Genetic diversity of Plotosus canius (Hamilton, 1822) inferred from the mitochondrial control region

Abstract

Grey-eel catfish (Plotosus canius) is the only species of the Plotosidae family previously reported in the Mekong Delta. This catfish species distributes in a wide range of salinity levels, raising the question whether there are genetic differences between the freshwater and brackish water populations. To look for an answer, a total of 84 P. canius individuals were collected in four provinces in the Mekong Delta, including An Giang (AG, N=20), Soc Trang (ST, N=22), Tra Vinh (TV, N=24) and Bac Lieu (BL, N=19). Sequencing the cytochrome c oxidase subunit I (COI) gene of representative samples and mitochondrial DNA control region (CR) of all collected fish revealed the occurrence of two separated groups within four populations. Each of the two groups consisted of 42 individuals, in which, the members in Group 1 had the origin from brackish water in ST, TV and BL and Group 2 inhabited freshwater conditions in AG, ST and TV. The 915 base-pair fragments of CR yielded 34 polymorphic sites and 22 haplotypes for Group 1, while these genetic indices in Group 2 were 22 and 11, respectively. Additionally, the higher genetic diversity in Group 1 (haplotype diversity Hd=0.971±0.011 and nucleotide diversity pi=0.009±0.008) compared to Group 2 (Hd=0.664±0.08 and pi=0.005±0.001) reflects the effect of habitat type on genetic diversity. Besides, the Kimura-2 parameters distances between Group 1 and Group 2 were high, at 8.14±0.93% based on CR and 8.34% based on COI, showing the congeneric relationship between the two groups. Therefore, the findings of this study provided genetic evidence for the presence of two Plotosidae species which had the same gross appearance in the Mekong Delta of Viet Nam, however, morphological studies must be conducted to confirm the possibility of cryptic species.