Latin name

Caranx melampygus

Other names

Bluefin jack, bluefin kingfish, bluefinned crevalle, blue ulua, omilu, spotted trevally.

Identification

Body elongated, slightly compressed at the sides, covered with small cycloid scales. The thorax is completely covered with scales. The upper body profile is moderately convex anteriorly to the beginning of the second dorsal fin. Lower body profile is only slightly convex. The snout is slightly pointed, not rounded as in other members of the genus Caranx. The tip of the upper jaw reaches to a vertical line passing through the beginning of the orbit. Eyes with thick eyelids. The eyelid is small in the anterior part of the eye and reaches the posterior margin of the pupil in large adults. The teeth on the upper jaw are arranged in two rows. The front row is strong, widely spaced, and fanglike. The inner row has small teeth. The teeth on the lower jaw are in one row. They are strong, conical in shape, widely spaced in adults. The first gill arc has 25-29 gill stamens (including rudimentary ones), of which 5-9 stamens on the upper part and 17-21 stamens on the lower part. The lateral line forms a high arc in the anterior part and then continues straight to the caudal peduncle. The curved part of the lateral line has 55-70 scales, the straight part has 0-10 scales and 27-42 bony flaps. Vertebrae: 10 trunk vertebrae and 14 tail vertebrae.

Features of fish fins

This species has two dorsal fins. The first dorsal fin has 8 hard rays and the second has 1 hard ray and 21-24 soft rays. The anal fin has 1 barbed ray and 17-20 soft rays, with two separate barbs in front of the fin. The anterior soft rays in the dorsal and anal fins are elongated. Pectoral fins elongated, sickle-shaped; their length exceeds the length of the head. Pelvic fins with 1 hard and 20 soft rays. Caudal fin sickle-shaped. 

Fish colouring

Adults have a coppery blue head and upper body covered with small bluish spots and black dots. The spots and dots appear on individuals with a standard body length of 16 to 22 cm, increasing in number as the fish grows. The underside of the body and belly are silvery white. The second dorsal, anal and caudal fins are bright blue. The pelvic fins are whitish. Pectoral fins are pale yellow. There is no spot on the gill covers. In juveniles and small immature individuals, the head and body are silvery gray. Fins are dark gray except for yellow pectoral fins.

Distribution

Widespread in subtropical and tropical waters of the Indo-Pacific and eastern Pacific. Indian Ocean: From the southern tip of Africa along the east coast of Africa to the Red Sea and Persian Gulf. Occurs along the entire coast of South and Southeast Asia to Indonesia and northern and western Australia. The most southerly point of occurrence is the Northwest Cape Peninsula. Also found off hundreds of oceanic islands in the Indian Ocean, including the Maldives, Seychelles, Madagascar, and Cocos Islands. Western Pacific: from southern Japan, Hong Kong and Taiwan, along the entire coast of the People's Republic of China to Vietnam, Malaysia, Philippines; all islands and archipelagos of the central western Pacific (Tonga, Samoa, Polynesia, Hawaiian Islands) and south to the east coast of Australia (to Sydney). Eastern Pacific: from Mexico to Ecuador, including the Galapagos Islands.

Habitat

A marine, brackish, tropical (35°N - 35°S, 30°E - 78°W), reef associated species. It prefers a depth range from 0 to 190 m. 

Size

Maximum body length 117 cm, usually up to 60 cm. Body weight is 43.5 kg.

Behavior

When ambushed, blue fins will hide between corals or in any hiding place on the bottom. The body coloration changes to almost black, and the fish exhibit aggressive territorial behavior, expelling conspecifics from the area. Ambush behavior is usually observed during the spawning season of small reef fish that form large aggregations. Specialized ambush behavior is not characteristic of other members of the Carangidae.

Food and feeding habits

Adults may actively pursue prey in thin water, ambush prey, or feed on fish and crustaceans disturbed by larger predators. Usually active during daylight hours, especially at dawn and dusk, although night hunting has been reported in the coastal waters of South Africa. When hunting collectively, they charge a school of fish, scattering them and then feeding on individual fish that have broken away from the school. There can be up to 20 individuals in a group. More often they hunt alone or in pairs.

The diet includes ray-finned fishes: Labridae, Monacanthidae, Mullidae, Priacanthidae, Pomacentridae, Scaridae. Small amounts of cephalopods and a variety of crustaceans (mainly shrimp, mantis shrimp and crabs). 

Reproduction

Off the coast of East Africa, these fish first mature at a body length of 30-40 cm. They spawn during the summer months in the southern hemisphere from September to March. Off Hawaii, they also first mature at a body length of 35 cm at two years of age. They spawn from April to November with a peak from May to August. Fecundity depends on the size of the female and ranges from 49700 eggs for individuals weighing 760 g to 4270,000 eggs for individuals weighing 6490 g.

Long-term observations of captive bluefin tuna (Oceanic Institute of Hawaii) showed that spawning occurred during the summer months (May-August). During the spawning season, females incubated up to 8 portions of eggs at varying intervals (at least 5 days). Spawning was observed during night hours and was not associated with lunar phases (although it was more frequent during new moon and third quarter). Fecundity depended on fish size and reached 6 million eggs per spawning season, with a relative fecundity of 1545 eggs per gram of female body weight. Mean egg diameter ranged from 0.721 to 0.787 mm.

Fishing

This fish is a popular sport fishing target. 

Relationship with a person

Cases of ciguatera have been reported after eating large specimens of this species.