About Acanthurus olivaceus Bloch & Schneider, 1801
The orange band surgeonfish (Acanthurus olivaceus Bloch & Schneider, 1801) is a deep-bodied, laterally compressed oval fish. Its body length is just over twice its depth, with a maximum recorded length of 35 cm (14 in), and a more common adult length of 25 cm (10 in). Both its dorsal and anal fins are long and low, stretching all the way to the caudal peduncle. The dorsal fin contains 9 spines and 23 to 25 soft rays, while the anal fin contains 3 spines and 22 to 24 soft rays. Its caudal (tail) fin is crescent-shaped, and the fin points grow longer as the fish ages. Adult orange band surgeonfish are greyish-brown, and a sharp vertical line usually separates the paler front half of the body from the darker hind portion. A distinctive orange bar with a purplish-black border sits directly behind the top of the gill cover, and blue and orange lines mark the bases of the fins. Like all surgeonfish, this species has a pair of scalpel-shaped scales that point upward from the caudal peduncle. Larger males develop a convex snout, which clearly distinguishes them from females. Juvenile orange band surgeonfish are solid yellow. This species occurs in the tropical eastern Indian Ocean and western Pacific Ocean. Its range extends from Christmas Island and the Cocos Keeling Islands to southern Japan, Western Australia, Northern Australia, Eastern Australia, Indonesia, the Philippines, and Hawaii. It is a reef-associated fish, most often found on outer reef slopes and in more exposed locations. Adults are solitary or sometimes form schools, and occur at depths between approximately 9 m (30 ft) and 46 m (150 ft). Juveniles live in shallower, sheltered water in small groups. The orange band surgeonfish feeds on detritus, algae growing on the seabed, and the film of diatoms and filamentous algae that covers sand and other substrates. It often forms mixed schools with parrotfish, tangs, and other surgeonfish species that share similar diets. Their grazing helps maintain biodiversity by clearing excessive algal growth from rock surfaces, leaving suitable open habitat for coral larvae to settle. This fish can change its body color from dark to pale almost instantly.
