First classical and molecular cytogenetic analyses of sperata acicularis (Siluriformes, Bagridae)

The first chromosomal analysis of Salween shovelhead catfish (Sperata acicularis) was undertaken by classical cytogenetic and fluorescence in situ hybridization (FISH) techniques in the present study. Ten male and ten female fish were obtained from Salween River, Mae Hong Son Province, Northern Thailand. The mitotic chromosome preparation was directly performed from kidney tissues. Conventional Giemsa staining, Ag-NOR staining, and molecular cytogenetics techniques with FISH using 5S, 18S rDNAs, and microsatellites d(CA)15 and d(GC)15 repeats as probes were conducted. The results indicated that the diploid chromosome number of S. acicularis was 2n = 56. The fundamental number (NF) was 110 both for males and females. The karyotype is composed of 18 large metacentric, 10 large submetacentric, 14 medium metacentric, 12 medium submetacentric and 2 medium acrocentric chromosomes; sex chromosomes could not be identified. NORs localized at the subtelomeric region of the short arm of metacentric chromosome pair 3, which coincides with location of 18S rDNA probe. 5S rDNA probe signal was detected on the short arm of the metacentric chromosome pairs 5 and 8. The distribution patterns of each analysed microsatellite repeat on the chromosomes differed from each other. Microsatellite d(CA)15 repeats were highly accumulated at telomeric regions of all chromosome pairs, and throughout the chromosome in some pairs while the microsatellite d(GC)15 repeats were scattered and less accumulated in some chromosome pairs. Overall, we present the karyotype of S. acicularis providing insights into species’ evolution and enabling undoubtedly species identification.