Chromosomal analysis and nors polymorphism of bagarius suchus (Siluriformes: Sisoridae) by conventional banding and fish techniques

Abstract

In the present study, conventional staining and NORs banding as well as Fluorescence in situ hybridizat ion (FISH) using the 18S rDNA and telomeric (TTA GGG)n probes were applied to stain the chromosomes of crocodile catfish, Bagariussuchus (Siluriformes, Sisoridae) fro m the Chao Praya River, Thailand. Kidney cells of 6 male and 6 female crocodile catfishes were used as a sample. The mitotic chro mosome preparations were done directly fro m kidney cells. The results showed that the diploid chro mosome 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 nucleo lar organizer reg ions (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 chro mosome is only one chromosome of the 1st chromosome pair (1a 1b, poly morphic characteristic) at the subtelomeric region of the short arm. Moreover, FISH with telomeric probe showed hybridizat ion signals on each telomere of all chro mosomes and interstitial telomeric sites were not detected. There were variations in signals of FISH and their position in the karyotype along with variat ion in DNA sequences. These markers are useful for future discrimination of population of closely related species and their poly morphis m.