Effects of habitat on mercury concentrations in fish: a case study of Nile perch (Lates niloticus) in Lake Nabugabo, Uganda
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This study focused on variation in fish mercury (Hg) concentrations in 185 Nile perch (Lates niloticus) samples collected across four different habitat types in Lake Nabugabo, Uganda, a tropical lake located proximate to Lake Victoria. We quantified the stomach contents of Nile perch using the % index of relative importance, as well as, nitrogen and carbon isotopic concentrations to assess the role of diet and trophic level on Hg concentrations. In each habitat, we also evaluated a suite of chemical and physical characteristics that are commonly associated with variation in Hg bioavailability in temperate systems. Using linear mixed models and ANOVA, we demonstrate that habitat of capture is an important predictor of Hg concentrations in Nile perch from Lake Nabugabo and that the relationship between habitat and Hg is size and diet dependent. Nile perch diet as well as dissolved oxygen concentration and pH were also correlated with observed differences in fish Hg. Overall, Hg concentrations in Nile perch were all well below the WHO/FAO recommended guideline of 500 ng/g (mean 13.6 ± 0.4 ng/g wet weight; range 4.9 and 29.3 ng/g wet weight). This work contributes to a growing awareness of intra-lake divergence in Nile perch, as well as, divergence in Hg concentrations between varying aquatic habitat types, particularly wetlands.
KeywordsBiomagnification Wetlands Freshwater Contaminants Africa
We would like to thank two anonymous reviewers for feedback on an earlier version of this manuscript, as well as, Amanda E. Poste and Hans Frederick Braaten from the Norweigian Institute of Water Research for their interest in Lake Nabugabo and their help with lab work. Thank you Vincent Fugère and Catherine Baltazar for help with statistical analyses and to the Timothy Moore lab at McGill University for their help running DOC and TN samples, as well as, the Marc Amyot lab at Université de Montréal, for guidance regarding field procedures.. Thank you to Kevin Regan at the Biodiversity Research Institute for assistance with mercury analysis on the DMA. Michael Collyer assisted with code in R for the isotopic analysis. This project would not have been possible without the help of dedicated Ugandan field assistants Jackson Mutebe, Geoffry Kiberu, and Fred Sseguya, as well as, Dr. Dennis Twinomuguisha. Funding for the project was provided by the Natural Science and Engineering Research Council of Canada (NSERC), the Fonds de recherche du Québec en nature et technologie, the Quebec Center of Biodiversity Science, the Norwegian Institute for Water Sciences, the National Geographic Society, and McGill University, as well as funds to Lauren Chapman (NSERC Discovery Grant, Canada Research Chair research funds).
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Conflict of interest
The authors declare that they have no conflict of interest.
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