Anadromous: Anadromous fish are those that are born in freshwater, migrate to the ocean to grow and mature, and then return to freshwater to reproduce. Examples of anadromous fish include salmon, steelhead trout, and striped bass.
These fish typically spend the first part of their lives in freshwater streams and rivers, where they hatch and grow. As they mature, they undergo physiological changes that allow them to adapt to saltwater environments, and they migrate to the ocean. In the ocean, they feed and grow until they reach sexual maturity.
When it's time to reproduce, anadromous fish return to their natal streams or rivers. They use their keen sense of smell to navigate their way back to the same waters where they were born. This migration can be incredibly long and arduous, and many fish do not survive the journey.
Once they reach their spawning grounds, anadromous fish lay their eggs in freshwater. The eggs hatch and the young fish remain in freshwater for a period before eventually migrating back to the ocean.
Catadromous: Catadromous fish, in contrast, are those that are born in freshwater but migrate to the ocean to spawn and reproduce, and then return to freshwater to live. These fish typically spend most of their lives in freshwater, but they undertake a migration to the ocean when it's time to reproduce.
Examples of catadromous fish include American eels and European eels. These fish spend most of their lives in freshwater rivers and lakes. When it's time to spawn, they undergo physiological changes that allow them to adapt to saltwater, and they migrate to the ocean.
In the ocean, catadromous fish reproduce. After spawning, they begin the long and arduous journey back to their freshwater habitats. Many fish do not survive this migration, and it is estimated that less than 1% of eels successfully return to their natal waters.
Once back in freshwater, catadromous fish resume their normal life cycle. They may live for several years before embarking on another reproductive migration.