Over 30 different species, principally belonging to the family Scombridae, are commonly referred to as mackerel. The term “mackerel” means “marked” or “spotted”, and derives from the Old French maquerel, around 1300, meaning a pimp or procurer. The connection is not altogether clear, but mackerel spawn enthusiastically in shoals near the coast, and medieval ideas on animal procreation were creative.
Most mackerel belong to the family Scombridae, which also includes tuna and bonito. Generally mackerel are much smaller and slimmer than tuna, though in other respects they share many common characteristics. Their scales, if present at all, are extremely small. Like tuna and bonito, mackerel are voracious feeders, and are swift and manoeuvrable swimmers, able to streamline themselves by retracting their fins into grooves on their body. Like other scombroids, their bodies are cylindrical with numerous finlets on the dorsal and ventral sides behind the dorsal and anal fins, but unlike the deep-bodied tuna, they are slim.
The type species for scombroid mackerels is the Atlantic mackerel, Scomber scombrus. These fish are iridescent blue-green above with a silvery underbelly and twenty to thirty near vertical wavy black stripes running across their upper body.
Mackerel typically have vertical stripes on their backs and deeply forked tails. Many species are restricted in their distribution ranges, and live in separate populations or fish stocks based on geography. Some stocks migrate in large schools along the coast to suitable spawning grounds, where they spawn in fairly shallow waters. After spawning they return the way they came, in smaller schools, to suitable feeding grounds often near an area of upwelling. From there they may move offshore into deeper waters and spend the winter in relative inactivity. Other stocks migrate across oceans.