Description
The blackfin scad has a body profile very similar to that of the other round scads of the genus Alepes, in particular to Alepes apercna, but can be distinguished quite easily by the prominent black colouration of the dorsal fin. The species has a tendency, like other carangids, to become more elongated with age, thus changing their body proportions slightly. It has an oblong, compressed body with dorsal and ventral profiles that are nearly equally convex in shape. The nose somewhat blunter than others in the genus, and has a mouth full of numerous comb like teeth. Like other members of Alepes, it has an adipose eyelid which is well developed only on the posterior section of the eye. The dorsal fin is split into two sections like in all of the Carangidae, the first with 7 or 8 spines and the second with one spine followed by 23 to 26 soft rays. The anal fin consists of two detached spines followed by a single spine and 18 to 21 soft rays, with both the anal and dorsal fins have a low profile. The pectoral fin is falcate and extends to beyond the junction of the curved and straight sections of the lateral line. The lateral line itself is strongly arched anteriorally, with the curved and straight sections of the line intersecting just after the commencement of the spinous dorsal fin. The curved section of the lateral line holds 31 to 50 scales and up to 2 scutes, while the straight section holds up to 4 scales and 49 to 69 scutes. The gill rakers number 24 to 30 and the species has 24 vertebrae. The blackfin scad has a maximum known length of 25 cm.
The upper body of the fish is silvery blue above grading to a silvery white below with a diffuse black spot. The membranes of the first, spinous dorsal fin are black, giving the species its common name. All other fins are pale to hyaline with the exception of the caudal fin which is a dusky yellow with darker edges.
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