Two new miniature translucent catfish species of the rare genus Tridens (Siluriformes: Trichomycteridae) from the Madeira River basin, northern Brazil.

Two new miniature species of the trichomycterid genus Tridens are described from the Madeira River drainage, Acre and Rondônia States, Brazil. Until this work, Tridens was a monotypic genus composed solely of Tridens melanops, from the Putumayo/Içá River drainage, upper Amazonas River basin. Tridens vitreus sp.n. is known from upper and middle Madeira River drainage and differs from all other congeners by the lack of pelvic fins and girdle and by vertebra and dorsal-fin ray counts. Tridens chicomendesi sp.n. is known from Abunã River, middle Madeira River drainage and is distinguished from all other congeners by the number of vertebrae, dorsal-fin ray count and anal-fin base colouration pattern. Tr. chicomendesi sp.n. is further distinguished from T. vitreus by a combination of character states regarding the position of urogenital opening, dorsal-fin position, anal-fin position, maxillary barbel length, number of premaxillary teeth, number of dorsal-fin rays, number of anal-fin rays, number of lateral-line system pores, frontal bone anatomy, degree of ossification of maxilla, anatomy of quadrate-hyomandibular joint, size of posterodorsal process of hyomandibula, length of opercular patch of odontodes, number of interopercular odontodes, proportion of upper hypural plate cartilage relative to its area ; by the absence of a proximal, distal and ventral cartilages on ventral hypohyal; by the absence of a lateral process on basibranchial 4; by the presence of a cartilage block on the lateral process of autopalatine, the presence of a well-developed ossification on proximal margin of ventral hypohyal, the presence of hypobranchial foramen; and by the presence of an anterior cartilaginous joint between quadrate and base of posterodorsal process of hyomandibula. This work represents the first species description for the subfamily Tridentinae in more than 30 years and for the genus Tridens since its original description in 1889.

A new species of Odontostilbe cope (Characiformes: Cheirodontinae) from rio Madeira basin diagnosed based on morphological and molecular data.

A new species of Odontostilbe is described from the rio Jaciparaná, rio Madeira basin, Rondônia, Brazil. Odontostilbe pacaasnovos differs from all its congeners, except O. pequira, by the colour pattern. Additionally, it differs from its congeners by the terminal mouth, number of cusps in the teeth of the premaxilla (5-7), number of branched rays in the anal fin (19-22), by the shape of dentary teeth (5-7 cusps with central cusp larger and longer than laterals cusps) and by the number of lamellae of the olfactory rosette (17-18 in male and 14 in female). Morphological and molecular comparisons corroborate the distinctiveness between O. pacaasnovos and its congeners, justifying its recognition as a new species.

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

This study describes Characidium nambiquara, a new species from the upper rio Guaporé, rio Madeira basin, Brazil. The new species differs from most congeners by the presence of isthmus and area between the contralateral pectoral-fin bases completely naked. From congeners with some degree of scaleless ventral surface of the body C. nambiquara differs by having 10 circumpeduncular scales. The new species is also distinguished from congeners by the spotted colour pattern on body of the large-sized specimens and by having black dashes on all fins and conspicuous midlateral longitudinal dark stripe or conspicuous vertical bars absent. Characidium nambiquara further differs from most congeners by the presence of 34-36 pored scales on the lateral line, 3 horizontal scale rows above the lateral line and 3 horizontal scale rows from the lateral line to the midventral scale series. Remarks on intraspecific colour variation within the genus, not related to sexual dimorphism, are also provided.

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.

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 wing-like shape, robustness, and inclination of the pectoral fin.

A database of freshwater fish species of the Amazon Basin.

The Amazon Basin is an unquestionable biodiversity hotspot, containing the highest freshwater biodiversity on earth and facing off a recent increase in anthropogenic threats. The current knowledge on the spatial distribution of the freshwater fish species is greatly deficient in this basin, preventing a comprehensive understanding of this hyper-diverse ecosystem as a whole. Filling this gap was the priority of a transnational collaborative project, i.e. the AmazonFish project - https://www.amazon-fish.com/. Relying on the outputs of this project, we provide the most complete fish species distribution records covering the whole Amazon drainage. The database, including 2,406 validated freshwater native fish species, 232,936 georeferenced records, results from an extensive survey of species distribution including 590 different sources (e.g. published articles, grey literature, online biodiversity databases and scientific collections from museums and universities worldwide) and field expeditions conducted during the project. This database, delivered at both georeferenced localities (21,500 localities) and sub-drainages grains (144 units), represents a highly valuable source of information for further studies on freshwater fish biodiversity, biogeography and conservation.

A new species of Microschemobrycon (Characiformes: Characidae) from Rio Xingu basin, Brazil.

