Karyotypic characterization of Centromochlus schultzi Rössel 1962 (Auchenipteridae, Centromochlinae) from the Xingu River basin: New inferences on chromosomal evolution in Centromochlus.

Centromochlinae is a widely diverse subfamily with more than 50 species and several taxonomic conflicts due to morphological similarity between Tatia and Centromochlus species. However, cytogenetic studies on this group have been limited to only four species so far. Therefore, here we present the karyotype of Centromochlus schultzi from the Xingu River in Brazil using classic cytogenetic techniques, physical mapping of the 5S and 18S rDNAs, and telomeric sequences (TTAGGG)n. The species had 58 chromosomes, simple NORs and 18S rDNA sites. Heterochromatic regions were detected on the terminal position of most chromosomes, including pericentromeric and centromeric blocks that correspond to interstitial telomeric sites. The 5S rDNA had multiple sites, including a synteny with the 18S rDNA in the pair 24st, which is an ancestral feature for Doradidae, sister group of Auchenipteridae, but appears to be a homoplastic trait in this species. So far, C. schultzi is only the second species within Centromochlus to be karyotyped, but it has already presented characteristics with great potential to assist in future discussions on taxonomic issues in the subfamily Centromochlinae, including the first synteny between rDNAs in Auchenipteridae and also the presence of heterochromatic ITSs that could represent remnants of ancient chromosomal fusions.

Are scattered microsatellites weak chromosomal markers? Guided mapping reveals new insights into Trachelyopterus (Siluriformes: Auchenipteridae) diversity.

The scattered distribution pattern of microsatellites is a challenging problem in fish cytogenetics. This type of array hinders the identification of useful patterns and the comparison between species, often resulting in over-limited interpretations that only label it as "scattered" or "widely distributed". However, several studies have shown that the distribution pattern of microsatellites is non-random. Thus, here we tested whether a scattered microsatellite could have distinct distribution patterns on homeologous chromosomes of closely related species. The clustered sites of 18S and 5S rDNA, U2 snRNA and H3/H4 histone genes were used as a guide to compare the (GATA)n microsatellite distribution pattern on the homeologous chromosomes of six Trachelyopterus species: T. coriaceus and Trachelyopterus aff. galeatus from the Araguaia River basin; T. striatulus, T. galeatus and T. porosus from the Amazonas River basin; and Trachelyopterus aff. coriaceus from the Paraguay River basin. Most species had similar patterns of the (GATA)n microsatellite in the histone genes and 5S rDNA carriers. However, we have found a chromosomal polymorphism of the (GATA)n sequence in the 18S rDNA carriers of Trachelyopterus galeatus, which is in Hard-Weinberg equilibrium and possibly originated through amplification events; and a chromosome polymorphism in Trachelyopterus aff. galeatus, which combined with an inversion polymorphism of the U2 snRNA in the same chromosome pair resulted in six possible cytotypes, which are in Hardy-Weinberg disequilibrium. Therefore, comparing the distribution pattern on homeologous chromosomes across the species, using gene clusters as a guide to identify it, seems to be an effective way to further the analysis of scattered microsatellites in fish cytogenetics.

Identifying fish eggs and larvae: from classic methodologies to DNA metabarcoding.

Studies involving fish eggs and larvae date back to the end of the nineteenth century. Since then, studies with ichthyoplankton have proved to be an essential tool, generating information for the knowledge of the ichthyofauna and the environmental inventory. Most of these studies reveal the difficulty of obtaining a precise taxonomic identification of the collected materials, making research with ichthyoplankton extremely challenging. With the advent of molecular biology, the use of markers such as COI enabled greater taxonomic precision, helping to understand events involving ichthyofauna. Now we can observe the evolution of the molecular identification tool for ichthyoplankton via DNA barcoding, which has been increasingly used over the last few decades. From 2000 to 2010, we found six publications; from 2011 to 2021, 75 papers were published, and in 2022 four studies. Our survey also showed the accuracy of molecular identification when compared to the taxonomic identification of these. In this review, we show the state of the art of studies that used barcode and DNA metabarcoding to identify fish eggs and larvae in different environments and discuss their importance as the best practice for working with these organisms.

