The fishes popularly known as small-mouthed fish are small in size, around 3 cm. During preliminary collections in a stream of the Teles Pires river basin, two syntopic species belonging to the subfamily Hypoptopomatinae, Hisonotus chromodontus and Curculionichthys luteofrenatus were observed. This project investigates the life history of these loricarids, their spatial and seasonal distribution, weight / length ratio, diet and reproductive biology. In addition, intraspecific and interspecific interactions will be investigated both among species of fish, as well as crustaceans and insects.