Translocated oysters are well known to act as vectors of marine alien species, but to date this topic has received scant attention in South Africa, despite the fact that oysters have been imported into this region since 1894. Surveys of oyster farms in South Africa revealed four newly-recorded alien species: the black sea urchin, Tetrapygus niger, from Chile; the European flat oyster, Ostrea edulis (thought to be extinct since its intentional introduction in 1946); Montagu's crab, Xantho incisus, from the North Eastern Atlantic seas of Europe, and the brachiopod Discinisca tenuis from Namibia. Oyster imports are the most likely vector of all these species. The biological attributes of each species, the possible threats posed by their introduction, and the needs for additional control measures to limit or prevent further introduction and spread of alien species via oyster culture are discussed.