Tuna are built for speed. The body is streamlined. The tail is sharply forked, and the tendons in it connect it to the swimming muscles, providing strength and force. The vascular system of the tuna keeps its body temperature above the water temperature. This helps to speed nerve impulses and increase power in the muscles. The shiny blue on top of the body and the gray-silver spotting on the bottom helps in camouflage. What do tuna eat? They aren't that picky-lobsters, crabs, shrimps, and barnacles. clams, snails, oysters and mussels, and even each other.