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A man holding a living salmon.
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What’s Diadromy?
The vast majority of aquatic species live exclusively in either fresh or salt water. However, some species, which are called diadromous, migrate between the two environments. They move between freshwater habitats and the oceans at predictable phases in their life cycles. Activities in one habitat are restricted to reproduction; the other habitat is for eating and growing. Around 250 fish species are considered diadromous, as are a few mollusks and crustaceans. For such species, dams can be a fatal problem.
Diadromous fish can be categorized as anadromous or catadromous, depending on where they spend most of their lives. Anadromous fish live most of their adult lives in the ocean but return to fresh water to spawn and live as juveniles. Probably the most well-known example is the salmon, which is born in the headwaters of freshwater rivers, migrates downstream to estuaries as developing juveniles, and grows to adulthood in the sea.
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