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 pumarinri n. sp. is described from the affluents of Río Huallaga, a tributary of Río Marañón that drains the eastern slopes of the Andes, in the Peruvian Amazon. The new species has a deep body (24-31% in LS ), 11-17 well-marked dark bars and remarkable sexual dimorphism related to colour pattern, in which males have darker anal, dorsal, pectoral and pelvic fins than females. C. pumarinri resembles some species allocated in Clade C4, mainly by having a high number of transversal bars and a deep body. In addition, a thorough review and further descriptions of the secondary sexual characteristics in Characidium are provided.

A new species of Hyphessobrycon (Characiformes, Characidae) from the upper Rio Jequitinhonha basin, Minas Gerais, Brazil, with comments on morphological similarities with Stethaprioninae species from headwater environments.

A new species of Hyphessobrycon is described from a marshland area in the headwaters of Rio Jequitinhonha basin, Minas Gerais, Brazil. The new species differs from congeners by presenting a single well-delimited conspicuous humeral blotch, rounded to vertically oval, restricted to the area dorsal to the lateral-line row of scales, without a narrower downward extension, greatest body depth anterior to dorsal-fin origin, bony processes in anal and pectoral-fin rays of males and four teeth in the inner row of the premaxillary bone. The new species presents a set of morphological features shared by some species currently assigned to Hasemania, Myxiops and to the Astyanax scabripinnis complex. Some of these features are discussed.

Unexpected species diversity in electric eels with a description of the strongest living bioelectricity generator.

Is there only one electric eel species? For two and a half centuries since its description by Linnaeus, Electrophorus electricus has captivated humankind by its capacity to generate strong electric discharges. Despite the importance of Electrophorus in multiple fields of science, the possibility of additional species-level diversity in the genus, which could also reveal a hidden variety of substances and bioelectrogenic functions, has hitherto not been explored. Here, based on overwhelming patterns of genetic, morphological, and ecological data, we reject the hypothesis of a single species broadly distributed throughout Greater Amazonia. Our analyses readily identify three major lineages that diverged during the Miocene and Pliocene-two of which warrant recognition as new species. For one of the new species, we recorded a discharge of 860 V, well above 650 V previously cited for Electrophorus, making it the strongest living bioelectricity generator.

Hyphessobrycon rheophilus, a new species from rapids of the Amazon and Orinoco river basins (Characiformes: Characidae: Stethaprioninae).

A new species from rapids of Rio Aripuanã, Rio Madeira basin, in Brazil, and from the same type of habitat in the upper Rio Negro and upper Rio Orinoco basins in Brazil, Colombia, and Venezuela is described and assigned to the genus Hyphessobrycon. The new species presents an interrupted lateral line plus a single perforated scale on caudal peduncle and a small dark blotch on dorsal procurrent caudal-fin rays, features not found in the other species of Hyphessobrycon. Comments on the phylogenetic position of the new species, its rheophilic habits, and the biogeographic implications of its distribution are presented.

Two new species of Leporinus Agassiz, 1929 (Characiformes: Anostomidae) from tributaries of the lower Amazon basin in Brazil.

Two new species of Leporinus (Characiformes, Anostomidae) are described. Both new species are diagnosed by having one dark blotch on midline of anterior portion of the flank (between opercle and pelvic-fin origin) surrounded by five to seven dark blotches; and a subinferior mouth with three premaxillary teeth. Leporinus multimaculatus, new species, is distributed in small and medium-sized tributaries of the rio Tocantins and rio Xingu basins, and also in the rio Jari and coastal drainages of Amapá state, whereas L. torrenticola, new species, is endemic to the rapids of the rio Xingu and its main tributaries. The number of scale rows around the caudal peduncle is the main feature distinguishing L. multimaculatus from L. torrenticola. Comments on the diagnostic features of the newly described species are provided. In addition, the phylogenetic position and generic assignment of the new species are discussed based on available information from recent morphological and molecular analyses.