The Blue Reef Chromis, Chromis cyanea, is a compressed, oval-bodied damselfish from the Western Atlantic, ranging from the southeastern United States and Bermuda through the Gulf of Mexico and the Caribbean. Adults display a bright to deep electric-blue body marked with a dark dorsal stripe and black edging along the dorsal fin, the upper and lower lobes of the forked tail, and the leading edge of the anal fin. The absence of a black spot at the pectoral-fin base is a reliable identification point. In nature, these fish hover in loose aggregations above outer reefs and large coral heads, picking food from passing water.

Adults reach roughly 5 inches, and a 30-gallon aquarium is the minimum footprint for a single specimen. Open water matters more than raw volume for this species, since it spends daylight hours suspended in the current rather than perched on rock. Pair that swimming room with aquascaping that provides caves, crevices, and overhangs, as the fish retreats into shelter at night and whenever startled. If a group is planned, step well beyond the minimum and choose a considerably larger system with rockwork arranged to break sight lines, which reduces the continual chasing that develops among established individuals. Where spawning is a goal, include a flat sand or similar open substrate area, since males prepare nest sites on the bottom.