We cannot protect what we do not know. Species-level diversity of the freshwater tetra Bryconops melanurus is underestimated and still relatively unknown. A greater level of understanding of species distribution within the genus Bryconops and species-level diversity of B. melanurus will allow for more data driven and effective conservation management decisions. Although there is literature on B. melanurus, there has not been a thorough examination of morphometrics and patterns of body shape differences. This thesis analyzes the effects of geographic variation on body shape within the melanurus species-group across South America using modern techniques of morphometrics. Relative warp analysis (RWA) of 14 landmarks and principal component analysis (PCA) of 28 interlandmark distances formed the basis of this study. 554 specimens were examined from a total of 59 localities in South America. Specimen were examined from 16 river basins. Results suggest that within river-basin populations, variation in shape is proportional to sample size. However, despite this limitation, the study identifies the presence of a possible new species of Bryconops in the Pantanal (Bryconops cf. melanurus), as well as redescribes B. melanurus.