Methylmercury causes changes in the cardiac activity of an Amazonian fish (Colossoma macropomum): an electrocardiographic study.

Pollution from gold mining has been a major problem in the Amazon River basin. Mercury in its main organic form, methylmercury (MeHg), is potentially toxic to fish, which are mainly affected by inadequate disposal of this pollutant. The present study aimed to evaluate the cardiac graphoelements over the 1-h exposure of Colossoma macropomum to an immersion bath using different concentrations of MeHg. For that purpose, 45 fish were used, assayed into four groups according to the following concentrations: 10 µg/ml, 20 µg/ml, 30 µg/ml and 40 µg/ml MeHg (n = 9). Exposure to different concentrations of MeHg demonstrated the triggering of arrhythmia over the time, and higher concentrations (30 and 40 µg/ml) had deleterious cardiac effects, with atrioventricular block. Such effects became more severe depending on the length of the exposure time to MeHg, demonstrating the susceptibility of tambaqui fish C. macropomum to this intoxication.