Genetic characterization and interspecies gene flow among the Oreochromis species in the Lake Victoria and Kyoga basins, Uganda: Implications for conservation

Despite the significant fishery contribution of the Victoria and Kyoga basins, the ecosystems have continuously been threatened by overfishing and introduction of alien species, among others. These activities have contributed to a significant decline of the native tilapiines, the Singida tilapia (Oreochromis esculentus) and Victoria tilapia (Oreochromis variabilis). As a consequence, the native species have been relegated to smaller satellite lakes and replaced by non-native species comprising Nile tilapia (O. niloticus) and blue spotted tilapia (O. leucostictus). Therefore, to better understand the implications of these events, it is important to assess the status of both native and non-native species in the Victoria and Kyoga basins for sustainable science-based informed management options. Utilizing both microsatellite and mitochondrial (mt) DNA markers, we sequenced a total of 739 individuals from the Victoria and Kyoga basins comprising O. niloticus (333), O. esculentus (151), and O. leucostictus (258). Generally, all the species and their respective populations exhibited lower genetic diversity as well as genetic differentiation. The principal coordinate analysis showed three main distinct groups corresponding to the three species studied highlighting their genetic differentiation. However, some evidence of introgressive hybridization observed between O. niloticus and O. esculentus as well as O. esculentus and O. leucostictus suggests a need for a tailored management strategy to preserve the genetic integrity of all three Oreochromis species while minimizing the hybridization risks. The study recommends that the satellite waterbodies containing pure stocks of O. esculentus should be conserved separately with higher priority.