Diadromous fish

…Ayu are called amphidromous fish because they are quite different from anadromous fish such as eels. The above anadromous, anadromous and amphidromous fish are collectively called diadromous fish, which is the opposite of potadromous fish, which are river migratory fish that migrate only in freshwater areas, and oceanodromous fish, which are ocean migratory fish that migrate only in the sea. Mullet, black porgy and sea bass sometimes go upstream in rivers as juveniles, but this behavior is rather random and there is no regularity in their life cycle that they enter freshwater or seawater areas at a certain time, so even if they go upstream in rivers, they are not generally called anadromous or anadromous fish. …

*Some of the terminology that mentions "diadromous fish" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…このように，アユの場合はウナギのような降河魚とはだいぶ違うので両側回遊魚amphidromous fishと呼ばれる。上記の遡河魚，降河魚および両側回遊魚を総称して通し回遊魚diadromous fishというが，これは淡水域だけを回遊する河川回遊魚potadromous fish，海の中だけを回遊する海洋回遊魚oceanodromous fishに対することばである。ボラ，クロダイ，スズキなどは幼魚期に川をさかのぼることがあるが，これらの行動はむしろ任意的なもので，生活史の一定の時期に淡水域に，または海水域にはいるというような規則性はないので，川をさかのぼった場合でも一般には遡河魚とか降河魚とは呼ばない。…

※「diadromous fish」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報