A new species of Microschemobrycon with a restricted distribution was recently discovered in the Rio Curuá, Rio Xingu basin, Pará, Brazil. Microschemobrycon cryptogrammus new species can be promptly distinguished from all congeners by the presence of a rounded, dark, conspicuous caudal-peduncle blotch and by a subjacent dark midlateral stripe visible in life. Additionally, the new species can be distinguished from all its congeners, except M. elongatus, by the presence of a longitudinal dark stripe along the lower jaw. The new species can be distinguished from M. elongatus by presenting lateral line with 36-38 pored scales, anterior and posterior nostrils coalescend, dark chromatophores concentrated along the ventral margin of the caudal peduncle and by the presence in life of a dark spot at the base of the dorsal-fin origin.

A new species of Eigenmannia Jordan & Evermann (Gymnotiformes: Sternopygidae) from rio Tapajós, Brazil, with discussion on its species group and the myology within Eigenmanniinae.

A new species of Eigenmannia is described from the rio Mutum, tributary of upper rio Juruena, rio Tapajós basin, Comodoro, Mato Grosso, Brazil. The new species is distinguished from all congeners by coloration pattern, position of the mouth, number of scales rows above lateral line, number of premaxillary and dentary teeth, number of precaudal vertebrae, orbital diameter, mouth width, relative depth of posterodorsal expansion on infraorbitals 1+2 and relative size of coronomeckelian bone. Comments on potentially useful characters in phylogenetic studies derived from musculature, discussion on Eigenmannia species-group and the first dichotomous key for Eigenmannia are provided.

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.

Genetic diversity and population structure of Brycon nattereri (Characiformes: Bryconidae): a Neotropical fish under threat of extinction

Brycon nattereri is an endangered Neotropical fish reported along conserved stretches of the upper Paraná, Tocantins and São Francisco rivers. Populations of this species have been very rare in some Paraná River sub basins. This study analyzes the genetic diversity and population structure of B. nattereri in a restricted area of occurrence recently identified in upper Paraná River basin. Seven microsatellite loci and 497 bp of D-Loop mitochondrial region were examined in 92 individuals from four points along the area of occurrence. Both molecular markers indicated a single population distributed along a stretch of the river approximately 80 km long. Although some of the data suggest an ancient bottleneck, current levels of genetic diversity (H E = 0.574 and h = 0.616) were similar to those of other species of the genus Brycon. The results suggest that the population of B. nattereri has been able to maintain satisfactory levels of genetic diversity, in spite of the small area of occurrence. These data have highlighted an important conservation area and action may prove essential to improve the quality of the environment, and especially the water and riparian plant life, if the area is to be managed and conserved efficiently.(AU)

Brycon nattereri é um peixe Neotropical ameaçado de extinção reportado para trechos conservados dos rios Paraná, Tocantins e São Francisco. Populações desta espécie têm sido muito raras em algumas sub-bacias do rio Paraná. Este estudo analisou a diversidade genética e a estrutura populacional de B. nattereri em uma área de ocorrência restrita recentemente identificada na bacia do alto rio Paraná. Sete locos microssatélites e 497 pb da região mitocondrial D-Loop foram examinados para 92 indivíduos de quatro pontos ao longo da área de ocorrência. Ambos os marcadores moleculares indicaram uma única população distribuída em um trecho de aproximadamente 80 km do rio. Embora alguns dados tenham sugerido um antigo gargalo genético, os atuais níveis de diversidade genética (H E = 0,574, h = 0,616) foram similares aos de outras espécies do gênero Brycon. Estes resultados sugerem que a população de B. nattereri tem mantido níveis satisfatórios de diversidade genética, apesar da pequena área de ocorrência. Estes dados destacaram uma importante área de conservação e ações podem melhorar a qualidade do ambiente, especialmente para a vida aquática e mata ciliar, se a área for eficientemente manejada e conservada.(AU)

A new species of Brachychalcinus (Characiformes: Characidae) from the rio Xingu basin, Serra do Cachimbo, Brazil.

Brachychalcinus reisi, a new species of characid fish, is described from the rio Curuá, tributary of rio Iriri, rio Xingu basin, Serra do Cachimbo, Pará State, Brazil. The new species can be distinguished from its congeners by the presence of a series of longitudinal black wavy stripes on the entire body and by a lower number of longitudinal scale rows between dorsal-fin origin and lateral line (7-8 vs. 8-12). Additionally, the new species differs from B. copei, B. parnaibae, and B. retrospina by the lower number of branched dorsal-fin rays (9 vs.10). This is the first description of a new species of the subfamily since the revisionary study of Stethaprioninae, published almost 30 years ago.

Hyphessobrycon petricolus, a new species of tetra (Characiformes: Characidae) from the rio Madeira basin, Mato Grosso, Brazil.

A new species of Hyphessobrycon is described from the rio Roosevelt, rio Madeira basin, Mato Grosso State, Brazil. Hyphessobrycon petricolus sp. n. can be distinguished from its congeners by the unique combination of the following features: a well-defined, relatively narrow dark midlateral stripe on body extending from immediately behind posterior margin of opercle to the middle caudal-fin rays, relatively conspicuous humeral blotch, and 16-20 branched anal-fin rays. Comments on the remaining Hyphessobrycon species presenting a conspicuous dark midlateral stripe are presented.

