The Yellow Boxfish Ostracion cubicus is a species of boxfish. It 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 centimetres (18 in).
As the name suggests, it is box-shaped. When juvenile, it is bright yellow in color. As it ages, the brightness fades and very old specimens will have blue-grey to black colouration with faded yellow. It feeds mainly on algae, but will also feed on sponges, crustaceans and molluscs.