Butterflyfish

Butterflyfish are the brightly patterned mid-size reef fish that pair-bond for life. You almost never see one alone, always in twos, moving in synchrony along coral heads. 130+ species across the Indo-Pacific, each with a distinct geometric pattern.

Scientists treat them as ocean-health indicators: butterflyfish abundance correlates closely with live-coral cover, and they're the first species to disappear from declining reefs. Counting them on transects is a standard reef-health survey method.

Present at every FF destination: yellow longnose, vagabond, racoon, threadfin and copperband, easy to identify even for beginners. Andaman, Maldives, Bali and Red Sea all have 10+ resident species each.