Description
The giant trevally is the largest member of the genus Caranx, and the fifth-largest member of the family Carangidae (exceeded by the yellowtail amberjack, greater amberjack, leerfish and rainbow runner), with a recorded maximum length of 170 cm and a weight of 80 kg. Specimens this size are very rare, with the species only occasionally seen at lengths greater than 80 cm. It appears the Hawaiian Islands contain the largest fish, where individuals over 100 lbs are common. Elsewhere in the world, only three individuals over 100 lbs have been reported to the IGFA.
The giant trevally is similar in shape to a number of other large jacks and trevallies, having an ovate, moderately compressed body with the dorsal profile more convex than the ventral profile, particularly anteriorly. The dorsal fin is in two parts, the first consisting of eight spines and the second of one spine followed by 18 to 21 soft rays. The anal fin consists of two anteriorly detached spines followed by one spine and 15 to 17 soft rays. The pelvic fins contain 1 spine and 19 to 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 below the lobe of the second dorsal fin. The curved section of the lateral line contains 58-64 scales, while the straight section contains none to four scales and 26 to 38 very strong scutes. 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 conical teeth. The species has 20 to 24 gill rakers in total and 24 vertebrae are present. The eye is covered by a moderately well-developed adipose eyelid, and the posterior extremity of the jaw is vertically under or just past the posterior margin of the pupil. The eye of the giant trevally has a horizontal streak in which ganglion and photoreceptor cell densities are markedly greater than the rest of the eye. This is believed to allow the fish to gain a panoramic view of its surroundings, removing the need to constantly move the eye, which in turn will allow easier of detection of prey or predators in that field of view.
At sizes less than 50 cm, the giant trevally is a silvery-grey fish, with the head and upper body slightly darker in both sexes. Fish greater than 50 cm show sexual dimorphism in their colouration, with males having dusky to jet-black bodies, while females are a much lighter coloured silvery-grey. Individuals with darker dorsal colouration often also display striking silvery striations and markings on the upper part of their bodies, particularly their backs. Black dots of a few millimetres in diameter may also be found scattered all over the body, although the coverage of these dots varies between widespread to none at all. All the fins are generally light grey to black, although fish taken from turbid waters often have yellowish fins, with the anal fin being the brightest. The leading edges and tips of the anal and dorsal fins are generally lighter in colour than the main part of the fins. There is no black spot on the operculum. Traces of broad cross-bands on the fish's sides are occasionally seen after death.
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