This study reports the presence of Henneguya sp. in the blood of Astyanax fasciatus of natural enviroment, in a stream of the Muriaé River sub-basin, that belongs to the basin of the ParaÃba do Sul River from Itaperuna, Rio de Janeiro Estate, Brazil. Eight colects were perfomed between october 2009 and september 2010 with 45 days of interval, in each colect were captured ten specimen of Astyanax fasciatus giving a total of 80 slides of blood. This study reports the presence of Henneguya sp. in two specimens collected in november 2009. The low incidence of parasites ocurred because the genus Henneguya has already been registered in various organs of species of genus Astyanax, though the gill filaments are the sites with the highest tropism, so has the highest prevalence, but there is no register in the literature of parasites from this genus in the blood of fishes.
