Hoplosternum littorale (Teleostei, Callichthyidae) from a Coastal River basin in Brazil - Cytogenetic analysis and gene mapping of 5S and 18S rDNA

Abstract

-Cytogenetic studies were carried out in a population of Hoplosternum littorale from a coastal river basin in the southeastern region of Brazil. The results were identical to those of all populations already described for this species, involving the maintenance of karyotype macrostructure and the distribution pattern of heterochromatin, as well as its composition. The report on localization of ribosomal genes is new for this species. The diploid number observed was 2n=60 chromosomes (6M+2SM+52A) for both sexes. A single pair of acrocentric chromosomes bearing rDNA sites on the short arms was identified, both by silver nitrate staining and by FISH (Fluorescent in situ hybridization) with an 18S rDNA probe. Four 5S rDNA clusters were identified using FISH methodology. C-banding revealed a great amount of heterochromatin blocks, present in most chromosomes, preferentially located in subterminal and interstitial regions. Four GC-rich regions were identified by chromomycin A 3 staining. The data are discussed based on ecological and genetic aspects of this fish group.