Characteristics of marine migratory fish

The surface of the ocean is very vast, and the difference between depth and depth is also very huge. Although each kind of fish has its own geographical distribution in the ocean, in order to find relatively concentrated food and suitable places for spawning and overwintering, they are more or less always active and make long-distance movements. This action is rarely scattered and occurs regularly in a certain season every year, forming a typical migration. Those oceanic fish that live on the surface of the open ocean spend almost every year in a state of migration. These fish are highly mobile and have a spindle-shaped body shape that is conducive to swimming. Fish migration in the upper ocean often serves two purposes, namely reproduction and feeding. Schools of huge tuna appear at sea in one area within weeks or months, and completely invisible in another period. The migration of tuna may be based on the movement of several types of fish they often eat, such as sardines, herring and other small fish. The mackerel fish that inhabit the Yellow Sea and the East China Sea in my country migrate south to the southern Yellow Sea and the East China Sea to overwinter every autumn. Every year from April to May, four branches migrate northward along the coast to spawn and breed in the coastal areas of Yantai. Generally, after laying eggs in the sea off Yantai and Weihai from May to July, they migrate to the coast of Liaodong Peninsula and the Bohai Sea for feeding. From September to October, the fish turn back and swim southward to overwinter at the wintering grounds. All stages of the migration of the Yellow Sea mackerel schools are carried out continuously, and the migration distance is at least one to two thousand kilometers.

The migration routes and distances of hairtail fish in the Yellow and Bohai Seas of my country have similar characteristics to those of mackerel. Its wintering place is in the southern part of the Yellow Sea. The spawning migration to the north begins in mid-April. They are divided into two branches along the way. One branch travels to Haizhou Bay and the southern coast of Shandong Peninsula to lay eggs, and is fattened along the coast after spawning. The other branch continues northward and enters the Bohai Sea to lay eggs. After laying eggs from mid-May to mid-July, they are scattered along the coast for fattening. From October to the end of December, schools of feeding fish begin to swarm and migrate from the north to the wintering grounds in the southern part of the Yellow Sea.

Mackerel is a warm-water fish that lives offshore in winter. In summer, when the water temperature in the inner bay rises, it goes to the offshore waters on both sides of the northern Atlantic to live and feed. They spawn offshore from May to June, and then inhabit inner bays and estuaries. Large schools of larvae and juvenile fish live in inner bays and estuaries. In November, the mackerel swims offshore to overwinter, until it returns to coastal waters in May of the following year.

The migration of sardines is closely related to the movement of food. Although they spawn in distant seas, from July to November, the adults swim to the northern coast, but the juveniles never appear in large groups along the coast.

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