Crevalle Jack - Description

Description

The crevalle jack is one of the largest members of Caranx, growing to a known maximum length of 124 cm and a weight of 32 kg, although it is generally rare at lengths greater than 60 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.