Between sea and river
Fish that migrate between salt and fresh water to breed, like salmon and hilsa. 43 fish on EveryFish so far.
Some fish move between the sea and fresh water to breed. Anadromous fish, such as salmon, hilsa, shad, many sturgeons and the sea lamprey, grow at sea and swim up rivers to spawn. Catadromous fish, such as freshwater eels, do the opposite, living in rivers and travelling to the sea to spawn. These journeys can run to thousands of kilometres and link the ocean to the heart of the continents.
Journeys between waters
Pacific salmon return to the stream where they hatched, often finding it by smell, after years at sea. The hilsa enters the rivers of Bengal in the monsoon, and its run sets the fishing season in Bangladesh and West Bengal. European eels cross the Atlantic to the Sargasso Sea to spawn. Each of these fish has to rebuild its body's salt balance as it moves between salt and fresh water, a change controlled by hormones.
Blocked rivers
Migratory fish need open rivers. Dams, barrages and weirs block their way, and the Living Planet Index for migratory freshwater fish found an average fall of 76 per cent in monitored populations between 1970 and 2016. The Farakka Barrage cut the hilsa run up the Ganges, and dams on the Volga cut sturgeon from their spawning grounds. Fish ladders and lifts help some species, and removing old dams, as on the Elwha River in the United States, has let salmon return.
Famous between sea and river fish
Still to be written: Ilish, Atlantic salmon, European eel, Japanese eel, American shad, Beluga (sturgeon).
Further reading
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Photo credits on this page
The small pictures above come from Wikimedia Commons under free licences. Some are cropped to fit.
- Sea lamprey: Fernando Losada Rodríguez, CC BY-SA 4.0, source
- Sockeye salmon: Timothy Knepp of the Fish and Wildlife Service., Public domain, source