A new species of Chrysobrycon Weitzman & Menezes, 1998 (Characiformes, Characidae, Stevardiinae) with remarkable sexually dimorphic pigmentation from the upper Río Vaupés basin, Colombian Amazon, with taxonomic key

This study describes Chrysobrycon calamar, a new stevardiine fish from the upper Río Vaupés basin in Colombia. The new species differs from its congeners by the following combined characters: adult males have a dark vertical blotch on the abdominal flanks that is confined to a small area immediately dorsal to the urogenital region and anterior to the third anal-fin ray; adult males with a well-developed vertically humeral blotch, numerous tiny bony hooks on nearly all the upper lobe caudal-fin rays (except C. guahibo, C. hesperus, and C. mojicai), and bony hooks on nearly all branched anal-fin rays (except C. hesperus); the number of vertebrae (43 vs. 38–42); an elongated maxillary anterior process, representing 40% or more of the total length of the bone (vs. with a shorter maxillary anterior process, representing less than 40% of that length); and the posterior portion of the maxilla not reaching the vertical through the anterior border of the eye when the mouth is closed (except from C. yoliae). Additionally, C. calamar differs from C. mojicai by the number of maxillary teeth (2–4 vs. 9–17) and shape of the distal tips of most maxillary teeth (straight along their lengths vs. lateroventrally curved). Remarks on the interspecific color variation associated with sexual dimorphism and other characteristics of the genus are provided. A key to the species of Chrysobrycon is presented. The discovery of C. calamar is a key advance in the understanding of fish biodiversity associated with endemism-rich regions that could be explored after the guerrilla demobilized in Colombia.