Acanthurus achilles (Acanthuridae)
Surgeonfishes, Tangs and Unicornfishes
Distribution: Indo-Pacific.
Habitat: Clear seaward reefs, primarily in the
surf zone to 4 m. Usually in small groups.
Appearance: Length to 24 cm. Ovate compressed
body black with a large orange caudal spot. Caudal
fin has a broad vertical orange band.
Diet: Diurnal herbivores of filamentous and
small fleshy algae.
Reproduction and Development: Spawners.
Juveniles lack the orange spot.
Mortality/Longevity: An important food fish
on tropical islands.
Remarks: Highly territorial.
“Tang” in British dialect means dagger or knife.
Thus the common name refers to the caudal
peduncle spines.
Single scalpel-like peduncular spine folds
into a groove on each side of the tail. Spines
are used offensively or defensively, against
conspecifics in struggles for dominance or
against predators.
Whether a fish has a common name of
“surgeonfish” or “tang” seems to be a matter
of convention, not substance.