Species boundaries of the whiptail catfish Rineloricaria (Siluriformes: Loricariidae) from the Paraíba do Sul River drainage, southeastern Brazil, with species redescriptions and description of a new species.

Species of the catfish genus Rineloricaria are common in the Paraíba do Sul River basin, in southeastern Brazil; here we present a revision of the taxonomic diversity and geographic distribution of the species of the genus inhabiting the basin, based on novel morphologic and molecular data. Five species delimitation methods based on cytochrome C oxidase subunit 1 nucleotide sequences yielded comparable molecular operational taxonomic units. The automatic barcode gap discovery, assemble species by automatic partitioning, barcode index number, and Bayesian implementation of the Poisson tree process methods supported the recognition of five evolutionary lineages. These taxonomic units were assigned to the previously described Rineloricaria nigricauda, Rineloricaria steindachneri, Rineloricaria zawadzkii, and Rineloricaria nudipectoris, and an additional undescribed species. R. zawadzkii was further divided into two intraspecific geographically structured lineages using the generalized mixed Yule coalescent delimitation method. A maximum likelihood phylogenetic analysis revealed that the five lineages from the Paraíba do Sul have closer relationships to different species from southern and southeastern Brazil (Ribeira de Iguape, Lagoa dos Patos, Uruguay, Paraguay, and Parana river basins) than to each other. Based on the analysis of lectotypes, recently collected material, and specimens from ichthyological collections, the poorly described R. nigricauda and R. steindachneri are redescribed following current descriptive standards. The undescribed species from the middle and upper Paraíba do Sul River basin is formally described. The description of a new species, along with the description of species boundaries in R. nigricauda and R. steindachneri, contributes to the knowledge of the ichthyofauna of the Paraíba do Sul River basin and adjacent coastal drainages of southeastern Brazil. An identification key for the species of Rineloricaria occurring in the Paraíba do Sul River basin is provided.

Bilateral genital asymmetry in livebearer fishes of the genus Phalloceros Eigenmann, 1907, with description of a new species from coastal drainages of southern Brazil (Cyprinodontiformes: Poeciliidae).

A new species of Phalloceros is described from the Tijucas, Maruim, Aririú, Cubatão do Sul, Rio da Madre, D'Una and Tubarão river basins in southern Brazil. The new species is diagnosed among congeners by the bilateral asymmetry of a hood-like structure located immediately anterior to the urogenital papilla of females. The hood is fused with the urogenital papilla on the right side, but free from the papilla on the left side. This hood is reported for the first time in the genus and is present in six of the 21 valid species of Phalloceros, but its bilateral asymmetry is an exclusive condition of the new species. These species do not constitute a monophyletic group. The new species is likely to be phylogenetically related to P. caudimaculatus, whose females have a symmetrical hood.

The freshwater fishes from the Costa Verde Fluminense region of southeastern Brazil / Os peixes de água doce da região da Costa Verde Fluminense do sudeste do Brasil

Abstract The region between the Brazilian Shield and the Atlantic Ocean is characterized by the presence of numerous hydrographic basins isolated by mountainous terrain that flow directly into the ocean without forming wide coastal plains. However, knowledge about the diversity and distribution of freshwater fish in several coastal areas is still incipient. One of these areas is the Costa Verde Fluminense region, situated between the municipalities of Mangaratiba and Paraty in the Brazilian State of Rio de Janeiro. In order to eliminate the gap of knowledge about the freshwater fish fauna of this region, we prepared a list of the species, and dichotomous identification keys and illustrations of all species. We examined material from expeditions carried out between 1942 and 2019, deposited in the Ichthyological Collection of the Museu Nacional, Universidade Federal do Rio de Janeiro, Brazil. The material comes from 29 continental coastal rivers and four drainages on Ilha Grande island. We recognized 54 fish species belonging to 16 families and 9 orders. The order Siluriformes was the most diverse with 18 species, followed by Characiformes with 14 species, Cyprinodontiformes with 10 species, Cichliformes with four species, Gobiiformes with three species, Syngnathiformes with two species, and Gymnotiformes, Salmoniformes and Synbranchiformes with one species each. These records include two putative undescribed species and four introduced species. Phalloceros anisophallos was the most widely distributed species, recorded in 24 drainages. More than a half (52 %) of the native species occur exclusively in coastal streams, demonstrating the importance of the area for biogeographic and conservation studies.

