Fish community structure and diversity in the Ningxia section of the main stream of the Yellow River in China.

The Ningxia section of the Yellow River represents a critical habitat for freshwater fish biodiversity, yet its ecological integrity faces increasing threats from anthropogenic activities. To comprehensively assess the fish community structure, diversity, and its relationship with environmental factors in the Ningxia section of the Yellow River, we conducted seasonal surveys of fish resources and environmental conditions at 15 selected sites from July 2022 to September 2023. Our study employed quantitative analyses to evaluate fish community characteristics, spatiotemporal distribution patterns, and their interactions with environmental variables. A total of 42 fish species, belonging to 34 genera, 11 families, and six orders, were identified, with Cyprinidae being the dominant family (57.14%). Carnivorous species were the most abundant (22 species), followed by omnivorous (16 species) and herbivorous (four species) fish. The Relative Importance Index (IRI) identified Gobio huanghensis and Carassius auratus as the dominant species in this region. Biodiversity indices revealed a mean Margalef richness index of 3.066, Pielou evenness index of 0.5911, Shannon-Wiener diversity index of 1.791, and Simpson dominance index of 0.7083. The Abundance-Biomass Comparison (ABC) curve indicated moderate disturbances to fish communities in spring and autumn, while communities remained stable in summer and winter. Spatially, six sites (Nanchangtan, Shapotou, Jinshawan, Meijiawan, Linhe, and Taole) exhibited significant disturbances, while others showed moderate or stable conditions. The results of cluster analysis and non-metric multidimensional scaling (NMDs) indicated no significant differences in fish community structure among the sampling sections in the Ningxia reach of the Yellow River. Redundancy analysis (RDA) identified water temperature and ammonia nitrogen as the primary environmental factors influencing fish community structure. Our findings highlight the combined impacts of human activities and environmental changes on fish communities in the Ningxia section of the Yellow River. These results provide a scientific basis for the conservation and sustainable management of fishery resources in this ecologically sensitive region.