The world of inhabitants of the seas, oceans, rivers, lakes is very diverse. Scientists count about 12, 000 species of fish in a salty environment, and about 6, 800 specimens in freshwater bodies of water. Often many species of fish migrate regularly: from rivers to the sea, from the sea to rivers. Some do it once a year, some daily. Why is such a movement necessary and what types of species does all migrating living silver fall into? Many have heard of anadromous, catadromous, and transboundary fish species. About them and will be discussed in the article.
What you need to know about migratory fish
Migratory (migratory fish) differ from impassable ones in that they have the ability to swim for some time in the seas, and another half in the rivers flowing into them. Some migratory fish easily switch to a freshwater habitat (anadromous species of fish), while others to marine (catadromous individuals). Many travel long distances for such transitions. Such movements are associated either with the extraction of food, or with reproduction.
Anadromous and catadromous fish species have their own characteristics associated with changes in water salinity. Migrating, such individuals seek favorable conditions for the development of fry, food for nutrition. When moving from one medium to another, a lot of energy is expended and all kinds of obstacles are encountered: waterfalls, rapids, high-speed currents. For this, adult migrants need to accumulate reserve substances in the form of fat. After migrating eggs, many migratory fish will die, and some may spawn repeatedly in this way. Such fish are an important object for fishing and feeding some animals.
Known Anadromes
Anadromous species of fish for spawning from the marine environment moves to fresh. The most prominent representatives are salmon, herring, sturgeon. The most striking example is the salmon of the Pacific Ocean. Adult individuals can weigh 6 kg and have a length of 60 cm. Spawning is carried out in the rivers of the Japanese Peninsula, Primorsky Territory, Kuril Islands, Sakhalin. This species is born in river water, then individuals swim to the deep sea, where they spend from 1 to 6 years. After that, they return to their original habitats, spawn and die. It should be noted that this movement occurs against the flow of rivers.
In the Black and Azov Seas, there is also an anadromous species of fish, such as herring. For migration, they swim in the deltas of European rivers. Anadromous heats are made by sturgeon, lamprey and cyprinids. The list of anadromous species of fish is replenished with shrimp, trout, and three-spined stickleback. Of the known cyprinids, we can call the rudd ugai.
In addition to salmon, lamprey is a rarer representative. It is found in the deltas of the Volga. Caviar spawns in rocky and sandbanks. A very famous anadrome is stellate sturgeon. She lives in the basins of the Black, Caspian and Azov Seas, lays eggs in the Volga, Urals, and Kura.
Another anadromous feature of the Black and Caspian Seas is the spike. He may not leave the river for several years. Chum, salmon, nelma, and whitefish also belong to this species. Some fish make daily migrations to rivers for surface feeding (at night), and in the afternoon they return to the salty environment.
Catadrome Representatives
The most prominent representative of catadromous individuals is the family of eels (eel). His eggs can travel in the open ocean for months and even years. Then it belongs to the European shores, where they swim in the rivers and begin their development. Eel loves a strong current, silty or sandy soil. It is very difficult to notice him, in the afternoon he hides in burrows or under stones. As night falls, he leaves his refuge. European eel spends most of its life in a freshwater environment.
Cross-border fish
Individuals living in one halo, a single economic zone, are called cross-border. Basically, these include semi-migratory fish that live in a salty environment, close to rivers, and spawn in fresh water. These include breams, carp. In the Azov and Aral seas, the North Caspian, zander, ram, roach are found.
Anadromous fish species of the Caspian Sea
The living world of the Caspian basin is striking in its diversity. There are very small gobies and giant representatives - beluga. Salmon and lampreys, which spawn in the Kura, often die from exhaustion. The following species are classified as anadromous fish in this basin: salmon, whitefish, stellate sturgeon, spike, sturgeon. This sea was fond of pike perch, pike, catfish, carp, silver carp and grass carp.
Sturgeons here are not very large, but there are individuals who have lived more than 30 years. Some stellate sturgeons in the Caspian reach 40 kg of weight. But salmon in this sea come across less and less. An important fish for catching here is pike. A significant part of the catches is made by rudd, which are kept aground, covered with dense vegetation.
