The large barbs of East Africa are well known for their morphological plasticity. Mitochondrial DNA sequences were compared for specimens of three distinctive barb morphotypes collected syntopically from the Genale River in southeastern Ethiopia. The “normal,” “lipped,” and “large-mouthed” morphotypes are putatively referable to Barbus gananensis. An analysis of molecular variance revealed that the lipped and normal morphotypes are not genetically distinct (ϕST < 0.0001, P = 0.80) and that the group of large-mouthed haplotypes is significantly differentiated from a combined group of normal and lipped haplotypes (ϕST = 0.54, P < 0.001). The evolutionary relationships among the haplotypes were assessed with phylogenetic and minimum-length spanning trees. The results of the phylogenetic and spanning tree analyses are consistent with the analysis of molecular variance. The normal and lipped morphotypes represent morphological variants of B. gananensis, and the large-mouthed morphotype represents a genetically distinctive undescribed species.

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