Change patterns of fish community assembly and composition at low and high-water levels during the first year of a 10-year Yangtze fishing ban in the Three Gorges Reservoir Area (TGRA), China

The Three Gorges Dam is the largest water conservancy project in the world, and theThree Gorges Reservoir Area (TGRA) possesses precious fish resources. Currently,due to the lack of efficient biodiversity monitoring tools, the precise evaluation of fishcommunity composition in a riverine reservoir has been restricted. Here, weinvestigated fish resources using 12S-rDNA barcoding in the TGRA before and after175 m water level during the first year of a 10-year Yangtze fishing ban. Our resultsshowed that the fish composition exhibited obvious seasonal differences. Theenvironmental water levels, land use, and spatial characteristics less influenced thedevelopment of fish communities. Based on Infer Community Assembly Mechanisms(iCAMP) by phylogenetic bin-based null model analysis, 66.12% of unexplainedvariables were driven by stochastic processes of community assembly andunmeasured key factors. We developed a growth-limiting index (GLI) and firstly appliedit for inferring fish environmental adaptability, revealing the growth adaption responseof reservoir fish species to environmental pressure. Compared to the downstream fromthe dam, fish population growth at the low- or high-water levels was partly inhibited.However, seven species of tiny or medium-sized fish showed strong adaptability in thereservoir region at both water levels. Taken together, this study clarified the patterns offish community assembly in the TGRA and provided unique insights for chronicmonitoring fish diversities in a reservoir.