Surgeonfish Information

Surgeonfish belong to the family Acanthuridae.  There are at least 75 different species of surgeonfish, some of which are referred to as tang, doctorfish or unicornfish.  They have been around for more than 50 million years.  Surgeonfish only inhabit marine waters, but can be found in all tropical and subtropical seas with the exception of the Mediterranean.  They have small scales and a single dorsal fin.  Their bodies are oval and laterally compressed.  They have one or more sharp spines located on either side of the tail base.  The name surgeonfish may refer to the fish’s spines that resemble a surgeon’s scalpel and can cut deep.  These spines are either fixed in place or hinged at the rear depending on the species.  The scalpel-like spine serves as the fish’s defense mechanism against predators.  A powerful burst from their tail can slash a target.  During the planktonic larval stages, predation is a much bigger concern for surgeonfish.

Their mouths are small for nibbling and scraping organisms of rocks and corals, but most surgeonfish consume algae.  Surgeonfish that are more herbivorous might have heavy-walled gizzard like stomachs because of the sand and coral they pick up when feeding.  Species with thin-walled stomachs graze mostly on algae, fronds and filament and consume very little calcareous material when feeding.  They feed during the daytime and hide at night.  As grazers and planktivores, surgeonfish play a crucial role in keeping filamentous and leafy algae from smothering reefs.  When surgeonfish hide and deposit feces in the crevices, this also promotes growth and diversity of corals. 

Surgeonfish come in a variety of colors and patterns, but the larvae start out transparent.  The larvae start in the pelagic zone before sinking to the bottom of the ocean and developing into their juvenile form.  Sexual maturity may be reached after one to two years. There are bottom-dweller adult species along shallow rocky shores and exposed coral reefs, and adult plankton feeders well above the bottom over sandy areas.  Depending on the species, surgeonfish may grow anywhere between 20 cm to 200 cm in length.  There is sexual dimorphism visible among surgeonfish, but not usually permanent dimorphism.  It differs from genera, but size difference between males and females is one of the most common.  Like most fish, surgeonfish can sometimes be territorial.  They are still good in large communities of fish and other tangs though, both in the wild and in aquariums.  Collectors enjoy their colors and durability.  At this time, there do not appear to be any conservation threats to any members of this family.