Acanthuridae
Marine fishes with scalpel-like spines on the tail.
The Acanthuridae family, made up of ray-finned fish, includes surgeonfishes, tangs, and unicornfishes. Around 86 living species of these marine fish inhabit tropical seas, typically near coral reefs. Their bright colors make many of them popular choices for aquariums.
The family name comes from the Ancient Greek words for "spine" and "tail," referring to the sharp, scalpel-like bony plates found on the tail stalk of the type species. In the 1800s, this family was called Hepatidae.
Living subfamilies and genera within Acanthuridae are: Subfamily Nasinae (genus *Naso*), and Subfamily Acanthurinae, which includes the tribes Acanthurini (genera *Acanthurus* and *Ctenochaetus*), Prionurini (genus *Prionurus*), and Zebrasomini (genera *Paracanthurus* and *Zebrasoma*).
Several extinct genera are known from fossils dating from the Eocene to the Miocene. A particularly rich collection of fossil surgeonfish comes from the Monte Bolca Lagerstätte in Italy, representing some of the earliest members of the family's tribes. Eocene genera include *Acanthuroides*, *Eorandallius*, *Gazolaichthys*, *Lehmanichthys*, *Metacanthurus*, *Metaspisurus*, *Padovathurus*, *Pesciarichthys*, *Proacanthurus*, *Protozebrasoma*, *Sorbinithurus*, *Tauichthys*, and *Tylerichthys*. Oligocene genera are *Arambourgthurus*, *Caprovesposus*, *Glarithurus*, and possibly *Eonaso*. The Miocene genus is *Marosichthys*.
The family’s key feature is one or more scalpel-like modified scales on each side of the tail stalk. These spines are dangerously sharp and can seriously injure anyone handling the fish carelessly. The dorsal, anal, and tail fins are large, running most of the body’s length. Their mouths are small, with a single row of teeth suited for grazing on algae. Surgeonfish sometimes feed alone, but often travel and feed in schools, which may help them overwhelm the aggressive defenses of small, territorial damselfish guarding algae patches on reefs.
Most species are fairly small, reaching 15–40 cm (6–15.5 in) at most, but some in the genera *Acanthurus* and *Prionurus*, and most in *Naso*, grow larger. The whitemargin unicornfish (*Naso annulatus*) is the largest, up to 1 m (3 ft 3 in). These fish can grow quickly in aquariums, so average growth size and suitability should be checked before adding them to a marine tank.
The larval stage, called an acronurus, looks
- Common name
- Surgeonfishes, tangs, unicornfishes
- Number of extant species
- About 86
- Habitat
- Tropical seas, usually around coral reefs
- Distinctive feature
- Scalpel-like modified scales on the caudal peduncle
- Largest species
- Whitemargin unicornfish (Naso annulatus), up to 1 m
- Typical size range
- 15–40 cm (6–15.5 in)
- Earliest known fossils
- Eocene epoch
Lore & Background
The family name Acanthuridae comes from Ancient Greek terms ἄκανθα (ákantha), meaning 'spine', and οὐρά (ourá), meaning 'tail', referencing the scalpel-like bony plates on the type species's caudal peduncle. In the 1800s, the family was called Hepatidae. The family contains two extant subfamilies: Nasinae and Acanthurinae, with several tribes and genera including Acanthurus, Ctenochaetus, Prionurus, Paracanthurus, and Zebrasoma.
Several extinct genera are known from fossils dating from the Eocene to Miocene. A particularly large diversity of fossil surgeonfish is known from the Monte Bolca Lagerstätte of Italy, representing some of the earliest
Reader's Guide
The Acanthuridae family holds significance as a diverse group of marine fishes that are both ecologically important on coral reefs and popular in the aquarium trade. Their defining feature—the scalpel-like spines on the caudal peduncle—gives them their common name and serves as a defense mechanism. The family's evolutionary history is well documented through fossils from the Eocene to Miocene, with the Monte Bolca Lagerstätte providing a rich record of early representatives. Their feeding behavior, often in schools, helps them overcome territorial damselfishes while grazing on algae. The unique larval stage, the acronurus, highlights a complex life cycle adapted to pelagic dispersal before settling on reefs. Additionally, acanthurids are the only known hosts of the bacteria Epulopiscium, which aid in digesting algae. Their bright colors and manageable size make them popular in aquaria, though potential owners should check growth size and suitability. The family's taxonomic history includes a former name, Hepatidae, and a well-organized subfamily and tribe structure that reflects evolutionary relationships.
Did You Know?
- The family name comes from Ancient Greek for 'spine' and 'tail', referring to the scalpel-like plates on the tail peduncle.
- In the early 1900s, the family was called Hepatidae.
- A larval acanthurid, called an acronurus, is mostly transparent and lives in open water before settling near shore.
- Acanthurids are the only known hosts of the bacteria Epulopiscium, which help digest algae.
Frequently Asked Questions
What is Acanthuridae?
Acanthuridae is a family of ray-finned marine fish that groups together surgeonfishes, tangs, and unicornfishes. Roughly 86 living species belong to this family, and they are most commonly encountered in tropical waters surrounding coral reefs.
What makes surgeonfishes and tangs distinctive?
The most recognizable trait of Acanthuridae is a pair of sharp, scalpel-like bony plates on the tail stalk that the fish can deploy as a defensive weapon. These modified scales are the feature behind the common nickname 'surgeonfish.'
Where do Acanthuridae live and how large do they get?
Members of this family inhabit tropical seas, typically in close association with coral reef structures. Most species measure between 15 and 40 cm, though the whitemargin unicornfish (Naso annulatus) can grow to a full meter in length.
What does the name Acanthuridae mean?
The family name is built from two Ancient Greek words for 'spine' and 'tail,' pointing directly to the blade-like spines on the caudal peduncle of the original type species. In the early 1900s the group was classified under the different name Hepatidae before being reorganized into its current family.
Why are Acanthuridae popular in home aquariums?
Many species display vivid, eye-catching coloration that makes them a favorite among reef-keeping hobbyists. Their generally compact size and active, curious swimming behavior also make them well-suited to typical aquarium setups.
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