Resumo A região entre o Escudo Brasileiro e o Oceano Atlântico é caracterizada pela presença de inúmeras bacias hidrográficas isoladas por terrenos montanhosos que deságuam diretamente no oceano sem formar amplas planícies costeiras. No entanto, o conhecimento sobre a diversidade e distribuição de peixes de água doce em diversas áreas costeiras ainda é incipiente. Uma dessas áreas é a região da Costa Verde Fluminense, situada entre os municípios de Mangaratiba e Paraty no Estado do Rio de Janeiro. A fim de eliminar a lacuna de conhecimento sobre a ictiofauna de água doce desta região, elaboramos uma lista das espécies, chaves de identificação dicotômicas e ilustrações de todas as espécies. Examinamos material de expedições realizadas entre 1942 e 2019, depositado na Coleção Ictiológica do Museu Nacional da Universidade Federal do Rio de Janeiro, Brasil. O material é proveniente de 29 rios costeiros continentais e quatro drenagens da Ilha Grande. Reconhecemos 54 espécies de peixes pertencentes a 16 famílias e 9 ordens. A ordem Siluriformes foi a mais diversa com 18 espécies, seguida de Characiformes com 14 espécies, Cyprinodontiformes com 10 espécies, Cichliformes com quatro espécies, Gobiiformes com três espécies, Syngnathiformes com duas espécies e Gymnotiformes, Salmoniformes e Synbranchiformes com uma espécie cada. Esses registros incluem duas espécies presumidamente não descritas e quatro espécies introduzidas. Phalloceros anisophallos foi a espécie mais amplamente distribuída, registrada em 24 drenagens. Mais da metade (52 %) das espécies nativas ocorrem exclusivamente em córregos costeiros, demonstrando a importância da área para estudos biogeográficos e de conservação.

Evolutionary units delimitation and continental multilocus phylogeny of the hyperdiverse catfish genus Hypostomus.

With 149 currently recognized species, Hypostomus is one of the most species-rich catfish genera in the world, widely distributed over most of the Neotropical region. To clarify the evolutionary history of this genus, we reconstructed a comprehensive phylogeny of Hypostomus based on four nuclear and two mitochondrial markers. A total of 206 specimens collected from the main Neotropical rivers were included in the present study. Combining morphology and a Bayesian multispecies coalescent (MSC) approach, we recovered 85 previously recognized species plus 23 putative new species, organized into 118 'clusters'. We presented the Cluster Credibility (CC) index that provides numerical support for every hypothesis of cluster delimitation, facilitating delimitation decisions. We then examined the correspondence between the morphologically identified species and their inter-specific COI barcode pairwise divergence. The mean COI barcode divergence between morphological sisters species was 1.3 ± 1.2%, and only in 11% of the comparisons the divergence was ≥2%. This indicates that the COI barcode threshold of 2% classically used to delimit fish species would seriously underestimate the number of species in Hypostomus, advocating for a taxon-specific COI-based inter-specific divergence threshold to be used only when approximations of species richness are needed. The phylogeny of the 108 Hypostomus species, together with 35 additional outgroup species, confirms the monophyly of the genus. Four well-supported main lineages were retrieved, hereinafter called super-groups: Hypostomus cochliodon, H. hemiurus, H. auroguttatus, and H. plecostomus super-groups. We present a compilation of diagnostic characters for each super-group. Our phylogeny lays the foundation for future studies on biogeography and on macroevolution to better understand the successful radiation of this Neotropical fish genus.

Barcoding the Neotropical freshwater fish fauna using a new pair of universal COI primers with a discussion of primer dimers and M13 primer tails.

