Researchers identify opah as first fully warm-blooded fish

Researchers identify opah as first fully warm-blooded fish

HONOLULU (HawaiiNewsNow) - The opah, or moonfish, has been identified as the first fully warm-blooded fish that circulates heated blood throughout its body like mammals and birds, according to new research.

Scientists with the National Oceanic and Atmospheric Administration found that being warm blooded gives the opah a competitive advantage in the cold ocean depths, enabling it to be a vigorous predator. Fish that typically inhabit cold depths tend to be slow and sluggish, conserving energy by ambushing prey instead of chasing it, researchers said. But the opah's constant flapping of its fins heats its body which speeds up metabolism, movement and reaction times.

The opah, a silvery fish roughly the size of a large automobile tire, dwells hundreds of feet in chilly, dimly lit waters. It swims by rapidly flapping its fins like wings through the water.

Biologist Nicholas Wegner first made the discovery when he recognized a unique location of a heat exchange within the opah's gills, which allowed the fish's entire body to maintain an elevated temperature, even in the chilly depths. Researchers found that the opah's body temperatures was generally warmer that the surrounding water.

Even though mammals and birds typically maintain much warmer body temperatures, the opah is the first fish found to keep its whole body warmer than the environment.

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