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Biodiversity inventories are not yet complete, with potentially thousands of species unknown to science. This paper aims to (1) elucidate the historical discovery rate of endemic southern African marine fishes and (2) to estimate the number of potentially undescribed endemic marine fishes in the region using a statistical model and which factors (e.g. size/depth) contribute to unknown diversity. Thirdly, all species described globally for eight families (Blennidae, Clinidae, Gobiidae, Lutjanidae, Rajidae, Sciaenidae, Scyliorhinidae, Sparidae) were analysed to elucidate unknown diversity in these groups. The oceans of southern Africa, including Namibia, South Africa and Mozambique, encompassing sections of the south-eastern Atlantic Ocean and the western Indian Ocean. Literature surveys from a number of sources were carried out to compile lists of species descriptions from 1758 onwards. Species-accumulation curves were plotted for all endemic species, as well as for different components of size and depth. A maximum likelihood model was used to estimate the number of undescribed endemic marine fishes in southern Africa, as well as for all other categories, including global families. Fish discovery rates in southern Africa have varied with time. Estimates suggest that at least 25% of the total endemic fish fauna remain unknown and that size is the greatest predictor of whether a fish has been described. Smaller-sized fishes and those inhabiting shallow areas are most likely to be undersampled. It is likely that most undescribed fishes inhabit the subtropical/tropical waters of the east coast. At the current rate of fish description, it will take at least 50 years to describe the total endemic fish fauna. However, estimates of unknown species are probably higher because of cryptic species within currently recognized taxa. Climate change may also contribute to range expansions of marine species, further complicating the status of endemicity in southern African marine fishes. [ABSTRACT FROM AUTHOR]