Diplodus capensis, the Cape white seabream or blacktail seabream, is a species of marine ray-finned fish belonging to the family Sparidae, which includes the seabreams and porgies. This fish is found around the coasts of Southern Africa.

Taxonomy Diplodus capensis was first formally described as Sparus capensis in 1844 by the Scottish surgeon, explorer, ethnologist and zoologist Andrew Smith with its type locality given as the southeastern coast of South Africa. This taxon was previously considered to be a subspecies of the sargo (D. sargus) but is now considered to be a valid species. There are two disjunct populations of this species, one in southern Angola and Namibia, and the other in southern and eastern South Africa and Mozambique, these may be separate species, in addition, the taxonomic status of the southern Madagascan population also requires study. The genus Diplodus is placed in the family Sparidae within the order Spariformes by the 5th edition of Fishes of the World. Some authorities classify this genus in the subfamily Sparinae, but the 5th edition of Fishes of the World does not recognise subfamilies within the Sparidae.

Etymology Diplodus capensis has the specific name capensis which means "of the Cape", a reference to its type locality in, what was then, the Cape Colony.

Description Diplodus capensis has a deep, oval body with a thin lipped, slightly protrusible mouth. There are 8 incisor-like teeth in the front of each jaw with 3 rows of molar-like teeth in the upper and 2 rows in the lower jaw.