Mackerel n. (Zool.) Any species of the genus Scomber of the family Scombridae, and of several related genera. They are finely formed and very active oceanic fishes. Most of them are highly prized for food. Note: The common mackerel (Scomber scombrus), which inhabits both sides of the North Atlantic, is one of the most important food fishes. It is mottled with green and blue. The Spanish mackerel (Scomberomorus maculatus), of the American coast, is covered with bright yellow circular spots. Bull mackerel, Chub mackerel. (Zool.) See under Chub. Frigate mackerel. See under Frigate. Horse mackerel. See under Horse. Mackerel bird (Zool.), the wryneck; so called because it arrives in England at the time when mackerel are in season.
Mackerel cock (Zool.), the Manx shearwater; so called because it precedes the appearance of the mackerel on the east coast of Ireland.
Mackerel guide. (Zool.) See Garfish (a). Mackerel gull (Zool.) any one of several species of gull which feed upon or follow mackerel, as the kittiwake.
Mackerel midge (Zool.), a very small oceanic gadoid fish of the North Atlantic. It is about an inch and a half long and has four barbels on the upper jaw. It is now considered the young of the genus Onos, or Motella.
Mackerel plow, an instrument for creasing the sides of lean mackerel to improve their appearance.
Mackerel shark (Zool.), the porbeagle.
Mackerel sky, or Mackerel-back sky, a sky flecked with small white clouds; a cirro-cumulus. See Cloud. "Mackerel sky and mare's-tails Make tall ships carry low sails." 
