Blue Reef Chromis Identification Guide

Key identification features

• Slender, streamlined body in vivid electric blue
• Deeply forked tail fin, often edged with a thin dark line
• Small, terminal mouth suited for picking plankton from the water column
• Color can shift to a duskier blue-grey with age or under stress
• Small size, generally 2-4 inches (5-10 cm)

Common look-alikes

• Yellowtail blue damselfish shares a similarly blue body but has a solid bright yellow tail, while the blue reef chromis stays blue through the tail.
• Sergeant major damselfish has a similar streamlined body shape but shows dark vertical bars on a pale background rather than solid blue.
• Blue-green chromis is a smaller, more greenish-blue relative typically found schooling in tighter, denser groups above staghorn coral.

Where you'll see one

Blue reef chromis form loose to dense schools hovering in the water column just above reef structure, feeding on drifting plankton. They favor current-swept outer reef edges and drop-offs where plankton is abundant, retreating into coral crevices as a group whenever a predator approaches.