Expanding the Distribution and Phylogenetic Insights of Chrysobrycon mojicai in the Peruvian Amazon: Morphological and Molecular Analyses with Taxonomic Corrections

This study focuses on the genus Chrysobrycon, particularly Chrysobrycon mojicai, which was initially described in the Amacayacu National Natural Park in Colombia. Here, we document a new geographical record of C. mojicai in various locations of the Peruvian Amazon, including the Nanay, Putumayo, Tapiche, and Tigre Rivers basins. Based on morphological, morphometric, and molecular analyses, we confirm the presence of C. mojicai in these new locations, expanding its known distribution. Morphological features such as the distinct shape of the hypertrophied scales and the specific arrangement of teeth were used to confirm its identity. Molecular data, obtained through cytochrome oxidase I (COI) gene sequencing, provide additional validation and contribute to understanding its phylogenetic relationships within the Stevardiini tribe. Our phylogenetic analysis reveals unresolved relationships within the tribe, particularly in the genus Gephyrocharax, and highlights discrepancies in the current taxonomic framework, with C. mojicai showing close genetic affinity to C. myersi from the Pachitea River basin. The study also presents morphometric information of the holotype of C. mojicai, specifically the percentages of measurements relative to the head, which were not included in the original description. It also includes ecological observations of the habitats where C. mojicai was collected, noting its presence in blackwater and mixed water streams characterized by fluctuating water levels and specific physical and chemical parameters. Additionally, the study restricts the distribution of C. guahibo for Colombia and invalidates the COI sequence of Hysteronotus megalostomus available in molecular databases. This research not only expands the known distribution of C. mojicai but also underscores the need for further taxonomic and ecological studies to resolve existing ambiguities within the Stevardiini subfamily.