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The nucleotide sequences of the first internal transcribed spacer (ITS-1) of the ribosomal RNA gene cluster have been determined for 11 species of closely related endemic cichlid fishes of the Lake Victoria region (LVR) and 6 related East African cichlids. The ITS-1 sequences confirmed independently derived basal phylogenies, but provide limited insight within this species flock. The line leading to Pseudocrenilabrus multicolor arose early, close to the divergence event that separated the tilapiine and haplochromine tribes of the "African Group" of the family Cichlidae. In this phylogeny, Astatoreochromis alluaudi and the riverine Astatotilapia burtoni are sister taxa, which together are a sister group to a monophyletic assemblage including both Lake Victoria and Lake Edward taxa. The ITS-1 data support the monophyly of haplochromine genera across lakes. Since Lake Victoria is believed to have been dry between 14, 500 and 12,400 BPE, the modern assemblage must have been derived from reinvasion by the products of earlier cladogenesis events. Thus, although the regional superflock is monophyletic, the haplochromines of Lake Victoria itself did not evolve in situ from a single ancestor., (Copyright 1999 Academic Press.)