Description
The Pacific jack mackerel is very similar to all other members of Trachurus and a number of other carangid genera, having an elongate, slightly compressed body with both the dorsal and ventral profiles of the body having the same degree of curvature. It is a medium- to large-sized fish, growing to a maximum known length of 81 cm (32 in), although more common at below 55 cm. There two separate dorsal fins are composed of eight spines and one spine followed by 31 to 35 soft rays, respectively. The anal fin is composed of two spines anteriorly detached followed by one spine connected to 26 to 30 soft rays. In some larger individuals, the last few rays at the posterior of the soft dorsal and anal fins are almost entirely separate from the rest of the fin, forming finlets. The caudal fin is strongly forked, typical amongst the Carangidae, while the ventral fin consists of 1 spine and five soft rays. The pectoral fin terminates before the front of the anal fin, having 22 to 24 rays in total. The lateral line dips strongly after the pectoral fin, having 50 to 53 scales on the upper section and 43 to 52 keeled scutes posteriorly. The species teeth are minute, with a patch of teeth on the tongue in a narrow club shaped strip. There are 24 vertebrae in total.
Pacific jack mackerel are metallic blue to olive-green dorsally, becoming more silvery ventrally, before transitioning to a white belly. The top of the head and area near eye is quite dark with a dark spot on the upper rear of the gill cover. The fins are mostly hyaline to dusky, although caudal fin may be yellow to reddish.
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