A mackerel is a sea fish with a dark, patterned back. They'd gone out to fish for mackerel. Mackerel is this fish eaten as food. mackerel a sea fish that has oily flesh and a strong taste. Swift-moving, carnivorous, torpedo-shaped food and sport fishes (family Scombridae, order Perciformes) of temperate and tropical seas worldwide. Mackerels are 1-5.5 ft (30-170 cm) long. The common mackerel (Scomber scombrus) of the North Atlantic Ocean and the chub mackerel (S. colias) of the Pacific and Atlantic oceans are economically important, as are the Indian mackerels (genus Rastrelliger) and the frigate mackerels (genus Auxis). Other species (genus Scomberomorus) are favourite game fish. The name mackerel also refers to certain shark species (see mackerel shark), tuna, and bonito