Designing primers for DNA barcoding is a significant challenge for the rich Neotropical fish fauna, which is comprised of ∼6000 species. Previously, researchers required multiple pairs of PCR primers or primer cocktails to obtain standard COI (i.e., mitochondrial cytochrome c oxidase subunit I) barcode sequences from assemblages of freshwater fish in this region. To simplify DNA barcoding and metabarcoding studies of Neotropical freshwater fish, we present a new pair of COI primers, which have yielded high quality barcodes across six teleost orders-Characiformes, Cichliformes, Cyprinodontiformes, Gymnotiformes, Siluriformes, and Synbranchiformes-native to South America. Following previous fish barcoding studies, we also tailed our primers with M13 forward and reverse primers to facilitate the DNA sequencing process. Although this practice generates primer dimers, we obtained complete and high quality COI barcode sequences for all samples. We discuss the problem of primer dimers and suggest strategies for neutralizing their influence on data quality.

Poor taxonomic sampling undermines nomenclatural stability: A reply to Roxo et al. (2019).

A recent study based on genomic data by Roxo et al. (2019) provided a phylogeny of the Loricariidae, the largest catfish family and second largest Neotropical fish family with approximately 1,000 species. The study represents a valuable and innovative contribution for understanding higher-level relationships within the family. The phylogenetic tree inferred by Roxo et al. (2019) thoroughly corroborates the monophyly and relationships of most currently accepted subfamilies of Loricariidae, based on a fair taxon sampling (nearly 14% of the species in the family) representing most genera of each but one of the subfamilies, the Lithogeninae, the sister-group of the remaining members of the family (Pereira & Reis, 2017; Reis et al., 2017). In addition to a hypothesis of relationships, Roxo et al. (2019) also proposed a series of lower-level taxonomic changes, which are deemed premature considering that the taxonomic sampling of the study targeted higher-level clades, and go against one of the pillars of biological classification: nomenclatural stability (e.g., Heterick & Majer, 2018; Beninger & Backeljau, 2019). Here we (1) discuss implications of inadequate taxonomic sampling as a basis for changes in classification of species; (2) explain why the taxonomic sampling design of Roxo et al. (2019) is inadequate for the proposed nomenclatural changes; and (3) advocate that changes to classifications must be grounded on phylogenies with dense sampling of taxa at the relevant level.

A new species of Characidium (Characiformes: Crenuchidae) from coastal basins in the Atlantic Rainforest of eastern Brazil, with phylogenetic and phylogeographic insights into the Characidium alipioi species group

A new species of Characidium from southeastern Brazil is described based on morphological and molecular evidence from specimens collected between the rio Jucuruçu and rio Doce basins. The new species belongs to a group of species within Characidium with an unscaled area in the isthmus and is distinguished from these species, except C. alipioi, C. fasciatum, C. hasemani, and C. kamakan, by the greater distance (greater than 10% SL) and presence of 5-7 scales between the anus and the anal fin, and presence of 14 series of scales around the caudal peduncle. The species is distinguished from C. alipioi by having 4 series of scales above the lateral line (vs. 5 series) and greater distance between the anus and the anal fin; from C. fasciatum and C. kamakan, by the smaller body depth at the dorsal-fin origin, at the anal-fin origin, and at the caudal peduncle; from C. hasemani, by the short distances between the tip of the snout and the pelvic fin, the tip of the snout and the anal fin, and the tip of the snout and the tip of anal fin. The new species forms a presumably monophyletic group with C. alipioi and C. kamakan.(AU)

Uma nova espécie de Characidium do sudeste do Brasil é descrita com base em evidências morfológicas e moleculares provenientes de exemplares coletados entre as bacias dos rios Jucuruçu e Doce. A nova espécie pertence a um grupo de espécies de Characidium com área desprovida de escamas no ístmo e difere dessas espécies, exceto C. alipioi, C. fasciatum, C. hasemani e C. kamakan, pela grande distância (maior que 10% do comprimento padrão, CP) e presença de 5-7 escamas entre o ânus e a nadadeira anal, e pela presença de 14 séries de escamas em torno do pedúnculo caudal. A espécie difere de C. alipioi pela presença de 4 séries de escamas acima da linha lateral (vs. 5 séries) e maior distância entre o ânus e a nadadeira anal; de C. fasciatum e C. kamakan, pela menor altura do corpo na origem da nadadeira dorsal, na origem da nadadeira anal, e no pedúnculo caudal; de C. hasemani, pela menor distância entre a ponta do focinho e a nadadeira pélvica, a ponta do focinho e a nadadeira anal, e a ponta do focinho e a ponta da nadadeira anal. A nova espécie forma um grupo presumidamente monofilético com C. alipioi e C. kamakan.(AU)

Reducing the information gap on Loricarioidei (Siluriformes) mitochondrial genomics.

