A new species of grouper, Epinephelus insularis is described based on 12 specimens (271.6–528.0 mm standard length: SL) from the western Pacific Ocean. The new species, previously confused with Epinephelus chlorostigma (Valenciennes in Cuvier and Valenciennes 1828), is distinguished from all congeners by the following combination of characters: dorsal-fin rays XI, 16 (rarely XI, 17); longitudinal scale series 114–132; total gill rakers 21–24; posterior margin of anal fin rounded; caudal fin truncate, its posterior margin with a narrow white line; head, body, and all fins with small polygonal brown spots (expanded on head and body undersurface) on a pale background, forming a reticulate pattern; and pectoral fin brownish. In addition, Serranus areolatus japonicus Temminck and Schlegel 1843, which has been regarded as a junior synonym of E. chlorostigma, is redescribed as a valid senior synonym of Serranus reevesii Richardson 1846 and Epinephelus tankahkeei Wu, Qu, Lin, Tang and Ding 2020. Epinephelus japonicus is characterized as follows: dorsal-fin rays XI, 17; longitudinal scale series 101–119; total gill rakers 23–26; posterior margin of anal fin rounded; caudal fin convex, without white lines; head, body (lateral surface only), dorsal, pelvic, anal, and caudal fins with small polygonal brown spots forming a pale reticulate pattern; and pectoral fin yellowish.
