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World’s First Warm-Blooded Fish Discovered

Ralph Pace Photography

For the first time in history, mammals and birds are not the only warm-blooded creatures on the planet.

Up until recently, scientists classified mammals and birds as being the only warm-blooded species on the planet. That classification might have to be rethought after the recent discovery of the world’s first fully warm-blooded fish, the opah.

The opah was thought to be just like every other fish on the ocean floor, slow-moving and sluggish at best. But after watching their behavior, NOAA researchers noticed something different about them. They swam faster, reacted quicker, and could see more sharply than anything else around them.

They began placing monitors on the opahs of the coast of the western United States to track their movements and body temperatures. That’s when they discovered the fish was actually warm-blooded and could raise its temperature higher than the surrounding water when needed.

Opahs circulate warm blood through their bodies by constantly moving their fins around. This allows them to keep their body temperature a few degrees warmer than the water around them in depths down to a 1,000 feet below the surface.

Being warm-blooded isn’t the only cool thing about this discovery. Its gills are unique, counter-current heat exchangers. This means that as warm blood is leaving its body core it helps heat up the cold blood, bringing new oxygen in from the icy water.

This ability also gives this fish a huge advantage when going after prey. Since all other fish are cold-blooded, they move more sluggish the colder the water is, so they must wait out prey to come to them. The opah is far from sluggish, making it an extremely active predator on the ocean floor where it chases down squid.

Due to their solitary nature, opah are not actively sought out by most commercial fishermen. They are considered a prize catch when snagged by fishermen on charter boats and apparently have very delectable fillets.

Discoveries like this are exciting and shows us how mysterious Mother Nature is. Who knows what other weird things she has in store for us the deeper we research the ocean.

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World’s First Warm-Blooded Fish Discovered