淡水鳗是一种降河性洄游鱼类，原产于海中，溯河到淡水内长大，后回到海中产卵。每年春季，大批幼鳗（也称白仔、鳗线）成群自大海进入江河口。
日本七鳃鳗可以迁移到黄海及江苏省淡水中。
Lampetra japonica could migrate to the Yellow Sea region and freshwater in Jiangsu Province.
七鳃鳗，八目鳗一种七鳃鳗科的原始细长淡水或溯河产卵鱼，特点是长有无。
Any of various primitive elongated freshwater or anadromous fishes of the family Petromyzontidae, characteristically having a jawless sucking mouth with rasping teeth.
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