Acanthuridae


The Acanthuridae are a family of ray-finned fish which includes surgeonfishes, tangs, and unicornfishes. The family includes about 86 extant species of marine fishes living in tropical seas, usually around coral reefs. Many of the species are brightly colored and popular in aquaria.

Etymology

The family name comes from Ancient Greek ἄκανθα, meaning "spine", and οὐρά, meaning "tail", a reference to the scalpel-like bony plates on the type species' caudal peduncle. In the early 1900s, the family was called Hepatidae.

Subfamilies and genera

Acanthuridae contains these extant subfamilies and genera:
Several extinct genera are known from fossils dating from the Eocene to Miocene:

Eocene genera

A particularly large diversity of fossil surgeonfish is known from the Monte Bolca lagerstatte of Italy. These represent some of the earliest representatives of the individual tribes within the Acanthuridae.
  • †Acanthuroides Blot & Tyler, 1990
  • †Eorandallius Blot & Tyler, 1990
  • †Frigosorbinia Bannikov & Tyler, 2012
  • †Gazolaichthys Blot & Tyler, 1990
  • †Lehmanichthys Blot & Tyler, 1990
  • †Metacanthurus Blot & Tyler, 1990
  • †Metaspisurus Blot & Tyler, 1990
  • †Padovathurus Tyler, 2005
  • †Pesciarichthys Blot & Tyler, 1990
  • †Proacanthurus Blot & Tyler, 1990
  • †Protozebrasoma Sorbini & Tyler, 1998
  • †Sorbinithurus Tyler, 1999
  • †Tauichthys Tyler, 1999
  • †Tylerichthys Blot, 1980

    Oligocene genera

  • †Arambourgthurus Tyler, 2000
  • †Caprovesposus Daniltshenko, 1960
  • †Glarithurus Tyler & Micklich, 2011
  • ?†Eonaso Blot, 1984

    Miocene genera

  • †Marosichthys Whitley, 1951

    Morphology

The distinctive characteristic of the family is that they have scalpel-like modified scales, one or more on either side of the peduncle of the tail. The spines are dangerously sharp and may seriously injure anyone who carelessly handles such a fish. The dorsal, anal, and caudal fins are large, extending for most of the length of the body. Their mouths are small and have a single row of teeth adapted to grazing on algae.
Surgeonfishes sometimes feed as solitary individuals, but they often travel and feed in schools, which may be a mechanism for overwhelming the highly aggressive defense responses of small territorial damselfishes that vigorously guard small patches of algae on coral reefs.
Most species are fairly small, with a maximum length of, but some in the genus Acanthurus, some in the genus Prionurus, and most species in the genus Naso may grow larger; the whitemargin unicornfish is the largest species in the family, reaching a length up to. These fishes may grow quickly in aquaria, so average growth size and suitability should be checked before adding them to any marine aquarium.
A larval acanthurid, known as an acronurus, looks strikingly different from the juvenile and adult forms of the same individual. It is mostly transparent and tends to have a pelagic lifestyle, living in open water for an extended period of time before settling on the ocean bottom near the shore, where it develops into the juvenile and ultimately the adult form.

Symbiotic bacteria

Acanthurids are the only known hosts of the bacteria of the genus Epulopiscium. These bacteria affect the digestion of surgeonfish, enabling them to digest the algae in their diet.

In the aquarium

Tangs are very sensitive to disease in the home aquarium. However, if fed enough algae and the aquarium is properly maintained, disease should not be a problem. Quarantining the animals for a period is usually needed before introducing them to the aquarium.
Adults range from in length and most grow quickly even in aquaria. When considering a tang for an aquarium, the size to which these fish can grow must be considered. Larger species such as the popular Pacific blue tang surgeonfish, Naso or lipstick tang, lined surgeonfish, Sohal surgeonfish, and Atlantic blue tang surgeonfish can grow to and require swimming room and hiding places.
Many also suggest adding aggressive tangs to the aquarium last as they are territorial and may fight and possibly kill other fish.
Tangs primarily graze on macroalgae from genera such as Caulerpa and Gracilaria, although they have been observed in an aquarium setting to eat meat-based fish foods. A popular technique for aquarists is to grow macroalgae in a sump or refugium. This technique not only is economically beneficial, but also serves to promote enhanced water quality through nitrate absorption. The growth of the algae can then be controlled by feeding it to the tang.