ABSTRACT This study aimed to estimate the parameters of length-weight relationship, sex ratio, and diet of three freshwater fish species that inhabit streams in the Pomba River basin (Rio de Janeiro, Brazil). Fishes were sampled with seine nets (2.0 × 1.20 m, 2 mm mesh size) and dip nets (0.46 × 0.33 m, 2 mm mesh size) from October to December 2018. Measurements were taken for total length (TL - 0.1 cm precision) and total weight (TW - 0.01 g precision). Growth model parameters were estimated. This study provides new length-weight relationship data for Deuterodon intermedius (Eigenmann, 1908), Australoheros paraibae Ottoni & Costa, 2008, and Hypostomus punctatus Valenciennes, 1840. All of them ingested a wide variety of food items, including plant material like algae, animal material such as terrestrial and aquatic insects, and undefined matter such as detritus or mud. The three species showed a higher number of females. Our study provides basic information for functional diversity studies, as well as for future investigations associated with the evaluation of anthropic impacts, either occasional or chronic, on the fish assemblage structure of the Pomba River basin.