Abstract
Karyotypic data are presented for four species of fish belonging to the Pimelodidae family. These species show a conserved diploid number, 2n = 56 chromosomes, with different karyotypic formulae. The analyzed species showed little amount of heterochromatin located preferentially in the centromeric and telomeric regions of some chromosomes. The nucleolus organizer regions activity (Ag-NORs) and the chromosomal location of ribosomal genes by fluorescent in situ hybridization (FISH), with 18S and 5S probes, showing only one chromosome pair marked bearer of ribosomal genes, the only exception was Pimelodus britskii that presented multiple NORs and syntenic location of the 18S and 5S probes. Non-Robertsonian events, as pericentric inversion and NORs duplication are requested to explain the karyotype diversification in Pseudoplatystoma from the rio Paraguay (MS), Pimelodus from the rio Iguaçu (PR), Sorubim from the rio Paraguay (MS) and Steindachneridion from the rio Paraíba do Sul (SP). The obtained data for the karyotype macrostructure of these species corroborates a conserved pattern observed in Pimelodidae. On the other hand, interspecific variations detected by molecular cytogenetics markers made possible cytotaxonomic inferences and differentiation of the species here analyzed.
Highlights
According to Lundberg & Littmann (2003), Pimelodidae is considered one of the most diversified families among Neotropical Siluriformes
Fluorescent in situ hybridization for the simultaneous location of 18S and 5S rDNA was performed based on the Pinkel et al (1986) protocols, using the 18S rDNA probes described for Prochilodus argenteus (Hatanaka & Galetti, 2004) and 5S rDNA probes described for Leporinus obtusidens (Martins & Galetti, 1999)
The diploid number of 56 chromosomes in here analyzed species supports the hypothesis that this is the modal number verified in most catfish families (Oliveira & Gosztonyi, 2000) and likely a basal condition found among species of the Pimelodidae
Summary
According to Lundberg & Littmann (2003), Pimelodidae is considered one of the most diversified families among Neotropical Siluriformes. Clustering 29 genera, 93 species and four nominal fossil species (Ferraris, 2007). The Steindachneridion and Pseudoplatystoma genera occupy the top of the alimentary chain; present great load and migrate in at least a phase of the life (Miranda, 1997; Revaldaves et al, 2005). The genus Pimelodus has the greatest diversity in the Pimelodidae family, with 26 species distributed from Panama to Argentina, ranging from small to medium-size (Lundberg & Littmann, 2003; Ribeiro & Lucena, 2006a, 2006b). The genus Sorubim is distributed in hydrographic basins of the Amazon, Orinoco, Paraná and Paraíba Rivers (Froese & Pauly, 2002)
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