The peacock grouper is a member of the Serranidae family, native to the Indo-Pacific and common in home aquaria and as an invasive species.
It is a mid-sized fish, growing up to 60cm. Thye have large mouths with thick lower lips and small fins.
Its body is brown, but notable for the iridescent dark blue that tints it, particularly the edges of its fin. The peacock grouper is usually covered in hundreds of dark blue spots with cyan of white centres. As it ages, it commonly develops four to six thick white bars across the back portion of its body. One of its common names "argus grouper" is drawn from the many-eyed giant "Argus" of Greek mythology.
The peacock grouper has a wide distribution throughout the Indian and Pacific Oceans. It most commonly occurs in the Red Sea and along the East African coast until KwaZulu-Natal. It is also common in the waters of Australia and Japan, and as an invasive alien species in Hawaii and other Polynesian island waters.
Its preferred habitat is the exposed margins of tropical and sub-tropical reefs. Here, the peacock grouper lies passively against rocks and on the ocean floor - ready to surge forward and ambush its prey. Their preferred prey is juvenile surgeonfish and benthic crustaceans.
The peacock grouper is a social species, harems of up to six females will defend a territory from other females and will only allow a preferred male to enter. This male will present a raised dorsal fin to each female daily to maintain their bond, the action that earns them the name "peacock" grouper.
Males sometimes fight for the right to mate with a particular harem. The two males will darken their colours and will then switch the colours of their white bars repeatedly back and forth. The loser of this "colour battle" will lighten its colours and swim away, or attempt to physically attack the victor.
These colours are also used for mating. A female that is ready to spawn will darken its entire body, except a single small white patch in the centre to signal her willingness to mate.
What is a grouper?
A grouper is a fish in the subfamily Ehinephelinae, part of the family Serranidae which also includes sea basses. While fish from a large number of genera are often referred to as “groupers”, in the strictest sense it only refers to fish from the Epinephelus (eg. Brindle bass) and Mycteroperca genera.
Groupers generally have stout, muscular bodies and large mouths. Some species of grouper can grow incredibly large – specimens of Atlantic goliath grouper (Epinephelus itajara) have grown to over 300 kg.
They have few or no teeth, instead swallowing their prey whole and crushing them with bony plates inside their throats. All groupers are predators, but their hunting strategies and prey are highly variable – from ambushing small fish to actively hunting sharks. Some groupers even pair up with moray eels – encouraging the eel to scare prey out from cracks in rocks.
Groupers are slow swimmers and do not travel large distances. Most species have a home region that they patrol and use the powerful sucking motion of their gills to excavate shelters underneath large rocks for themselves.
Large grouper species are protogynous hermaphrodites. All are without sex until they reach a weight of about 3kg. At this point, they mature and become female. Groups of up to 15 form and the largest amongst this group will become male.
Small species have discrete sexes, with distinct males and females. In these species, the groupers do not form harems.