Meet the Opah, the World's Only Warm-Blooded Fish

The manhole cover-sized opah, or moonfish, is the world's only known fully warmed-blooded fish. Though it's not as warm as mammals or birds, a 2015 NOAA study says its blood gives it an advantage over its deep sea dwelling neighbors.
Published: 5:42 AM EDT September 12, 2019
Updated: 4:56 PM EDT September 11, 2019