A new fish species of Bryconamericus Eigenmann 1907 is described from the Fonce river, Magdalena Basin of Colombia. The species can be distinguished from all congeners by the number of anterior anal fin rays covered by a scales row (4-11 vs.11-26, except B. orinocoense Román-Valencia 2003 with 1-6, from which is distinguished by the higher number of branched anal fin rays 19 -26 vs. 16-17) and lateral line scales (39-45 vs.31-32); in males, by the spines number on each fins rays (anal 2-10 vs. 9-23, pelvic 2-9 vs. 8-20, pectorals 2-6 vs.9-28 and dorsal 3-6 vs. 6-18). Ecological data of the aquatic habitat of the new taxon are presented and a key to species of Bryconamericus from Cauca-Magdalena, Sinú and Ranchería rivers in Colombia is provided.