Many species of fish make regular migrations, the frequency of which varies from daily to annual, and the distance from several meters to thousands of kilometers . Migrations are usually associated with food extraction or reproduction , although in some cases the causes of migration have not yet been clarified.
Classification of migratory fish
- Diadromes ( ancient Greek δια- —a prefix with the value of through movement) migrate from salt water to fresh water and vice versa ( fish through passage ). There are three types of diadromes:
- Anadrome ( ancient-Greek. Ἀνα- - up) live in the seas , breed in fresh water
- Catadroms ( ancient Greek κατα- down) live in fresh water, breed in the sea
- Amphidromas ( ancient Greek ἀμφι- - both) move between fresh and saline waters during the life cycle, but not for the purpose of reproduction
- Potamodromes ( ancient Greek ποταμός - river ) migrate only in fresh waters.
- Oceanogroms ( ancient Greek ὠκεανός - ocean ) migrate only in salt water
The best known species of migratory fish
The most famous anadroms are Pacific salmon . They hatch from caviar in freshwater rivers and lakes, migrate downstream and live in the sea for one to six years, then return to the places from which they originally migrated, spawn and soon die. Salmonids are able to travel hundreds of kilometers upstream, and people must install fish ladders on dams to allow the fish to swim. Also anadroms are kumzha , a three-needle stickleback , shad . In the carp family, the representatives of the anadromous species are Ugai rudd .
An example of catadroms is the freshwater eel of the eel family, whose larvae can move for several months and even years in the open ocean before returning to their native river hundreds of kilometers away.
Such a bull shark belongs to amphidromas (it lives in Lake Nicaragua in Central America and in the African Zambezi River ). In the first case, the migration occurs in the Atlantic Ocean , in the second - in the Indian .
Daily vertical migrations are also common: many marine species feed at the surface at night and return to the depth during the daytime. Some large marine fish, such as tuna , migrate annually from north to south and vice versa, following changes in ocean temperature . Fish migrations in fresh water are usually shorter: as a rule, they come from a lake into a river and back for breeding purposes.
- Sardine stroke