A surgeonfish is a type of fish of which there are more than 70 different specific species that typically belong to the family of Acanthuridae. They are usually tropical fish, and different species can be found all over the world, often inhabiting reefs and other similar areas. Strongly territorial and defensive, they are not often part of a large private aquarium but can be kept with a bit of extra effort by an owner. A surgeonfish gets its popular name due to two small blades located near the rear fin of the fish, one on each side, used for defense against potential predators.
Sometimes also called unicornfish or tangs, surgeonfish can vary widely in appearance and are often brightly colored. They often have fairly flat bodies that are typically oval in shape and vertical in orientation. Surgeonfish are herbivorous and usually feed on microscopic algae. They tend to only have small mouths with some teeth for eating but not for use in defense or attack. The two blades from which they get their popular name are usually only used for defense, and typically are somewhat retracted within a pair of slots on the body of the fish.
When agitated, a surgeonfish will begin to thrash about with its tail, at which point the two blades or spines will come out from the slot where they are located and can damage a predator or attacker. This makes handling a surgeonfish after catching it fairly hazardous, and some species may even have venom that can cause serious infection and illness when introduced after puncturing the skin with a blade or spine. These spines are located toward the rear of the fish, in a region called the caudal peduncle, which is found just before the caudal fin at the posterior end of the fish.
The family of fish to which they belong, Acanthuridae, comes from two Greek words meaning “thorn tail.” This spine or blade at the tail of a surgeonfish can often appear fairly similar to a scalpel used during medical procedures such as surgery, providing the modern popular name for the fish. Surgeonfish do not generally taste good and so are not often caught for food and are fairly prone to infection in a fish tank so they do not always make great additions to such a tank. They can also be quite territorial and somewhat aggressive, so if they are being added to a tank with other fish, they should be added last to try to avoid issues with these tendencies.