Caranx lugubris Poey, 1860

Taxonomic Identification

The black jack (Caranx lugubris Poey, 1860) is a large fish.

Documented Size

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.

Unconfirmed Size Record

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.

General Body Shape

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.

Head 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.

Mouth Structure

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.

Dentition

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.

Dorsal Fin Structure

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.

Anal Fin Structure

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.

Paired Fin Structure

The pelvic fins contain 1 spine and 21 soft rays, while the pectoral fins are falcate and longer than the head.

Lateral Line Structure

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.

Caudal Peduncle Features

The caudal peduncle has paired bilateral keels.

Body Scales

The entire chest is covered in scales; like the scales on the rest of the body, they are small and cycloid.

Internal Anatomical Features

This species has a total of 23 to 30 gill rakers and 24 vertebrae.

Body Coloration

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.

Fin and Scute Coloration

The fins are grey to black, and the scutes are black.

Operculum Marking

There is often a small dark spot on the upper edge of the operculum, which is usually smaller than the fish's pupil.

Overall Distribution Range

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.

Indian Ocean Coastal Distribution

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.

Indian Ocean Island Distribution

The species is well recorded from many Indian Ocean islands, including the Seychelles, Réunion, Mauritius, and Cargados Carajos.

Western and Central Pacific Distribution

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.

Eastern Pacific Distribution

In the eastern Pacific, its range extends from Mexico and the Revillagigedo Islands in the north to Costa Rica in the south.

Western Atlantic Distribution

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.

Eastern Atlantic Distribution

In the eastern Atlantic, the species has been recorded from the Azores, Madeira, St. Paul's Rocks, Ascension Island, and the Gulf of Guinea.

Habitat Type

The black jack is a benthopelagic species that is rarely found in shallow inshore waters.

Depth Range

It prefers deep, clear offshore waters at depths between 12 and 354 m.

Preferred Habitat Locations

It is most common in insular oceanic habitats and around offshore islands, and rarely occurs close to continents.

Specific Habitats

It inhabits deep reefs and reef drop-offs, and is also common around oceanic seamounts.

Unusual Habitat Record

It has been recorded in lagoons in the Solomon Islands.

Social Structure

Black jack can live either alone or in schools of up to 30 individuals.

Schooling Cue

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.

Interspecific Schooling

In the Atlantic, the species has been video recorded schooling alongside the almaco jack (Seriola rivoliana) and the greater amberjack (Seriola dumerili).

Diet Documentation Notes

The diet of the black jack has been documented on two occasions.

Easter Island Diet

At Easter Island in the south Pacific, its diet consisted mainly of fish and crustaceans, including stomatopods and isopods.

Brazilian Diet

In Brazil, the species consumes a variety of fish, crustaceans, and molluscs.

Dietary Competition

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.

Unusual Feeding Behavior

Black jack is also known to follow spinner dolphins to feed on their excrement.

Life History Study Location

Parts of the species' life history have been studied from waters off Jamaica.

Jamaican Sex Ratio

There, the male-to-female sex ratio is 1:0.55, meaning males are nearly twice as common as females.

Sexual Maturity Lengths

Females reach sexual maturity at 34.6 cm in length, while males reach sexual maturity at 38.2 cm.

Spawning Timing

The timing of spawning is poorly understood, with spawning events recorded in February, April, May, and July to September.

Unstudied Reproductive Aspects

The reproductive behaviour and early life history of the black jack are completely unknown.

Average Catch Lengths

Analysis of black jack catches indicates the average length is 50 cm for males and 48 cm for females.