Mackerel

Mackerel is a common name applied to a number of different species of pelagic fish, mostly from the family Scombridae. They are found in both temperate and tropical seas, typically in the open ocean but occasionally along the coast. Mackerel species typically have deeply forked tails and vertical "tiger-like" stripes on their backs with an iridescent green-blue quality. Many 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. Smaller mackerel are forage fish for larger predators, including larger mackerel and Atlantic cod. Flocks of seabirds, whales, dolphins, sharks, and schools of larger fish such as tuna and marlin follow mackerel schools and attack them in sophisticated and cooperative ways. Mackerel flesh is high in omega-3 oils and is intensively harvested by humans. In 2009, over 5 million tons were landed by commercial fishermen. Sport fishermen value the fighting abilities of the king mackerel.

Species Over 30 different species, principally belonging to the family Scombridae, are commonly referred to as mackerel. The term "mackerel" is derived from Old French and may have originally meant either "marked, spotted" or "pimp, procurer". The latter connection is not altogether clear, but mackerel spawn enthusiastically in shoals near the coast, and medieval ideas on animal procreation were creative.

Scombroid mackerels About 21 species in the family Scombridae are commonly called mackerel. The type species for the scombroid mackerel is the Atlantic mackerel, Scomber scombrus. Until recently, Atlantic chub mackerel and Indo-Pacific chub mackerel were thought to be subspecies of the same species. In 1999, Collette established, on molecular and morphological considerations, that these are separate species. Mackerel are smaller with shorter lifecycles than their close relatives, the tuna, which are also members of the same family.

Scombrini, the true mackerels

The true mackerels belong to the tribe Scombrini. The tribe consists of seven species, each belonging to one of two genera: Scomber or Rastrelliger.

Scomberomorini, the Spanish mackerels The Spanish mackerels belong to the tribe Scomberomorini, which is the "cousin tribe" of the true mackerels. This tribe consists of 21 species in all—18 of those are classified into the genus Scomberomorus, two into Grammatorcynus, and a single species into the monotypic genus Acanthocybium.

Other mackerel In addition, a number of species with mackerel-like characteristics in the families Carangidae, Hexagrammidae and Gempylidae are commonly referred to as mackerel. Some confusion had occurred between the Pacific jack mackerel (Trachurus symmetricus) and the heavily harvested Chilean jack mackerel (T. murphyi). These have been thought at times to be the same species, but are now recognized as separate species.

The term "mackerel" is also used as a modifier in the common names of other fish, sometimes indicating the fish has vertical stripes similar to a scombroid mackerel:

Mackerel icefish—Champsocephalus gunnari Mackerel pike—Cololabis saira Mackerel shark—several species Shortfin mako shark—Isurus oxyrinchus Mackerel tuna—Euthynnus affinis Mackerel tail goldfish—Carassius auratus By extension, the term is applied also to other species such as the mackerel tabby cat, and to inanimate objects such as the altocumulus mackerel sky cloud formation.

Characteristics (Scombridae)

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 bodies. Like other scombroids, they lack a swim bladder, and 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 near-vertical wavy black stripes running along their upper bodies. The prominent stripes on the back of mackerels seemingly are there to provide camouflage against broken backgrounds. That is not the case, though, because mackerel live in midwater pelagic environments which have no background. However, fish have an optokinetic reflex in their visual systems that can be sensitive to moving stripes. For fish to school efficiently, they need feedback mechanisms that help them align themselves with adjacent fish, and match their speed. The stripes on neighbouring fish provide "schooling marks", which signal changes in relative position. The lateral line also helps with orderly schooling.

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