Srijanya Sukmanomon

A study on phylogeny and biogeography of mahseer species (Pisces: Cyprinidae) using sequences of three mitochondrial DNA gene regions

The cyprinid fishes of the three genera Tor, Neolissochilus and Naziritor, often referred to as mahseer, are an important group of fish. Mahseer are endemic to Asia with natural distribution encompassing the trans-Himalayan region in the northwest to Sumatra and Borneo islands in the southeast, across a number of countries such as Nepal, Pakistan, India, Sri Lanka, Myanmar, China, Thailand, Laos, Cambodia, Vietnam, Indonesia and Malaysia. These species are large-scaled barbels that live in upstream, clear, running waters (Shrestha, 1990; Ng, 2004). They are attractive as sport fish (Ng, 2004), and some species are of great economical value and of conservation concern (Nguyen et al., 2006), as well as of aquaculture potential (Haque et al., 1995; Ingram et al., 2005). Currently 46 mahseer species are recognized, of which 23 species are of genus Tor Gray, 22 species belong to genus Neolissochilus Rainboth and one species of genus Naziritor Mirza (Eschmeyer et al., 2004). However, there is still much confusion with regard to taxonomy and systematics, and uniformity in diagnosis of this group. Fishes of the genus Tor are considered as ‘‘true mahseer” with the presence of the median lobe, as opposed to Neolissochilus and Naziritor, where the median lobe is not present. The shape, size and length of the median lobe, the features that have often been used to distinguish species of Tor (Zhou and Cui, 1996), are highly variable (Roberts, 1999) and are also being influenced by environmental factors, leading

Genetic diversity of wild mekong giant catfish Pangasianodon gigas collected from Thailand and Cambodia

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.

PHYLOGENETIC RELATIONSHIPS AMONG NINE SCALLOP SPECIES (BIVALVIA: PECTINIDAE) INFERRED FROM NUCLEOTIDE SEQUENCES OF ONE MITOCHONDRIAL AND THREE NUCLEAR GENE REGIONS

Abstract Current knowledge of the evolutionary relationships among scallop species (Mollusca: Bivalvia: Pectinidae) in the Indo-Pacific region is rather scanty. To enhance the understanding of the relationships within this group, phylogenies of nine species of scallops with the majority from coastal regions of Thailand, were reconstructed by maximum parsimony, maximum likelihood, and Bayesian methods using sequences of the 16S rRNA of the mitochondrial genome, and a fragment containing the ITS1, 5.8S and ITS2 genes of the nuclear DNA. The trees that resulted from the three methods of analysis were topologically identical, however, gained different levels of support at some nodes. Nine species were clustered into two major clades, corresponding to two subfamilies (Pectininae and Chlamydinae) of the three currently recognized subfamilies within Pectinidae. Overall, the relationships reported herein are mostly in accordance with the previous molecular studies that used sequences of the mtDNA cytochrome oxidase subunit I, and the classification system based on microsculpture of shell features and morphological characteristics of juveniles. Levels of divergences were different among genes (i.e., the 5.8S gene showed the lowest levels of nucleotide divergence at all levels, whereas the 16S rRNA showed the highest level of variation within species, and ITS2 gene revealed the highest level of divergence at higher levels).