The bignose unicorn is a large member of the surgeonfish family and, although it is a unicornfish, it does not have the characteristic "horn" seen in many other species. Adults are a deep magenta-grey colour with small vertical blue bars on their sides, small blue spots near their belly and a characteristic, thick blue bar from eye to snout.
Juvenile bignose unicorns are a dull yellow-green, with small blue spots and blue lips. They develop their hues of magenta and purple as they mature.
This fish is capable of changing it's colour for camouflage and will turn grey-brown when threatened or when resting.
The bignose unicorn has a wide range throughout the Pacific and Indian Oceans, ranging from the KwaZulu-Natal coast to Japan, the Great Barrier Reef and the Galapagos Islands.
Its preferred habitat is deep lagoons and the seaward margins of coral reefs, where they sometimes gather into large groups to feed on small zooplankton, particularly copepods. However, they are mostly solitary and feed on algae growing on the reef.
The surgeonfish family:
Surgeonfish, tang or unicornfish is the collective name for fish of the Acanthuridae family. These are usually brightly coloured, oval fish with sharp spines on both sides of their peduncle.
Their main characteristic is the presence of a “tail thorn”, one or more small, razor-sharp spines that are present on one, or both, sides of their tails. Their name “surgeonfish” comes from their possession of this “scalpel”, and their scientific name is Greek for “thorny tail”.
There are 31 species of surgeonfish, sometimes called unicornfish, inhabiting the coral reefs of southern Africa and 86 species globally.
What is life like for an Acanthurid?
Almost all surgeonfish display a mix of solitary and group behaviours. They will often move about as groups, using their numbers to wrestle territory away from damselfishes. Once the damselfish have been scared off, it’s every surgeonfish for itself!
Why are some called unicornfishes?
A unicornfish is a surgeonfish that belongs to the genus called Naso. They get the name “unicorn” because of their protruding rostrums (fish foreheads) that look like horns.
The Two Oceans Aquarium is home to a few unicornfishes, a popular favourite being the orange-spined unicorn (Naso litaratus).