Rio Madeira Basin Research Articles

A new restricted-range Melanorivulus (Cyprinodontiformes: Rivulidae) from the upper rio Guaporé, Chapada dos Parecis, Brazil

A new species of Melanorivulus, belonging to the Melanorivulus zygonectes species group, is described from the rio Galera, a tributary of the right bank of the upper rio Guaporé, Amazon basin, Mato Grosso state, Brazil. It is diagnosed from congeners by the following combination of characters: absence of pelvic fins; presence of a black band along the entire caudal-fin margin in males, typically more conspicuous on dorsal and ventral portions; presence of a wide oblique bars anteriorly and wide chevron-like marks posteriorly to middle of flank. This is the first record of the genus Melanorivulus for the rio Madeira basin.

On a new colorful species of Moenkhausia (Characiformes: Characidae) from the upper rio Madeira basin at the Chapada dos Parecis, Brazil, with comments on its conservation and putative biogeographic history.

A new species, Moenkhausia iris, is described from the upper rio Madeira basin, Mato Grosso State, Brazil. The new species is unique among congeners by its color in life, which is the dorsal half of body blue or green and ventral half red, more intense above the anal fin. Additionally, it can be distinguished by having a single, vertically elongated humeral spot, a lateral surface of body, caudal peduncle, and anal fin without distinct blotches or oblique marks and 18-19 branched anal-fin rays. The new species is endemic from a small tributary of the Rio Guaporé, rio Madeira drainage at Chapada dos Parecis. Its putatively close relatives are endemic to the upper rio Juruena located at the same shield. Both headwaters are very close to each other, sharing other restricted range species, and their hydrogeological topography indicates the upper rio Juruena stretch was captured by the rio Guaporé through a headwater capture event. Moenkhausia iris is much appreciated in the international aquarium trade, as well as many other tetras endemic from the same area. Exportation is based on the capture of wild individuals so sustainable exploitation is necessary for its conservation.

A new sexually dichromatic miniature Characidium (Characiformes: Crenuchidae) from the rio Guaporé, rio Madeira basin, Brazil, with remarkable morphological novelties to the genus

Abstract A new miniature species of Characidium is described from the midde rio Guaporé, rio Madeira basin, Rondônia, Brazil. The new species can be readily distinguished from all congeners by the sexual dichromatism, with females having narrow dark bars on body absent in males, and by the presence, in both sexes, of a black midventral dashed line extending from area between contralateral pectoral fins to at least the anal-fin origin. It can also be diagnosed from congeners by having strongly tricuspid teeth, with well developed and similar sized cusps in the premaxilla and outer series of dentary, and short lateral line with 6–8 perforated scales. Morphological novelties to Characidium observed in the new species include a rounded process on the first pleural rib near the vertebra, three or four haemal spines of the first caudal vertebrae distinctly elongate, neural and haemal spines of the antepenultimate vertebra not reaching origins of dorsal and ventral procurrent rays nor the origin of the caudal-fin rays.

A new species of Corydoras (Siluriformes: Callichthyidae) from the rio Madre de Dios basin, Peruvian Amazon, with comments on Corydoras aeneus identity

Abstract A new species of Corydoras is described from tributaries to the rio Araza, an affluent of the rio Inambari, itself a tributary to the rio Madre de Dios, rio Madeira basin in the Peruvian Amazon. The new species can be distinguished from its congeners by the following features: (I) absence of contact between the posterior process of the parieto-supraoccipital and the nuchal plate, (II) a single, large conspicuous dark brown or black blotch on anterodorsal portion of flank; blotch somewhat rounded to roughly diamond shaped, and (III) absence of dark blotches on fins. General comments on the identity of Corydoras aeneus are also provided.

Revision of Prodontocharax and revalidation of Amblystilbe (Teleostei: Characidae: Cheirodontinae), with description of a new species

Abstract Prodontocharax species are revised and the genus Amblystilbe is revalidated based on analysis of type-material and additional specimens. Both genera are diagnosed based on unique synapomorphies among members of the Cheirodontinae related to shape, size, number and arrangement of teeth in the jaw bones. Prodontocharax melanotus, from the upper rio Madeira basin, Brazil and Bolivia, is redescribed, and a new species is described from the rio Huallaga basin, Peru. The genus Amblystilbe and its type-species, A. howesi, are redescribed from the Amazonas River basin, Bolivia, Brazil, and Peru, and Prodontocharax alleni is considered a junior synonym of A. howesi. The two species of Prodontocharax are distinguished by the color pattern, number of lamellae of the olfactory rosette in male and female and number of gill rakers, and differ from A. howesi by the number and shape of teeth, color pattern and number of branched anal-fin rays. According to recent studies, the species of Prodontocharax and A. howesi cluster into two distinct clades among the cheirodontines.