Ichthyofauna of Santa Helena Relevant Ecological Interest Area (REIA), Paraná, Brazil / Ictiofauna da Área de Relevante Interesse Ecológico (ARIE) de Santa Helena, Paraná, Brasil

Abstract The Relevant Ecological Interest Area (REIA), popularly known as "Refúgio Biológico de Santa Helena", is part of the Atlantic Forest Biome and one of the 78 ecoregions mapped by IBAMA as basic unit for planning priorities focused on national biodiversity conservation. Quarterly collections were carried out from November 2017 to November 2019 to inventory the ichthyofauna of this Conservation Unit. Specimens were captured with the aid of gillnets, fishing sieve and seine. In total, 3,919 specimens belonging to two class, eight orders, 27 families and 74 species were sampled. Characiformes and Siluriformes presented the highest species richness; they accounted for 40 (54%) and 17 (23%) species, respectively. Geophagus sveni (181 individuals = 17%), Trachelyopterus galeatus (109 individuals = 10%) and Schizodon borellii (105 individuals = 10%) were the most abundant fish species captured with gillnet. Moenkhausia was the most abundant genus captured with seine and fishing sieve, with emphasis on species Moenkhausia bonita (930 individuals = 33%) and Moenkhausia gracilima (845 individuals = 30%). Moreover, two "endangered" species (Brycon orbignyanus and Pseudoplatystoma corruscans) were registered. Therefore, we present an updated inventory of species belonging to the ichthyofauna of REIA, and it may contribute to future management plans focused on this Conservation Unit.

Resumo A Área de Relevante Interesse Ecológico (ARIE), popularmente conhecida como "Refúgio Biológico de Santa Helena", faz parte do Bioma Mata Atlântica, uma das 78 ecorregiões mapeadas pelo IBAMA como unidade básica de planejamento e prioridades para a conservação da biodiversidade nacional. Foram realizadas coletas trimestrais de novembro de 2017 a novembro de 2019 para inventariar a ictiofauna desta Unidade de Conservação. Os espécimes foram capturados com o auxílio de redes de emalhar, peneira e rede de arrasto. No total, foram amostrados 3.919 exemplares pertencentes a duas classes, oito ordens, 27 famílias e 74 espécies. Characiformes e Siluriformes apresentaram a maior riqueza de espécies; somando um total de 40 (54%) e 17 (23%) espécies, respectivamente. Geophagus sveni (181 indivíduos = 17%), Trachelyopterus galeatus (109 indivíduos = 10%) e Schizodon borellii (105 indivíduos = 10%) foram as espécies de peixes mais abundantes capturadas com rede de espera. Moenkhausia foi o gênero mais abundante capturado com rede de arrasto e peneira, com destaque para as espécies Moenkhausia bonita (930 indivíduos = 33%) e Moenkhausia gracilima (845 indivíduos = 30%). Além disso, duas espécies "ameaçadas" (Brycon orbignyanus e Pseudoplatystoma corruscans) foram registradas. Assim, apresentamos um inventário atualizado das espécies pertencentes à ictiofauna da ARIE, podendo contribuir para futuros planos de manejo voltados para esta Unidade de Conservação.

Contributions to the taxonomy of Trachelyopterus (Siluriformes): comparative cytogenetic analysis in three species of Auchenipteridae

