Author : Thipsuda Tangprakhon

Summary : Black ear catfish, Pangasius larnaudii Bocourt, 1866 is one of the dominant food fish and commercially important pangasiid species in Thailand. The Thai Department of Fishes (DoF) has engaged in breeding programmes of this fish for aquaculture as well as for restocking natural waterways for enhancing fish production. Presently, the P. larnaudii fingerlings are produced from ten DoF hatcheries with the broodstocks either from the wild (P0), F1 or F2 progenies some of which were transferred among the fisheries. Little is known about the history of the stock as no record was properly kept. Thus, this study was undertaken to determine the genetic variation, relationships and differentiation among ten of DoF hatchery populations and three natural populations from rivers using microsatellite markers. Four microsatellite primer pairs, namely PSP-G507, PSP-G513, PSP-G576, and PSP-G579 were used in this study. DNA was extracted from individual fin clips using a single tube extraction procedure for fish blood with some modifications. This procedure was used to extract DNA with good quality for PCR amplification. A total of 27 primer pairs were used to screen and optimize microsatellite loci for studying genetic variation in P. larnaudii, of which only four microsatellite primer pairs were selected for further analysis. The results indicated a wide range of genetic variability among the populations. The average number of alleles per locus ranged from 2.8 to 15.8 and the observed heterozygosity ranged from 0.319 to 0.864. A wide range of allele frequencies were observed over all the loci, with the highest in the Uthaitani population, followed by the Mekong population while the lowest was found in the Chainat population. The average genetic distance (DT) and genetic differentiation (FST) between populations ranged from 0.120 to 0.539 and 0.013 to 0.349, respectively.