Bigeye Tuna, Thunnus obesus (Lowe 1839)
Part of a large school of Bigeye Tuna, Thunnus obesus, off Barwon Heads, Victoria, March 2017. Source: Rebecca Lloyd / iNaturalist.org. License: CC by Attribution-NonCommercial
A large commercially important species found worldwide in tropical and subtropical oceanic waters. This is one of the largest tuna species, growing to a length of more than 230 cm and a weight of almost 200 kg.
Bigeye Tuna, Thunnus obesus (Lowe 1839)
More Info
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Distribution |
Found worldwide in all tropical and sub-tropical waters, except the Mediterranean Sea. In Australia restricted to the northern half of the coastline, from the Recherche Archipelago, Western Australia, to about Cape Howe, Victoria. Bigeye Tuna are a highly migratory species found in the epi- and mesopelagic zones of the ocean from surface waters to a depth of 250 m. Juveniles and smaller adult fish usually school at or near the surface in groups of mixed sizes, or with other species, whereas larger adults are found in deeper water. Although the preferred surface water temperate range is between 17°C and 22°C, data from commercial longline catches has shown that the species occurs at a wide range of water temperatures (13-29°C). near ocean features such as current fronts, floating objects and thermoclines. |
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Features |
Meristic features: Dorsal fin XI-XIV, 12-16; Analfin 11-16; Pectoral fin 30-36; Gill rakers 23-31; Vertebrae 39. Body fusiform, elongate and slightly compressed, deepest at midle of spinous dorsal fin; caudal peduncle with a well-developed keel, flanked on each side by a smaller keel. Spinous and soft dorsal fins separated by a narrow space. Both dorsal and anal fins are followed by 7-10 finlets. Pectoral fins moderately long, 22-31% fork length. Each jaw with a single series of small, conical teeth. Body covered in small scales, anterior corselet of larger scales indistinct. Swimbladder present. |
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Size |
To at least 230 cm and 197 kg. |
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Colour |
Bigeye Tuna are a metallic blue on top, whitish on the lower sides and belly, with no dark spots or stripes. The dorsal and anal fins are yellow, and the finlets are bright yellow with a black margin. Live fish have an iridescent blue lateral band running along the sides. |
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Feeding |
Bigeye Tuna are opportunistic predators, feeding on a range of fishes, squid and crustaceans. Juveniles consume planktonic invertebrates, especially crustaceans such as copepods and cladocerans. Large adults often feed below the thermocline, even occasionally diving below 500 metres. |
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Biology |
The sexes are separate and fertilisation is external. Eggs and larvae are pelagic. Spawning occurs a night on the full moon in tropical waters. Females spawn more than 2 million tiny pelagic eggs. The larvae and juveniles grow rapidly and mature during their second or third year between 100-130 cm in length. They grow to a maximum age of 16 years. |
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Conservation |
IUCN: The species is listed as Vulnerable on the IUCN Red List of Threatened Species http://www.iucnredlist.org/apps/redlist/details/21859/0, and the Pacific stock is listed as Endangered on the IUCN Red List of Threatened Species http://www.iucnredlist.org/apps/redlist/details/21859/0 |
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Species Citation |
Thynnus obesus Lowe 1839, Proc. Zool. Soc. Lond. 7: 78, Madeira. |
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Author |
Dianne J. Bray & Sascha Schultz |
Bigeye Tuna, Thunnus obesus (Lowe 1839)
References
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