The tuna is a sleek and streamlined fish, adapted for speed. It has two closely spaced dorsal fins on its back; the first being "depressible” it can be laid down, flush, in a groove that runs along its back. Seven to 10 yellow finlets run from the dorsal fins to the tail, which is lunate curved like a crescent moon and tapered to pointy tips. The caudal peduncle, to which the tail is attached, is quite thin, with three stabilizing horizontal keels on each side. The tuna's dorsal sides is generally a metallic dark blue, while the ventral side, or underside, is silvery or whitish, for camouflage.