Integrative taxonomy reveals a new species of pacu (Characiformes: Serrasalmidae: Myloplus) from the Brazilian Amazon

Abstract

Pacus of the genus Myloplus represent a formidable taxonomic challenge, and particularly so for the case of M. asterias and M. rubripinnis, two widespread and common species that harbor considerable morphological diversity. Here we apply DNA barcoding and multiple species discovery methods to find candidate species in this complex group. We report on one well-supported lineage that is also morphologically and ecologically distinct. This lineage represents a new species that can be distinguished from congeners by the presence of dark chromatophores on lateral-line scales, which gives the appearance of a black lateral line. It can be further diagnosed by having 25-29 branched dorsal-fin rays (vs. 18-24), 89-114 perforated scales from the supracleithrum to the end of hypural plate (vs. 56-89), and 98-120 total lateral line scales (vs. 59-97). The new species is widely distributed in the Amazon basin, but seems to have a preference for black- and clearwater habitats. This ecological preference and black lateral line color pattern bears a striking similarity to the recently described silver dollar Metynnis melanogrammus.

Universal Set of Primers for DNA Identification of Alien Fish Species in Central Russia (Volga-Kama Region)

“…The calculations were performed on the COI gene tree using the algorithm [53] in the "Microsoft R-Open and MKL" 64-bit v.3.5 software (http://mran.microsoft.com/). This implementation is suitable for single-locus studies, correlates well with morphological data, and at the same time is not prone to excessive taxa fragmentation [54].…”

Comparative cytogenetics of Serrasalmidae (Teleostei: Characiformes): The relationship between chromosomal evolution and molecular phylogenies

“…g . 6 , 7 , 53 ]. Despite the advances in species description of Serrasalmidae, 14 new taxa in the last decade [ 5 ], none of them included a Serrasalmus discovery, even with the several evidences of new species using COI [ e .…”

“…Despite the occurrence of some species in environments such as rapids, these fishes typically inhabit lakes and floodplains [ 4 ]. It is the fourth most diverse family within Characiformes, with 101 valid species, distributed in 16 extant genera [ 5 – 7 ], with more than 70 species occurring in the Amazon basin [ 8 ]. These fishes have different feeding habits, and can be frugivorous, herbivorous, piscivorous, and lepidophagous (consumer of scales) [ 9 – 11 ].…”

“…In the Brazilian Amazon, various lineages may represent new species, especially concerning Myloplus and Serrasalmus [ 21 ]. Two new species were recently described using the same marker, Catoprion absconditus Mateussi, Melo & Oliveira 2020 and Myloplus nigrolineatus Ota, Machado, Andrade, Collins, Farias & Hrbek 2020 [ 6 , 7 ]. In the basins of the Paraná-Paraguay and Tocantins rivers, a species complex was detected in Serrasalmus maculatus Kner 1858 [ 22 ] and five lineages were recognized in Pygocentrus nattereri Kner 1858 in different river basins [ 23 ].…”

“…In the basins of the Paraná-Paraguay and Tocantins rivers, a species complex was detected in Serrasalmus maculatus Kner 1858 [ 22 ] and five lineages were recognized in Pygocentrus nattereri Kner 1858 in different river basins [ 23 ]. This underestimation of diversity is a consequence of the difficulty in identifying many species and their intra- and interspecific limits, due to the variation in body shape, sexual dimorphism, ontogeny [ 1 , 4 , 7 , 24 ], and water color in Amazon basin [ 7 , 25 ]. In addition, we highlight the scarcity of recent taxonomic revisions, with identification keys, of species-rich genera, such as Metynnis , Myloplus , and Serrasalmus .…”