BACKGROUND: The genetic diversity of Neotropical fish fauna is underrepresented in public databases. This distortion is evident for the order Siluriformes, in which the suborders Siluroidei and Loricarioidei share equivalent proportion of species, although far less is known about the genetics of the latter clade, endemic to the Neotropical Region. Recently, this information gap was evident in a study about the structural diversity of fish mitochondrial genomes, and hampered a precise chronological resolution of Siluriformes. It has also prevented molecular ecology investigations about these catfishes, their interactions with the environment, responses to anthropogenic changes and potential uses. RESULTS: Using high-throughput sequencing, we provide the nearly complete mitochondrial genomes for 26 Loricariidae and one Callichthyidae species. Structural features were highly conserved. A notable exception was identified in the monophyletic clade comprising species of the Hemiancistrus, Hypostomini and Peckoltia-clades, a ~60 nucleotide-long deletion encompassing the seven nucleotides at the 3' end of the Conserved Sequence Block (CSB) D of the control region. The expression of mitochondrial genes followed the usual punctuation pattern. Heteroplasmic sites were identified in most species. The retrieved phylogeny strongly corroborates the currently accepted tree, although bringing to debate the relationship between Schizolecis guntheri and Pareiorhaphis garbei, and highlighting the low genetic variability within the Peckoltia-clade, an eco-morphologically diverse and taxonomically problematic group. CONCLUSIONS: Herein we have launched the use of high-throughput mitochondrial genomics in the studies of the Loricarioidei species. The new genomic resources reduce the information gap on the molecular diversity of Neotropical fish fauna, impacting the capacity to investigate a variety of aspects of the molecular ecology and evolution of these fishes. Additionally, the species showing the partial CSB-D are candidate models to study the replication and transcription of vertebrate mitochondrial genome.

DNA barcoding reveals species level divergence between populations of the microhylid frog genus Arcovomer (Anura: Microhylidae) in the Atlantic Rainforest of southeastern Brazil.

The microhylid frogs belonging to the genus Arcovomer have been reported from lowland Atlantic Rainforest in the Brazilian states of Espírito Santo, Rio de Janeiro, and São Paulo. Here, we use DNA barcoding to assess levels of genetic divergence between apparently isolated populations in Espírito Santo and Rio de Janeiro. Our mtDNA data consisting of cytochrome oxidase subunit I (COI) nucleotide sequences reveals 13.2% uncorrected and 30.4% TIM2 + I + Γ corrected genetic divergences between these two populations. This level of divergence exceeds the suggested 10% uncorrected divergence threshold for elevating amphibian populations to candidate species using this marker, which implies that the Espírito Santo population is a species distinct from Arcovomer passarellii. Calibration of our model-corrected sequence divergence estimates suggests that the time of population divergence falls between 12 and 29 million years ago.

The complete mitochondrial genome of Corydoras nattereri (Callichthyidae: Corydoradinae)

The complete mitogenome of Corydoras nattereri , a species of mailed catfishes from southeastern Brazil, was reconstructed using next-generation sequencing techniques. The mitogenome was assembled using mitochondrial transcripts from the liver transcriptomes of three individuals, and produced a circular DNA sequence of 16,557 nucleotides encoding 22 tRNA genes, two rRNA genes, 13 protein-coding genes and two noncoding control regions (D-loop, OrigL). Phylogeographic analysis of closely related sequences of Cytochrome Oxydase C subunit I (COI) demonstrates high diversity among morphologically similar populations of C. nattereri . Corydoras nattereri is nested within a complex of populations currently assigned to C. paleatus and C. ehrhardti . Analysis of mitogenome structure demonstrated that an insertion of 21 nucleotides between the ATPase subunit-6 and COIII genes may represent a phylogenetically informative character associated with the evolution of the Corydoradinae.

