A southwestern Indian Ocean (SWIO) percoid fish Serranus knysnaensis Gilchrist, 1904, was long synonymised with the comber, Serranus cabrilla (Linnaeus, 1758), from the eastern Atlantic Ocean, Mediterranean and Black Sea. However, when the species was brought out of synonymy by Heemstra Heemstra (2004), reasons for this decision were not given. This study aims to revalidate the present taxonomic status of S. knysnaensis using morphological and molecular assessments. The two species are distinguished by the number of circumpeduncular scales (2634 in S. knysnaensis versus 3438 in S. cabrilla) and total gill rakers (1822 versus 2224). Serranus knysnaensis is also distinct from S. novemcinctus Kner, 1864, the other SWIO species of Serranus, based on total gill raker counts (1822 versus 3135). Genetic analysis of mitochondrial DNA barcode (COI) sequences for 17 Serranus species revealed three closely-related monophyletic clusters corresponding to S. cabrilla, S. novemcinctus and S. knysnaensis that were supported (P 0.001) by species delimitation methods. Even though the genetic distances among the three species were the lowest in the genus (1.60-1.99%), these species may be ecomorphs or lineages that have only recently diverged from each other. These three species also have allopatric distributions and our morphological and molecular data thus confirm that S. knysnaensis is a valid species.