FIRST RECORD OF OREOCHROMIS MACROCHIR (BOULENGER, 1912) (PISCES:CICHLIDAE) FROM THE LIMPOPO RIVER IN SOUTHERN AFRICA.

Abstract

During 1973/74, Barbus poechii, Oreochromis macrochir, O. andersonii, Serranochromis angusticeps, S. codringtonii, S. robustus and S. thumbergi from the Okavango System were introduced into the Shashe Dam (Limpopo System, Botswana). These species are alien to the Limpopo System. A fish survey during September 1991 disclosed the presence of two specimens of the greenhead tilapia O. macrochir in a large natural pool in the Limpopo River 7 tan downstream from the Shashe/Limpopo confluence. In August 1992 another specimen was caught in this pool. It is surmised that the likely origin of these specimens is the Shashe Dam. There is a possibility that the greenhead tilapia may interbreed with the indigenous Mocambique tilapia O. mossambicus. Consequently the genetic integrity of O. mossambicus in the Limpopo River may become suspect. If the other alien species introduced into the Shashe Dam reach the Limpopo River, O. andersonii may also interbreed with O. mossambicus while the Serranochromis spp. could be detrimental for feeding relationships in the Limpopo River and its tributaries. The impact that B. poechii could have is uncertain but it does not appear to co-exist with the closely related B. trimaculatus of the Limpopo System. Eradication of O. macrochir in the Limpopo River is not practical. Further stocking of the Shashe Dam as well as other impoundments in the Limpopo System with alien fish species should be discouraged.