Thunnus

Thunnus is a genus of ocean-dwelling, ray-finned bony fish from the mackerel family, Scombridae. More specifically, Thunnus is one of five genera which make up the tribe Thunnini – a tribe that is collectively known as the tunas. Also called the true tunas or real tunas, Thunnus consists of eight species of tuna (more than half of the overall tribe), divided into two subgenera. The word Thunnus is the Middle Latin form of the Greek thýnnos (θύννος, "tuna, tunny") – which is in turn derived from thynō (θύνω, "to rush; to dart").[3][4] The first written use of the word was by Homer.

True tunas Temporal range: Tertiary–holocene PreꞒ Ꞓ O S D C P T J K Pg N [1][2]
Yellowfin tuna
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Scombriformes
Family:	Scombridae
Tribe:	Thunnini
Genus:	Thunnus South, 1845
Type species
Scomber thynnus Linnaeus, 1758
Subgenus
T. (Thunnus) (bluefin group) T. (Neothunnus) (yellowfin group)
Synonyms
Albacora Jordan, 1888 Germo Jordan, 1888 Kishinoella Jordan & Hubbs, 1925 Neothunnus Kishinouye, 1923 Orcynus Cuvier, 1816 Parathunnus Kishinouye, 1923 Semathunnus Fowler, 1933

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 swimmers, and the yellowfin 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 are warm-blooded, which is a rare trait among fish; this enables them to tolerate cold waters and to dive to deeper depths.[5] Bluefin tunas, for example, are found in Newfoundland and Iceland, and also in the tropical waters of the Gulf of Mexico and the Mediterranean Sea, where some individuals go each year to spawn.

Due to overfishing, the range of this genus has declined significantly, having been effectively extirpated from the Black Sea, for example.[6]

Taxonomy

Based on morphology and short-length mitochondrial DNA sequence data,[7] the genus Thunnus is currently classified into two subgenera: Thunnus (Thunnus) (the bluefin group), and Thunnus (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 subgenus Neothunnus, not subgenus Thunnus.[8] Earlier nuclear ribosomal DNA phylogenetic reconstructions also showed similar results.[10]

Fossil specimen

This genus has eight species in two subgenera:

• Subgenus Thunnus (Thunnus):
  • Albacore, T. alalunga (Bonnaterre, 1788)
  • Southern bluefin tuna, T. maccoyii (Castelnau, 1872)
  • Bigeye tuna, T. obesus (Lowe, 1839)
  • Pacific bluefin tuna, T. orientalis (Temminck & Schlegel, 1844)
  • Atlantic bluefin tuna, T. thynnus (Linnaeus, 1758)
• Subgenus Thunnus (Neothunnus):
  • Yellowfin tuna, T. albacares (Bonnaterre, 1788)
  • Blackfin tuna, T. atlanticus (Lesson, 1831)
  • Longtail tuna, T. tonggol (Bleeker, 1851)

Relative sizes of various tunas, with the Atlantic bluefin tuna (top) at about 8 ft (2.4 m) in this sample

The True Tunas of the genus Thunnus, within the Family Scombridae

Scombridae  Gasterochismatinae   Butterfly kingfishes (1 genus)   Scombrinae      Scombrini   Mackerels (2 genera)          Scomberomorini   Spanish Mackerels (3 genera)          Sardini   Bonitos (4 genera)    Thunnini    Allothunnus, slender tunas        Auxis, frigate tunas        Euthynnus, little tunas        Katsuwonus, skipjack tunas      Thunnus   subgenus Thunnus  bluefin group    subgenus Neothunnus  yellowfin group    (true tunas)          (Tunas)

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]

Alternative evolutionary tree for Thunnus

T. albacares     T. obesus         T. tonggol     T. atlanticus         T. maccoyii         T. thynnus     T. orientalis         T. alalunga

An alternative phylogenetic reconstruction for the genus Thunnus, based on nuclear DNA sequence data, which modifies the traditionally recognized bluefin and yellowfin clades by placing Thunnus obesus within the yellowfin clade instead of in the bluefin clade.[8]

Species

Until recently, seven Thunnus species were thought to exist, and Atlantic bluefin tuna and Pacific bluefin tuna were subspecies of a single species. In 1999, Collette established that based on both molecular and morphological considerations, they are, in fact, distinct species.[11][12]