A new species of Hyphessobrycon Durbin (Characiformes: Characidae) from rio Aripuanã, rio Madeira basin, Brazil.

A new species of Hyphessobrycon is described from the rio Aripuanã, rio Madeira basin, Amazonas State, Brazil. Hyphessobrycon procyon can be distinguished from its congeners by the unique combination of the following features: elongation of the dorsal fin in mature males, absence of dark blotches on the dorsal fin, and presence of two humeral blotches. The possibility of a relationship of the new species within H. elachys, H. heliacus, H. loweae, H. moniliger, and H. peugeoti is discussed based on the sharing of characteristics related to the sexual dimorphism and tooth morphology.

A new species of Characidium Reinhardt (Ostariophysi: Characiformes: Crenuchidae) from headwaters of Rio Pacaás Novos, Rio Madeira basin, Rondônia, Brazil.

Characidium summus, new species, is described from rio Pacaás Novos, rio Madeira basin, Rondônia, Brazil. The new species is the unique among congeners for completely lacking an adipose fin and having a complete lateral line. Characidium summus can be further distinguished from congeners, including C. vestigipinne that also has a complete lateral line and adipose fin absent, vestigial or reduced by the absence of dark bars or spots on head, body or fins, except for a dark blotch on the rear of the opercle, a narrow midlateral dark stripe, and a dark basicaudal spot. In addition, C. summus possess a vestigial supraorbital and a remarkably small pseutotympanum. The possible mimetic relationship between the new species with Erythrinus erythrinus is discussed.

Hyphessobrycon lucenorum (Characiformes: Characidae), a new species from the rio Madeira basin, Rondônia State, Brazil.

A new species of characid is described from the upper rio Machado, a tributary of the rio Madeira basin, Rondônia, Brazil. Hyphessobrycon lucenorum can be distinguished from all congeners by the unique combination of the presence of a conspicuous rounded humeral blotch and a broad and diffuse longitudinal stripe. The new species is included within the Hyphessobrycon agulha group. The high number of endemic species of fishes occurring in the headwater tributaries of three river systems (rio Madeira, rio Tapajós, and rio Paraguai) draining the watershed defined by the Chapada dos Parecis is discussed.

Redescription of Astyanax guaporensis Eigenmann, 1911 (Characiformes: Characidae), a small characid from the rio Madeira basin.

During recent expeditions to several localities in the rio Madeira basin, a poorly known species of Characidae described more than a century ago, Astyanax guaporensis Eigenmann, was collected. The species is herein redescribed based on the type material and many recently collected specimens. The species seems to occur only in the rio Madeira basin, rio Amazonas drainage. The species is mainly recognized among its congeners by having five to nine maxillary teeth, a series of V-shaped marks on the midlateral line of body, and the absence of a black mark on the caudal peduncle.

Jupiaba citrina, a new species from rio Aripuanã, rio Madeira basin, Amazonas and Mato Grosso States, Brazil (Characiformes: Characidae)

A new species of Jupiaba Zanata is described from tributaries of the rio Aripuanã, rio Madeira basin, Amazonas and Mato Grosso States, Brazil. The new species can be diagnosed from its congeners (except J. abramoides, J. anteroides, and J. poranga) by having two vertically-elongated humeral blotches, the anterior usually with a darker median portion forming an horizontally-elongated trace pointed anteriorly, and a well defined dark longitudinal line extending from the second humeral blotch to the caudal peduncle. The new species differs from J. abramoides, J. anteroides, and J. poranga by having an elongated blotch over caudal peduncle that extends to the distal tip of the caudal-fin median rays. Also, it can be distinguished from most congeners by the combination of relatively high number of lateral line scales, predorsal median line without a series of scales, dentary teeth decreasing abruptly in size towards posterior portion, and presence of a larger central teeth cusp.(AU)

Uma nova espécie de Jupiaba Zanata é descrita de afluentes do rio Aripuanã, bacia do rio Madeira, Estados do Amazonas e Mato Grosso, Brasil. A nova espécie é diagnosticada de suas congêneres (exceto J. abramoides, J. anteroides e J. poranga) por apresentar duas manchas umerais alongadas verticalmente, a anterior usualmente com porção mediana mais escura formando um traço horizontalmente alongado, com projeção anterior, e uma linha escura bem definida estendendo-se da segunda mancha umeral até o pedúnculo caudal. A nova espécie difere de J. abramoides, J. anteroides,e J. poranga pela presença de uma mancha alongada sobre o pedúnculo caudal, que se estende até o final dos raios caudais medianos. Também pode ser diagnosticada da maioria das congêneres pela combinação de número relativamente alto de escamas na linha lateral, linha mediana pré-dorsal sem uma série de escamas, dentes do dentário decrescendo abruptamente em tamanho posteriormente e dentes com uma cúspide central maior que as demais.(AU)