O mitogenoma completo de Corydoras nattereri , uma espécie de bagres encouraçados do sudeste do Brasil, foi reconstruído através de técnicas de sequencimento de DNA de próxima geração. O mitogenoma foi produzido a partir de produtos de transcrição mitocondrial dos transcriptomas hepáticos de três indivíduos, resultando numa sequência de DNA circular de 16.557 nucleotídeos abrangendo 22 genes de tRNA, dois genes de rRNA, 13 genes codificadores de proteínas e duas regiões de controle não codificadoras (D-loop, OrigL). A análise filogenética de sequências proximamente relacionadas da subunidade I do gene Citocrome Oxidase C (COI) demonstrou a existência de elevada diversidade entre populações morfologicamente similares de C. nattereri . Corydoras nattereri está inserida num complexo de populações atualmente identificadas como C. paleatus e C. ehrhardti . A análise da estrutura do mitogenoma demonstra que a inserção de uma sequência de 21 nucleotídeos entre os genes da subunidade 6 da ATPase e do COIII representa um caráter filogeneticamente informativo associado à evolução de Corydoradinae.

A new species of Characidium Reinhardt, 1867 (Characiformes: Crenuchidae) endemic to the Atlantic Forest in Paraná State, southern Brazil

A new species of Characidium is described based on specimens obtained from the highland streams of the Serra do Mar, Atlantic Forest Biome, in Paraná State, Southern Brazil. The new species is possibly a member member of the C. lauroi group, which is diagnosed by having the isthmus unscaled, bars poorly marked, and spots on sides of body, and is composed by four additional species: C. japuhybense ; C. lauroi ; C. oiticicai ; and C. schubarti . The new species differs from its congeners with naked isthmus, except C. helmeri , by having 15-18 principal caudal-fin rays; and 10-12 pectoral-fin rays; and from C. helmeri , by having a slender body, tip of pectoral fin not reaching origin of pelvic fin, tip of pelvic fin not reaching beyond anus, supraorbital present and well developed, and by lacking vertically elongated dashes on sides of body. The new species is known from tributaries of the rio Jordão, in the rio Iguaçu Basin, and rio Taquari, a tributary of the rio Ribeira de Iguape coastal drainage.(AU)

Uma nova espécie de Characidium é descrita com base em exemplares obtidos de riachos de altitude da Serra do Mar, no bioma Mata Atlântica, do Estado do Paraná, Sul do Brasil. A nova espécie é possivelmente um membro do grupo C. lauroi , que pode ser diagnosticado por possuir o istmo sem escamas, barras pouco marcadas e pontos nos lados do corpo, e é composto por quatro espécies adicionais: C. japuhybense ; C. lauroi ; C. oiticicai ; e C. schubarti . A nova espécie difere de seus congêneres com istmo nú, exceto C. helmeri , por possuir 15-18 raios principais na nadadeira caudal, e 10-12 raios na nadadeira peitoral; e de C. helmeri , por possuir o corpo mais alongado, pela ponta da nadadeira peitoral não alcançar a nadadeira pélvica, pela ponta da nadadeira pélvica não alcançar o ânus, pelo supraorbital presente e bem desenvolvido, e pela ausência de manchas verticalmente alongadas na porção ventral do corpo. A nova espécie é conhecida de duas drenagens, nos tributários do rio Jordão, na bacia do rio Iguaçu, e no rio Taquari, um tributário da bacia costeira do rio Ribeira de Iguape.(AU)

A new species of Hyphessobrycon Durbin(Characiformes: Characidae) from the rio Juruena basin, Central Brazil, with notes on H. loweae Costa & Géry