Auchenipteridae is divided into subfamilies Centromochlinae and Auchenipterinae. Parauchenipterus is included in the latter and is subject of taxonomic discussions concerning its validation or synonymization with Trachelyopterus. Herein, three species from two hydrographic basins were cytogenetically analyzed: Parauchenipterus striatulus from Doce River and two sympatric species, P. galeatus and Trachelyopterus coriaceus, from the Araguaia River. Diploid number of 58 chromosomes was verified for all species, but P. striatulus has different karyotype formula from the others. The three species have heterochromatin located in terminal regions of almost all chromosomes and in pericentromeric region on acrocentric chromosomes. Simple NORs was verified on a subtelocentric chromosome for all species. 5S rDNA sites were detected in three submetacentric chromosome pairs in P. striatulus; in a metacentric chromosome pair and submetacentric pair in T. coriaceus; and in one metacentric chromosome pair in P. galeatus. The similarities found in the karyotypes of the three species suggest the existence of only one genus, Trachelyopterus; therefore, our data refutes the validation of Parauchenipterus. Moreover, the differences in 5S rDNA distribution in P. galeatus in comparison with other populations already studied, indicate the existence of a new taxonomic unit, which suggests a species complex in P. galeatus.(AU)

Auchenipteridae é dividida nas subfamílias Centromochlinae e Auchenipterinae. Parauchenipterus encontra-se incluído na última e tem sido alvo de discussões relacionadas com a problemática taxonômica de validação ou sinonimização com Trachelyopterus. Foram analisadas citogeneticamente três espécies de duas bacias hidrográficas: Parauchenipterus striatulus do rio Doce, P. galeatus e Trachelyopterus coriaceus, simpátricas do rio Araguaia. Todas as espécies analisadas apresentaram número diploide de 58 cromossomos, com diferença na fórmula cariotípica de P. striatulus. A heterocromatina foi localizada nas regiões terminais de quase todos os cromossomos e na região pericentromérica nos cromossomos acrocêntricos das três espécies. AgNORs e DNAr 18S detectaram RONs simples em um par de cromossomos subtelocêntricos nas três espécies. DNAr 5S foi detectado em três pares de cromossomos submetacêntricos em P. striatulus; em um par de cromossomos metacêntricos e um par submetacêntrico em T. coriaceus; e em apenas um par de cromossomos metacêntricos em P. galeatus. As semelhanças encontradas nos cariótipos das três espécies analisadas indicam a existência de somente Trachelyopterus (não validação de Parauchenipterus) e a diferença encontrada na distribuição de DNAr 5S de P. galeatus em relação às outras populações já estudadas sugere a existência de uma nova unidade taxonômica, portanto P. galeatus compreende um complexo de espécies.(AU)

Possible Common Origin of B Chromosomes in Neotropical Fish (Siluriformes, Auchenipteridae) Reinforced by Repetitive DNA Mapping

Abstract The aim of this paper was to present the second case of B chromosomes in Auchenipteridae (Trachelyopterus sp.), and to test the hypothesis that the B chromosomes of this species and Parauchenipterus galeatus might have a common origin, since these two species have phylogenetic proximity. Both species have 58 chromosomes in the A complement, heterochromatin preferentially located at terminal region of the most of chromosomes, simple Ag-NORs located at the short arm of a subtelocentric pair, which was confirmed by hybridization with 18S rDNA, two submetacentric pairs carrying 5S rDNA sites, and presence of B chromosomes. The B chromosomes of the two species are small, metacentric, and almost totally heterochromatic, with variation of number intra and interindividual. In addition, for the first time in fish, the telomeric sequence [TTAGGG]n was dispersed along the B chromosomes (both species). The [GATA]n microsatellite were scattered in all chromosomes of the A complement and absent in the B chromosomes, in both species. These aspects confirm the phylogenetic proximity between the genus Parauchenipterus and Trachelyopterus, and they suggest the hypothesis that the B chromosomes of the two species might have common origin, previous to the diversification of these genera.

Divergent Chromosome Evolution in Hypostominae Tribes (Siluriformes: Loricariidae): Correlation of Chromosomal Data with Morphological and Molecular Phylogenies.

