Tuna - WikiHQ

A tuna (: tunas or tuna) is a saltwater fish that belongs to the tribe Thunnini, a subgrouping of the Scombridae (mackerel) family. The Thunnini comprise 15 species across five genera,

Found in warm seas, the tuna is commercially fished extensively as a food fish, and is popular as a bluewater game fish. As a result of overfishing, some tuna species, such as the southern bluefin tuna, are threatened with extinction. ' is derived from used for the Atlantic bluefin tuna, that name in turn is ultimately derived from thýnō, meaning "to rush, dart along".

A dated alternative term is "tunny".

In English, tuna has been referred to as Chicken of the Sea. This name persists today in Japan, where tuna as a food can be called , literally "sea chicken".

Taxonomy

The Thunnini tribe is a monophyletic clade comprising 15 species in five genera:

:* family Scombridae

:** tribe Thunnini: tunas

:*** genus Allothunnus: slender tunas

:*** genus Auxis: frigate tunas

:*** genus Euthynnus: little tunas

:*** genus Katsuwonus: skipjack tunas

:*** genus Thunnus: albacores and true tunas

:**** subgenus Thunnus (Thunnus): bluefin group

:**** subgenus Thunnus (Neothunnus): yellowfin group

The cladogram is a tool for visualizing and comparing the evolutionary relationships between taxa, and is read left-to-right as if on a timeline. The following cladogram illustrates the relationship between the tunas and other tribes of the family Scombridae. For example, the cladogram illustrates that the skipjack tunas are more closely related to the true tunas than are the slender tunas (the most primitive of the tunas), and that the next nearest relatives of the tunas are the bonitos of the tribe Sardini.

|cladogram=

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True species

thumb|Relative sizes of various tunas, with the [[Atlantic bluefin tuna (top) at about in this sample]]

The "true" tunas are those that belong to the genus Thunnus. Until recently, it was thought that there were seven Thunnus species, and that 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.

The genus Thunnus is further classified into two subgenera: Thunnus (Thunnus) (the bluefin group), and Thunnus (Neothunnus) (the yellowfin group).

Other species

The Thunnini tribe also includes seven additional species of tuna across four genera. They are:

:{| class="wikitable"

! colspan="9" | Other tuna species

! style="width:10em" | Common name

! style="width:11em" | Scientific name

! Maximum length

! Common length

! Maximum weight

! Maximum age

! Trophic level

! Source

! style="width:11em" |IUCN status

| Slender tuna

| Allothunnus fallai (Serventy, 1948)

| style="text-align:right;" |

| style="text-align:center;" | 3.74

| style="text-align:center;" |

| LC IUCN 3 1.svg Least concern

| Bullet tuna

| Auxis rochei (Risso, 1810)

| style="text-align:right;" |

| style="text-align:right;" | 5 years

| style="text-align:center;" | 4.13

| style="text-align:center;" |

| Frigate tuna

| Auxis thazard (Lacépède, 1800)

| style="text-align:right;" |

| style="text-align:right;" | 5 years

| style="text-align:center;" | 4.34

| style="text-align:center;" |

| LC IUCN 3 1.svg Least concern

| Mackerel tuna, Kawakawa

| Euthynnus affinis (Cantor, 1849)

| style="text-align:right;" |

| style="text-align:right;" | 6 years

| style="text-align:center;" | 4.50

| style="text-align:center;" |

| Little tunny

| Euthynnus alletteratus (Rafinesque, 1810)

| style="text-align:right;" |

| style="text-align:right;" | 10 years

| style="text-align:center;" | 4.13

| style="text-align:center;" |

| LC IUCN 3 1.svg Least concern

| Black skipjack tuna

| Euthynnus lineatus (Kishinouye, 1920)

| style="text-align:right;" |

| style="text-align:center;" | 3.83

| style="text-align:center;" |

| Skipjack tuna

| Katsuwonus pelamis (Linnaeus, 1758)

| style="text-align:right;" |

| style="text-align:right;" | 6–12 yrs

| style="text-align:center;" | 3.75

| style="text-align:center;" |

Biology

thumb|[[Bigeye tuna Thunnus obesus showing finlets and keels. Finlets are found between the last dorsal and/or anal fin and the caudal fin. They are rayless and non-retractable. Drawing by Dr Tony Ayling.]]

Description

The tuna is a sleek, elongated and streamlined fish, adapted for speed. It has two closely spaced but separated dorsal fins on its back; The first fin is "depressible" – it can be laid down, flush, in a groove that runs along its back; it is supported by spines. Seven to ten yellow finlets run from the dorsal fins to the tail, which is lunate – curved like a crescent moon – and tapered to pointy tips. A tuna's pelvic fins are located below the base of the pectoral fins. Both dorsal and pelvic fins retract when the fish is swimming fast.

Tunas achieve endothermy by conserving the heat generated through normal metabolism. In all tunas, the heart operates at ambient temperature, as it receives cooled blood, and coronary circulation is directly from the gills. This allows the tuna to elevate the temperatures of the highly-aerobic tissues of the skeletal muscles, eyes and brain, which supports faster swimming speeds and reduced energy expenditure, and which enables them to survive in cooler waters over a wider range of ocean environments than those of other fish.

Also unlike most fish, which have white flesh, the muscle tissue of tuna ranges from pink to dark red. The red myotomal muscles derive their color from myoglobin, an oxygen-binding molecule, which tuna express in quantities far higher than most other fish. The oxygen-rich blood further enables energy delivery to their muscles. Even if they have the power to swim faster, dolphins may have to restrict their speed, because collapsing cavitation bubbles on their tail are too painful. Cavitation also slows tuna, but for a different reason. Unlike dolphins, these fish do not feel the bubbles, because they have bony fins without nerve endings. Nevertheless, they cannot swim faster because the cavitation bubbles create a vapor film around their fins that limits their speed. Lesions have been found on tuna that are consistent with cavitation damage.

Based on catches from 2007, the report states: