Unlike the majority of fishes, most tuna are endothermic, which means that their body temperature is kept higher than that of the surrounding water. This enables more efficient muscle action and faster swimming even in colder water.

Muscle action generates heat, but in most fishes this heat is quickly lost through the skin and gills. Tuna have a system of heat exchangers in the blood supply known as “rete mirable”, which direct heat back into the body and maintain a temperature up to 10°C above that of the water.

Being warm-blooded lets tuna swim rapidly, but it also means that they must eat more frequently than normal ectothermic fishes.

« »