Are fish warm-blooded?

Generally they are cold blooded. However, some tuna, shark and swordfish have warm blooded features. The Blue Fin Tuna use various techniques to keep their muscles and system warm such as having swimming muscles near the center of their bodies instead of near the surface. They are also able to warm their entire bodies through a heat exchange mechanism called the rete-mirabile, which helps minimize the loss of heat through the gills. Blue Fin Tuna must eat more food than other tuna to help maintain their ability to produce heat.