Thunnus South, 1845
Body fusiform, slightly compressed. Gillrakers on first arch 19-43. 2 dorsal fins, separated only by a narrow interspace, the second followed by 7-9 finlets; anal fin followed by 6-8 finlets; pectoral fins with 31-35 rays. Inter-pelvic process small and bifid. Very small scales on body; corselet of larger and thicker scales well-developed but not very conspicuous. Caudal peduncle with a strong lateral keel between 2 smaller ones. Bony caudal keels on caudal peduncle vertebrae well developed. Swimbladder present in most species. Intestine with a loop. Dorsal and vertral branches of the cutaneous artery about equally well developed. Right or middle lobe of liver longest. Vertebrae 18 + 21 or 19 + 20 = 39.
Epipelagic. Schooling and migratory. Feeding on fishes, crustaceans and cephalopods. Spawn in warm waters; eggs and larvae planktonic.
Species 7; in Clofnam area 4.
Subgenera Thunnus s.s., Germo, Neothunnus, Parathunnus are not accepted by Gibbs and Collette, 1967.
Recent revision: Gibbs and Collette (1967).
Species of this genus in the program:
Thunnus alalunga
Thunnus albacares
Thunnus obesus
Thunnus thynnus