Mackerel is a common name applied to a number of different species of fish, mostly, but not exclusively, from the family Scombridae. They may be found in all tropical and temperate seas. Most live offshore in the oceanic environment but a few, like the Spanish mackerel (Scomberomorus maculatus), enter bays and can be caught near bridges and piers. Common features of mackerel are a slim, cylindrical shape (as opposed to the tunas which are deeper bodied) and numerous finlets on the dorsal and ventral sides behind the dorsal and anal fins. The scales are extremely small, if present. A female mackerel lays about one million eggs at a time.
Shearwater, tuna, dolphins, whales, orca, seagulls, marlins, sharks, and humans may hunt mackerel. Mackerel are prized (and are highly harvested) for their meat, which is often very oily. They are known for their fighting ability, and are an important recreational and commercial fishery. The meat can spoil quickly, especially in the tropics, causing scombroid food poisoning—it must be eaten on the day of capture, unless properly refrigerated or cured. For this reason, mackerel is commonly salt-cured sushi. According to the U.S. Food and Drug Administration (FDA) and the Natural Resources Defense Council king mackerel is contaminated with high levels of mercury.