The blackback butterflyfish or blackbacked butterflyfish, Chaetodon melannotus is a member of the family Chaetodontidae. Red Sea and East Africa to Samoa, to southern Japan and throughout Micronesia.
The blackback butterflyfish grows up to 18cm long, and may live for up to 20 years. They are oviparous, forming pairs during breeding. When observed at night, or when frightened, this species changes color; The dorsal portion of the body turns black except for two white patches. It feeds primarily on the polyps of soft and hard corals. Common on staghorn coral thickets, less seen on exposed parts of reefs. They are generally found between 4 and 20m depth, usually solitary or in pairs. Juveniles are more commonly found inshore, In pairs or traveling in small groups. (text source: Wikipedia)