As a juvenile, its diet consists primarily of plankton. Adults are omnivorous and feed on plankton, but will also graze on algae. Spawning occurs during late afternoon and evening hours. This event is indicated by a change in color from a uniform dark blue to a pale blue. The fish is important for coral health as it eats algae that may otherwise choke it by overgrowth. Paracanthurus hepatus has a royal blue body, yellow tail, and black "palette" design. The lower body is yellow in the west-central Indian Ocean. It grows to 12 in. Adults typically weigh around 600 g (21 oz) and males are generally larger than females.