The Atoll butterflyfish (Chaetodon mertensii) is a species of marine fish known for its white body with grey chevron patterns, a black eye stripe, and a bright yellow/orange rear section, including its fins. Also called Merten’s butterflyfish, it lives in the western Pacific, feeds on algae and invertebrates, and inhabits deep lagoons and reefs. It’s a popular aquarium fish that needs a peaceful, spacious tank with live rock for grazing. 

Appearance

Body: White with 4-5 dark grey, V-shaped (chevron) bands on the sides. 

Head: A black bar runs through the eye and over the head, bordered in white. 

Rear: The back of the body, dorsal fin, anal fin, and tail are bright yellow to orange. 

Habitat and Diet

Range: Western Pacific Ocean, from East Africa to the Tuamotu Islands, and north to the Philippines and Japan. 

Environment: Found in deep lagoons and seaward reefs, from 10 to 400 feet deep. 

Diet: Feeds on algae, stony coral polyps, and small benthic invertebrates. 

Aquarium Care

Tank: Requires a large, peaceful fish-only tank with plenty of open swimming space and live rock for grazing.

Diet: Needs a varied diet, including algae-rich foods, and may eat glass anemones (Aiptasia).

Behavior: Can be aggressive towards its own kind and should be kept alone or in a mated pair.