belmont stream is the main tributary of the madeira river in the area immediately downriver from the santo antonio fall. samplings were carried out using gill nets in the mouth of this stream between may 2005 and april 2006 and resulted in a list of 74 species. the analyses included values of composition, constancy of occurrence, species richness, abundance, catch per unit of effort and trophic structure about the ten most abundant species. characiformes and siluriformes were dominant order in the samples and curimatidae (popularly known as "branquinhas") was the most abundant family, represented by psectrogaster rutiloides (32.57% of the collected specimens), potamorhina altamazonica (10.72%), and potamorhina latior (7.79%). the most of species were considered accessory and accidental and richness suggests high values in the rising and high water. belmont maybe considered as a moderate richness when compared to those found for others amazon rivers. detritivorous fishes composed 60% of the assemblage and the constancy of the most abundant species of this family suggests belmont as an important area to these migratory fishes.