Trophic niche segregation in the Nilotic ichthyofauna of Lake Albert (Uganda, Africa)
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Nile perch, <i>Lates niloticus</i>, and Nile tilapia, <i>Oreochromis niloticus</i>, were originally transplanted from Lake Albert in western Uganda to the African Great Lakes, Lake Victoria and Lake Kyoga, where they are partially implicated in reduction of the ﬁsh species diversity. Lake Albert is facing multiple environmental changes, including declining ﬁsh species diversity, hyper-eutrophication, hypoxia, and reduced ﬁsh catches. To examine the role of Nile perch and Nile tilapia in the food web in their native Lake Albert, we estimated their diets using stable nitrogen and carbon isotopes. In Lake Albert, the tilapiine congeners (closely related species), <i>Tilapia zillii</i>, <i>Oreochromis leucostictus</i>, and <i>Sarethorodon galilaeus</i>, and the centropomid Nile perch congener, <i>Lates macrophthalmus</i>, have narrower diet breath in the presence of the native <i>O. niloticus</i> and <i>L. niloticus</i>. A computerized parameter search of dietary items for ﬁve commercially important ﬁsh species (<i>Hydrocynus forskahlii</i>, <i>Bagrus bayad</i>, <i>L. niloticus</i>, <i>Alestes baremose</i> and <i>Brycinus nurse</i>) was completed using a static isotopic mixing model. The outcome of the simulation for most ﬁsh species compared favorably to previously published stomach contents data for the Lake Albert ﬁshes dating back to 1928, demonstrating agreement between stable isotope values and analyses of stomach contents. While there were some indications of changes in the diets of <i>L. niloticus</i> and <i>A. baremose</i> diets over the past 20 years in parallel with other changes in the lake, for the most part, food web structure in this lake remained stable since 1928. The Lake Albert ﬁsh assemblage provides insight into the invasion success of <i>L. niloticus</i> and <i>O. niloticus</i>.