The body of the Pacific mackerel tapers at both ends, is rather elongate, and somewhat compressed. The head is pointed and the mouth is large. The head is dark blue, the back is dark blue with about 30 dark wavy lines, and the undersides are silver green. The widely separated first and second dorsal fins serve to distinguish Pacific mackerel from all of the other tuna-like fishes, except for the frigate and bullet mackerel. Pacific mackerel and bullet mackerel can be differentiated by counting the dorsal finlets. Pacific mackerel typically have four to six, while bullet and frigate mackerel have seven to eight finlets.