A new species of Hyphessobrycon, H. peugeoti, is described from the middle portions of the rio Juruena drainage, upper rio Tapajós basin, Mato Grosso State, Brazil. It can be distinguished from all congeners, with the exception of H. loweae and H. heliacus, by a filamentous elongation of the dorsal fin and the approximately straight margin of the anal fin in adult males. It can be distinguished from both H. loweae and H. heliacus by an overall red coloration in life (vs. a golden coloration in life in the latter). Additionally, it can be distinguished from H. heliacus by the lack of chevron-like dark markings along the midline (vs. presence of chevron-like dark-markings in H. heliacus), and from H. loweae by the presence of only five horizontal scale rows between the dorsal-fin origin and the lateral line (vs. 6-7 in H. loweae), and the higher number of branched anal-fin rays (21-24, modally 22, vs. 17-21, modally 20, in H. loweae). Additional meristic, morphometric, and distributional data are provided for Hyphessobrycon loweae, including its first record in the rio Araguaia/Tocantins basin. Comments on a putative monophyletic group including H. peugeoti, H. loweae, H. heliacus, H. elachys, and H. moniliger are presented.

Uma espécie nova de Hyphessobrycon, H. peugeoti, é descrita do trecho médio da drenagem do rio Juruena, bacia do alto rio Tapajós, estado de Mato Grosso, Brasil. Ela difere de todas as congêneres, com exceção de H. loweae e H. heliacus, pelo alongamento em forma de filamento da nadadeira dorsal e pela margem aproximadamente reta da nadadeira anal em machos adultos. Ela difere de H. loweae e H. heliacus por possuir coloração geral vermelha em vida (vs. colorido dourado em vida em H. loweae e H. heliacus). Além disto, a espécie nova difere de H. heliacus por não possuir marcas em forma de divisas ao longo da linha média do corpo (vs. marcas em forma de divisas presentes em H. heliacus), e de H. loweae por possuir apenas cinco séries de escamas horizontais entre a origem da nadadeira dorsal e a linha lateral (vs. 6-7 em H. loweae) e por possuir elevado número de raios ramificados na nadadeira anal (21-24, moda 22, vs. 17-21, moda 20 em H. loweae). Dados merísticos, morfométricos e de distribuição geográfica adicionais são fornecidos para H. loweae, incluindo os primeiros registros da espécie na bacia do rio Tocantins-Araguaia. Discute-se um grupo presumidamente monofilético que inclui H. peugeoti, H. loweae, H. heliacus, H. elachys e H. moniliger.

A new miniature species of Characidium Reinhardt (Ostariophysi: Characiformes: Crenuchidae) from the headwaters of the rio Araguaia, Brazil.

Characidium inirim is described from the rio das Mortes, rio Araguaia basin in Central Brazil. The new species is distinguished from its congeners by having an incomplete lateral line, a conspicuous dark longitudinal stripe and dark transverse bars not extending ventrally to the lateral line, and by lacking the adipose fin and the dark caudal blotch. A phylogenetic hypothesis based on the available data on the phylogenetic relationships of the subfamily Characidiinae is presented. Results suggest that the new species is closely related to C. bahiensis, C. interruptum, C. lagosantense, C. nupelia, C. lanei, C. laterale, C. occidentale, C. orientale, C. rachovii, C. stigmosun, C. vestigipinne and C. xavante.

Restricted-range fishes and the conservation of Brazilian freshwaters.

