Thunnus obesus (Lowe, 1839)
Bigeye tuna
Thunnus obesus
photo by Chow, S.

Family:  Scombridae (Mackerels, tunas, bonitos), subfamily: Scombrinae
Max. size:  250 cm TL (male/unsexed); max.weight: 210 kg; max. reported age: 11 years
Environment:  pelagic-oceanic; marine; depth range 0 - 1500 m, oceanodromous
Distribution:  Atlantic, Indian and Pacific: in tropical and subtropical waters. Absent in the Mediterranean. Highly migratory species, Annex I of the 1982 Convention on the Law of the Sea (Ref. 26139).
Diagnosis:  Dorsal spines (total): 13-14; Dorsal soft rays (total): 14-15; Anal spines: 0-0; Anal soft rays: 14-14; Vertebrae: 39. This large species is distinguished by the following characters: robust, fusiform body, slightly compressed from side to side; total gill rakers on first gill arch 23-31; dorsal fins separated only by a narrow interspace, the second followed by 8-10 finlets; anal fin followed by 7-10 finlets; pectoral fins moderately long (22 to 31% of fork length) in large specimens (over 110 cm FL), but very long (as long as in Thunnus alalunga) in smaller specimens; 2 flaps (interpelvic process) between pelvic fins; very small scales on body; corselet of larger and thicker scales developed, but not very distinct; caudal peduncle very slender, with a strong lateral keel between 2 smaller keels; ventral surface of liver striated; swimbladder present. Colour of back metallic dark blue, lower sides and belly whitish; a lateral iridescent blue band runs along sides in live specimens; first dorsal fin deep yellow, second dorsal and anal fins light yellow, finlets bright yellow edged with black (Ref. 9684).
Biology:  Occur in areas where water temperatures range from 13°-29°C, but the optimum is between 17° and 22°C. Variation in occurrence is closely related to seasonal and climatic changes in surface temperature and thermocline. Juveniles and small adults school at the surface in mono-species groups or mixed with other tunas, may be associated with floating objects. Adults stay in deeper waters (Ref. 5377). Eggs and larvae are pelagic (Ref. 6390). Feed on a wide variety of fishes, cephalopods and crustaceans during the day and at night (Ref. 9340). Meat is highly prized and processed into sashimi in Japan. Marketed mainly canned or frozen (Ref. 9684), but also sold fresh (Ref. 9340).
IUCN Red List Status: Vulnerable (VU); Date assessed: 18 February 2011 (A2bd) Ref. (123251)
Threat to humans:  harmless
Country info:   
 

Entered by: Luna, Susan M. - 17.10.90
Modified by: Kesner-Reyes, Kathleen - 31.01.18
Checked by: Luna, Susan M. - 19.08.99

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