Genetic diversity and population structure of Thymallus sp. in China based on morphological and molecular markers

Thymallus sp. is a native fish species distributed in the Irtysh River Basin in China. Unfortunately, environmental damage and overfishing have led to a significant decline in Arctic grayling resources, pushing them towards endangerment. However, there is a lack of comprehensive genetic information regarding the wild populations of Thymallus sp., which poses challenges for the development of effective conservation strategies for their genetic resources. In response, this study collected 180 samples from six major tributaries within the Irtysh River Basin. It conducted a thorough investigation of Thymallus sp.'s morphological and genetic variations using morphometric measurements and microsatellite markers. The results showed that the morphological differences among the six populations were relatively minor, and none of the morphological traits reached the subspecies level or higher. Genetic analysis showed that all six populations of Thymallus sp. possessed high genetic diversity, with genetic variations among populations accounting for only 6.30 % of the total variation, suggesting that the current status of the germplasm resources was relatively good. However, due to overfishing, which had led to a decline in the number of effective breeding groups, some inbreeding has occurred within populations. Moreover, the construction of dams has hindered gene exchange, leading to a certain tendency towards genetic differentiation within the populations. This was evidenced by the clustering of Burqin and Haba into one genetic group, while Kuirt, Kayit, Kalaerzis, and Crane were classified into another genetic group. This study offers an important reference for the management and conservation of Thymallus sp. populations in the Irtysh River Basin.