Description
The bar jack is a moderately large species, growing to a recorded maximum length of 69 cm, and a weight of 6.8 kg, but is commonly encountered at lengths of less than 40 cm. The bar jack displays the typical body shape of most of the jacks, having an elongate, moderately deep and compressed form, with dorsal and ventral profiles of approximately equal convexity. The dorsal fin is divided into two sections, the first consisting of 8 spines while the second has 1 spine followed by 26 to 30 soft rays. The anal fin is composed of 2 anteriorly detached spines followed by 1 spine and 23 to 26 soft rays, with both the anal and soft dorsal fin lobes being slightly elongated. The pectoral fins are falcate and longer than the head, consisting of 19 to 21 soft rays. The lateral line is moderately arched anteriorly, and possesses 17 to 104 scales including 23 to 29 scutes posteriorly; also having bilateral paired caudal keels present. The chest is completely scaled, which easily distinguishes it from the similar crevalle jack, Caranx hippos. The snout is moderately pointed, with both the jaws containing narrow bands of villiform teeth, with the bands becoming wider anteriorly. The upper jaw also contains an outer row of enlarged recurved teeth. There are 10 to 14 upper limb gill rakers, and 31 to 38 on the lower limb and 24 vertebrae.
The bar jack has a gray to grayish blue upper body with a silvery tint, which fades ventrally to a white belly. As indicated by their common name, adult bar jack have a horizontal stripe running along their back and through the lower lobe of the caudal fin. This bar is a golden brownish to blackish color, often with an electric blue bar running parallel immediately underneath it. All other fins are pale dusky to hyaline. Juveniles have up to 6 dark bands on their body and a darker lower caudal lobe than the upper lobe, foreshadowing the bar that develops at a later stage. At these early stages, they are difficult to distinguish from Carangoides bartholomaei, with the best identifier being gill raker counts. The entire body has been observed to change colour to a blackish colour when the fish is feeding near the bottom.
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