TAF PUBLISHING

In the present study, conventional staining and NORs banding as well as Fluorescence In Situ Hybridization (FISH) using the 18S rDNA and telomeric (TTAGGG)n probes were applied to stain the chromosomes of crocodile catfish, Bagariussuchus (Siluriformes, Sisoridae) from the Chao Phraya River, Thailand. Kidney cells of six male and six female crocodile catfishes were used as a sample. The mitotic chromosome preparations were done directly from kidney cells. The results showed that the diploid chromosome number of B. suchus was 2n=56, the Fundamental Numbers (NF) were 102 in both male and female. The karyotype comprises 17m+17sm+12a+10t. The Nucleolar Organizer Regions (NORs) were detected by Ag-NORs banding and 18S rDNA probe mapping. The 18S rDNA are terminally located on the short arm adjacent to the telomere of the single pair of the 1st chromosome pair whereas NOR-bearing chromosome is only one chromosome of the 1st chromosome pair (1a 1b, polymorphic characteristic) at the subtelomeric region of the short arm. Moreover, FISH with telomeric probe showed hybridization signals on each telomere of all chromosomes and interstitial telomeric sites were not detected. There were variations in signals of FISH and their position in the karyotype along with variation in DNA sequences. These markers are useful for future discrimination of population of closely related species and their polymorphism.