Corydoras fulleri (Siluriformes: Callichthyidae), a new catfish species from the rio Madeira basin, Peru.

A new long-snouted Corydoras species is described from two tributaries of the río Manuripe and a tributary of the río Madre de Dios, rio Madeira basin, Peru. Corydoras fulleri can be distinguished from its congeners by having the following features: (a) branch of the temporal sensory canal at sphenotic, which gives rise to the supraorbital canal, with two pores; (b) upper tooth plate of branchial arch with three series of teeth; (c) area at the corner of the mouth, ventral to the maxillary barbel, with a small fleshy flap; (d) two moderate-sized dark-brown or black blotches on caudal-fin base, one on its lateral portion and another one on its dorsal portion, blotches variably diffuse and/or fused with each other; (e) absence of a dark-brown or black stripe transversally crossing the orbit; (f) a longitudinal dark-brown or black stripe on the postdorsal region of flank midline, variably fused with the lateral peduncular blotch, some specimens with slender, longitudinally elongated, dark-brown or black blotch on flank midline, forming a dash-like marking, stripe or dash-like blotch diffuse in some specimens; and (g) region around dorsal-fin origin generally lacking dark brown or black blotch, or displaying diffuse blotch.

A new species of Moenkhausia (Characiformes: Characidae) from the rio Madeira basin, Brazil, with comments on the evolution and development of the trunk lateral line system in characids

Abstract A new species of Moenkhausia is described from the rio Machado drainage, Amazon basin, Brazil. It is diagnosed from congeners by its color pattern, consisting of the concentration of chromatophores on the anterior portion of body scales, the horizontally elongate blotch on caudal peduncle, a bright golden coloration of the dorsal portion of eye when alive, and a dark line crossing the eye horizontally. The new species has variable morphology regarding trunk lateral-line canals. Most fully grown individuals do not have enclosed bony tube in many lateral line scales, resembling early developmental stages of tube formation of other species. This paedomorphic condition is interpreted as a result of developmental truncation. Such evolutionary process may have been responsible for the presence of distinct levels of trunk lateral line reductions in small characids. Variation in this feature is common, even between the sides of the same individual. We reassert that the degree of trunk lateral-line tube development must be used with care in taxonomic and phylogenetic studies, because reductions in the laterosensory system may constitute parallel loss in the Characidae. We suggest the new species to be categorized Near Threatened due to the restricted geographical distribution and continuing decline in habitat quality.

Revalidation and redescription of Moenkhausia madeirae Fowler from the rio Madeira basin in Brazil and Bolivia (Characiformes: Characidae)

Based on the examination of type and recently collected specimens, Moenkhausia lepidura madeirae Fowler is resurrected from the synonymy of M. intermedia and redescribed as a valid species. Moenkhausia madeirae can be diagnosed from all congeners by the following combination of characters: presence of two symmetrical dark blotches on caudal fin (one on each lobe), a conspicuous humeral blotch, 18-22 branched anal-fin rays, and mature males with two (rarely three) well-developed hooks on the last simple and first branched anal-fin rays, respectively. The species occurs in the middle and upper rio Madeira basin in Brazil and Bolivia. Comparisons are made with the other species of Moenkhausia presenting symmetrical dark blotches on the caudal-fin lobes, i.e., M. barbouri, M. bonita, M. dichroura, and M. intermedia.

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 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.

Taxonomic study of Moenkhausia cotinho Eigenmann, 1908 and Hemigrammus newboldi (Fernández-Yépez, 1949) with the description of two new speciesof Moenkhausia (Teleostei: Characiformes: Characidae).

