new species from Argentina:
Characidium koerberi Méttola, Terán, Serra, Aguilera, Montes, Benitez, Alonso, Ruíz Díaz & Mirande, 2026
published in:
Méttola, V.E., G.E. Terán, W.S. Serra, G. Aguilera, M.M. Montes, M.F. Benitez, F. Alonso, F. Ruíz Díaz & J.M. Mirande (2026):
Removing stripes from the zebra: Two new species of Characidium (Characiformes: Crenuchidae) from the Paraná and Uruguay River basins.
Acta Zoológica Lilloana 70 (1): 281-332
abstract (from publication):
An integrative taxonomic analysis based on morphological and molecular data reveals the presence of two new species of Characidium from the Paraná and Uruguay River basins. These new taxa were historically identified as Characidium cf. zebra or Characidium fasciatum. However, biogeographic, morphological, and molecular evidence indicates that they more closely related to C. borellii than to the species of the C. zebra complex. Both species are distinguished from their congeners by a unique combination of characters: a completely scaled isthmus, a complete lateral line, 14 scales around the caudal peduncle, two rows of dentary teeth, mostly hyaline fins, regular dark transverse bars on the body, the presence of the parietal branch of the supraorbital canal, and specific osteological traits. The new species are distinguished from each other by their pectoral-fin ray counts (13–14 vs. 12 or fewer), coloration patterns (a diffuse vs. a well-defined longitudinal stripe), and internal anatomical features, specifically the number of pseudotympanum openings and vertebral counts. Additionally, we provide data regarding their phylogenetic position, sexual dimorphism, morphological variation, and conservation status. These findings highlight a previously unrecognized diversity of Characidium within the lower La Plata basin.