Thunnus Explained

See main article: Tuna.

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.

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 long and weigh up to . All tunas are extremely strong, muscular swimmers, and the yellowfin tuna is known to reach speeds of up to 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.[1] 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.[2]

Taxonomy

The word Latin: Thunnus is the Middle Latin form of the Greek ("tuna, ") – which is in turn derived from (Greek, Ancient (to 1453);: θύνω, "to rush; to dart").[3] The first written use of the word was by Homer.

Based on morphology and short-length mitochondrial DNA sequence data,[4] 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.[5] [6] 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. Earlier nuclear ribosomal DNA phylogenetic reconstructions also showed similar results.[7]

This genus has eight species in two subgenera:

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.[8] [9]

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Overfishing

The worldwide demand for sushi and sashimi, coupled with increasing population growth, has resulted in global stocks of the species being overfished[10] and bluefin is the most endangered and considered "a serious conservation concern".[11] 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.[12] Though this fish has been farmed in captivity by the Japanese and by the Australians with the help of the Japanese,[13] yields are lower than other farmed fish due to the slow growth rate of bluefin tuna, therefore keeping prices high.[12] On December 30, 2012, a 222kg (489lb) 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).[14]

Further reading

External links

Notes and References

  1. 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. en. 27. 4. 843–880. 10.1007/s11160-017-9497-7. 20554689. 1573-5184. 2019-12-01. 2020-06-17. https://web.archive.org/web/20200617191618/https://www.research.manchester.ac.uk/portal/en/publications/sharing-the-water-column-physiological-mechanisms-underlying-speciesspecific-habitat-use-in-tunas(ad10e79b-2fb8-4bb2-bc86-96eb245d23b9).html. live.
  2. Hogan, C. Michael, Overfishing. Encyclopedia of Earth. eds. Sidney Draggan and Cutler Cleveland. National council for Science and the Environment, Washington DC
  3. .
  4. 10.1111/j.1095-8649.1997.tb01948.x . 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. 2016 . Alvarado Bremer . J.R. . Naseri . I. . Ely . B. .
  5. 10.1016/j.ympev.2016.06.002 . 27286653. RAD-seq derived genome-wide nuclear markers resolve the phylogeny of tunas . Molecular Phylogenetics and Evolution. 102 . 202–207. 2016 . Díaz-Arce . Natalia . Arrizabalaga . Haritz . Murua . Hilario . Irigoien . Xabier . Rodríguez-Ezpelata . Naiara . 10754/612968. free .
  6. 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. en. 36. 1. 84–96. 10.1093/molbev/msy198. 0737-4038. 6340463. 30364966.
  7. 10.1111/j.0022-1112.2006.00945.x . Phylogenetic relationships among Thunnus species inferred from rDNA ITS1 sequence . Journal of Fish Biology . 68 . A. 24–35. 2006 . Chow . S. . Nakagawa . T. . Suzuki . N. . Takeyama . H. . Matsunaga . T. .
  8. Collette . B.B. . 5th Indo-Pacific Fish Conference: Nouméa, New Caledonia, 3–8 November 1997 . Séret, B. . Sire, J.Y. . Mackerels, molecules, and morphology . 1999 . Société Française d'Ichtyologie [u.a.] . Proceedings . Paris . 978-2-9507330-5-4 . 149–164 . 2017-09-16 . 2023-11-30 . https://web.archive.org/web/20231130165207/https://books.google.com/books?id=-0cWAQAAIAAJ . live .
  9. Tanaka . Y. . K. . Satoh . M. . Iwahashi . H. . Yamada . Growth-dependent recruitment of Pacific bluefin tuna Thunnus orientalis in the northwestern Pacific Ocean . Marine Ecology Progress Series . 2006 . 319 . 225–235 . 10.3354/meps319225 . 2006MEPS..319..225T . free .
  10. Book: Introduction to Marine Biology. 522. Cengage Learning. George Karleskint . Richard Turner . James Small . 2009. 978-0-495-56197-2.
  11. Web site: Tuna, Bluefin . dead . https://web.archive.org/web/20110722190940/http://www.montereybayaquarium.org/cr/SeafoodWatch/web/sfw_factsheet.aspx?gid=69 . 2011-07-22 .
  12. News: Managed to death . The Economist . 2008-10-30 . 2011-01-08 . 2011-02-11 . https://web.archive.org/web/20110211161804/http://www.economist.com/node/12502783?story_id=12502783 . live .
  13. [Thunnus orientalis#Farming]
  14. News: A bluefin tuna sells for record $1.76M in Tokyo. USA Today. 5 January 2013. 4 January 2013. 28 July 2018. https://web.archive.org/web/20180728072830/https://www.usatoday.com/story/news/world/2013/01/04/bluefin-tuna-tokyo-sushi/1810557/?dlvrit=206567. live.

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