Chronic Effects of Methylmercury on Astronotus ocellatus, an Amazonian Fish Species

Abstract Background: Bioassays are very useful tools to establish cause-effect relationships as they do not allow other confounding factors to interfere within the results. Methylmercury is known as a highly toxic substance and bioassays have demonstrated several effects of this pollutant on different fish species, especially on reproduction and hematology. The aim of this study was to evaluate the effects of chronic methylmercury exposure on Astronotus ocellatus biomarkers (hematology, acetylcholinesterase activity, micronucleus frequency, histopathology of liver and gonads), as consequence of methylmercury exposure through artificially contaminated food (10 μg.g-1). Methods and findings: The experiment was performed during 6 months. Blood samples were collected bimonthly for hematology analysis and total mercury determination. In the end of the experiment, samples of different tissues were collected for total mercury analysis and effect biomarkers assessment. Mercury bioaccumulation was clearly observed in all fish tissues (102 higher on test group). Methylmercury exposure caused hematological damages, especially in corpuscular volume and can activate leukocytes production and possibly influences the acetylcholinesterase activity. The frequency of genotoxic effects (bilobed nuclei) and damage on liver and gonad tissues were also increased. Conclusion: Methylmercury exposure caused, decrease in erythrocytes number, corpuscular volume and in monocytes frequency; increase in hepatocytes volume, degeneration, hypertrophy and hyperplasia of follicular layer, follicular atresia, yolk degeneration and presence of proteic material and inflammatory infiltrate on liver and gonads, genotoxic effects were not clear and acetylcholinesterase activity seemed to be higher after exposure