All about Mackerel

Mackerel (belonging to family Scombridae) are found off all British coasts.
The family Scombridae is a large family of marine fishes, containing fish such as the Tuna. Members of this family are well streamlined for efficient and fast movement through the water.
Mackerel are predatory fish, primarily feeding on crustaceans, fish eggs, small fish and even other mackerel fry.

There are a number of different types of Mackerel found on either side of the Atlantic Ocean, but only those found in and around the UK are described here.
An important commercial species fished by drift nets as food fish or for industrial use, but popularly fished from boats for sport. They grow on average to about 12" long (30cm) and are coloured blue/green above the lateral midline and silver below. The also have wavy black vertical lines covering their backs. The common mackerel has two well separated dorsal fins with 5 dorsal and anal finlets. Two keel like fins are also present on the underside of the fish.

Mackerel winter in deep water (approximately 300m) but return to the shallows around the coast in May-June to spawn. The fish will then spawn, the resulting eggs released into the sea in great numbers, up to 90,000 per spawning. The eggs are between 1 and 1.4mm in size. They consist of an unsegmented yolk surrounded by a greeny-black pigmented oil globule. Hatching occurs after 2-6 days. The juvenile fish stay offshore for about 2 years until they are sexually mature. At this time they join the great shoals of mackerel that form at spawning time.

The shoals of mackerel that form at this time consist of hundreds of fish. Larger shoals have been estimated in the thousands. The shoals are constantly on the move, as the mackerel must keep moving. The common mackerel has no swimbladder and uses a passive gill ventilation form of breathing. The fish swim mouth open and the gill chambers expanded, thus water flows through the gills. (Ramjet effect) This saves energy which is used by other fish to pump water through the gills when the mouth closes. Therefore it must move to live, if the fish is not swimming it will drown. The fish also are on the move after it's prey, they feed in the summer where there will be currents, thus around headlands, breakwaters, piers and beaches that experience a strong tidal flow.
If common mackerel are not caught then they can live to about 20 years, when they can be 2kg or more in weight.

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