Masked Bannerfish Heniochus monoceros

The Masked Bannerfish is native to external slopes of coral reefs and coral lagoons of the Indo-Pacific from the east coast of Africa to Polynesia. It grows to 23cm long. Most have the white trailing thread of the first dorsal fin that gives the family its name, but the one shown seems to be missing it. They also have a small protrusion on their high forehead.