Flood-pulse and trophic position modulate mercury concentrations in fishes from an Amazon floodplain lake

Mercury (Hg) bioaccumulation can be influenced by biological characteristics (e.g., trophic position) and environmental changes (e.g., seasonal flood-pulse), as it can create site conditions conducive to methylation and alter the availability of food to biota. This study aimed to relate total mercury (THg) and methylmercury (MeHg) concentrations in fishes of an Amazonian lake (Catalao Lake) to their dietary changes during different hydrological seasons (rising-, high-, falling-, and low-water). Levels of THg, MeHg, and stable isotopes of nitrogen and carbon (delta N-15 and delta C-13) were determined in the muscles of six fish species: Rhytiodus microlepis, Hemiodus sp., Triportheus albus, Anodus elongatus, Pellona flavipinnis and Acestrorhynchus falcirostris. Triportheusalbus, an omnivorous fish, showed a significant relationship between Hg concentrations and delta C-13 signatures (negative regression; THg: p = 0.0001 and MeHg: p = 0.0002), as well as between Hg and delta N-15 signatures (positive regression; THg: p = 0.003 and MeHg: p = 0.021), indicating that changes in feeding habits influenced the Hg concentrations in this species. The herbivorous R. microlepis presented the highest MeHg concentrations during the high-water season, reflecting Hg methylation in its diet (macrophyte roots) during flooded season. The piscivorous A. falcirostris had the lowest THg concentrations during this season because of lower prey availability. Slopes of the regressions between the Hg concentrations and delta N-15 values followed the sequence of rising-< high-< falling-water seasons (THg: 0.06 < 0.11 < 0.15; MeHg: 0.07 < 0.10 < 0.17), indicating that the difference between the THg and MeHg concentrations observed for lower-and higher-trophic-level fish increased during the falling-water season, resulting in trophic biomagnification. The present study shows that feeding habit and the flood-pulse influence mercury concentrations in the muscle of fishes from Catalao Lake.