Cytogenetic analysis of orange-spotted grouper, Epinephelus coioides, using chromosome banding and fluorescence in situ hybridization

Abstract

The orange-spotted grouper, Epinephelus coioides, is one of the most important commercial fish species in Southeast Asia. Although it has been widely cultured in China, basic cytogenetic information on this species is limited. In this study, we used Giemsa-staining, C-banding, argyrophilic nucleolar organizer regions (Ag-NORs), and repetitive sequencing (including 5S, 18S, and (TTAGGG)n) techniques to analyze the cytogenetics of the orange-spotted grouper. Our results showed that the karyotypic formula of the orange-spotted grouper was 2n = 2SM + 46A, NF = 50. C-banding patterns indicated that centromeric regions of all chromosomes were C-band positive except in pair no. 12. Heterochromatin was detected at the subcentromeric regions of both pair no. 5 and no. 12. In the smallest chromosome pair, no. 24, either the entire short arm or the end of the short arm was C-band positive. After Ag-NORs staining, one pair of nucleolar organizer regions was observed on the short arm of pair no. 24. FISH results showed that 5S rDNA was located at a pair of A-type chromosomes, while 18S rDNA appeared at the same location in the short arm of pair no. 24 where Ag-NORs were detected. The telomeric sequence (TTAGGG)n detected by FISH was located at both ends of each chromosome. Some of these chromosomal markers showed species-specific variations. Thus, despite the apparent karyotype stability (2n = 48), several microstructural chromosome changes must have occurred during chromosomal evolution, resulting in significant changes in the karyotype structure during the evolutionary diversification of the genus Epinephelus.