The Yellow boxfish, Ostracion cubicus, is a boxfish of the genus Ostracion, and can be found in reefs throughout the Pacific Ocean and Indian Ocean as well as the south eastern Atlantic Ocean. It reaches a maximum length of 45 cm.
As the name suggests, it is box shaped. When juvenile, it is very bright yellow in color. As it ages, the brightness fades and very old specimens will have blue-grey coloration with the faded yellow. It feeds mainly on algae, but will also feed on sponges, crustaceans and mollusks. (text source: wikipedia)