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.
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RBINS Staff Publications 2023
The dry weight concentration of suspended particulate material, [SPM] (units: mg L-1), is measured by passing a known volume of seawater through a preweighed filter and reweighing the filter after drying. This is apparently a simple procedure, but accuracy and precision of [SPM] measurements vary widely depending on the measurement protocol and experience and skills of the person filtering. We show that measurements of turbidity, T (units: FNU), which are low cost, simple, and fast, can be used to optimally set the filtration volume, to detect problems with the mixing of the sample during subsampling, and to quality control [SPM]. A relationship between T and `optimal filtration volume', V opt, is established where V opt is the volume at which enough matter is retained by the filter for precise measurement, but not so much that the filter clogs. This relationship is based on an assessment of procedural uncertainties in the [SPM] measurement protocol, including salt retention, filter preparation, weighing, and handling, and on a value for minimum relative precision for replicates. The effect of filtration volume on the precision of [SPM] measurement is investigated by filtering volumes of seawater ranging between one fifth and twice V opt. It is shown that filtrations at V opt maximize precision and cost effectiveness of [SPM]. Finally, the 90\% prediction bounds of the T versus [SPM] regression allow the quality control of [SPM] determinations. In conclusion it is recommended that existing [SPM] gravimetric measurements be refined to include measurement of turbidity to improve their precision and quality control.
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