Genetic differences in nuclear and mitochondrial DNA genes among some species of the family Pangasiidae

Abstract

Pangasiidae is a large family of freshwater catfishes found throughout South and Southeast Asia. Some pangasiids, such as Pangasianodon hypophthalmus, Pangasius krempfi and Pangasius mekongensis are highly valuable, representing for the two genera of this family. This study investigated their genetic relationships by estimating genetic distances based on nuclear and mtDNA genes. A total of 10 samples of each fish species were collected at Hau River. DNA templates of these samples were amplified mtDNA cytochrome c oxidase subunit I (COI) and nuclear rhodopsin (Rho) genes. Segments of 634 bp COI and 814 bp Rho were successfully sequenced. The results from both genes showed similar trends of genetic distances for K2P and nucleotide between the three species. P. krempfi is closer to P. mekongenis rather than P. hypophthalmus and the distance between P. mekongensis and P. hypophthalmus is the largest. Genetic distances in mtDNA COI (ranging from 9.48 to 12.56%) are greater than those in nuclear Rho gene (0.87 to 1.37%) among the three pangasiid species. Similarly, nucleotide differences are greater in COI (55 to 72 nucleotides) than Rho gene (7 to 11 nucleotides). Furthermore, the phylogenetic relationship of three species based on mitochondrial DNA and nuclear genes produced similar topologies, showing P. krempfi was closer to P. mekongenis than to P. hypophthalmus.