Marine relict species

...This refers to the situation where an animal that lived in the sea is confined in brackish or freshwater lakes and ponds, and as a result, it grows as a freshwater animal there. Most crustaceans of the mysid family are marine, but the mysid fish caught in Lake Kasumigaura and other places is a species that lives its entire life in lakes and ponds, and is also called a marine relict species. Among fish that go back and forth between freshwater and the sea during their lives, such as salmon, there are some that go down to the sea and grow up in the ocean, and others that spend their entire lives in freshwater and grow up there.

*Some of the terminology used to refer to "marine relict species" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…海にすんでいた動物が汽水あるいは淡水の湖沼などに封じ込められた結果，そこで淡水動物として世代を重ねるようになることをいう。甲殻類のアミの仲間は大部分が海産であるが，霞ヶ浦などで漁獲されるイサザアミは湖沼で一生を送る種で，海産系遺存種とも呼ばれる。またサケの仲間のように一生の間に淡水と海の間を往復する魚類のなかには，同種でありながら海へ下って海洋で育つものと，淡水中で一生を過ごして世代を重ねるものとがある。…

※「海産系遺存種」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