Thunnus, the true tunas
Image	Common name	Scientific name	Maximum length	Common length	Maximum weight	Maximum age	Trophic level	Source	IUCN status
Thunnus (Thunnus) – the bluefin group
	Albacore tuna	T. alalunga (Bonnaterre, 1788)	1.4 m (4.6 ft)	1.0 m (3.3 ft)	60.3 kg (133 lb)	9–13 yrs	4.31	[13][14]	Near threatened[14]
	Southern bluefin tuna	T. maccoyii (Castelnau, 1872)	2.45 m (8.0 ft)	1.6 m (5.2 ft)	260 kg (570 lb)	20–40 yrs	3.93	[15][16]	Critically endangered[16]
	Bigeye tuna	T. obesus (Lowe, 1839)	2.5 m (8.2 ft)	1.8 m (5.9 ft)	210 kg (460 lb)	5–16 yrs	4.49	[17][18]	Vulnerable[18]
	Pacific bluefin tuna	T. orientalis (Temminck & Schlegel, 1844)	3.0 m (9.8 ft)	2.0 m (6.6 ft)	450 kg (990 lb)	15–26 yrs	4.21	[19][20]	Vulnerable[20]
	Atlantic bluefin tuna	T. thynnus (Linnaeus, 1758)	4.6 m (15 ft)	2.0 m (6.6 ft)	684 kg (1,508 lb)	35–50 yrs	4.43	[21][22]	Endangered[22]
Thunnus (Neothunnus) – the yellowfin group
	Blackfin tuna	T. atlanticus (Lesson, 1831)	1.1 m (3.6 ft)	0.7 m (2.3 ft)	22.4 kg (49 lb)		4.13	[23]	Least concern[24]
	Longtail tuna, northern bluefin tuna, tongol tuna	T. tonggol (Bleeker, 1851)	1.45 m (4.8 ft)	0.7 m (2.3 ft)	35.9 kg (79 lb)	18 years	4.50	[25][26]	Data deficient[26]
	Yellowfin tuna	T. albacares (Bonnaterre, 1788)	2.4 m (7.9 ft)	1.5 m (4.9 ft)	200 kg (440 lb)	5–9 yrs	4.34	[27][28]	Near threatened[28]

Maximum reported sizes of Thunnus species.

Overfishing

The worldwide demand for sushi and sashimi, 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 the Tsukiji fish market in Tokyo for a record 155.4 million yen ($1.76 million) – a unit price of JP¥ 1.274 million/kg (US$3,600/lb).[33]

