The ultrastructure of the pre-meiotic and meiotic stages of spermatogenesis in Plagioscion squamosissimus (Teleostei, Perciformes, Sciaenidae)

Spermatogenesis of 'corvina' P. squamosissimus starts from a stem cell that gives rise to germ cells. These cells are enveloped by Sertoli cells, forming cysts. The germ cells in the cysts are all at the same stage of development and are interconnected by cytoplasmic bridges. Spermatogonia are the largest germ cells. In the cysts, these cells differentiate into primary spermatogonia and secondary spermatogonia. The primary spermatogonia are isolated in the cyst and give rise to the secondary spermatogonia. After several mitotic divisions, they produce spermatocytes I, which can be identified by synaptonemal complexes in the nucleus. The spermatocytes I enter the first phase of meiosis to produce the spermatocytes II. These are not very frequently seen because they rapidly undergo a second phase of meiosis to produce spermatids.

The ultrastructural aspects of vitellogenesis or oocyte secondary growth in Serrasalmus spilopleura (Teleostei, Characiformes, Serrasalminae)

Oocyte secondary growth in S. spiloleura corresponds to the period in which different vesicular structures are formed, including the cortical alveoli and the yolk granules. The oocytes with cortical alveolus formation show vesicular structures with filamentous content in the cortical cytoplasmic region, which are the cortical alveolus precursors. In these oocytes, electron-dense vesicles of heterogenous content are dispersed in the inner cytoplasmic region and their nuclei are irregular, showing many nucleoli of different sizes. The oocytes in vitellogenesis are filled with many vesicles. The cortical alveolus precursors are in the peripheral region, and electron-dense granules are seen near to the nucleus. These fuse and form yolk granules. The oocytes in vitellogenesis show a very irregular nucleus that has nucleoli of different sizes. In the oocytes in final vitellogenesis, the yolk granules are scattered throughout the cytoplasm, displacing the cortical alveoli toward cell periphery. The nucleus is similar to the other stages.

Cytogenetic analysis of five species of the subfamily Tetragonopterinae (Teleostei, Characiformes, Characidae)

The subfamily Tetragonopterinae is composed by a large number of species distributed in South and Central America. This subfamily has many taxonomic and phylogenetic problems, being considered by several authors as an artificial group. With the objective to better understanding the relationships among the components of this fish group, cytogenetic studies were conduced on five species of Tetragonopterinae. Astyanax janeiroensis had 2n=50 chromosomes (6M+14SM+14ST+16A), Hyphessobrycon reticulatus had 2n=50 chromosomes (14M+20SM+16ST), Hollandichthys multifasciatus had 2n=50 chromosomes (10M+12SM+28ST), Ctenobrycon hauxwellianus had 2n=50 chromosomes (10M+6SM+34ST), and Phenacogaster cf. pectinatus had 2n=46 chromosomes (12M+2ST+32A). Only A. janeiroensis had multiple NORs, while all other species had simple NORs. Small heterochromatic blocks were observed in the chromosomes of all species in a pericentromeric position. A. janeiroensis also had some chromosomes with large heterochromatic blocks in a terminal position and a pair with an interstitial block. The karyotypic evolution of each genus is discussed.

Occurence of karyotypical mosaicism in Trichomycterus paolence (Teleostei, Trichomycteridae)

A chromosomal mosaic has at least two cell lineages with different karyotypes derived from a single zygote and the karyotype alteration can be numeric or structural as well. In the present paper were detected a numeric chromosomal alterations in a single specimen of Thichomycterus paolence from the Quinta stream (Itatinga, state of São Paulo, Brazil). In a total of 61 analysed metaphases, besides the normal chromosome number of this species (2n=54), other four chromosomal sets characterized by 2n=55 (54 plus a microchromosome), 2n=55 (54 plus a small subtelocentric chromosome), 2n=56 (54 plus a subtelocentric and a microchromosome) and 2n=57 (54 plus a subtelocentric pair and a microchromosome) have been detected. The mechanisms that have originated those abnormal karyotypical constitutions is discussed.

Karyotype variability in eight species of the subfamilies Loricariinae and Ancistrinae (Teleostei, Siluriformes, Loricariidae)

Loricariidae is one of the largest fish families of the world, with about 650 species separated into six subfamilies. To date, cytogenetic data on only 56 species of this family are available. In the present study, the karyotypes of three Ancistrinae species and five Loricariinae species were studied. The lowest diploid number, 2n=38, was observed in Ancistrus n.sp. 1 (Ancistrinae) and the highest diploid number, 2n=70, was observed in Rineloricaria n.sp. (Loricariinae). The nucleolar organizer regions (NORs) were seen at a terminal position in six species and at an interstitial position in two. The karyotypic analysis of Loricariinae and Ancistrinae species revealed that these groups exhibit a large diversity of diploid numbers, suggesting the occurrence of intense karyotypic evolution during their evolutionary history.

