Résumé
The introduction in natural environment of any species can have genetic impacts. These can be defined not only as alterations in the gene pool of native species but also as alterations in the introduced populations themselves. After having established the list of possible alterations, their causes and their consequences, the introduced species in.Africa for which there are available data an the genetic impact were in reviewed : the hybrids between Oreochromis niloticus and O. mossambicus in Itasy Lake in Madagascar; these same hybrids in Lake Ihema in Rwanda; the case of Lake Victoria with O. niloticus, O. variabilis and O. esculentus: that of the Bouake strain of O. niloticus in the waters of Cote d'Ivoire, and finally the case of Limnothrissa miodon, the Clupeidae originally from Lake Tanganyika and introduced into Lake Kivu.