It is very similar in appearance to other members of its genus, Trachurus, especially T. murphyi, which was once thought to be a subspecies of T. symmetricus, and inhabits waters further south.

Pacific jack mackerel travel in large schools, ranging up to 600 miles offshore and to depths of 400 m, generally moving through the upper part of the water column.

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.

[3] Pacific jack mackerel are metallic blue to olive-green dorsally, becoming more silvery ventrally, before transitioning to a white belly.

Jack mackerel is considered safer to consume than tuna because it is a smaller fish, and not a top predator, thus avoiding accumulation of heavy metals such as mercury.

[6] Recent genetic studies have divided the Carangidae into four subfamilies, with the genus Trachurus falling into Caranginae (or tribe Carangini), being most closely related to the 'scads' of the genera Decapterus and Selar.

[7][8] The species was first scientifically described by William Orville Ayres in 1855 based on the holotype specimen taken from San Francisco Bay, California.

[9] He named the species Caranx symmetricus, correctly identifying its relationship to the jacks, but incorporating it into what was later found to be the wrong genus.

The fish was redescribed in 1944 under a different name, Decapterus polyaspis, from a specimen caught in Oregon,[4] which under the ICZN rules classifies as a junior synonym, and it is therefore discarded.