A new rheophilic South American darter (Crenuchidae: Characidium) from the rio Juruena basin, Brazil, with comments on morphological adaptations to life in fast‐flowing waters

Abstract

Characidium iaquira, a new species from the upper rio Juruena, rio Tapajós basin, Brazil, is described. The new species can be promptly distinguished from all congeners by having a unique v-shaped dark mark lying along the caudal-fin extension, in medium-and large-sized specimens, and a remarkable iridescent green colouration in life. Characidium iaquira is closely related to Characidium crandellii and Characidium declivirostre by sharing unambiguous synapomorphies such as branchiostegal membranes united to each other across the isthmus, a scaleless area extending from the isthmus to the pectoral girdle, and dermal flaps surrounding anterior and posterior naris independent, but touching each other distally. Morphological specializations of the paired fins in the three riffle-dwellers species are discussed, including the winglike shape, robustness, and inclination of the pectoral fin.

Past riverine connectivity effects in population structure and distribution of an endemic freshwater fish from northeastern Brazilian rivers: Phylogeographic, taxonomic, and conservation implications

“…According to Tedesco et al (2012), some biological traits are associated with the dispersal capacity of freshwater fishes, in which small‐bodied species have less dispersal capacity and can exhibit greater isolation and lower gene flow between populations. Characidium bahiense is a small‐bodied species that occurs in slow water currents and does not possess adaptations cited for congeners that inhabit fast water current environments (e.g., Buckup et al, 2000; Zanata et al, 2020). Considering these traits associated with information from the history of the area, it may be possible to draw scenarios that could explain its current distribution, as detailed below.…”

A new species of Characidium (Characiformes: Crenuchidae) from the rio Madeira basin, Brazil

“…Characidium Reinhardt includes 75 valid species (Fricke et al ., 2020; Zanata et al ., 2020) widely distributed in the Neotropical region, between eastern Panama and northeastern Argentina, with at least 23 of them occurring in the rivers of the Amazon basin. Particularly in the rio Madeira basin, five species of Characidium were described: Characidium barbosai, Flausino‐Junior, Lima, Machado & Melo, C. bolivianum Pearson, Characidium heinianum Zarske & Géry, Characidium schindleri Zarske & Géry and Characidium summum Zanata & Ohara.…”

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

“…Characidium Reinhardt is the most diversified genus of the family Crenuchidae, including so far 79 valid species spread out in the Neotropical region (Agudelo‐Zamora et al ., 2020; Buckup, 1993a; Flausino Junior et al ., 2020; Fricke et al ., 2020; Zanata et al ., 2020a,b; Zanata & Ohara, 2020). Buckup (1993a) proposed the most inclusive phylogenetic hypothesis available so far, recovering Characidium as monophyletic based on a single synapomorphy, the presence of a caudal dot on the base of the middle caudal‐fin rays.…”