Surgeon fishes are medium-sized tropical fishes and common, easily recognized inhabitants of Galapagos reefs. There are three species in the islands, the yellow-tailed (Prionurus laticlavius, see below), which is the commonest, the purple (Acanthurus xanthopterus) and the goldrimmed (A. nigricans). In some places they are very abundant, with schools comprising hundreds. They are called surgeon fish on account of sharp spines protruding just in front of the tail, which are a defense against predators. These are as sharp as a surgeon's scalpel and they can cut through skin. Surgeon fish eat algae and small organisms growing on reefs. They move en masse, overwhelming smaller, less numerous inhabitants such as damselfish that guard small gardens of algae.
During tours to the Galapagos Islands, snorkelers would always ask how this fish got its name! Look closely just in front the tail and you can see three silvery spotsthese are the 'scalpels', hence 'surgeonfish'. This picture was taken at the invertebrate wall just off Red Beach on Rabida Island.