降こう河か回かい遊ゆう

noun

downstream migration

Technical term in biology/ecology for the migration of aquatic animals downstream, typically to spawn or as part of their life cycle. Often contrasted with 遡河回遊 (upstream migration).

• ウナギは降こう河か回かい遊ゆうをする魚さかなとして知しられている。

  Eels are known as fish that undertake downstream migration.