Molecular cytogenetic analysis in Pseudorasbora parva (Cypriniformes: Gobionidae)-important invasive fish species in...

Topmouth gudgeon Pseudorasbora parva is a small invasive cyprinid fish widely distributed across Eurasia, including Türkiye. Although extensive, the available cytogenetic data from Asian populations is confined to standard karyotyping. Here we present the first molecular cytogenetic characterization of P. parva by analyzing the population from the Sakarya spring (Eskişehir Province, Türkiye). The aim was to examine the chromosomal organization and distribution of selected repetitive DNA sequences and this way to provide novel insights into karyotype evolution within Gobionidae and evaluate the utility of cytogenetic markers for freshwater management of this invasive species. To that end, we combined conventional karyotyping, C-banding, fluorescent and silver-nitrate staining with fluorescence in situ hybridization (FISH) using probes for tandemly repeated genes for ribosomal RNA (18S and 5S rDNA), small nuclear RNA (U1 and U2 snDNA), and telomeric (TTAGGG)_n sequences. Analyzed individuals (N = 10) showed a diploid chromosome number of 2n = 50 with the karyotype being composed of 18 metacentric, 26 submetacentric, and 6 subtelocentric chromosomes (FN = 94), and with constitutive heterochromatin confined to pericentromeric regions. Silver staining as well as Chromomycin A₃ and 18S rDNA FISH probe revealed invariably a single pair of major 45S rDNA cluster on the short arms of the subtelocentric pair 23, with notable size heteromorphism between the homologs. 5S rDNA occupied (peri)centromeric regions of the submetacentric pair 10 and short arms of the subtelocentric pair 25, whereas the U1 and U2 snDNA clusters were co-localized on the short arms of subtelocentric pair 24. The telomeric probe marked chromosomal ends only. The Turkish P. parva population exhibits a conserved karyotype but the heterochromatin and repetitive DNA patterns allow to infer its closer relationship to European lineages. These findings provide new insights into Gobionidae genome organization and the chromosomal evolution and reveal the possible utility of cytogenetics in monitoring the dispersal of populations of invasive freshwater fishes.