Abstract: Investigating fish species diversity across different ecological systems and analyzing community structure through species co-occurrence networks are crucial for understanding fish community assemblage and resource conservation. Using environmental DNA technology and species co-occurrence network analysis, we investigated fish composition and community characteristics in six ecological units in the Anhui Shengjin Lake National Nature Reserve, including the inflow river, upper lake, middle lake, lower lake, diversion channel of the reservoir dam, and the Yangtze River. The results showed that: (1) A total of 64 fish species were detected, belonging to 8 orders, 14 families, and 46 genera. The inflow river exhibited the highest species diversity, and the diversion channel of the reservoir dam had the lowest. Migratory fish species in the Yangtze River were also found in the lake region. (2) Fish community predominantly exhibited a random co-occurrence pattern. 70.31% of fish species showed significant associations with at least one other species, with positive correlations being the most prevalent. The invasive species Coptodon zillii exhibited a significant negative correlation with the native species Rhinogobius cliffordpopei. (3) The co-occurrence network was most complex in the inflow river and simplest in the diversion channel of the reservoir dam. The network complexity of the upper lake, middle lake, lower lake, and the Yangtze River was similar. Differences were observed in density and clustering coefficient. There were significant variations in key species across all six ecological units. Overall, the random co-occurrence pattern was the primary interspecies co-occurrence pattern, but complex and significant interspecific relationships were identified, indicating that non-random co-occurrence patterns also played a crucial role in shaping community structure across these ecological units. Fish species diversity and co-occurrence network complexity were positively correlated. Although the diversion channel of the reservoir dam had the lowest species diversity, it did not significantly block the migratory fish species between Shengjin Lake and the Yangtze River.

Key words: fish community, species diversity, species co-occurrence network, co-occurrence pattern, random co-occurrence