Potential risks of natural mercury levels to wild predator fish in an Amazon reservoir Grazyelle Sebrenski da Silva & Francisco Filipak Neto & Helena Cristina Silva de Assis & Wanderley Rodrigues Bastos & Ciro Alberto de Oliveira Ribeiro Received: 11 April 2011 /Accepted: 24 August 2011 /Published online: 17 September 2011 # Springer Science+Business Media B.V. 2011 Abstract Mercury (Hg) is a toxic metal that bio- accumulates in aquatic organisms and along food chain. Many studies have reported the problem of mercury exposure in aquatic systems from Amazon basin, but very few have focused on the potential risks to wild fish. The present study reports the bioaccumulation of mercury and alterations in target organs of the predator fish Hoplias malabaricus (traíra) from Samuel reservoir, Amazon basin, Northern Brazil. About 18% of fish had mercury levels in muscle exceeding the safe limit for ingestion through food, established by WHO (0.5 μg Hg g -1 ). Fish were separated in two groups according to mercury bioaccumulation in liver (<0.2 μg Hg g -1 —group I and >0.2 μg Hg g -1 —group II) for biomarker comparisons. Catalase activity and number of macrophage centers were statistically higher in group II, confirming the potential of Hg to interfere with redox balance and to recruit defense cells to the liver. Conversely, erythrocyte nuclear alterations were less frequent in group II, indicating a more rigorous selection of erythrocytes or hormesis pattern of response. Glutathione S-transferase activity, lipid per- oxidation, and histopathological analyses were not statistically different in the liver and gills of both groups. Comparison of lipid peroxidation levels of these fish with others captured in Southern Brazil during another study and the high incidence of morphological alterations in the liver and gills suggest that the bioaccumulation of mercury during continuous exposure is posing potential risks to the species. Keywords Mercury . H. malabaricus . Amazon . Reservoir . Biomarkers . Biomonitoring Introduction Mercury (Hg) is a non-essential toxic metal widely distributed in many aquatic environments by natural processes and human activities, such as domestic and industrial wastes, fossil fuels, agriculture, industry, and gold mining (Malm et al. 1995; Pfeiffer et al. 1993; Tchounwou et al. 2003). Although some of these Hg sources are important in Amazon aquatic ecosystems, forest burning, deforestation followed by soil erosion, watershed export, and flooding of terrestrial landscapes are now also recognized as important sources of Hg to wildlife (Berzas Nevado et al. 2010). Particularly, seasonal flooding is considered Environ Monit Assess (2012) 184:4815–4827 DOI 10.1007/s10661-011-2304-3 G. S. da Silva : F. Filipak Neto : C. A. de Oliveira Ribeiro (*) Departamento de Biologia Celular, Universidade Federal do Paraná, Cx. Postal 19031, CEP: 81.531-990, Curitiba, Paraná, Brazil e-mail: ciro@ufpr.br H. C. Silva de Assis Departamento de Farmacologia, Universidade Federal do Paraná, CEP. 81531-980, Curitiba, PR, Brasil e-mail: helassis@ufpr.br W. R. Bastos Laboratório de Biogeoquímica Ambiental, Wolfgang C. Pfeiffer, Universidade Federal de Rondônia, Porto Velho, Rondonia, Brazil