Electrophoretic identification and phylogenetic relationships of indigenous tilapiine species of Zimbabwe

In order to characterize Zimbabwean tilapias 34 populations of seven specie s, two in the genus Tilapia and five in Oreochromis, were analysed using ho rizontal starch gel electrophoresis. Twenty-seven loci were polymorphic whi le five were monomorphic but had fixed allelic differences among some speci es and six were monomorphic for the same allele in all species. No fixed al lelic differences were found between O. mossambicus and O. mortimeri, and o nly one locus distinguished O. andersonii from O. mossambicus and O. mortim eri. Pairwise comparisons of O. mossambicus or O. mortimeri populations of genetic distances frequently showed a greater degree of difference within t he species than was evident in some O. mossambicus x O. mortimeri pairs. Th is study failed to distinguish O. mortimeri as a distinct species from O. m ossambicus The Tilapia species formed distinct clusters from Oreochromis in both consensus neighbour-joining and distance Wagner topologies. Oreochrom is mossambicus, O. mortimeri and O. andersonii clustered together consisten tly. Although some differences from the taxonomic arrangement of Trewavas a re discussed, the principal relationships revealed in our analysis are cons istent with most recent studies. (C) 1998 The Fisheries Society of the Brit ish Isles.