Cephalopholis argus
Cephalopholis argus, the peacock hind, roi, bluespotted grouper, and celestial grouper, is a species of marine ray-finned fish, a member of the subfamily Epinephelinae, the groupers, and part of the family Serranidae, which also includes the anthias and sea basses. They come from the Indo-Pacific and are variously a commercial gamefish, an invasive species, and occasionally an aquarium resident. Its species name comes from its resemblance to the "hundred staring eyes" of the monster Argus who had a hundred eyes and was the shepherd of the goddess Hera in Greek mythology.
Description
This is a medium-sized fish that can reach a length of. Small individuals are dark brown with hundreds of small, dark-edged iridescent blue spots. Larger specimens sometimes develop four to six lighter vertical bars on the back half of its body.Distribution and habitat
The species is extremely widely distributed, occurring in warm waters from the Red Sea to South Africa and east to French Polynesia and the Pitcairn group. It is also present in northern Australia, Lord Howe Island, and Japan, and has been introduced to the Hawaiian Islands. It makes use of a variety of habitats but prefers the exposed fronts of reefs, at depths of up to 40 m.Ecology
Feeding
Hunting, they lie on the bottom and surge forward, preferring juvenile surgeonfish and crustaceans. Alternatively they may hover motionless in the water column before attacking.This grouper may follow and cooperate with another predator species, such as an octopus or eel or camouflage themselves in a school of surgeonfish. Multiple individuals may cooperate to harass an eel to get it to flush prey for them.
In the Red Sea, they hunt in the morning and evening.
Behavior
The species typically sit on a coral head, retreating when startled.Red Sea males defend harems of 2–6 females in territories ranging up to. Each female defends part of the territory from the other females. The male visits each female daily, raising his dorsal fin to signal his approach. The females emerges from hiding, erecting her own dorsal fin and changing to a lighter color. They swim together, rubbing flanks before he departs until the next day.
Territorial disputes may involve "color fights" in which two males positioning themselves at right angles to each other. They then darken their color and repeatedly switch their bars from dark to light. The loser becomes pale and retreats. If the color fight ends in a draw, the two males may attack each other.
Reproduction
In Micronesia, spawning usually occurs territorially at dusk. During courtship, both sexes darken except for a white keyhole-shaped patch at the center of the body.In the aquarium
Cephalopholis argus is a hardy aquarium fish for those who have a large marine aquarium. Its large size combined with its aggressive nature means it is best housed either alone or with other large aggressive fish such as lionfish, and moray eels. As a predator it will eat any smaller aquarium inhabitants such as damselfish.Introduced status in Hawaii
Known in Hawaii as roi, the state introduced the species in the 1950s to enhance local fisheries. Hawaii's Division of Aquatic Resources finds that roi have become the reefs' dominant predator. The Roi population there has increased 15 fold since the 1980s. From 1999 to 2005 there was a 23% increase in their population. Their biomass is now greater than that of all other reef fish predators combined.These predators threaten native reef fish such as parrotfish and goatfish. A University of Hawaii study estimated that in a three-square-mile area off the Kona Coast of Hawaii Island, Roi eat of reef fish annually— equivalent to 8.2 million fish.