Fish Community Diversity and Its Relationships With Water‐Level Fluctuations in the Waterway Connecting Poyang Lake and the Yangtze River

Poyang Lake, with an obviously fluctuating water level, is connected to the Yangtze River by only one important waterway. To understand how water level fluctuation drives fish community diversity in this waterway, 12 indices across three dimensions (species diversity, taxonomic diversity and functional diversity) were calculated. Meanwhile, redundancy analysis (RDA) and generalized additive models (GAM) were used to evaluate the response of fish community diversity to water level fluctuations. We collected 63 fish species belonging to 7 orders, 13 families and 39 genera, with Cypriniformes being the dominant order. According to RDA, habitat changes driven by water level fluctuations were the primary factors underlying the shifts in fish community diversity. The GAM model further revealed that water level changes directly impacted the diversity of the fish community, leading to a decrease in the taxonomic distinctness index but an increase in species diversity, taxonomic diversity and functional diversity. Particularly, the number of species, the variation in the taxonomic distinctness index and the functional richness index exhibited highly significant correlations with water levels ( p < 0.001). Therefore, high water levels were the primary and crucial factor in maintaining the fish community diversity in the waterway connecting Poyang Lake and the Yangtze River. These results could provide a scientific basis for the conservation and management of the fishery resources in the water body and provide important guidance to strengthen the protection and management of the lake ecosystem.