Fish migration is mass relocation by fish from one area or body of water to another. Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousands of kilometres. Such migrations are usually done for better feeding or to reproduce, but in other cases the reasons are unclear.
Many species of salmon are anadromous and can migrate long distances up rivers to spawn
Life cycle of anadromous fish. From a U.S. Government pamphlet. (Click image to enlarge.)
Animal migration is the relatively long-distance movement of individual animals, usually on a seasonal basis. It is the most common form of migration in ecology. It is found in all major animal groups, including birds, mammals, fish, reptiles, amphibians, insects, and crustaceans. The cause of migration may be local climate, local availability of food, the season of the year or for mating.
Mexican free-tailed bats on their long aerial migration
Wildebeest on the Serengeti 'great migration'
Flocks of birds assembling before migration southwards
Many species of salmon migrate up rivers to spawn