A fish ladder on a river in Germany, to help with migration.Many species of salmon are anadromous and can migrate long distances up rivers to spawnAllowing fish and other migratory animals to travel the rivers can help maintain healthy fish populations
Many species of fish move from one body of water to another. Many fish do this on a regular basis. If it is done by many fish, it is usually called fish migration. The timespans and distances vary. Some migrations occur everyday, others take months or years. Some migrations are seasonal. Sometimes fish move within the same body of water. They may spend the day near the surface and move to deeper sections at night, for example.
Forms of migration
Common forms of migration:
anadromous migration: The adult fish live in the sea, they migrate up a river to spawn. The young fish will then migrate back to the sea. Salmon species are examples of such migrants
catadromous migration: The adult fish live in a river or lake, they will migrate to the sea to spawn. Some eel species fall into this category
diadromous migration: term used to include both therms above.
amphidromous migration: Fish that live in or near the estuaries of rivers, and regularly change between the river, its estuary and the sea. Examples for this are certain species of flounder.
Reasons for migration
Common reasons for migrations include that they find more food at the other place, or that they move there to spawn. In some cases, the reasons for the migration are unknown.
