Fish movements during migrations are diverse in their length, direction and character. There are different classifications of migrations. Counternatant migrations are spawning migrations carried out by fish against the current. The movement of fish against the current (counternatant migrations) usually alternates with downstream movements (denatant migrations).

Migrations are divided into anadromous and catadromous migrations based on the direction of migration and their connection with the current. The former include movements from the depths of the sea to the shores, from the sea to the rivers, from the lower reaches of the river to the upper reaches, and against the current. The latter include downstream movements down the river, from the river to the sea, from the shores to the depths. This classification is generally accepted and widely used. The terms counter-natant migrations and denatant migrations are used much less frequently.