Abstract-Fifty three species (48 species valid) belonging to the Pimelodidae, Heptapteridae and Pseudopimelodidae families have been studied cytogenetically, and in the present paper the chromosome number, the presence of B chromosomes and other relevant data were examined. The diploid number varies from 2n=42 to 2n=58 and were detected three cases of triploids with 3n=87 in Rhamdia species. The karyotypes show a high fundamental number because there are constituted predominantly by meta/submetacentric chromosomes.

Conventional karyotype and nucleolar organizer regions (NORs) of C. macropomum x P. brachypomus hybrids and parental species are reported. A modal diploid number of 54 chromosomes and a fundamental number (NF) of 108 were found for C. macropomum, P. brachypomus and their hybrids. P. brachypomus shows a pair of silver stained chromosomes, while cells with three and four Ag-NOR bearing chromosomes were observed in C. macropomum. The hybrids consistently presented cells with a single metacentric Ag-NOR bearing chromosome and cells with three Ag-NOR bearing chromosomes. The FISH technique was employed to localize 18S rDNA in the chromosomes of the parentals and the hybrids. In P. brachypomus the FITC signals appeared in the SM pair as when stained with silver salts. In C. macropomum the signals were evidenced in six chromosomes. In the hybrids, as expected, the FITC dots were observed in four chromosomes. All the techniques employed in the present work represent good tools to identify the parentals and distinguish them of the hybrids.

Only 33 species among about 300 belonging to the families Pimelodidae and Rhamdiidae have been studied cytogenetically. The diploid number varies from 2n = 46 to 2n = 63 chromosomes, with the karyotypes often being of the meta/submetacentric type. As a result, there is generally a very elevated fundamental number.

-Specimens of Pinirampus pirinampu were analyzed cytogenetically. Fifteen individuals were obtained from the Tibagi river near Sertaneja, PR, Brazil. A karyotypic struc ture consisting of 50 chromosomes distributed as 26M+12SM+2ST+10A was observed. The nucleolar organizing regions ( NORs) were identified on the short arm of a pair of subtelocentric chromosomes. A variation in size of the NOR regions was observed among the paired chromosomes. Chromomycin (CMA 3 ) staining established not only the nucleolar chromosome pair, but also fluorescent marking in the telomeric and centromeric regions of other chromosomes which seem to correspond to the distribution patterns of the constitutive heterochromatin. Restriction enzyme Alu I was employed and the reaction pattern obtained also corresponded to the heterochromatin constitutive distribution.

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In Pimelodidae fish the available chromosome numbers range from 2nϭ46 to 2nϭ63, the value 2nϭ56 being the most frequent one. In the present paper 6 species belonging to the Rhamdiinae subfamily were analyzed: Rhamdia hilarii, R. quelen, Cetopsorhamdia sp., C. iheringhi, Imparfinis cf. piperatus and Imparfinis aff. schubarti. Chromosome preparations were obtained by direct and short term culture methods from kidney cells and analysed under standard Giemsa staining, C-banding and NOR silver staining. Rhamdia species present a basic karyotype composed by 58 chromosomes and the NORs are located on the short arm of a subtelocentric chromosome pair. Cetopsorhamdia sp., C. iheringhi and Imparfinis aff. schubarti. also shows 2nϭ58, while I. cf. piperatus is the only analyzed species presenting 2nϭ56. However, these 4 species show an interstitial NOR location. These chromosomal data agree with the occurrence of subgroups in the Rhamdiinae subfamily, proposed on the basis of their morphological traits.

Summary The ribosomal RNA genes of Pinirampus pirinampu have been localized by fluorescence in situ hybridization (FISH) with 18S rDNA probe. This method allowed the location of FITC signals on the short arm of the biggest subtelocentric chromossomic pair and evidenced a size heteromorphism of hybridization signals between homologous chromosomes. This difference has been attributed to variation in the amount of rRNA genes per cluster, probably due structural modifications (i.e. duplications by unequal crossing over or transpositions) of NOR involving homologous segments. Key words Pinirampus pirinampu, Chromosomes, FISH, rRNA genes.Genes of ribosomal RNA are arranged in long tandem repeated segments, which each gene unit presents conserved coding regions for the 18S, 5.8S and 28S RNAs, separated by intergenic spacers or IGS (Miller et al. 1983). The chromosomal location and activity of the NORs are easily demonstrated by silver staining, once the AgNO3 react with acid proteins associated with rDNA (Jordan 1987). These regions are important chromosome markers, used in animal and plant studies (Almeida-Toledo et al. 1996). Variation on the number, position and size of Ag-NORs patterns have been found in different fish groups, which can be at intra-and/or interspecific levels (Almeida- Toledo et al. 1985, Pendas et al. 1993a, b, Rossi et al. 1997.Treatment by specific fluorochromes, such as chromomycin A3 (CMA3) and/or Mithramycin, has been commonly employed to localize some GC-rich heterochromatin (Schmid 1980, Schweizer 1980, has been also used to evidence NORs since these regions are associated to GC-rich DNA families (Schmid and Guttenbach 1989). In Pinirampus pirinampu of Tibagi's river, the NOR pair is the first subtelocentric one and silver impregnation has evidenced a conspicuous size heteromorphism among the homologues (Swarca et al. 1999). When stained with CMA3 several blocks have been found distributed on the centromeres or telomeric regions. In the last case the fluorochrome binds besides the Ag-NOR bearing chromosome regions, evidencing differences in homologue size (Swarca et al. 1999). Furthermore, the most precise procedure that reveals all the chromosomes involved in nucleolar organization as well the exact location of the ribosomal genes is represented by the fluorescence in situ hybridization (FISH) with rDNA probes. The aim of this communication is to verify the nature of the NOR polymorphism previously reported in P pirinampu as well as to the determined the precise location and relative amount of rDNA loci by FISH. Material and methodsSpecimens of Pinirampus pirinampu were collected at Tibagi river, Parana, Brazil. The specimens were deposited at the Zoological Museum of the Universidade Estadual de Londrina, Parana, * Corresponding author , e-mail: anadias@uel.br Brazil, and received the numbers 1150 and 1151. Mitotic chromosomes were prepared from pooled cephalic kidney. The 18S rDNA segment containing 1700 by of the fish Oreochromis niloticus was used for in situ hybridization and labeled ...

We present the karyotypic characterization of 26 specimens of the side-necked turtle Hydromedusa tectifera collected in the upper Iguaçu River, Paraná state, Brazil. The turtles were cytogenetically analyzed using Giemsa staining and other banding techniques (C, G, Ag-NOR and CMA 3 ) as well as fluorescence in situ hybridization (FISH) with a rDNA 18S probe. All the specimens showed a diploid number of 58 composed of 22 macro and 36 microchromosomes. The Ag-NOR, CMA 3 and FISH techniques permitted the identification and characterization of the chromosome pairs bearing nucleolus organizer regions (NORs), while G-banding facilitated a better recognition and pairing of macrochromosomes. These data agree with some information available in the literature and should be very useful for further cytotaxonomic and cytosystematic studies.