A fish which is born in fresh water and spends most of its life span in the sea but it again returns to freshwater to spawn(to produce or deposit eggs) , these types of migration is called anadromous migration. Example: Salmon, Smelt, Shad and so on.

Which fishes show anadromous migration?

Some of the best-known anadromous fishes are the Pacific salmon species, such as Chinook (king), coho (silver), chum (dog), pink (humpback) and sockeye (red) salmon. These salmon hatch in small freshwater streams. From there they migrate to the sea to mature, living there for two to six years.

Does Cyclostomes show anadromous migration?

Cyclostomes are marine vertebrates but they show migration to fresh water for the process of spawning.