Scarlet Hawkfish (Neocirrhites armatus)

Hawkfish don't have a swim bladder, which sounds like a design flaw until you realize what they actually do with that limitation: instead of swimming freely through the water column like most reef fish, they perch, using their thickened lower pectoral fin rays almost like tiny legs to prop themselves on a rock or coral branch and watch for food to drift by. The Scarlet Hawkfish, easily one of the most vividly colored small fish in the trade, spends most of its day doing exactly that from a perch in the rockwork, darting out for a meal and returning to the same spot. It's reef safe with corals and generally peaceful, though it will treat small ornamental shrimp as a snack given the chance, so know your tankmates before adding one.