Author : Kieu Thi Huyen

Summary : The study was carried out to analyze characteristics of distribution, morphology, and genetic diversity of Marbled eel (Anguilla marmorata Quoy & Gaimard, 1824) in Thua Thien Hue. This will supply information about the biological characteristics and adaptability related to the changing habitat of the Marbled eel in Thua Thien Hue. Moreover, it will contribute to the research and the conservation activities of eel resources in Thua Thien Hue and Vietnam. Research information and 350 samples were collected at 350 points in the catchment of seven areas: 02 estuaries, 01 lagoon and 04 major river systems in Thua Thien Hue during the study period from November 2017 to December 2018. Eleven parameters including temperature, salinity, dissolved oxygen (DO), tidal regime, pH, water color, flow, coordinates, time of appearance, moon phase and bottom were analyzed to clarify the environmental characteristics. The external morphological characteristics were identified based on 21 indexes of 350 observed samples. The internal morphological and anatomical characteristics were carried out based on 189 specimens. The principal component analysis (PCA) and cluster analysis (CA) were used to analyze structure of the Marbled eel population distributed in Thua Thien Hue. A study on the genetic diversity of the Marbled eel population was performed on two gene segments COI and 16S rRNA belonging to the mitochondrial gen of 48 samples by using DNA barcode technology. The results of the study have described the morphological characteristics of the Marbled eel population collected in Thua Thien Hue with weight from 3.0 to 4500.0 g, corresponding to four development stages: juvenile, fingerling, pre-adult and adult. The morphological characteristic changes for each stage were body color, fins color, and spots. The suitable environmental characteristics of water for living of Marbled eel is temperature: 21-32 °C, pH: 6.5-8.6, DO: 6.5-9, 5 mg/L, salinity: 0-15%, depth: 0.3-11 m, the bottom has many holes (72.0%); disturbance of water flows, changes of water color, tidal regime, weather and flood (72.9%), and moon phase. There was a high diversity in the Marbled eel populations' structure in Thua Thien Hue related to morphological and environmental characteristics from PCA and CA analysis results with 95,665% and 59,901% of the cumulative rate, respectively. It shows the high adaptability of Marbled eel population in Thua Thien Hue. For distribution characteristics, Marbled eel appears year round in all water bodies with flow Eastward in two seasons: the dry season from January-March, corresponding to the migration of juvenile (TL=100-200 mm) from coast areas to the upstreams, and the rainy season from August to December, corresponding to the time of spawning migration of adult eels. The two gene segments COI and 16S rRNA belonging to the Marbled eel's mitochondrial genome in Thua Thien Hue have been isolated with a total length of 843 bp and 641 bp, respectively. The access codes on the Genbank data of COI sequences and 16S rRNA sequences are from MN067923 to MN067970 and from MN633308 to MN633355, respectively. They have higher composition of Guanime (G) + Cytosine (C) than Adenine (A) + Thymine (T). High substitution rates were found between A - G and T - C. There were 18 amino acids encoded by COI sequences while only four amino acids encoded by 16S rRNA sequences. Twenty polymorphic sites and 17 haplotypes were found from the COI sequences; 7 polymorphic sites and 8 haplotypes also were found from the 16S rRNA sequences show a high diversity in Marbled eel population. Negative values of the neutral tests showed the tendency of random selection and evolution towards the population scale expansion of Marbled eel in Thua Thien Hue. The phylogenetic tree was built based on four algorithms that confirmed the eel's population close relationship in Thua Thien Hue with the eel populations in the Indo-Pacific region. The results obtained from the study have shown a lot of information related to the relationship between the habitat and the distribution, morphology, genetic structure, and evolution of the Marbled eel in Thua Thien Hue and in area.