References

1. Graham, Jeffrey B.; Dickson, Kathryn A. (2004). "Tuna Comparative Physiology". The Journal of Experimental Biology. 207 (23): 4015–4024. doi:10.1242/jeb.01267. PMID 15498947.
2. Sepkoski, Jack (2002). "A compendium of fossil marine animal genera". Bulletins of American Paleontology. 364: 560. Archived from the original on 2011-07-23. Retrieved 2008-01-08.
3. θύννος in Liddell, Henry George; Scott, Robert (1940) A Greek–English Lexicon, revised and augmented throughout by Jones, Sir Henry Stuart, with the assistance of McKenzie, Roderick. Oxford: Clarendon Press. In the Perseus Digital Library, Tufts University.
4. θύνω in Liddell and Scott.
5. Bernal, Diego; Brill, Richard W.; Dickson, Kathryn A.; Shiels, Holly A. (2017-12-01). "Sharing the water column: physiological mechanisms underlying species-specific habitat use in tunas". Reviews in Fish Biology and Fisheries. 27 (4): 843–880. doi:10.1007/s11160-017-9497-7. ISSN 1573-5184. S2CID 20554689.
6. Hogan, C. Michael, Overfishing. Encyclopedia of Earth. eds. Sidney Draggan and Cutler Cleveland. National council for Science and the Environment, Washington DC
7. 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.
8. Díaz-Arce, Natalia; Arrizabalaga, Haritz; Murua, Hilario; Irigoien, Xabier; Rodríguez-Ezpelata, Naiara (2016). "RAD-seq derived genome-wide nuclear markers resolve the phylogeny of tunas". Molecular Phylogenetics and Evolution. 102: 202–207. doi:10.1016/j.ympev.2016.06.002. hdl:10754/612968. PMID 27286653.
9. Ciezarek, Adam G.; Osborne, Owen G.; Shipley, Oliver N.; Brooks, Edward J.; Tracey, Sean R.; McAllister, Jaime D.; Gardner, Luke D.; Sternberg, Michael J. E.; Block, Barbara; Savolainen, Vincent (2019-01-01). "Phylotranscriptomic Insights into the Diversification of Endothermic Thunnus Tunas". Molecular Biology and Evolution. 36 (1): 84–96. doi:10.1093/molbev/msy198. ISSN 0737-4038. PMC 6340463. PMID 30364966.
10. Chow, S.; Nakagawa, T.; Suzuki, N.; Takeyama, H.; Matsunaga, T. (2006). "Phylogenetic relationships among Thunnus species inferred from rDNA ITS1 sequence". Journal of Fish Biology. 68 (A): 24–35. doi:10.1111/j.0022-1112.2006.00945.x.
11. 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. ISBN 978-2-9507330-5-4.
12. Tanaka, Y.; Satoh, K.; Iwahashi, M.; Yamada, H. (2006). "Growth-dependent recruitment of Pacific bluefin tuna Thunnus orientalis in the northwestern Pacific Ocean" (PDF). Marine Ecology Progress Series. 319: 225–235. Bibcode:2006MEPS..319..225T. doi:10.3354/meps319225. Archived from the original (PDF) on 2012-12-11.
13. Froese, Rainer and Pauly, Daniel, eds. (2012). "Thunnus alalunga" in FishBase. January 2012 version.
14. Collette B; et al. (2011). "Thunnus alalunga". IUCN Red List of Threatened Species. 2011. Retrieved 9 January 2015.old-form url
15. Froese, Rainer and Pauly, Daniel, eds. (2012). "Thunnus maccoyii" in FishBase. January 2012 version.
16. Collette B; et al. (2011). "Thunnus maccoyii". IUCN Red List of Threatened Species. 2011. Retrieved 9 January 2015.old-form url "This species has been intensively fished since the early 1950s. Its generation length is conservatively estimated to be 12 years. Estimated spawning stock biomass has declined approximately 85% over the past 36 years (1973–2009) and there is no sign that the spawning stock is rebuilding. It is therefore listed as Critically Endangered. Implementation of effective conservation and management measures are urgently needed."
17. Froese, Rainer and Pauly, Daniel, eds. (2012). "Thunnus obesus" in FishBase. January 2012 version.
18. Collette B; et al. (2011). "Thunnus obesus". IUCN Red List of Threatened Species. 2011. Retrieved 9 January 2015.old-form url
19. Froese, Rainer and Pauly, Daniel, eds. (2012). "Thunnus orientalis" in FishBase. January 2012 version.
20. Collette B; et al. (2014). "Thunnus orientalis". IUCN Red List of Threatened Species. 2014. Retrieved 9 January 2015.old-form url
21. Froese, Rainer and Pauly, Daniel, eds. (2012). "Thunnus thynnus" in FishBase. January 2012 version.
22. Collette B; et al. (2011). "Thunnus thynnus". IUCN Red List of Threatened Species. 2011. Retrieved 9 January 2015.old-form url
23. Froese, Rainer and Pauly, Daniel, eds. (2012). "Thunnus atlanticus" in FishBase. January 2012 version.
24. Collette B; et al. (2011). "Thunnus atlanticus". IUCN Red List of Threatened Species. 2011. Retrieved 9 January 2015.old-form url
25. Froese, Rainer and Pauly, Daniel, eds. (2012). "Thunnus tonggol" in FishBase. January 2012 version.
26. Collette B; et al. (2011). "Thunnus tonggol". IUCN Red List of Threatened Species. 2011. Retrieved 9 January 2015.old-form url
27. Froese, Rainer and Pauly, Daniel, eds. (2012). "Thunnus albacares" in FishBase. January 2012 version.
28. Collette B; et al. (2011). "Thunnus albacares". IUCN Red List of Threatened Species. 2011. Retrieved 9 January 2015.old-form url
29. George Karleskint; Richard Turner; James Small (2009). Introduction to Marine Biology. Cengage Learning. p. 522. ISBN 978-0-495-56197-2.
30. "Tuna, Bluefin". Archived from the original on 2011-07-22.
31. "Managed to death". The Economist. 2008-10-30.
32. Thunnus orientalis#Farming
33. "A bluefin tuna sells for record $1.76M in Tokyo". USA Today. 4 January 2013. Retrieved 5 January 2013.

Further reading

• Charles Clover. 2004. The End of the Line: How Overfishing Is Changing the World and What We Eat. Ebury Press, London. ISBN 0-09-189780-7
• 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. doi:10.1007/s10641-006-9069-5. ISSN 0378-1909. S2CID 12596873.

External links

• Froese, Rainer and Pauly, Daniel, eds. (2006). Species of Thunnus in FishBase. January 2006 version.
• Nutritional benefits of tuna dead link]
• The International Commission for the Conservation of Atlantic Tunas