Analysis of the spatial differentiation characteristics of fish community structures in different water body types in the upper reaches of the Taihu Lake Basin based on environmental DNA technology

Fish are the key groups for maintaining the health and stability of aquatic ecosystems. However, due to limitations in existing fish survey techniques, there has been insufficient systematic research on fish resources and community structures in the context of Yangtze River fish conservation. Given this, taking the upstream area of the Taihu Lake Basin, a region with a developed freshwater fishery in China, as a case study, this research adopted environmental DNA (eDNA) technology to monitor the structural characteristics, diversity, and spatial distribution of fish communities in different water body types. The research findings showed that a total of 88 fish species were detected at 127 monitoring sites, with 79 species in rivers, 71 species in lakes, 73 species in reservoirs, and 57 species in streams. Among them, the fish composition in rivers and lakes presented homogenisation, with pollution-tolerant fish such as Carassius auratus, Cyprinus carpio, and Aristichthys nobilis being the dominant species. Although the fish communities in some reservoirs and streams also showed a slight trend of homogenisation, more fish species with higher water quality requirements, like the Rhinogobius giurinus and Odontobutis potamophila were retained. In areas with a high degree of human aggregation, namely the Yangtze River-the Grand Canal (CY), the Tao Lake-Ge Lake area (TG), and the area flowing into Lake Taihu (RT), the fish communities were dominated by tolerant fish species. In the Maoshan-Tianmu Mountain area (MT), where human activities were sparsely dispersed, the fish communities were relatively richer in clear-water fish species. TN, EC, pH, WT, and the natural shoreline retention rate (NSR) were the key environmental influencing factors for the composition of fish communities in the study area. The fish communities in rivers and lakes were more significantly affected by water environmental quality factors such as TN, EC, pH, and WT, while the fish communities in reservoirs and streams were more influenced by the aquatic habitat factor NSR. There was a significantly positive correlation between NSR and the fish diversity in rivers and lakes, and a significantly negative correlation between NSR and that in reservoirs and streams. This study has completed the inventory of fish species resources in the upper reaches of the Taihu Lake Basin, laid a scientific foundation for the restoration and protection of fish resources in the Taihu Lake Basin, and contributed to the sustainable protection and restoration of the aquatic ecosystem in the Taihu Lake Basin.