Hypostominae is the largest subfamily of Loricariidae, and is widely distributed throughout the Neotropic. In the present article, we analyze three Loricariidae species that were considered part of Hypostominae, from three different tribes, to discuss chromosome evolution in this fish group and to review the existent data for the subfamily. Rhinelepis aspera had 54 chromosomes (20m + 26sm+8st), whereas Pterygoplichthys ambrosettii and Megalancistrus parananus had 52 chromosomes, with 16m+24sm+8st+4a and 18m+24sm+10st, respectively. The karyological data were compared with existent phylogenetic hypotheses, indicating a common ancestor with 2n = 52 chromosomes for the Acanthicus, Hemiancistrus, and Peckoltia clades, as well as for Hypostomini. Shared recurrent characteristics of the tribes are discussed, as well as peculiarities of genera Ancistrus and Hypostomus. We propose that the occurrence of fragile sites demonstrated for Ancistrus facilitated chromosomal rearrangements that decreased the proportion of metacentric/submetacentric chromosomes and the diploid number in many species from this genus. Although Hypostominae is usually considered a subfamily with derived chromosome features, our revision shows that this is valid only for Hypostomini and Ancistrini, which have a divergent chromosome evolution from other tribes that seems to conserve plesiomorphic features.

Karyotype Diversity and Evolutionary Trends in Armored Catfish Species of the Genus Harttia (Siluriformes: Loricariidae).

Most species of the genus Harttia inhabits the headwaters of small tributaries, but some species are restricted to the main channel of some rivers. This feature, combined with limited dispersal ability, leads to the formation of small isolated populations with reduced gene flow. Currently, there are 23 taxonomically defined and recognized species, and 17 of these are found in Brazil, distributed in several hydrographic basins. Despite this diversity, few chromosomal data for the species belonging to this genus are found in the literature. Thus, this study analyzed, by classical and molecular cytogenetics methodologies, the chromosomal diversity of this genus, to discuss the processes that are involved in the evolution and karyotype differentiation of the species of the group. Seven species of Harttia were analyzed: H. kronei, H. longipinna, H. gracilis, H. punctata, H. loricariformis, H. torrenticola, and H. carvalhoi. The chromosomal diversity found in these species includes different diploid and fundamental numbers, distinct distribution of several repetitive sequences, the presence of supernumerary chromosomes in H. longipinna and multiple sex chromosome systems of the type XX/XY1Y2 in H. carvalhoi and X1X1X2X2/X1X2Y in H. punctata. Lastly, our data highlight the genus Harttia as an excellent model for evolutionary studies.

Chromosome Analyses of Apareiodon argenteus and Apareiodon davisi (Characiformes, Parodontidae): An Extensive Chromosomal Polymorphism of 45S and 5S Ribosomal DNAs.

This study analyzed two Apareiodon species without available chromosome data: Apareiodon argenteus and Apareiodon davisi. Both species have 54 metacentric/submetacentric chromosomes, with centromeric blocks of heterochromatin. Nucleolus organizer regions were active in chromosome pair 2 in A. argenteus and pairs 4 and 9 in A. davisi. In A. argenteus, 45S and 5S ribosomal genes were located in chromosome pairs 2 and 18, respectively. Polymorphisms were observed in these ribosomal sequences in A. davisi, with variations in the number/position of sites, and colocalization of these genes in some chromosome pairs. The WAp repetitive fraction was dispersed along the chromosomes of the two species. The satellite DNA pPh2004 was identified in chromosome pairs 7, 8, 10, 11, and 18 in A. argenteus and in pair 24 in A. davisi. The present study describes the first case of chromosomal polymorphisms involving two ribosomal sequences in Parodontidae and discusses the role of repetitive DNAs in the genome and karyotype diversity of this family.

Occurrence of Natural Hybrids Among Sympatric Karyomorphs in Hoplerythrinus unitaeniatus (Characiformes, Erythrinidae).

In this study, 43 specimens of Hoplerythrinus unitaeniatus from the São Francisco River basin were chromosomally analyzed by conventional Giemsa staining, C-banding, silver nitrate impregnation, and fluorescence in situ hybridization (FISH) with probes of 5S and 18S rDNA. The diploid numbers found were 50 and 52 chromosomes, showing the existence of two well-defined biological entities in sympatry. Specimens with 51 chromosomes, which showed three distinct karyotypic forms, were also found and are characterized as natural hybrids due to the correspondence with the chromosomes of the specimens with 50 and 52 chromosomes. By FISH using 5S and 18S rDNA probes, it was possible to detect specific chromosomal markers for the specimens with 50 and 52 chromosomes, as well as the occurrence of common sites in both. The specimens with 51 chromosomes showed intermediate patterns for these markers, reinforcing the hypothesis that these are actual natural hybrids. A review and new classification for the karyomorphs of H. unitaeniatus have also been proposed.

