The second smallest of all tunas (Thunnus sp.), the longtail tuna (Thunnus tonggol) is unique among the ‘true’ tunas, being the only species to lack a swim bladder (an air-filled sac which helps fish to maintain buoyancy). The slender body and forked tail of the longtail tuna are silvery white, with elongate oval spots arranged in horizontal rows along its length. The two dorsal fins on the back are blackish in colour, with the larger of the two, the second dorsal fin, tinged with yellow. The anal fin is silvery, with a yellow tint, the pectoral and pelvic fins are black and the caudal fin is blackish with streaks of yellowish-green.