The First of Its Kind: A Warm Blooded Deep Sea Fish Discovered

Aside from its funky flat shape and peach-pink-silver coloring, the opah or moonfish (Lampris guttatus) has something else entirely unique going for it: It’s warm-blooded, the first fish ever discovered to have this trait, according to new research from NOAA Fisheries West Coast Region.

The silvery fish, roughly the size of a large automobile tire, is known from oceans around the world and dwells hundreds of feet beneath the surface in chilly, dimly lit waters. It swims by rapidly flapping its large, red pectoral fins like wings through the water.

Fish that typically inhabit such cold depths tend to be slow and sluggish, conserving energy by ambushing prey instead of chasing it. But the opah’s constant flapping of its fins heats its body, speeding its metabolism, movement and reaction times, scientists report in the journal Science.

That warm-blooded advantage turns the opah into a high-performance predator that swims faster, reacts more quickly and sees more sharply, said fisheries biologist Nicholas Wegner of NOAA Fisheries’ Southwest Fisheries Science Center in La Jolla, Calif., lead author of the new paper.

The warm-bloodedness was discovered almost by accident, when Wegner and co-author biologist Owyn Snodgrass, were looking at the gill structure of the opah. “Fish have just a few large blood vessels that bring blood to and from the gills, where tiny vessels pick up oxygen from the water,” reports ScienceNews. “But the opah has an elaborate network of tiny blood vessels, in which arteries lie next to veins in tightly packed arrays.” This type of blood circulation helps the fish stay warm rather than taking on the temperature of the surrounding water.