The upper Bermejo River basin houses a great diversity of fishes, represented by the endemic species, the shared fauna between the Paraguay and the Amazon basins, and the elements from the Paraná River basin. During recent surveys in the area, many specimens of an undescribed Ernstichthys were collected in four different localities of northwestern Argentina and are herein described as a new species. The new species, Ernstichthys casalinuovoi , is distinguished from the remaining species of the genus by a combination of characters including the number of lateral plates on the body, the shape of the second pre-anal-fin plate, the presence of a rictal barbel, the coloration pattern, the number of total vertebrae, the unbranched maxillary barbel, and the number of serrations on the posterior margin of the pectoral-fin spine, among others. The large batch used to describe Ernstichthys casalinuovoi , new species, has allowed us to detect characters that should be treated carefully in the description of species belonging to Ernstichthys such as the number of serrations on the posterior margin of the pectoral-fin spine or the overlap between bony elements on the caudal peduncle given that they could vary according to ontogeny. The new species herein described represents the fifth species of the genus and the first record of Ernstichthys and the Hoplomyzontinae in Argentina.
Aguilera et al. (Fri,) studied this question.
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