Description
The shadow trevally is similar in form to a number of other jacks in the family Carangidae, having an almost ovate, strongly compressed body. It is fairly large fish, growing to a maximum known length of 85 cm and a recorded weight of 2.6 kg. The dorsal profile is strongly convex, while the ventral profile is less so, even tending to be concave between the snout and the anal fin, while the nape is elevated and almost straight in profile. There are two separate dorsal fins, the first consisting of 8 spines and second of a single spine and 17 to 19 soft rays. The lobe of the second dorsal fin is elongated, being greater than the head length. The anal fin is composed of two anteriorly detached spines followed by a single spine and 15 to 17 soft rays. The lateral line has a moderate arch anteriorly, with the junction of the curved and straight sections below the tenth or twelfth soft rays of the second dorsal fin. The curved section of the lateral line is slightly longer than the straight section, and contains 60 to 63 scales, while the straight part contains 0 to 6 scales followed by 23 to 30 scutes. The breast is devoid of scales ventrally to behind the pelvic fin origin and up to the pectoral fin base, although in rare cases this is interrupted by a lateral band of scales. Both jaws contain bands of small teeth, with the bands becoming wider anteriorly, and the upper jaw also has an irregular outer series of moderately large teeth, with large specimens also showing this in the lower jaw. There are a total of 24 to 28 gill rakers and 24 vertebrae.
In life, the shadow trevally is a blush green colour above, fading to a silvery white on the underside. It takes its common name from a series of small black-brown rectangular blotches which become larger posteriorly on its back between the bases of the second dorsal fin rays. There is also a dark brown diffuse blotch present on the operculum. The spinous dorsal fin is pale to dusky, while the second dorsal fin lobe is dusky with the ray tips yellowish. The anal fin has a distal margin which is whitish blue, the caudal fin has a yellowish upper lobe and pale trailing edges and lower lobe tip. The pectoral fins are hyaline and the pelvic fins are whitish to dusky.
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