Hemibrycon brevispini n. sp. can be distinguished from other species of the genus by the presence of hooks on all fins, and by an elongate projection on the fourth ventral neural arc near the first neural post-zygotic apophysis. Hemibrycon cairoense n. sp. can be distinguished from congeners by having nine proximal pteryigiophores in the dorsal fins including the terminal piece (vs. > 10). It can be distinguished from Hemibrycon species in the Upper and Middle Cauca Rivers by the number of pored lateral-line scales (43-46 vs. > 46 o < 43; F = 13.67; p < 0.000). Ecological data concerning the aquatic habitat of the taxa are presented.