A directed (not aimless) run and return occurring regularly in a species, usually at a definite stage in the life cycle, for example, anadromous (said of those fishes which spend most of their life in the sea and which migrate to freshwater to reproduce, e.g. Oncorhynchus, Stenodus, Petromyzon; the opposite is catadromous), catadromous (those fishes which spend most of their lives in freshwater and which migrate to the sea to reproduce, e.g. Anguilla, diadromous (those fishes which regularly migrate between fresh and salt water during a definite period of the life-cycle; includes anadromous and catadromous fishes), amphidromous (fishes which regularly migrate between the sea and fresh water or vice versa at some definite stage in their life cycle but not for the purpose of reproduction), potamodromous (those fishes which make true migrations wholly in freshwater, commonly rivers), oceanodromous (those fishes which make true migrations to sea water).
Одна из форм массового (коллективного, группового) поведения животных, вертикальные миграции также присущи и планктонным организмам.
Migraatiolla tarkoitetaan biologiassa tapahtumaa, jossa eläimiä muuttaa alueelta toiselle. Migraatio voi olla passiivista tai aktiivista riippuen siirtymisen tavasta. Esimerkki aktiivisesta on muuttolintujen kevät- ja syksymuutot. Passiivista on esimerkiksi merivirtojen mukana ajelehtiminen.
Bioloogias tähendab ränne sündmust, mille käigus loomad liiguvad ühest piirkonnast teise. Sõltuvalt rändeviisist võib ränne olla passiivne või aktiivne. Aktiivse rände näide on rändlindude kevad- ja sügisränded. Passiivse rände näiteks on merevooludega kaasa triivimine.