The adjective “anadromous” is demonstrated by a common metaphor for difficult activities: fish swimming against the current, or swimming upstream. “Anadromous” comes from the Greek “anadromos,” with “ana-” meaning “up” and “dromos” meaning “running.” Anadromous fish, such as Chinook salmon, are born in fresh water and migrate to the ocean as juveniles. Then they grow into adults before migrating back into fresh water to spawn. The direct opposite of “anadromous” is “catadromous.” Catadromous species, such as American eels, are born in salt water, migrate into fresh water as juveniles, grow into adults, then migrate back into the ocean to spawn.