What are the semi-migratory fish?

Semi-migratory fish refer to the migration of freshwater fish from one type of water body to another type of water body in freshwater waters, as well as the migration of fish that live in shallow sea areas or brackish water areas into rivers. To sum up, it can be mainly divided into two types, namely semi-migration from rivers and lakes and semi-migration from estuaries.

my country’s four famous major carp, grass carp, herring, silver carp, and bighead carp, are all semi-migratory fish. These fish usually feed and fatten in the affiliated lakes of the main rivers. During the breeding season, they migrate in groups upstream to spawning grounds in the main rivers to reproduce. After giving birth, the broodstock continue to migrate to lakes with abundant food in search of bait. The broodstock fish that inhabit the lower reaches of rivers also migrate to spawning grounds in the middle reaches or upstream to lay eggs. During their migration, their gonads gradually reach maturity. River semi-migratory fish, after foraging and fattening in lakes in autumn, migrate to overwinter in late autumn and early winter, that is, they swim from shallower lakes to the depths of river beds in main rivers to overwinter. However, the overwintering migration of these fish is sometimes not very obvious. When there are deep water areas suitable for overwintering in the lake, such as deep depressions or pools, they can also overwinter in these places. In the spring of the following year, when the water temperature rises, these fishes that have overwintered in pits and pools in the main rivers or deep water areas of lakes will migrate back into the lakes in search of food.

The semi-migratory habits of juvenile semi-migratory fish in rivers and lakes are also very obvious and regular. In the summer of the year they are born, when they have the ability to swim freely, they swim along the coast for feeding and migration. At the mouth of a tributary or the outlet of a lake, you can see schools of young fish struggling to overcome the larger flow speed and enter the tributary or lake to feed. The ability of young fish to overcome the flow speed may be due to the fish's own characteristics of countercurrent movement and the strong feeding requirements of young fish. The gradual abundance of food in the water flow may be a very important external condition. Although juvenile fish, like adult fish, have very obvious and regular migration habits for feeding, they have no obvious overwintering migration and reproductive migration. After the juvenile fish complete their feeding migration in autumn, they move from shallow water areas of lakes to deep water areas to overwinter in late autumn and early winter, and generally do not overwinter in the main rivers. After the water temperature rises in the following spring, they swim from the deep water area of the lake to the shallow water area along the coast where food organisms are rich in order to feed, grow, and fatten.

Another type of semi-migratory fish is the semi-migratory fish in the main stream of estuaries. These fish usually live in estuaries or brackish water areas. During the reproductive season, they enter rivers and travel upstream to suitable places in the middle and lower reaches to reproduce. For example, fishes of the genus Anchovy are typical semi-migratory fish in the mainstream of estuaries. The long-jawed catfish (also known as the sword catfish) is usually distributed in the brackish water areas of the Yangtze River and offshore areas. During the reproductive season, it enters fresh water from the estuary and goes up the main stream to the breeding grounds in the middle reaches of the Yangtze River for reproductive migration. It can reach as far as Dongting Lake, and some in rivers They spawn in the main stream, and also enter tributaries and lakes leading to rivers to spawn. After spawning, the broodstock disperse in fresh water to feed, and then slowly return to the estuary and offshore waters to continue fattening. The juveniles of long-jawed bream also migrate along the river to the estuary area to be fattened. In winter, long-jawed bream do not migrate long distances, but gather in deep offshore areas to overwinter.

There is no difference in the migratory properties of migratory fish and semi-migratory fish. The difference between them is that migratory fish have stricter requirements for spawning grounds, migrate farther, and the breeding period is more concentrated. But this difference is not absolute. The migratory habits of some fish are between migratory and semi-migratory. Some resident fish, due to their strong adaptability to the environment, mostly do not perform obvious migration or semi-migratory movements. However, if the environment permits, carp, for example, can also migrate to lakes and rivers for the winter, and to rivers and lakes in spring. Feeding and migration.

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