Longfin bannerfish

The Longfin bannerfish (Heniochus acuminatus), also known as the Pennant coralfish or Pennant butterflyfish, is a small fish reaching a maximum size of about 25 cm, but typically measuring around 15 cm in length. The dorsal fin is elongated into a long white filament. The body is mostly white with two large, distinct black bands. Its body is laterally compressed. The background body color is white with two large black diagonal bands. Behind the second black band, the soft dorsal and caudal fins are yellow. The pectoral fins are also yellow. The head is white, the eyes are black and connected by a black bar. The snout, speckled with black spots, is slightly elongated, with a small terminal protractile (extendable) mouth.

In juveniles, the area behind the second black band differs from that of adults. [Note: Original text mentioned a white area lacking in juveniles, which might be inaccurate; the development of the yellow posterior fins is the main change].

The Pennant coralfish is easily confused with the very similar Schooling bannerfish (Heniochus diphreutes). The main visible differences are: the Longfin bannerfish (H. acuminatus) has a longer snout, and the spots on the snout are darker; the ventral fin of the Longfin bannerfish is longer and has a rounded tip, unlike the Schooling bannerfish, whose ventral fin tip is shorter and more angular.

The Pennant butterflyfish is widely distributed in the tropical and subtropical waters of the Indo-Pacific, from the east coast of Africa to Polynesia, and from southern Japan to the southern Great Barrier Reef. It inhabits coastal areas and reefs, feeding on plankton. Due to its bright coloration, the Longfin bannerfish is often found in aquariums.