also: るりすずめだい
noun
sapphire devil; Chrysiptera cyanea
A small, brilliant blue damselfish common in coral reefs of the Indo-Pacific. Often seen in aquariums.
水族館でルリスズメダイの群れを見た。
I saw a school of sapphire devils at the aquarium.
The Japanese name combines 瑠璃 (lapis lazuli, deep blue) with 雀鯛 (damselfish). The exact derivation is uncertain, but it describes the fish's vivid blue color.