First Warm-Blooded Fish Discovered

  • Scientists have recently discovered that the Opah, or Moonfish, a large colorful salt-water fish is warm blooded. This is huge breakthrough, because it's the first warm-blooded fish to be discovered. Some species have been found to have partial warm-bloodedness. But scientists say the Opah actually circulates heated blood, which makes it first fish on record to do this.


    There's a clear advantage to being warm-blooded, and for the Opah this enables it to move faster than cold blooded species. Mammals such as Dolphins or Whales already take advantage of this. They will take a big breath and dive down at a fast pace, and scoop up live food such as squids, fish and shrimp. But until recently, it was thought to be that mammals were the only warm blooded species in the ocean.


    "A team from the NOAA SouthWest Fisheries Science Center in California, led by Nicholas Wegner, discovered the fish has a special insulated network of blood vessels between the heart and the gills. These vessels act as a heat exchanger in which warm blood from the heart reheats oxygenated blood leaving the gills before it goes to the body. In this way heat is retained and not dissipated into the ocean. This enables the opah to maintain a body temperature 5°C higher than the surrounding water and to dive 500 meters below the surface without cooling down. An insulating layer of fat in the skin keeps the heart, brain, muscles and vital organs warm.


    This discovery is surprising since we've know about the Opah for a long time, and is often a favorite in fish markets and restaurants. This large, tire sized fish, has been hiding in plain site; and we had no clue that it was warm blooded all these years.