Karyotypic variation in the long-whiskered catfish Pimelodus blochii Valenciennes, 1840 (Siluriformes, Pimelodidae) from the lower Tapajós, Amazonas and Trombetas Rivers

Abstract

The genus Pimelodus LaCépède, 1803 comprises 35 formally recognized species distributed along the major neotropical river basins. Despite conservatism in diploid number with 2n=56, an intense variation of chromosomal morphology (karyotypic formula) has been documented in Pimelodus species. In the present study, we analyzed karyotypes of 20 specimens, identified as Pimelodusblochii Valenciennes, 1840 and collected from the lower courses of the Tapajós, Amazonas and Trombetas Rivers. The karyotypes were characterized by Giemsa conventional staining, C-banding, silver staining (Ag-NOR) and fluorescent in situ hybridization (FISH) with 5S and 18S rDNA probes. The karyotypes showed 2n=56 chromosomes in fish from the Tapajós River. In contrast, fish from the Amazonas and Trombetas Rivers had 2n=58. The nucleolus organizing regions were labeled on the short arm of an acrocentric chromosome as demonstrated by silver staining and FISH. Signals for 18S and 5S rDNA were co-localized on one chromosome pair. Our results demonstrate karyotypic divergence between Tapajós and Amazonas-Trombetas populations of P.blochii, interpreted as supporting the existence of a species complex in this taxon.

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

“…However, several groups of Neotropical fish carry these ribosomal genes in synteny, distant or colocalized. Several recent studies in Siluriformes showed the synteny of these genes (e.g., Baumgärtner et al, 2018;Fonseca et al, 2018;Lorscheider et al, 2018;Takagui et al, 2019;Terra et al, 2019), being considered as a plesiomorphic feature in Tricomycteridae and Loricariidae (Ziemniczak et al, 2012), and an ancestral condition in the sister group of Auchenipteridae, the Doradidae family (Baumgärtner et al, 2018;Takagui et al, 2019).…”

First cytogenetic characterization of the Amazon Catfish Leiarius marmoratus (Gill, 1870) and its hybrid with Pseudoplatystoma reticulatum (Eigenmann & Eigenmann, 1889)

“…Despite that, a great amount of fish species has never been biologically or genetically studied. Recent findings showed efforts to cytogenetically characterize Pimelodidae species in the Amazonian region, providing important data for this group of fishes, as the described for Pimelodus (Fonseca et al 2018) and the giant catfishes Phractocephalus hemioliopterus (Swarça et al 2017) and Brachyplatystoma filamentosum (Gonçalvez et al 2014).…”

Molecular Evidence Reveals Taxonomic Uncertainties and Cryptic Diversity in the Neotropical Catfish of the Genus Pimelodus (Siluriformes: Pimelodidae)

“…A number of phylogenetic studies have demonstrated the complexity of this taxon, which still has unresolved questions on the status of species and their monophyly. In addition, the species with a more ample distribution, such as Pimelodus blochii Valenciennes, 1840, Pimelodus pictus Steindachner, 1876, and Pimelodus ornatus Kner, 1858, appear to represent species complexes [ 7 , 8 , 13 ].…”