Origin of the X1X1X2X2/X1X2Y sex chromosome system of Harttia punctata (Siluriformes, Loricariidae) inferred from chromosome painting and FISH with ribosomal DNA markers.

Harttia is a genus in the subfamily Loricariinae that accommodates fishes popularly known as armored catfishes. They show extensive karyotypic diversity regarding interspecific numerical/structural variation of the karyotypes, with the presence of the XX/XY1Y2 multiple sex chromosome system, as found in H. carvalhoi. In this context, this study aimed to characterize Harttia punctata chromosomally, for the first time, and to infer the rearrangements that originated the X1X1X2X2/X1X2Y multiple sex chromosome system present in this species. The data obtained in this study, with classical (Giemsa, C-banding and AgNORs) and molecular methodologies (fluorescence in situ hybridization) and chromosome microdissection, indicated that a translocation between distinct acrocentric chromosomes bearing rRNA genes, accompanied by deletions in both chromosomes, might have originated the neo-Y chromosome in this species. The data also suggest that the multiple sex chromosome systems present in H. carvalhoi and H. punctata had an independent origin, evidencing the recurrence of chromosome alterations in species from this genus.

Comparative chromosomal analysis and evolutionary considerations concerning two species of genus Tatia (Siluriformes, Auchenipteridae).

Auchenipteridae is divided in two subfamilies, Centromochlinae and Auchenipterinae. Centromochlinae has 31 valid species, from which 13 are included in the genus Tatia Miranda Ribeiro, 1911. Among these, Tatia jaracatia Pavanelli & Bifi, 2009 and Tatia neivai (Ihering, 1930) are the only two representative species from the Paraná-Paraguay basins. This study aimed to analyze cytogenetically these two species and thus provide the first chromosomal data for the genus. Although Tatia jaracatia and Tatia neivai presented 2n=58 chromosomes, some differences were observed in the karyotypic formula. The heterochromatin was dispersed in the centromeric and terminal regions of most chromosomes of Tatia jaracatia, and only in the terminal region of most chromosomes of Tatia neivai. The AgNORs were detected in the subtelocentric pair 28 for both species, which was confirmed by FISH with 18S rDNA probe. The 5S rDNA sites were detected in four chromosome pairs in Tatia jaracatia and three chromosome pairs in Tatia neivai. Both species of Tatia presented great chromosomal similarities among themselves; however, when compared to other species of Auchenipteridae, it was possible to identify some differences in the karyotype macrostructure, in the heterochromatin distribution pattern and in the number and position of 5S rDNA sites, which until now seems to be intrinsic to the genus Tatia.

The role of chromosomal fusion in the karyotypic evolution of the genus Ageneiosus (Siluriformes: Auchenipteridae)

Ageneiosus is the most widely distributed genus of the family Auchenipteridae among South American river basins. Although chromosome studies in the family are scarce, this genus has the largest number of analyzed species, with 2n = 54 to 56 chromosomes, differing from the rest of the family (2n = 58). This study aimed to analyze Ageneiosus inermis from the Araguaia River basin. The diploid number found was of 56 chromosomes. Heterochromatin was allocated in terminal region of most chromosomes, plus a pericentromeric heterochromatic block in pair 1, a pair distinguished by size in relation to other chromosomes pairs. AgNORs were detected in only one submetacentric chromosome pair, which was confirmed by FISH. 5S rDNA was present in only one metacentric chromosome pair. Hybridization with [TTAGGG]n sequence marked the telomeres of all chromosomes, in addition to an ITS in the proximal region of the short arm of pair 1. The repetitive [GATA]n sequence was dispersed, with preferential location in terminal region of the chromosomes. Ageneiosus has a genomic organization somewhat different when compared to other Auchenipteridae species. Evidences indicate that a chromosomal fusion originated the first metacentric chromosome pair in A. inermis, rearrangement which may be a basal event for the genus.

