Natural triploidy in Rhamdia quelen identified by cytogenetic monitoring in Iguacu basin, southern Brazil

The freshwater silver catfish from the genus Rhamdia belongs to a group of neotropical fish with wide distribution throughout Central and South America. The results obtained in the F1 generation of native specimens of this species bred in captivity using molecular cytogenetic tools revealed a high number of triploid specimens (46.8%) in the samples analyzed. The use of double fluorescent in situ hybridization (double-FISH) with 18S and 5S rDNA probes allowed highlighting the location of ribosomal sites with independent activity. This chromosome marker allowed the identification of triploid nuclei, in which three markers were visualized, in contrast to diploid fish, which only exhibited two fluorescent signals. As triploid specimens exhibit either total or partial gonad sterility, the present study demonstrates the importance of cytogenetic monitoring in restocking programs aimed at genetic conservation.