Cytogenetic analysis of A-, B-chromosomes and ZZ/ZW sex chromosomes of Characidium gomesi (Teleostei, Characiformes, Crenuchidae)

Different cytogenetic techniques were used to analyze the chromosomes of Characidium gomesi with the main objective of comparing the base composition of ZZ/ZW sex-chromosomes, B-chromosomes and the heterochromatin of A-chromosomes. The results of digestion of chromosomes with AluI restriction endonuclease (RE), silver and CMA3 staining, C-banding and fluorescence in situ hybridization (FISH) with the 18S rDNA probe suggested the existence of compositional differences between the heterochromatin of ZZ/ZW sex-chromosomes, A- and B-chromosomes, and indicated the presence of different numbers and morphology of B-chromosomes in the samples of this population.

Cytogenetic analysis of species of the genera Acestrorhynchus, Oligosarcus and Rhaphiodon (Teleostei: Characiformes)

In the present study the karyotypes and the number and position of nucleolus organizer regions (NORs) of four species of Characiformes are described. The analyses showed that Acestrorhynchus lacustris had 2n=50 chromosomes (8M+34SM+6ST+2A), Oligosarcus longirostris had 2n=50 chromosomes (2M+20SM+10ST+18A), Oligosarcus cf. paranensis from Keller and Mourão rivers had 2n=50 chromosomes (2M+26SM+8ST+14A), and Rhaphiodon vulpinus had 2n=54 chromosomes (32M+12SM+8ST+2A). The number of NOR-bearing chromosome pairs ranged from one to three among the species studied. The results available show that there is no variation in the diploid number within the genera analyzed. However, clear differences related to the karyotypic formulae and the number and position of Ag-NORs were found even in the comparison between populations. The possible relationships between the genera analyzed and other Characiformes are discussed.

Cytogenetic analyses of Pseudopimelodus mangurus (Teleostei: Siluriformes: Pseudopimelodidae)

The cytogenetic analyses showed that Pseudopimelodns mangurus has a diploid number of 2n=54 chromosomes (6M, 26SM, 12ST and 10A), single Ag-NORs on the short arm of a middle-sized ST pair, identified as pair 19, and a very small amount of C-band positive segments in two chromosome pairs. The Ag-NORs are C-band positive. The staining of the chromosomes of P. mangurus with CMA 3 reveled the occurrence of bright signals corresponding to the Ag-NORs segments, to the C-band positive segments and also to some C-band negative segments. The occurrence of a diploid number of 2n=54 in all species of the family Pseudopimelodidae and its absence among representatives of Pimelodidae and Heptapteridae, two related families previously considered, reinforces the hypothesis that Pseudopimelodidae is a monophyletic group. © 2004 The Japan Mendel Society.

Spatial distribution of characidiin fishes (Teleostei, Crenuchidae) in the Ribeirão Grande system, a tributary of Paraíba do Sul river basin, Brazil

This study analyses the spatial distribution of characidiin fishes Characidium lauroi and Characidium alipioi (Crenuchidae) in a forest stream system located in southeastern Brazil. Fish were sampled from Jury 2001 to April 2002. Collections were made with an electro-fishing device in five stream reaches of the Ribeirão Grande system. Conductivity, pH, water temperature and dissolved oxygen were measured at each site. The species have different distributions in Ribeirão Grande system. Characidium lauroi is abundant in montane-piedmont zones and Characidium alipioi occurs mainly in piedmont-plain zones. Streams' different features contribute to these species' distribution in the system.

Revision of the South American freshwater genus Plagioscion (Teleostei, Perciformes, Sciaenidae)

The South American freshwater sciaenid genus Plagioscion is reviewed. Five of the 15 nominal species assigned to the genus are considered to be valid: Plagioscion squamosissimus, widely distributed in Atlantic drainages east of the Andes; P. auratus from the Río Orinoco and Río Amazonas basins; P. magdalenae from the Río Magdalena and Río Amazonas basins; P. ternetzi from the lower Río Paraná, Río Paraguay and Rio Uruguay basins; and P. montei from the Río Amazonas basin. Copyright © 2005 Magnolia Press.

