noun
rainbow trout
Common freshwater fish, often farmed and used in cuisine.
ニジマスを釣りに行く。
I go fishing for rainbow trout.
この川にはニジマスが放流されている。
Rainbow trout have been released into this river.
Compound of 虹 (niji, 'rainbow') and 鱒 (masu, 'trout'), referring to the fish's iridescent coloration. The exact historical derivation is uncertain.