Answer: Opah

Outside of the mammals found in the sea like whales, warm blooded animals are quite rare. Prior to 2015, it was believed that no fish were fully warm blooded and the only examples of any sort of warm blooded mechanisms in any fish species were limited to some species of tuna and sharks that had what scientists call “regional endothermy” or warm-bloodedness limited to parts of the animal’s body core.

In the spring of 2015, however, researchers discovered that the Opah (also known as a spotted moonfish, cravo, kingfish, and Jerusalem haddock) had a complex system of blood vessels connected to the gills and fins that acted like a sort of radiator wherein heat could be exchanged throughout the entire body. By efficiently exchanging heat as well as introducing additional heat via movement of the fins, the Opah is able to hunt in deeper and colder waters where similar fish in the food chain would have trouble maintaining speed and agility (let alone surviving).