Body depth distinctly less than head length, body depth contained 2.7 to 3.2 times in standard length (for fish 10 to 40 cm standard length). Head length contained 2.4 to 2.7 times in standard length: eye small, its diameter distinctly less than snout length; interorbital area flat to slightly convex; preopercle rounded, finely serrate in young, virtually smooth in large adults, the lower edge fleshy; subopercle and interopercle smooth, maxilla scaly, reaching well past eye. Gill rakers 9 to 11 on upper limb, 17 to 19 on lower limb, the rudimentary rakers on lower limb difficult to distinguish from intercalated bony plates. Dorsal fin with IX spines and 15 to 17 rays, the membranes indented between the spines; anal fin with III spines and 9 rays; pectoral-fin rays 16 to 18; pectoral fins clearly longer than pelvic fins, pectoral-fin length contained 1.4 to 2.0 times in head length; pelvic fins not reaching anus, their length contained 1.9 to 2.4 times in head length; caudal fin well rounded. Lateral-body scales ctenoid, with a few auxiliary scales in adults; lateral-line scales 46 to 51; lateral-scale series 95 to 110.
Colour: Dark brown, covered with small black-edged blue ocelli; often with 5 or 6 pale bars on rear part of body and a large pale area over the chest; posterior margin of median fins usually with a narrow white edge; distal part of pectoral fins sometimes maroon brown; triangular membranes at tips of dorsal-fin spines orange-gold.

C. argus is the most widely distributed of the groupers, occurring from the Red Sea to South Africa and east to French Polynesia and the Pitcairn group, including northern Australia, Lord Howe Island, and Japan. Recently introduced to the Hawaiian Islands.

A common tropical species found in a variety of coral reef habitats from tide pools to depths of at least 40 m. In the Gulf of Aqaba, C. argus is found in social units comprising up to 12 adults, including one dominant male. Each group occupies a specific area (up to 2 000 m2) that is defended by the territorial male and subdivided into secondary territories, each inhabited by a single female (Shpigel and Fishelson, 1989b, 1991). The preferred habitat of C. argus is the 1 to 10 m reef zone. Primarily (75 to 95%) piscivorous, C. argus has been blamed for numerous cases of ciguatera in the Pacific region. In the Red Sea, Shpigel and Fishelson (1989a) found that this species feeds mainly in the early morning and late afternoon; but at Madagascar (Harmelin-Vivien and Bouchon, 1976), it appears to feed more at night.

Maximum total length 55 cm.

C. argus has been confused with C. cyanostigma, which has a generally similar colour pattern of small blue ocelli on a dark brown or reddish background. C. cyanostigma differs in having the pectoral fins yellow-orange at least distally, with a black margin and blue spots only proximally; also, the body often has pale spots containing 1 to 3 small blue spots and 5 or 6 chain-like dark bars. In addition to these differences in colour pattern, C. cyanostigma has only 8 anal-fin rays and fewer gill rakers (7 to 9 on upper limb and 14 to 18 on lower limb).