Moenkhausia cotinho is redescribed based on the examination of meristic and morphometric data and external morphological characters of specimens from the Amazon and Orinoco basins and from rivers in the Guyana. The species is distinguished from congeners based on the combination of a reticulate color pattern, the presence of dark spots on the posterior edge of scales of the longitudinal rows dorsal to the lateral line, the presence of a dark blotch on the caudal-fin base failing to reach the posterior tip of the middle caudal-fin rays; the dorsal region of the eyes red to orange in life; 5/3 longitudinal series of scales, above and below the lateral line, respectively; and the tips of the pectoral-fin rays not extending beyond the base of the pelvic fin. All specimens of M. cotinho have a completely pored literal line except for a few specimens from drainages in the Guyana. The redefinition of the taxonomic limits and geographic distribution of M. cotinho allowed us to reevaluate the taxonomic limits and geographic distribution of Hemigrammus newboldi, the identity of which has been previously questioned, but which is clearly diagnosed from M. cotinho based on the relatively longer pectoral fin, the presence of conical teeth in the posterior portion of the dentary, the absence of a reticulate color pattern of body and in the shorter longitudinal dark stripe on body. In addition, two new species of Moenkhausia are described: Moenkhausia rondoni sp n. from the rio Madeira basin, Brazil and Moenkhausia pirahan sp n. from the lower rio Madeira and rio Trombetas and rio Tapajós basins, Brazil.

A new species of Characidium Reinhardt (Characiformes: Crenuchidae) with a unique mid-water behavior from the upper rio Madeira basin, Brazil

A new species of Characidium is described from headwater tributaries of the upper rio Guaporé, Rio Madeira basin, Mato Grosso state, Brazil. The new species can be diagnosed from all congeners, except Characidium summus, for lacking the preorbital and postorbital stripes. It can be diagnosed from the latter species by having 12 circumpeduncular scales (vs. 14), by an adipose fin present (vs. adipose fin absent), and 10-12 bars along the body (vs. absence of bars), among other characters. The new species is so far only known from direct tributaries of the Rio Guaporé at the Serra da Borda, an isolated plateau 300-800 meters above sea level, and possess a behavior very uncommon within the genus, being a mid-water pelagic fish, instead of the benthic behavior of most congeners. Comments on the putative phylogenetic relationships of the new species, as well as some remarks on its unusual behavior within the genus, are presented.

A new species of Knodus (Characiformes: Characidae: Stevardiinae) from the rio Aripuanã, rio Madeira basin, Brazil

ABSTRACT A new species of the characid genus Knodus is described from the rio Aripuanã (rio Madeira basin). It can be distinguished from its congeners by its very low body depth, the presence of tri- to pentacuspid teeth on the outer premaxillary series, with the median cuspid larger than the lateral ones, the teeth of the inner premaxillary series pentacuspid, distinctly larger than those of the outer series, the maxillary teeth tri- to pentacuspid, with the median cusp slightly larger than the lateral ones, the four anteriormost dentary teeth pentacuspid, the smaller posterior teeth tri- to pentacuspid, a complete lateral line with 36-38 scales, 3 longitudinal scale series from pelvic fin origin to lateral line, and 11-12 circumpeduncular scales. The new species is also compared to incertae sedis species of ‘Bryconamericus’ from northern South America since phylogenetic studies suggest a closer relationship of those species with Knodus.

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.

On a remarkable sexual dimorphic trait in the Characiformes related to the olfactory organ and description of a new miniature species of Tyttobrycon Géry (Characiformes: Characidae).

Among the order Characiformes, secondary sexual dimorphism is commonly associated to the occurrence of bony hooks on fins, shape and length of the dorsal and anal fins, and sexual dichromatism. The analysis of a new miniature Characidae species of the genus Tyttobrycon, described herein, yielded to the discovery of a sexually dimorphic trait related to nostril aperture and number of olfactory lamellae. In this type of dimorphism, mature males present larger nostril aperture and higher number of olfactory lamella than females. A dimorphic olfactory organ is for the first time recorded and described for a member of the Characiformes. Gross morphology and development of brain and peripheral olfactory organ of Tyttobrycon sp. n. are described and compared to other species of Characidae. It is hypothesized that such dimorphic trait is related to male-male detection during cohort competition in small characids. The new species of Tyttobrycon is diagnosed from its congeners by the number of branched anal-fin rays (19–21) and the absence of a caudal-peduncle blotch. It occurs in a small tributary of Rio Madeira basin, near to the limit between Brazil and Bolivia, Acre State, Brazil.