BACKGROUND: Freshwaters are the most threatened ecosystems on earth. Although recent assessments provide data on global priority regions for freshwater conservation, local scale priorities remain unknown. Refining the scale of global biodiversity assessments (both at terrestrial and freshwater realms) and translating these into conservation priorities on the ground remains a major challenge to biodiversity science, and depends directly on species occurrence data of high taxonomic and geographic resolution. Brazil harbors the richest freshwater ichthyofauna in the world, but knowledge on endemic areas and conservation in Brazilian rivers is still scarce. METHODOLOGY/PRINCIPAL FINDINGS: Using data on environmental threats and revised species distribution data we detect and delineate 540 small watershed areas harboring 819 restricted-range fishes in Brazil. Many of these areas are already highly threatened, as 159 (29%) watersheds have lost more than 70% of their original vegetation cover, and only 141 (26%) show significant overlap with formally protected areas or indigenous lands. We detected 220 (40%) critical watersheds overlapping hydroelectric dams or showing both poor formal protection and widespread habitat loss; these sites harbor 344 endemic fish species that may face extinction if no conservation action is in place in the near future. CONCLUSIONS/SIGNIFICANCE: We provide the first analysis of site-scale conservation priorities in the richest freshwater ecosystems of the globe. Our results corroborate the hypothesis that freshwater biodiversity has been neglected in former conservation assessments. The study provides a simple and straightforward method for detecting freshwater priority areas based on endemism and threat, and represents a starting point for integrating freshwater and terrestrial conservation in representative and biogeographically consistent site-scale conservation strategies, that may be scaled-up following naturally linked drainage systems. Proper management (e. g. forestry code enforcement, landscape planning) and conservation (e. g. formal protection) of the 540 watersheds detected herein will be decisive in avoiding species extinction in the richest aquatic ecosystems on the planet.

Chromosomal evidence of downstream dispersal of Astyanax fasciatus (Characiformes, Characidae) associated with river shed interconnection.

In the 1960s, as a part of the construction of the Furnas Hydroelectric Power Dam, Minas Gerais, Brazil, the Rio Piumhi was diverted from the Rio Grande drainage to the São Francisco River basin, with the resulting introduction of species from one basin to the other. Chromosomal characteristics of various populations of Astyanax fasciatus sensu Eigenmann from the transect region were studied using cytogenetic techniques, with the goal to identify and map the dispersal of invasive species in the Rio São Francisco. Populations of the Rio Grande and Rio Piumhi are distinct from those of the São Francisco basin based on chromosome markers associated to the heterochromatin, Ag-NORs, 18S rDNA, 5S rDNA, and As-51 satellite DNA sites. Individuals with karyomorph originally present in the Piumhi drainage are now present in the São Francisco basin, downstream from the transposition channel. This expansion of the distribution corroborates a hypothesis of progressive substitution of native populations by the invasive Piumhi form.

Characidium xanthopterum (Ostariophysi: Characiformes: Crenuchidae): a new species from the Central Brazilian Plateau

Characidium xanthopterum is described from tributaries of the upper rio Paraná and upper rio Tocantins basins, in the Central Brazilian Plateau, Goiás State, Brazil. The new species is diagnosed among congeners by the absence of dark bars on the sides of the body in adult specimens, and by the deep yellow coloration in all fins. Ontogenetic change of color pattern is recorded for the first time for Characidium species. Specimens smaller than 32 mm SL possess dark bars on body. These bars disappear with growth between 32 and 35 mm SL, and are always absent in individuals larger than 35 mm SL.

Characidium xanthopterum é descrita de tributários das bacias do alto Paraná e do alto Tocantins, no Planalto Central do Brasil, Estado de Goiás, Brasil. Entre as congêneres, a nova espécie é diagnosticada pela ausência de barras escuras nas porções laterais do corpo em exemplares adultos, e pela presença de todas as nadadeiras fortemente amareladas, sem marcas ou manchas. Exemplares menores de 32 mm CP apresentam barras escuras no corpo. Estas barras desaparecem com o crescimento entre 32 e 35 mm CP, e estão sempre ausentes em indivíduos maiores do que 35 mm CP.

Chromosomal divergence and maintenance of sympatric Characidium fish species (Crenuchidae, Characidiinae).

Cytogenetic studies were performed in two syntopic species of Characidium, C. lauroi and Characidium sp. cf. C. alipioi, from Ribeirão Grande, Paraíba do Sul river basin. Both species have diploid number 2n=50 chromosomes, but differ in chromosome shape, C-banding pattern and location of nucleolar organizing regions. In Characidium sp. cf. C. alipioi a new type of ZW sex chromosome system composed of equal sized metacentric chromosomes is reported for the first time in the genus Characidium. Species of Characidium with a sex chromosome system form a monophyletic group. Variations in this system are interpreted as resulting from geographic isolation among allopatric species.