Ageneiosus é o gênero da família Auchenipteridae mais amplamente distribuído em bacias da América do Sul. Apesar dos estudos cromossômicos nesta família serem escassos, este gênero tem o maior número de espécies analisadas, com número diploide variando de 54 a 56 cromossomos, o que difere do restante da família (2n = 58). Este estudo objetivou analisar Ageneiosus inermis da bacia do rio Araguaia. O número diploide encontrado foi de 56 cromossomos. A heterocromatina se mostrou localizada na região terminal da maioria dos cromossomos, além de um bloco heterocromático pericentromérico no par 1, um par facilmente distinguível no cariótipo pelo seu maior tamanho quando comparado aos outros pares do complemento. AgRONs foram detectadas em somente um par de cromossomos submetacêntricos, que foi confirmado pela FISH. 5S rDNA se mostrou presente em somente um par de cromossomos metacêntricos. A hibridização com a sequência [TTAGGG]n marcou os telômeros de todos os cromossomos, além de um ITS (sequência telomérica intersticial) na região proximal do braço curto do par 1. A sequência repetitiva [GATA]n se mostrou dispersa, com localização preferencial na região terminal dos cromossomos. Ageneiosus apresenta uma organização genômica um pouco diferente quando comparada a outras espécies de Auchenipteridae. As evidências indicam que uma fusão cromossômica originou o primeiro par de cromossomos metacêntricos de A. inermis, rearranjo que parece ser um evento basal para o gênero.

Chromosomal characterization of armored catfish Harttia longipinna (Siluriformes, Loricariidae): first report of B chromosomes in the genus.

The B chromosomes are accessory elements that are widely distributed among eukaryotic genomes and often show non-Mendelian inheritance. They are considered dispensable for the growth, development, and reproduction of organisms. Some studies have suggested that these elements may affect sex determination. Harttia is a small armored catfish genus that shows sexual dimorphism, including hypertrophied odontodes on the pectoral fin spines and along the margins of the snout in mature males. They exhibit considerable karyotypic diversity with diploid number (2n) variation and heteromorphic sex system in H. carvalhoi. To date, no occurrences of B chromosomes in the Harttia genus were detected and no relation to sexual differentiation in Neotropical fish has been determined. To determine the validity of this claim, the present paper characterized specimens of Harttia longipinna by classical and molecular cytogenetic methods. The 2n found was 58 (16m + 12sm + 16st + 14a), but of the 50 specimens analyzed (30 male and 20 female), 23 specimens (16 males and seven females) show an intra-individual from 0 to 2 micro B chromosomes. The B chromosomes were completely heterochromatic. The single NORs were shown in the first acrocentric pair with silver staining and 18S rDNA probing. FISH performed with 5S rDNA probe showed a single cistron in the proximal region of the short arm of a small metacentric pair. Thus, the cytogenetic data obtained in this study of H. longipinna highlight the karyotypic diversity found within the genus Harttia, and represent the first description of B chromosomes for this genus.

A recent transposition of river involving Paraná and São Francisco basins: effects on the genetic variability and structure of the neotropical fish Parauchenipterus galeatus (Siluriformes, Auchenipteridae).

This study analyzed sequences of the control region of mitochondrial DNA (D-loop) in three populations of Parauchenipterus galeatus from the basins of the Paraná, São Francisco, and Piumhi rivers, of which the last river being a region that suffered transposition river. A fragment of 850 base pairs was obtained with a total of 65 polymorphic sites. The data discuss aspects related to the genetic distance between the populations through the phylogenetic reconstruction methods (neighbor-joining, maximum-likelihood, and Bayesian analysis). Moreover, the data suggest that the Piumhi River population (transposition region) has recently gone through a significant bottleneck effect, which must be directly related to the anthropic action that occurred in this region, since the drainage the old existing swamp was necessary for the construction of the transposition channel potentially leading this population in to the current lack of genetic diversity.

