Resumo. Aim: The aim of present study was to evaluate the Hg concentration in two species of fish (Astyanax sp and Corydoras paleatus) and its potential use as a biomonitor, in order to know if the use of pesticides and fertilizers in paddy can enhance the Hg contamination to adjacent aquatic environment.MethodsSoil, suspended particulate matter and fish samples were sampled in a paddy field in South Brazil. A cold vapor system, coupled with a GBC 932 atomic absorption spectrophotometer was used for total Hg determinations in samples.ResultsThe paddy soil shows Hg concentration 2-fold higher (mean 31 ng g-1) in comparison to background areas (not cultivated). Suspended particle matter Hg concentration in paddy channels (mean 232.5 ± 44.2 ng g–1) are 1.5 times higher than the regional background. The analyzed fish specimens Astyanax sp in paddy showed Hg concentration 4-fold higher and significant different to background area. The mean Hg concentration in fish was: 51.7 ± 19.5 ng g–1 in Astyanax sp and 156.8 ± 44.0 ng g–1 in Corydoras paleatus.ConclusionsConsidering the linear regression and Man whitney test hypothesis to Hg concentration in fish tissue from paddy suggests that Astyanax sp. can be a good biomonitor of Hg contamination, whereas Corydoras paleatus is a potential biomonitor. However, more studies with Corydoras are necessary in order to aggregate consistency to this hypothesis.