The yellowback fusilier (Caesio xanthonota) is a pelagic marine ray-finned fish, a fusilier belonging to the family Caesionidae. It is native to the tropical Indo-Pacific, being found in shallow water from the East African coast to Indonesia. The yellowback fusilier is a small to medium-sized fish which grows to about 40 cm (16 in) long. The mouth is small and terminal and is protusible, being able to be extended forward to swallow food. The body is fusiform or spindle-shaped. The dorsal fin has 10 spines and 14-15 soft rays. The anal fin has three spines and 11 or 12 soft rays. The caudal fin is deeply forked. The body coloration is greyish blue with a bright yellow zone on the back. The yellow area goes from the forehead, between the eyes, to the tail, and includes the dorsal fin and the caudal fin. This area corresponds more or less to the upper third of the body. The belly is plain white.
