Tuna

A tuna is any of several species of large, fast-swimming oceanic fish comprising the tribe Thunnini within the mackerel family, Scombridae. The group includes fifteen recognized species across five genera, of which the eight species of the genus Thunnus—including the albacore, yellowfin, bigeye, and the three bluefin tunas—are considered the "true tunas." Tunas inhabit tropical and temperate waters throughout the world's oceans and rank among the fastest, most powerful, and most commercially valuable of all marine fishes. Celebrated for their streamlined bodies and a rare among-fish capacity to regulate aspects of their body temperature, tunas have sustained human fisheries for millennia, from the ancient trap fisheries of the Mediterranean to today's global industry supplying sashimi markets in East Asia and the vast canned-tuna markets of Europe and North America.

Etymology and Taxonomy

The English word "tuna" derives from the Spanish atún, which entered Iberian languages through Andalusian Arabic ṭūn, itself from Latin thunnus. The Latin term was borrowed from Ancient Greek θύννος (thýnnos), a word used by Aristotle and other classical authors, and is generally thought to derive from the Greek verb θύνω, meaning "to rush" or "to dart along." Cognates such as French thon, Italian tonno, Portuguese atum, and German Thunfisch share this classical root.

Within the family Scombridae, tunas form the tribe Thunnini, which is closely related to the bonitos (tribe Sardini) and the mackerels (tribe Scombrini). The tribe comprises five genera: Thunnus (the true tunas), Katsuwonus (the skipjack), Euthynnus (little tunnies), Auxis (frigate and bullet tunas), and Allothunnus (the slender tuna). Molecular phylogenetic studies indicate that the genus Thunnus is monophyletic and is divided into two lineages: a bluefin group adapted to cooler waters and a yellowfin group characteristic of warmer seas.

Species

The eight species of true tuna (genus Thunnus) are:

• Atlantic bluefin tuna (T. thynnus) – the largest species, found in the North Atlantic and Mediterranean; individuals exceeding 450 kg have been recorded.
• Pacific bluefin tuna (T. orientalis) – native to the North Pacific, spawning mainly in the Sea of Japan.
• Southern bluefin tuna (T. maccoyii) – confined to temperate waters of the Southern Hemisphere.
• Yellowfin tuna (T. albacares) – a circumtropical species that can exceed 200 kg.
• Bigeye tuna (T. obesus) – a deep-diving tropical and subtropical species.
• Albacore (T. alalunga) – recognizable by its exceptionally long pectoral fins; marketed as "white tuna."
• Longtail tuna (T. tonggol) – an Indo-Pacific species favoring coastal waters.
• Blackfin tuna (T. atlanticus) – the smallest true tuna, restricted to the western Atlantic.

The remaining Thunnini species include the skipjack tuna (Katsuwonus pelamis), by far the most abundant and heavily caught species; the little tunny and kawakawa (Euthynnus); the frigate and bullet tunas (Auxis); and the slender tuna (Allothunnus fallai) of the Southern Ocean. Related but smaller fish such as the bonitos are often colloquially called tunas, though they belong to a separate tribe.

Anatomy and Physiology

Tunas possess a fusiform, torpedo-shaped body ending in a stiff, lunate (crescent-shaped) caudal fin, with a keeled peduncle and a row of finlets along the dorsal and ventral margins. Pectoral and first dorsal fins retract into slots in the body, reducing drag. The body is relatively rigid, generating propulsion mainly through rapid, high-frequency tail beats, and burst swimming speeds reported for larger species exceed 60 km/h.

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