Using eDNA to assess the fish diversity and spatial characteristics in the Changjiang River-Shijiu Lake connected system

Abstract

With the decrease in biodiversity in freshwater ecosystems, the monitoring of fish has become a current research hotspot. The eDNA-based method has been applied to a variety of single-type water systems (i.e., rivers, lakes, or oceans), but it has not been applied to river–lake-connected systems. We collected eDNA from water samples from the Changjiang River–Shijiu Lake connected system (including the lake area, river channel, and river section) and discussed the fish diversity characteristics of the connected system. A total of 180 samples were collected, and the fish community was analyzed using eDNA metabarcoding of the mitochondrial 12 s region. We finally identified 66 taxa of fish, including one at the order level, two at the family level, 9 at the subfamily level, 20 at the genus level, and 34 annotated to the species level. The number of fish species in the river–lake connected system was greater than that in a single-type water system. The lake area, river channel, and river section had a high degree of overlap in fish composition, and the maximum number of fish was in the river section. There was no significant difference in α diversity index among the three types of waters, but there were significant differences in fish relative abundance, which was dominated by different species. The distribution of three migratory fish (Elopichthys bambusa, Ctenopharyngodon idella, and Hypophthalmichthyinae sp.) accorded with the unique life history migration strategy in the middle and lower reaches of the Changjiang River. Our results provide detailed data on fish diversity and have important implications for the long-term management and conservation of river–lake connected systems in the lower reaches of the Changjiang River. Our research further proves that eDNA can be used to monitor the biodiversity of river–lake connected systems and reflect their spatial characteristics. As a continuously explored method, eDNA shows great potential in the study of fish diversity in river–lake systems.