Redescrição taxonômica do pacu-caranha (Serrasalmidae: Piaractus: Piaractus mesopotamicus)

Abstract

Integrative studies demonstrated that Serrasalmidae diversity is underestimated. Even Piaractus, which holds pacus of great commercial importance, had a species described from the Orinoco River basin just five years ago. Thus, three species became part of the genus: P. brachypomus, P. mesopotamicus and P. orinoquensis. On the other hand, phylogenetic studies using molecular markers recovered P. mesopotamicus, popularly known as pacu-caranha, as a lineage within P. brachypomus. Despite this evidence, the species was considered valid based on morphological and geographic distribution differences. Considering that P. mesopotamicus has not been subject of any taxonomic investigation since its original description in 1887, the main goal of this study is to realize a morphological taxonomic review of the species, including the largest possible number of individuals. Piaractus mesopotamicus is widely distributed in the basins of the Paraná, Paraguay and Uruguay rivers, and does not occur in sympatry with other congeners. The morphological characteristics indicated as diagnostic of the species in the literature were confirmed here, and the species is characterized by having tiny scales, resulting in higher counts on the lateral line (107–128 vs. 100 or less) and series of scales above and below the lateral line (49 or more vs. 38 or less). In addition, the color pattern in life is unique, consisting of a purplish anterior portion of the body and a yellowish posterior portion (vs. a grayish body anteriorly and reddish or whitish posteriorly).