Step aside, mammals and birds—there's a new member of the warm-blooded club. It turns out that a special type of fish called the opah (Lampris guttatus) is also a bonafide member. The opah is a silvery fish that lives in dark, deep ocean water, growing up to about 6.6 feet (2 meters) in length—about the size of a large car tire—and 100+ pounds (45+ kg), according to Earth Sky. It uses its large red pectoral fins to swim swiftly through the deep. That's unusual because most deepwater fish are slow-moving and sluggish—but the opah is a quick and active predator, researchers say. So how does the opah pull this off? Unlike most fish, which are exotherms that get heat from their environment, the opah is an endotherm that generates heat from within, Scientific American explains. They use something called counter-current heat exchange to achieve this: as cool, oxygenated blood moves from the gills into the body, it comes into contact with the warm, deoxygenated blood moving from the body to the gills, so that outgoing blood warms the incoming blood.
Interesting, there's so much we don't know about deepwater creatures.
70 procent what lives in the water we don't know. And every day we discover new animals