About Caranx lugubris Poey, 1860
The black jack (Caranx lugubris Poey, 1860) is a large fish. It is confirmed to grow up to 1 meter in length and 17.9 kg in weight, and most individuals are shorter than 70 cm. At least one source claims an unconfirmed record of a 2.21 m long black jack; if this is accurate, the species would be the second largest carangid, only smaller than the 2.5 m long yellowtail amberjack. Black jack shares a similar overall body shape with other members of the genus Caranx: it has an oblong, compressed body, with a dorsal profile that is more convex than the ventral profile. This convexity is most prominent on the head, which slopes steeply downward to create a very angular head profile. The profile between the snout and nape is concave, with the indentation centered near the nostrils. Compared to other species in its genus, the black jack has a fairly large mouth, where the maxilla extends to below the center of the eye. The upper jaw holds a series of strong outer canines with an inner band of smaller teeth, while the lower jaw has a single row of widely spaced conical teeth. The dorsal fin of the black jack is split into two sections: the first section has 8 spines, and the second section has 1 spine and 20 to 22 soft rays. The anal fin has 2 anteriorly detached spines and 16 to 19 soft rays. The lobes of both the dorsal and anal fins are elongated. The pelvic fins contain 1 spine and 21 soft rays, while the pectoral fins are falcate and longer than the head. The lateral line has a distinct, moderately long anterior arch, and its curved section intersects the straight section below the lobe of the second dorsal fin. The curved section of the lateral line has around 50 scales, while the straight section has 26 to 32 strong scutes. The caudal peduncle has paired bilateral keels. The entire chest is covered in scales; like the scales on the rest of the body, they are small and cycloid. This species has a total of 23 to 30 gill rakers and 24 vertebrae. The body of the black jack is a uniform olive to brown, grey, or even black along the back, fading to a grey-blue shade near the underside. The fins are grey to black, and the scutes are black. There is often a small dark spot on the upper edge of the operculum, which is usually smaller than the fish's pupil. The black jack has a circumtropical distribution, meaning it lives across tropical and subtropical regions of the Atlantic, Pacific, and Indian Oceans, around the Earth's equator. In the Indian Ocean, it occurs from Natal, South Africa in the west to northern Australia in the east. It is patchily distributed along the east African and Asian coastline of the Indian Ocean, and is absent from the Persian Gulf, Red Sea, and several countries bordering the ocean. The species is well recorded from many Indian Ocean islands, including the Seychelles, Réunion, Mauritius, and Cargados Carajos. In the Pacific Ocean, it is found from parts of the Indonesian-Australian archipelago north to Japan, and across many Pacific Islands such as Hawaii, New Caledonia, and Tonga. In the eastern Pacific, its range extends from Mexico and the Revillagigedo Islands in the north to Costa Rica in the south. In the western Atlantic Ocean, black jack occurs from North Carolina in the U.S. south to Rio de Janeiro, and is most common in the Caribbean and northern Gulf of Mexico. In the eastern Atlantic, the species has been recorded from the Azores, Madeira, St. Paul's Rocks, Ascension Island, and the Gulf of Guinea. The black jack is a benthopelagic species that is rarely found in shallow inshore waters. It prefers deep, clear offshore waters at depths between 12 and 354 m. It is most common in insular oceanic habitats and around offshore islands, and rarely occurs close to continents. It inhabits deep reefs and reef drop-offs, and is also common around oceanic seamounts. It has been recorded in lagoons in the Solomon Islands. Black jack can live either alone or in schools of up to 30 individuals. Like several other jack species, black jack can coordinate these aggregations over coral reefs based on the release of dimethylsulfoniopropionate (DMSP) from the reef. DMSP is a naturally occurring chemical produced by marine algae, and to a lesser extent by corals and their symbiotic zooxanthellae. In the Atlantic, the species has been video recorded schooling alongside the almaco jack (Seriola rivoliana) and the greater amberjack (Seriola dumerili). The diet of the black jack has been documented on two occasions. At Easter Island in the south Pacific, its diet consisted mainly of fish and crustaceans, including stomatopods and isopods. In Brazil, the species consumes a variety of fish, crustaceans, and molluscs. There is also some indication that in Brazil the black jack may compete for food with the red snapper (Lutjanus campechanus), as the two species have almost identical diets. Black jack is also known to follow spinner dolphins to feed on their excrement. Parts of the species' life history have been studied from waters off Jamaica. There, the male-to-female sex ratio is 1:0.55, meaning males are nearly twice as common as females. Females reach sexual maturity at 34.6 cm in length, while males reach sexual maturity at 38.2 cm. The timing of spawning is poorly understood, with spawning events recorded in February, April, May, and July to September. The reproductive behaviour and early life history of the black jack are completely unknown. Analysis of black jack catches indicates the average length is 50 cm for males and 48 cm for females.