Comparative cytogenetic studies in species of the subfamily Callichthyinae (Teleostei: Siluriformes: Callichthyidae)

In the present study, the karyotype of three species (nine populations) of the Callichthyinae subfamily were investigated with the objective of better understanding the pattern of relationship among the genera that compose the subfamily. Among the four populations of Callichthys callichthys studied, two showed 2n=56 chromosomes and two 2n=58 chromosomes. Up to eight additional microchromosomes were observed in the sample from Marilia. The three populations of Hoplosternum littorale displayed the same number of chromosomes, 2n=60, and karyotypic constitution, 6M+2SM+52A. The two populations of Megalechis personata showed 2n=62 chromosomes and similar karyotypic formulae, 8M+54A and 6M+2SM+54A. Terminal Ag-NORs were found in one chromosome pair of C. callichthys, H. littorale, and M. personata from Itiquira, and in two pairs in M. personata from Rio Branco. The populations of C. callichthys showed C-band positive segments in centromeric and pericentromeric position and the populations of H. littorale and M. personata exhibited C-band positive segments in centromeric and/or interstitial position. Contrarily to the extensive chromosome rearrangements verified in the Corydoradinae subfamily, in the Callichthyinae subfamily a small number of changes seems to have occurred in its karyotypic evolution.

Comparative cytogenetics of nine species of Hypoptopomatinae (Teleostei: Siluriformes: Loricariidae): The importance of structural rearrangements in chromosome evolution

Fishes of the subfamily Hypoptopomatinae are very common and found in the lowlands of cis-Andean South America from Venezuela to the north of Argentina. With the main objective of contributing for a better understanding of the importance of chromosome rearrangements in the loricariid evolution, cytogenetic analyses were conducted in nine species of Hypoptopomatinae. The results showed a marked gross karyotypic conservation with the presence of 2n=54 chromosomes in all species analyzed. The main differences were found in the karyotypic formulae level. Most species had a single interstitial Ag-NORs, however terminal Ag-NORs were observed in three species. One species exhibited two Ag-NOR-bearing chromosome pairs. The distribution of C-band positive segments was species specific but chromosome markers were observed among the species analyzed. The gross cytogenetic characteristics observed among the Hypoptopomatinae species are similar to those observed in other primitive Loricariidae species suggesting that small changes, mainly paracentric and pericentric inversion were the main events in the karyotypic evolution of this fish group.

Cytogenetic characterization of the silverside fish Odontesthes regia (Humboldt, 1833) (Teleostei: Atheriniformes: Atherinopsidae) from Iquique, Chile

This paper describes the karyotype of Odontesthes regia by means of Giemsa staining, C-banding, to reveal the distribution of the constitutive heterochromatin, and by Ag-staining and fluorescent in situ hybridization (FISH), to locate ribosomal genes (rDNA). The chromosome diploid modal count in the species was 2n = 48. The karyotype is composed of one submetacentric pair (pair 1), 16 subtelocentric pairs (pairs 2 to 17), and 7 acrocentric pairs (pairs 18 to 24). With the exception of pair 1 it was not possible to classify the homologous chromosomes accurately because differences in chromosome size were too slight between adjacent pairs. The distribution of C-banded heterochromatin allowed for a more accurate matching of the majority of chromosomes of the subtelocentric series. Silver staining of metaphase spreads allowed for the identification of Nucleolus Organizer Regions (Ag-NOR) on pair 1. FISH experiments showed that 18S rDNA sequences were located, as expected, in the same chromosome pair identified as the Ag-NOR-bearing one.

The karyotype of Scoloplax distolothrix (Teleostei: Siluriformes: Scoloplacidae)

The karyotype of a fish species belonging to the family Scoloplacidae, Scoloplax distolothrix, is described for the first time. Cytogenetic studies showed that this species has 2n=50 chromosomes, 18 metacentrics, 18 submetacentrics, 10 subtelocentrics and 4 acrocentrics. The Ag-NORs are restricted to a single large metacentric pair in the interstitial position on the long arm. © 2006 The Japan Mendel Society.

Cytogenetic analysis of three sympatric Gymnotus species (Teleostei: Gymnotidae) from the Fundo Stream, MG, Brazil

Three sympatric species of Gymnotus from the Fundo stream, a small tributary of the Sapucai river, Minas Gerais State, Brazil, were studied in relation to their karyology. Gymnotus sylvius presented 2n=40 chromosomes (36 m/sm+4 st/a), Gymnotus sp. presented 2n=50 (26 m/sm+ 24 st/a) and Gymnotus paraguensis had 2n=54 (50 m/sm+4 st/a). C-banding demonstrated positively stained heterochromatic blocks in the centromeric position of few chromosomes on G. sylvius and in the centromeric region of all chromosomes on G. paraguensis samples. The nucleolus organizer region (NOR) was located on the short arm of one st chromosome pair in G. sylvius and Gymnotus sp., and in the interstitial position on the short arm of the pair number one and below the centromere on a third chromosome on G. paraguensis. The cytogenetic data obtained indicate that Gymnotus sp. represent a new Gymnotus specie with a karyotypic constitution never observed on others species from this genus. Some aspects related to the chromosome diversification of these Gymnotus are discussed. © 2007 The Japan Mendel Society.