catadromous
kah-TAD-roh-mus
The opposite of anadromous — describing a fish that lives in freshwater and migrates to the sea to spawn. The American and European eels are the classic example: born in the Sargasso Sea, they drift as larvae across the Atlantic, enter rivers, live for decades in freshwater, then one autumn night they begin the long journey back to the open ocean to reproduce and die in a place none of them have seen since birth.
Etymology
From Greek katadromos — kata- (down) + dromos (running, course). Running downward, downstream, toward the sea.
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