Royal Gramma (Gramma loreto)

Royal Grammas orient to the nearest surface rather than to gravity, which is why you'll usually find one hovering upside down under a ledge instead of right-side up in open water — a trait called thigmotropism that it shares with its close relative, the Randall's Assessor. The clean purple-to-yellow color break has made it a reef staple for decades, and it never seems to go out of style.

Care level: Easy · Temperament: Peaceful · Max size: ~3" · Min tank: 30 gal, with caves/ledges · Diet: Carnivore, meaty foods