Peacock Grouper

The peacock grouper (Cephalopholis argus), also known as peacock hind or roi in Hawaii, is a medium-sized serranid widespread across the Indo-Pacific from East Africa to French Polynesia and north to Japan. It was deliberately introduced to Hawaiian waters in the 1950s, where it has become one of the most abundant reef predators and a subject of ongoing ecological study due to its impact on native reef fish populations. In its native range it is a typical coral-reef grouper, sheltering among reef structure and hunting smaller fish. Like other groupers, it is a protogynous hermaphrodite. It remains one of the most recognizable reef groupers due to its dark body covered in bright blue spotting.

Peacock grouper are distinguished by their dark coloration and bold blue spotting.

• Color: dark brown to blackish-grey body densely covered with small bright blue spots; faint pale bars often visible near the tail.
• Body shape: stocky and oval, typical of Cephalopholis groupers.
• Fins: rounded dorsal and pectoral fins; tail fin often edged in blue or pale margin.
• Size: typically 30-50 cm.
• Distinguished from the similarly spotted coral grouper by its much darker, brownish-black base color versus coral grouper's bright orange, and by larger, more scattered spotting rather than dense uniform speckling.

Peacock grouper occur naturally across the Indo-Pacific from the Red Sea and East Africa to the central and western Pacific, and have been introduced to Hawaii. They inhabit coral and rocky reefs, lagoons, and outer reef slopes from the shallows down to around 40 m, favoring areas with abundant coral or rock cover for shelter. The species prefers warm, clear tropical water and is commonly seen resting near ledges, caves, and coral heads during the day.

Peacock grouper are solitary, territorial ambush hunters that station themselves near reef structure and strike quickly at passing fish and crustaceans. They are diurnal, most active in daylight, and retreat to shelter at night. Like other groupers, they are protogynous hermaphrodites, maturing as females before some individuals change to males. In Hawaii, where the species was introduced, it has become a dominant nearshore predator, and studies have examined its effect on populations of native reef fish. Peacock grouper defend home territories around preferred shelter sites and play a significant role as an upper-level predator wherever they occur in high densities.