The Mozambique tilapia Oreochromis mossambicus (Teleostei, Cichlidae) has been transplanted worldwide during the 20th century, and now belongs to the list of the most invasive species. Using a geometric morphometric approach, we describe body shape differentiation among 15 populations from native (Mozambique) and invaded (New Caledonia and Guadeloupe) ranges. A dominant phylogeographic signal is detected, despite the broad range of environmental conditions at the local scale. This result suggests that phylogeographic background rather than phenotypic plasticity responding to environmental variation constitutes the main factor correlated with shape divergence. This could result from successive founder events that occurred during the process of colonization of new geographic areas, and therefore strongly suggests heritable phenotypic differentiation. In addition, shape changes along a major axis of divergence hypothetically refer to different swimming abilities, possibly related to divergent functional requirements between the native and invaded ranges. Overall, patterns of contemporary shape diversification in O. mossambicus probably result from both phylogenetic constraints and adaptive divergence processes. We show that critically taking into account recent phylogenetic history of populations as a constraint on rapid phenotypic divergence is necessary for an improved view of contemporary evolution. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105, 369–381.