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The Mekong giant catfish Pangasianodon gigas is endemic to the Mekong River and is a critically endangered species. The genotypes of the microsatellite DNA (msDNA) and mitochondrial DNA (mtDNA) markers (right domain of the control region) were detected to evaluate the present status of genetic divergence of this species from the Mekong River in Thailand and Cambodia. The observed and expected heterozygosity values of Mekong giant catfish in Thailand and Cambodia were relatively low in comparison with those of other nonendangered freshwater fish species. These two populations from Thailand and Cambodia showed similar levels of genetic diversity, as evaluated by the 384 nucleotides of the mtDNA control region with 13 haplotypes. The pairwise FST value between the two populations based on the genotype frequencies of msDNA and mtDNA markers suggested a close genetic relationship between the populations in Thailand and Cambodia. The results of this study support the conclusion that the Mekong giant catfish is critically endangered. Care should be taken to sustain the genetic diversity of this species, as the level of genetic variability has already decreased in the wild population. This species is a target species for an ongoing stock enhancement program in the Mekong River in Thailand. It is proposed to apply these markers for proper broodstock management, such as for minimal kinship selective breeding in the hatchery. [ABSTRACT FROM AUTHOR]

The Mekong giant catfish is one of the largest freshwater fish in the world, and is endemic to the Mekong basin. Recently, the number of Mekong giant catfish has drastically decreased. In this study, seven microsatellite DNA markers of the Mekong giant catfish were developed for evaluation of the species' genetic diversity. Mendelian inheritance of four of seven markers was confirmed using offspring (F1) produced from one pair. Number of alleles per locus in the founder population ranged 1-4 with a mean of 2.8, and that in F1 ranged 1-2 with a mean of 1 .6. The expected heterozygosity in the founder population ranged 0-0.66 with a mean of 0.38, and that in F1 ranged 0-0.5 with a mean of 0.28. The mean expected heterozygosity in the founder population is apparently lower than that in Pangasius bocourti and other freshwater species, but higher than that in endangered species. In the future, the microsatellite data in this study will be used in minimal kinship approaches, because these individuals constitute the basic seed for release into wild in an effort to conserve the native population of Mekong giant catfish. [ABSTRACT FROM AUTHOR]