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The African Lake Tanganyika clupeids play an important role in the lake's ecosystem and have a high regional economic and nutritional value. Using DNA metabarcoding, we analysed the prey item composition and microbiome of these two clupeid species, Stolothrissa tanganicae and Limnothrissa miodon. We sequenced the mitochondrial COI region of the gut content for prey analysis and the 16S rRNA region of the hindgut content for microbiome analysis of 140 fish sampled at five locations across Lake Tanganyika. Our research confirmed previously reported prey items and discovered prey items that were not reported before, including the jellyfish Limnocnida tanganjicae. The hindgut of the fish harboured 15 bacterial phyla, with the most common being Firmicutes and Proteobacteria. The two clupeid species differed in diet, but not in microbiome. Further, the diet of S. tanganicae, but not its microbiome, varied on a spatial scale, whereas the microbiome, but not the diet, of L. miodon showed spatial variation. Our findings suggest that the Lake Tanganyika clupeids are opportunists, with a diet reflecting the local zooplankton community's composition. These results can serve as a useful reference for monitoring the health status of economically important fish stocks. [ABSTRACT FROM AUTHOR]

This study highlights the value of museum collections in invasion biology. It focuses on introduced tilapias, Oreochromis niloticus and Coptodon rendalli in the Congo Basin and their monogenean (Platyhelminthes) gill parasite fauna. O. niloticus was introduced throughout the Congo Basin while C. rendalli was introduced into the Lower Congo, but is native to the Middle and Upper Congo. In order to study the impact of these stocking events on the native parasite community we investigate the co-introduction and host switching of their parasites. Post-introduction material is compared with pre-introduction samples from museum collections of 5 native tilapias in the Congo Basin. Nine of the known parasites of O. niloticus were co-introduced, while one, Cichlidogyrus rognoni, is missing and possibly not established. In contrast, no parasite species were found co-introduced with C. rendalli into the Lower Congo. The parasite fauna of Tilapia sparrmanii shared no species with O. niloticus. Oreochromis mweruensis shared five species with O. niloticus, but these were also found on the pre-introduction samples, and are considered native to both hosts. We report three putative host switches: Cichlidogyrus sclerosus and Cichlidogyrus tilapiae to Coptodon tholloni in the Lower Congo Basin and Gyrodactylus nyanzae to C. rendalli in the Upper Congo. [ABSTRACT FROM AUTHOR]