Kanji for Koi

鯉 is the only character for the fish, and in Japanese it covers more ground than the English word. It is the plain river carp as well as the ornamental varieties bred for color, which are 錦鯉 (nishikigoi), brocade carp. English borrowed only the second sense, so “koi” in English is narrower than 鯉 in Japanese.

The character carries a strong association with perseverance. The carp that swims up the waterfall and becomes a dragon is a story shared across East Asia, and it is why carp streamers, 鯉のぼり, are flown for children in May: the wish is that a child climb against the current.

There is also a homophone worth knowing about. 鯉 (koi) and 恋 (koi, romantic longing) sound identical, and Japanese writing plays on the pair. If you want the fish, only 鯉 will do. It is a Jinmeiyō character, so it is permitted in given names, though it is far more familiar as the animal than as a name.