A new species of Characidium Reinhardt (Characiformes: Crenuchidae) from the Río Huallaga, central Peruvian Amazon, with a review on secondary sexual characters in the genus.

Characidium pumarinri n. sp. is described from the affluents of Rio Huallaga, a tributary of Rio Maranon that drains the eastern slopes of the Andes, in the Peruvian Amazon. The new species has deep body (24-31% in LS ), 11-17 well-marked dark bars, and remarkable sexual dimorphism related to colour pattern, in which males have darker anal, dorsal, pectoral, and pelvic fins than females. Characidium pumarinri resembles some species allocated in Clade C4, mainly by having a high number of transversal bars and a deep body. In addition, a thorough review and further descriptions of the secondary sexual characteristics in Characidium are provided.