Cytogenetic characterisation of the ornamental freshwater fish, Piabucus melanostomus (Iguanodectinae) from Brazilian wetlands and its relation with species of Characidae basal group

Abstract

The genus is the only member of the subfamily Iguanodectinae found in the Pantanal of Mato Grosso State, where it is represented by Piabucus melanostomus. P. melanostomus from the Paraguay and Bento Gomes Rivers of the Pantanal wetlands were analysed using conventional and molecular cytogenetic techniques to cytogenetically characterise the species and broaden the knowledge of the subfamily. The results indicated no sex-related heteromorphisms. The diploid number for the species was 2n = 50 chromosomes, which were divided into six metacentric, eight submetacentric, 24 subtelocentric, and 12 acrocentric with a fundamental number (FN) of 88. Heterochromatin was visualised using the C-banding technique, which showed that it was mainly distributed in the centromeric and pericentromeric region of most chromosomes, but larger blocks were observed on the long arms of large subtelocentric chromosomes (8, 9, 10, 13, and 20 pairs). Nucleolar organising regions (Ag-NOR) were observed in the p-subterminal region of one subtelocentric chromosome pair (9) with a remarkable size polymorphism between homologues in individuals from the Paraguay River, which was confirmed using the FISH technique with 18S rDNA. In this population, in all individuals studied, one of the homologous shows block considerably larger. The karyotype was compared with those of other subfamilies considered basal in Characidae, according to morphological data.