Thunnus is agenus of ocean-dwelling,ray-finnedbony fish from the mackerel family,Scombridae. More specifically,Thunnus is one of fivegenera which make up thetribeThunnini – a tribe that is collectively known as thetunas. Also called thetrue tunas orreal tunas,Thunnus consists of eightspecies of tuna (more than half of the overall tribe), divided into twosubgenera.
Their coloring, metallic blue on top and shimmering silver-white on the bottom, helps camouflage them from above and below.Atlantic bluefin tuna, the largest member of this genus, can grow to 15 feet (4.6 m) long and weigh up to 1,500 pounds (680 kg). All tunas are extremely strong, muscular swimmers, and theyellowfin tuna is known to reach speeds of up to 50 miles per hour (80 km/h) when pursuing prey. As with all tunas, members of this genus arewarm-blooded, which is a rare trait among fish; this enables them to tolerate cold waters and to dive to deeper depths.[3] Bluefin tunas, for example, are found inNewfoundland andIceland, and also in the tropical waters of theGulf of Mexico and theMediterranean Sea, where some individuals go each year to spawn.
Due tooverfishing, the range of this genus has declined significantly, having been effectively extirpated from theBlack Sea, for example.[4]
The wordThunnus is theMiddle Latin form of the Greekthýnnos (θύννος, "tuna,tunny") – which is in turn derived fromthynō (θύνω, "to rush; to dart").[5][6] The first written use of the word was byHomer.[citation needed]
Based on morphology and short-lengthmitochondrial DNA sequence data,[7] the genusThunnus is currently classified into twosubgenera:Thunnus (Thunnus) (the bluefin group), andThunnus (Neothunnus) (the yellowfin group). However this classification has been questioned by a recent phylogenetic analysis of nuclear DNA sequence data, which resolved different relationships among species and did not support the traditional definition of the bluefin and yellowfin groups.[8][9] Specifically, these analyses substantiated the division of Pacific and Atlantic Tuna in two separate species and suggested that Bigeye Tuna were actually a member of subgenusNeothunnus, not subgenusThunnus.[8] Earlier nuclearribosomal DNA phylogenetic reconstructions also showed similar results.[10]
Cladogram:Thunnus (bottom-right in image above) is one of five genera that make up the Thunnini tribe. Known as the true tunas, it comprises 8 of the 15 extant tuna species.[1]
An alternative phylogenetic reconstruction for the genusThunnus, based on nuclear DNA sequence data, which modifies the traditionally recognized bluefin and yellowfin clades by placingThunnus obesus within the yellowfin clade instead of in the bluefin clade.[8]
Until recently, sevenThunnus species were thought to exist, and Atlantic bluefin tuna and Pacific bluefin tuna weresubspecies of a single species. In 1999, Collette established that based on both molecular and morphological considerations, they are, in fact, distinct species.[11][12]
The worldwide demand forsushi andsashimi, coupled with increasing population growth, has resulted in global stocks of the species being overfished[29] and bluefin is the most endangered and considered "a serious conservation concern".[30] Complicating the efforts for sustainable management of bluefin fish stocks within national exclusive economic zones (EEZ) is bluefin migrate long distances and hunt in the midocean that is not part of any country's EEZ, so have been vulnerable to overfishing by multiple countries' fishing fleets. International agreements and conventions are good-faith agreements and are difficult to monitor or enforce.[31] Though this fish has been farmed in captivity by the Japanese and by the Australians with the help of the Japanese,[32] yields are lower than other farmed fish due to the slow growth rate of bluefin tuna, therefore keeping prices high.[31] On December 30, 2012, a 222-kilogram (489 lb) bluefin tuna caught off northeastern Japan, was sold at theTsukiji fish market inTokyo for a record 155.4 million yen ($1.76 million) – a unit price of JP¥ 1.274 million/kg (US$3,600/lb).[33]
^Alvarado Bremer, J.R.; Naseri, I.; Ely, B. (2016). "ROrthodox and unorthodox phylogenetic relationships among tunas revealed by the nucleotide sequence analysis of the mitochondrial DNA control region".Journal of Fish Biology.50 (3):540–554.doi:10.1111/j.1095-8649.1997.tb01948.x.
^Chow, S.; Nakagawa, T.; Suzuki, N.; Takeyama, H.; Matsunaga, T. (2006). "Phylogenetic relationships amongThunnus species inferred from rDNA ITS1 sequence".Journal of Fish Biology.68 (A):24–35.Bibcode:2006JFBio..68...24C.doi:10.1111/j.0022-1112.2006.00945.x.
^Collette, B.B. (1999)."Mackerels, molecules, and morphology". In Séret, B.; Sire, J.Y. (eds.).Proceedings. 5th Indo-Pacific Fish Conference: Nouméa, New Caledonia, 3–8 November 1997. Paris: Société Française d'Ichtyologie [u.a.] pp. 149–164.ISBN978-2-9507330-5-4.Archived from the original on 2023-11-30. Retrieved2017-09-16.
Newlands, Nathaniel K.; Molly E. Lutcavage; Tony J. Pitcher (2006). "Atlantic Bluefin Tuna in the Gulf of Maine, I: Estimation of Seasonal Abundance Accounting for Movement, School and School-Aggregation Behaviour".Environmental Biology of Fishes.77 (2):177–195.Bibcode:2006EnvBF..77..177N.doi:10.1007/s10641-006-9069-5.ISSN0378-1909.S2CID12596873.
