Abstract:Cobia, Rachycentron canadum, the only species in the family Rachycentridae, is a candidate for cage culture in tropical and subtropical waters. Taiwan was the first to cage cobia in the early 1990s, and culturing of cobia has also been developed in Southeast Asia and other areas. Understanding the genetic diversity of cultured populations is important for the sustainable development and management of aquaculture. In the present study, 12 polymorphic microsatellite loci were selected to investigate and assess genetic diversity in five cultured populations of cobia from Beihai (BH), Lingshui (LS), Naozhou (NZ), Xuwen (XW), and Sanya (SY). As a result, 129 alleles were detected in the five populations. The mean number of alleles was between 3.833 and 6.750, the mean number of effective alleles ranged from 2.284 to 3.645, the mean of observed heterozygosity and expected heterozygosity was between 0.481 and 0.635, and 0.533 and 0.681, respectively, and the mean polymorphism information content ranged from 0.463 to 0.630. The population deviated significantly from a Hardy-Weinberg equilibrium at multiple microsatellite loci (P<0.05). Analysis of genetic differentiation indicated that the Fst range was from 0.055 to 0.150 and the genetic distance (D) range was from 0.240 to 0.635. BH and NZ had the highest Fst (0.150) and the highest D (0.635). The results of an analysis of molecular variance showed that 84% of the genetic variations were within cultured populations, and 16% were among cultured populations. A phylogenetic analysis using the unweighted pair group method with arithmetic mean and based on Nei’s genetic distance showed that one cluster comprising BH and SY, and the other cluster comprising LS and XW formed a branch, which was then clustered with NZ. These results provide data for further protection and improvement of the germplasm resources of cobia.
