constantly flapping its fins. It’s faster than other predators and therefore gets the choicest prey – primarily Squid. Its red pectoral fins look like horns and it lives hundreds of feet down in the ocean. The Opah also has keen eyesight and large eyes. This silvery behemoth is the first fully warm-blooded fish to ever be discovered.

NOAA Fisheries West Coast

From Discovery:

NOAA scientists have discovered the ocean’s first fully warm-blooded fish. The opah, also known as the moonfish, maintains its body temperature by circulating warm blood through its body.

The opah roams the depths of the ocean, where most of its neighbors are slow and sluggish. Unlike its friends, the opah constantly flaps its fins, which heats up its body and fuels its metabolism. In turn, it also has a distinct predatory advantage, as the opah can move more quickly than other marine predators.

“Before this discovery I was under the impression this was a slow-moving fish, like most other fish in cold environments,” said NOAA’s Nicholas Wegner, the lead author of the new study. “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.”

Wegner and his team unraveled the opah’s mystery by attaching temperature monitors to opahs off of the western United States. As the fish dived to the depths of the ocean, their body temperature remained considerably warmer than the surrounding water temperature.

The Opah has a unique physical attribute called counter-current heat exchange. That means that warm blood leaving the body core helps heat up cold blood returning from the respiratory surface of the gills where it absorbs oxygen. Resembling a car radiator, it’s a natural adaptation that conserves heat. The unique location of the heat exchange within the gills allows nearly the fish’s entire body to maintain an elevated temperature, known as endothermy, even in the chilly depths. Just fascinating. There has never been anything like this seen in a fish’s gills before, evidently. It gives them a ‘hunter’s’ edge and pushes them higher up the food and evolutionary chain. Nature finds a way, doesn’t it?

  1. NOAA Fisheries has discovered the Opah:

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