Crevalle jack

The crevalle jack (Caranx hippos), also known as the common jack, black-tailed trevally, couvalli jack, black cavalli, jack crevale or yellow cavalli, is a common species of large marine fish classified within the jack family, Carangidae. The crevalle jack is distributed across the tropical and temperate waters of the Atlantic Ocean, ranging from Nova Scotia, Canada to Uruguay in the west Atlantic and Portugal to Angola in the east Atlantic, including the Mediterranean Sea. It is distinguishable from similar species by its deep body, fin colouration and a host of more detailed anatomical features, including fin ray and lateral line scale counts. It is one of the largest fish in the genus Caranx, growing to a maximum known length of 124 cm and a weight of 32 kg, although is rare at lengths greater than 60 cm. The crevalle jack inhabits both inshore and offshore waters to depths of around 350 m, predominantly over reefs, bays, lagoons and occasionally estuaries. Young fish dispersed north by currents in the eastern Atlantic are known to migrate back to more tropical waters before the onset of winter; however, if the fish fail to migrate, mass mortalities occur as the temperature falls below the species' tolerance limits. The crevalle jack is a powerful, predatory fish, with extensive studies showing the species consumes a variety of small fish, with invertebrates such as prawns, shrimps, crabs, molluscs and cephalopods also of minor importance. Dietary shifts with both age, location and season have been demonstrated, which led some researchers to postulate the species is indiscriminant in its feeding habits. The crevalle jack reaches maturity at 55 cm in males and 66 cm in females, with spawning taking place year round, although peaks in activity have been documented in several sites. The larval and juvenile growth has been extensively studied, with the oldest known individual 17 years of age. The crevalle jack is an important species to commercial fisheries throughout its range, with annual catches ranging between 1000 and 30 000 tonnes over its entire range. It is taken by a variety of netting methods, including purse nets, seines and gill nets, as well as hook-and-line methods. The crevalle jack is also a revered gamefish, taken both by lures and bait. The species is considered of good to poor quality table fare, and is sold fresh, frozen, or preserved, or as fishmeal or oil at market. The crevalle jack is closely related to both the Pacific crevalle jack and the longfin crevalle jack, the latter of which has been extensively confused with the true crevalle jack until recently. The crevalle jack is classified within the genus Caranx, one of a number of groups known as the jacks or trevallies. Caranx itself is part of the larger jack and horse mackerel family Carangidae, a group of percoid fishes in the order Perciformes. The species belongs to what William Smith-Vaniz and Ken Carpenter refer to as the Caranx hippos complex, a group of closely related fishes which also includes Caranx caninus (Pacific crevalle jack) and Caranx fischeri (longfin crevalle jack). The crevalle jack was the first species of its genus to be scientifically described and named, and is also the type species of the genus Caranx. It was described and named in 1766 by the famed Swedish taxonomist Carl Linnaeus, based on the holotype specimen taken off the coast of the Carolinas, United States. He named the species Scomber hippos, placing it in the mackerel genus Scomber, a practice which was common prior to 1801 when the carangids were not yet recognised as separate from the scombrids. The specific epithet means 'horse' in Latin, with Scomber hippos literally translating in English as 'horse mackerel', which has become a common name for many species of carangid. As the state of fish taxonomy progressed, the species was transferred to both Caranx and Carangus, with the name Caranx hippos now accepted. Bernard Germain de Lacépède was the first person to separate the crevalle jack from the mackerels, placing it in its own genus Caranx, although he had redescribed the fish as Caranx carangua, which became the type species of Caranx. As well as Lacepede's renaming, the species has been independently redescribed a total of six times, with all of these names, including Lacepede's, categorised as invalid junior synonyms under ICZN rules. There has been extensive discussion in the scientific literature regarding the possible conspecifity of the Pacific crevalle jack, Caranx caninus, with Caranx hippos. Arguments ranged from the species being conspecific, subspecific or as individual species. This led to the creation of two trinomial names; Caranx hippos hippos and Caranx hippos tropicus. The former was an attempt to separate the 'subspecies' on each side of the Americas, while the latter was an unnecessary name to divide the Atlantic Caranx hippos into subspecies. The most recent review of the species complex by Smith-Vaniz and Carpenter treated the fish as separate species, citing differences in the development of hyperostosis and differing anal fin colours as evidence of species status. The species' most often used common name, crevalle jack (or 'jack crevalle') is based on the word 'cavalla', an earlier word used for the jacks. Other names include common jack, black-tailed trevally, couvalli jack, black cavalli, yellow cavalli and a host of generic names, such as horse mackerel and crevalle. The crevalle jack is one of the largest members of Caranx, growing to a known maximum length of 125 cm and a weight of 32 kg, although it is generally uncommon at lengths greater than 65 cm. Unverified reports of fish over 150 cm may also be attributable to this species. The crevalle jack is morphologically similar to a number of other deep-bodied carangids, having an elongate, moderately compressed body with the dorsal profile more convex than the ventral profile, particularly anteriorly. The eye is covered by a well-developed adipose eyelid, and the posterior extremity of the jaw is vertically under or past the posterior margin of the eye. The dorsal fin is in two parts, the first consisting of eight spines and the second of one spine followed by 19 to 21 soft rays. The anal fin consists of two anteriorly detached spines followed by one spine and 16 or 17 soft rays. The pelvic fins contain one spine and five soft rays, while the pectoral fins contain 20 or 21 soft rays. The caudal fin is strongly forked, and the pectoral fins are falcate, being longer than the length of the head. The lateral line has a pronounced and moderately long anterior arch, with the curved section intersecting the straight section midway below the second dorsal fin. The straight section contains 23 to 35 very strong scutes, with bilateral keels present on the caudal peduncle. The chest is devoid of scales with the exception of a small patch of scales in front of the pelvic fins. The upper jaw contains a series of strong outer canines with an inner band of smaller teeth, while the lower jaw contains a single row of teeth. The species has 35 to 42 gill rakers in total and 25 vertebrae are present. In 1972, a crevalle jack caught by fishermen off South Carolina displayed swollen, bulbous mandibles. These swellings were initially thought to be due to a copepod parasite, however radiographs and subsequent sectioning found them to be bony in nature. The cause of this calcified connective tissue is still unknown, and there remains only a single reported case of such an ailment in crevalle jack. The crevalle jack's colour ranges from brassy green to blue or bluish-black dorsally, becoming silvery white or golden ventrally. A dark spot is present on the pectoral fin, with a similar dark to dusky spot present on the upper margin of the operculum. Juveniles have around five dark vertical bands on their sides, with these fading at adulthood. The first dorsal fin, pectoral and pelvic fins range from white to dusky, occasionally with golden tinges throughout. The anal fin lobe is bright yellow, with the remainder of the fin ranging from golden to dusky, while the underside of the caudal peduncle often being yellow in adults. The caudal fin itself is also golden to dusky, with the lower lobe often brighter yellow than the upper, with both the lobes often having a black trailing edge.