Powder blue surgeonfish (Acanthurus leucosternon). This fish inhabits coral reefs in the tropical Indian Ocean. It feeds on algae and can reach a length of 54 centimetres. It takes the name surgeonfish from the sharp spine (yellow) at the base of its tail on each side. These can inflict painful injuries on those who handle the fish without due care. It is often caught as a food fish by local people. Photographed in the Andaman Sea, Thailand.