The present study evaluated potential Hg bioaccumulation and its morphological effects in different organs of the tropical fish, Gymnotus carapo, after a single acute intra-peritoneal exposure (0.6 Âµg.g-1) and over progressively longer exposure times (24 h, 48 h, 72 h and 96 h). The Hg accumulation was differential and time dependent for most target organs (testis > liver > gills > muscle). Â Hg exposure leads the highest accumulation potential in testis since the initial examination point (24 h) until the last (96 h). The liver showed progressive Hg accumulation, presenting its highest levels only at the 96 h exposure point. Hg concentrations in the gills and muscle oscillated over the exposure times; however, the highest values of both organs also occurred in 96 h exposed fish. Histopathological alterations were observed in testis, liver and gills from 24 h of Hg exposure, and the extent of the alterations and their severity increased out to 96 h of exposure. These results shows a correlation between Hg accumulation and the induced morphological damages in different organs along the time in a tropical fish species G. carapo, being the histopathology a sensitive technique for the observation of the initial damage from Hg exposure.