The internet is going crazy about this, quite frankly, daft looking fish. But why is it so interesting?
The answer is simply its warm blood. Or maybe not so simply; it is the only known fully warm-blooded fish. The Moonfish, or Opah, lives in the depths of the ocean, up to 1000ft below the surface- its a pretty cold place and usually this slows preying fish down. Not the Opah! While cold-blooded fish return to the surface of the ocean to warm up and give them a speed boost, researchers from the National Oceanic and Atmospheric Administration (NOAA) have discovered that the moonfish can do this by flapping its fins like wings. This warms the blood near the fins, which is circulated through the body. It effectively recycles the heat in its body by transferring it to cold blood vessels near its gills. This gives it and advantage deep in the cold ocean, where it can better outrun its cold-blooded prey.
Image credit: NOAA Fisheries West Coast/flickr CC BY-NC-ND 2.0