Fish mercury bioaccumulation as a function of feeding behavior and hydrological cycles of the Rio Negro, Amazon

The acidic black waters of the Rio Negro are unimpacted by anthropogenic sources and yet, are characterized by fish containing relatively high Hg concentrations. Regular annual flooding alters the aquatic environment, thereby affecting fish feeding strategies. We studied the impact of annual flooding on fish-Hg bioaccumulation. Tucunarés (Cychla spp, carnivorous), Peixe-cachorro (Hydrolycus scomberoides, carnivorous), Traíra (Hoplias malabaricus, carnivorous), Piranha-branca (Serrasalmus aff. eigenamanni, carnivorous), Piranha-preta (Serrasalmus rhombeus, carnivorous), Acará (Acarichthys heckellii, omnivorous), Aracú (Leporinus friderici, omnivorous), Orana-preta (Hemiodus unimaculatus, omnivorous), Sardinha (Triportheus elongatus, omnivorous), Branquinha (Potamorhina latior, detritivorous), Jaraqui-escama-fina (Semaprochilodus taeniurus, detritivorous), and Pacú-branco (Myleus torquatus, herbivorous) were studied during high (July) and low waters (February) and categorized by body mass. Regardless of hydrological period, ranges of total-Hg concentrations were higher for carnivorous than for omnivorous, detritivorous and herbivorous species. Some species (Traíra, Sardinha, Peixe-cachorro, Piranha branca, Piranha preta) showed changes in feeding patterns as indicated by an inverse trend of Hg bioaccumulation with season. Species with similar trends of Hg bioaccumulation showed higher Hg concentrations during the flooded season (Aracú, Pacú branco and Orana preta) and some had lower Hg (Acará, Branquinha and Tucunarés). Fish Hg concentration is species specific and reflects changes in feeding-behavior dominance brought by annual inundation.