First karyotype description of Hypostomus iheringii (Regan, 1908): a case of heterochromatic polymorphism.

In this study, which is the first karyotype analysis of Hypostomus iheringii, nine specimens collected in Córrego da Lapa (tributary of the Passa-Cinco River) showed a diploid number of 80 chromosomes. Silver nitrate staining and fluorescence in situ hybridization (FISH) with an 18S rDNA probe revealed the presence of multiple nucleolus organizer regions (NORs) (chromosome pairs 13, 20, and 34). FISH with a 5S rDNA probe showed that this cistron was only present in chromosome pair 2. When the karyotypes of individual animals were compared, unique heterochromatic polymorphisms were detected on chromosome pairs 1 and 5. Specifically, specimens had heterochromatic blocks (h+h+) on both chromosomes, one chromosome with heterochromatic blocks (h+h-) or chromosomes that lacked heterochromatic blocks (h-h-). Considering that heteromorphic pattern is not correlated with variation in size, the process of heterochromatinization might act on the long arms of these chromosomes. In summary, all chromosomal markers indicate that the karyotype of Hypostomus iheringii is highly differentiated and that the heterochromatinization of chromosomal segments may have contributed to its karyotypic differentiation.

Karyotypic diversity between allopatric populations of the group Hoplias malabaricus (Characiformes: Erythrinidae): evolutionary and biogeographic considerations

Three populations of the group Hoplias malabaricus from the hydrographic basins of the São Francisco, Araguaia/Tocantins and Xingu Rivers in Brazil were analyzed using classic cytogenetic methods (Giemsa staining, C-banding and Ag-NORs) and molecular methods (fluorescent in situ hybridization with 18S rDNA, 5S rDNA and 5SHindIII satellite DNA probes). The chromosome markers allowed the characterization of these populations as belonging to karyomorph A and the detection of inter-population divergences. These differences likely stem from different evolutionary histories resulting from geographic isolation between populations associated to the dispersive mode of these organisms, reinforcing genetic diversity in the group Hoplias malabaricus.

Três populações do grupo Hoplias malabaricus das bacias hidrográficas dos rios São Francisco, Araguaia/Tocantins e Xingu foram analisadas citogeneticamente utilizando-se métodos clássicos (coloração com Giemsa, bandamento-C e Ag-RONs) e moleculares (hibridização in situ fluorescente com sondas de rDNA 18S, rDNA 5S e DNA satélite 5SHindIII). Os marcadores cromossômicos foram fundamentais para a caracterização destas populações como pertencentes ao cariomorfo A e para detecção de claras divergências interpopulacionais. Estas diferenças são provavelmente oriundas de diferentes histórias evolutivas do isolamento geográfico entre as populações associado ao modo dispersivo destes organismos, reiterando a diversidade genética do grupo Hoplias malabaricus.

First description of B chromosomes in the family Auchenipteridae, Parauchenipterus galeatus (Siluriformes) of the São Francisco River basin (MG, Brazil).

B chromosomes are considered additional and non-essential; they likely originate from A chromosomes and follow a distinct evolution. In fish, approximately half of the Neotropical species with B chromosomes are Characiformes and 35% are Siluriformes. There has been no report of B chromosomes in Auchenipteridae until this moment. B chromosomes found in a population of Parauchenipterus galeatus from the São Francisco River basin in the state of Minas Gerais (Brazil) were small, metacentric, totally heterochromatic and exhibited intra-individual and inter-individual variation. The diploid number was 58 chromosomes (22 metacentric, 16 submetacentric, 12 subtelocentric and 8 acrocentric). The nucleolar organizing regions were simple and the heterochromatin intercalated in the ribosomal sites, characterized by CMA(3) and DAPI fluorochromes, was of a GC-rich constitution. The 5S rDNA genes were located in an intercalary position in only one chromosome pair. An hypothesis about the origin of the B chromosomes in P. galeatus and a review on B chromosomes in catfish are also presented in this study.