Tuna is a carnivore, primarily feeding of small bluefish species like pilchard and mackerel. It is one of the rare endothermic (warm-blooded) fish, and in contrary of dry land endothermic animals it doesn't keep it's body temperature inside narrow margin. Tuna's body temperature changes with water temperature, enabling it to migrate between very different environments, so tuna can be found from warm seas like Mediterranean or Caribbean to the cold coasts of Norway or Labrador. Their metallic blue coloring on top and shimmering silver–white on the bottom helps camouflage them from above and below. Their torpedo-shaped, streamlined bodies are built for speed and endurance. Even submarine engineers studied their shape and swimming mechanism. They even have several stability fins towards their tail. Bluefin tuna has very effective circulatory system with high hemoglobin concentration and exceptionally thin water-blood barrier that enables efficient oxygen intake.