Phylogeographic patterns and population connectivity of Cephalopholis aurantia in the spratly islands (Vietnam) inferred from COI gene sequences

The golden hind grouper (Cephalopholis aurantia) is a visually striking reef fish of high economic value in the Coral Triangle region, serving both as a food source and as an ornamental species in the aquarium trade. In addition to its economic significance, C. aurantia plays an important ecological role in maintaining the balance of coral reef ecosystems. However, the species is facing serious threats due to increasing fishing pressure and exploitation, often carried out without strict regulatory oversight. Assessing genetic variation is thus essential for understanding population diversity and structure, enabling the development of effective conservation strategies, particularly under intensifying environmental and anthropogenic stress. In this study, we examined the genetic diversity and population structure of C. aurantia in the Spratly Islands using the mitochondrial Cytochrome c Oxidase subunit I (COI) gene. This gene is a widely recognized marker in population genetics of marine fish. A total of 30 individuals were successfully sequenced, and COI variability was assessed. Results revealed high haplotype diversity but low nucleotide diversity, indicating a genetic disequilibrium within the population. Neutrality tests and population dynamic analyses supported a scenario of post-bottleneck demographic expansion. Phylogenetic and haplotype network analyses further corroborated this hypothesis, showing a dominant haplotype with closely related satellite haplotypes, along with evidence of new haplotypes entering the population. Such patterns may be driven by larval dispersal capabilities, strong reproductive potential, and the influence of oceanic currents facilitating gene flow. Documenting signs of population expansion and immigration is crucial for spatially explicit management and conservation of C. aurantia, ensuring the long-term sustainability of this ecologically and economically significant species in the Spratly Islands.