Yellowback Butterflyfish - Chaetodon mertensii

''Chaetodon mertensii'', the atoll butterflyfish, yellowback butterflyfish or Merten's butterflyfish, is a species of butterflyfish . It is found in the Pacific Ocean from the Ryukyu Islands to the Philippines and extending to Lord Howe Island, Rapa Iti and the Tuamotus.

It grows to a maximum of 12.5 cm long. Body color is white with 5-7 chevron-shaped dark grey bands on the sides. The posterior portion of the trunk, the adjacent dorsal and anal fins, and the posterior portion of the.. more