Queensland State Archives posted a photo:
Artwork by Frank Olsen.
Surgeonfish (or Tangs) are found throughout the world’s temperate and tropical oceans, and there are approximately 80 species, many of which are found on the Great Barrier Reef. The body is basically flat, and oval in shape, with a small mouth for grazing on algae (although some feed on zooplankton).
They get their name from highly modified scales that have evolved into weapon-like spines at the base of the tail. These spines are either fixed or mobile (like a flick knife) and there can be up to 6 per side, depending on the species. THey are mainly used when the fish feels threatened over territorial disputes, but fishermen have often been slashed when removing them carelessly from nets.
Like some other families of fish, they have the remarkable ability to change their colour according to their mood. The presence of a predator can cause