This picture shows Atlantic Bluefin Tunas (ABFT) (Thunnus thynnus) bursting through the surface to feed; just off Donegal (Ireland). ABFT are warm-blooded fish which display many physiological adaptations to regional endothermy in order to warm up their red muscle and increase their swimming performance. Swimming without stopping for thousands of kilometers every year: from spawning in the warm waters of the Mediterranean Sea and the Gulf of Mexico to the cold and productive Irish, Icelandic and Norwegian waters. Such is the life history of adult ABFT. Indeed, tunas evolve in a vast habitat where food resources are scarce. The open ocean is the marine equivalent of a desert in terms of the distribution of food resources. To sustain their high metabolic rate, it is in the northern feeding grounds that adults access highly caloric prey such as herring, mackerel and scad. The incredible profile of these powerful fish tells us how crucial it is for them to swim efficiently and minimize their drag and transport costs through morphological and behavioural adaptations.
Tuna are obligate swimmers (ram ventilators), meaning they breathe passively by opening their mouth while swimming. This highlights the importance of such adaptations for the survival of these endurance champions. This picture also illustrates that ABFT are one of the best sprinters of the oceans. By maximising their energetic surplus through behavioural adaptations such as dive gliding when they travel or search for food, they are able to capitalise this energy into impressive speed burst events to catch prey. Reaching speeds of 6 to 8 m.s-1, their fast twitch white muscle allows them to lift their 200 kg out of the water!