A new species of Poptella (Characiformes: Characidae: Stethaprioninae) from the Rio Juma, Rio Madeira basin, Brazil

ABSTRACT A new species of Poptella is described from the Rio Juma, a tributary of the lower Rio Aripuanã, Rio Madeira basin, Amazonas, Brazil. The new species is distinguished from all congeners, except P. brevispina, by having a lower number of scale rows between the lateral line and dorsal-fin origin (7 vs. 8-10). The new species can be readily distinguished from P. brevispina by the lower number of branched dorsal-fin rays (9 vs. 10). This is the first description of a new species of Poptella since the revisionary study of the Stethaprioninae, published 30 years ago.

A new species of Ancistrus Kner, 1854 (Siluriformes: Loricariidae) from rio Madeira basin, Amazonas State, Brazil

ABSTRACT During the Mosaico do Apuí expedition in 2006, a new species of Ancistrus was found in the rio Sucunduri, a large tributary of the rio Madeira basin in south Amazonas State. The new species has a unique color pattern for the genus and is distinguished by the presence of alternate light and dark vertical bars on the trunk. Other Ancistrini genera have species with a similar color pattern, but the new species is clearly distinguished by a lack of plates on the snout and presence of fleshy tentacles on the snout as in all Ancistrus representatives. We also provide comments on the taxonomic status of the A. bolivianus, A. heterorhynchus and A. marcapatae.

Description of a new Pimelodella (Siluriformes: Heptapteridae) species with a discussion on the upper pectoral girdle homology of Siluriformes

A new species of Pimelodella is described from several right-bank tributaries of the Rio Madeira basin in Amazonas and Rondônia states, Brazil. The new species differs from all congeners by the supraoccipital process not reaching the anterior nuchal plate, 43-45 total vertebrae, maxillary barbels reaching between adpressed anal-fin terminus and caudal-fin origin, epiphyseal branch of supraorbital laterosensory canal emerging as two distantly-positioned pores and a conspicuous black mark at distal third of dorsal fin, between dorsal-fin spine and third branched ray. A detailed description of the cephalic laterosensory system of the new species is provided and contrasted with other Siluriformes and Ostariophysi. A discussion regarding homology of the catfish upper pectoral girdle bones is offered in light of modifications of the postotic and supratemporal lateral-line canals. Based on the placement of the pterotic branch of the postotic canal, it is concluded that the extrascapula is fused to the pterotic in Siluriformes. Results presented herein offer an example of how lateral-line morphology can be used as a compelling source of evidence to help determine homology of cranial and upper pectoral girdle bones.

A new species of Hisonotus (Siluriformes: Loricariidae) from Aripuanã river, Amazon basin, Brazil.

A new species of Hisonotus from rio Juma, located at the right margin of the lower rio Aripuanã, rio Madeira basin is described. The new species is distinguished from its congeners mainly by a reddish-tipped premaxillary and dentary teeth, a V-shaped spinelet, three lateral plates in abdominal series, the coloration pattern of caudal fin with three transversal dark bars, and by morphometric characters.

Distribution and availability of mercury and methylmercury in different waters from the Rio Madeira Basin, Amazon.

Waters from the Amazon Basin have distinct physicochemical characteristics that can be optically classified as "black", "clear" and "white". We studied the distribution of total-Hg (THg) and methyl-Hg (MeHg) in these waters and respective suspended solids, sediment, phytoplankton, zooplankton, and benthic macroinvertebrates (BM) in the Madeira River Basin. Compared with the other types of water, the more acidic "black" kind had the highest THg and MeHg concentrations. The trend (black > clear > white) occurred for the concentrations of THg and MeHg in sediments and in the biotic compartment (plankton, macroinvertebrates). Organic Hg accounted for a small percentage (0.6-0.4%) of the THg in sediments but was highest in water (17-15%). For plankton and BM, the biota sediment accumulation factor (BSAFs) of MeHg (53-125) were greater than those of THg (4.5-15); however, the BSAF trend according to water type (black > clear > white) was only significant for MeHg. Sediment THg is correlated with all forms of Hg in biotic and abiotic matrices. The results indicate that water acidity in the Amazon is an important chemical characteristic in assessing Hg contamination of sediments and bioaccumulation in the aquatic food web. The differences in the BSAFs between THg and MeHg support the use of this factor for evaluating the bioaccumulation potential of sediment-bound Hg. The results add information critical to assessing environmental and health risks related to Hg methylation and potential fish-MeHg contamination, especially in tropical aquatic environments.