Fish Niche Responses to Hydrological and Water Quality Mutations in the Lower Yellow River

Based on data from 12 large‐scale hydrological, water quality, and aquatic ecological surveys conducted between 2014 and 2023 along the lower reaches of the Yellow River from Henan to Shandong, this study employed canonical correlation analysis to identify key environmental factors influencing the density and biomass of indicator fish species ( Carassius auratus Linnaeus, Hemiculter leucisculus Basilewsky, Rhodeus sinensis Günther and Cyprinus carpio Linnaeus), coupled with anomaly analysis and Mann–Kendall tests to identify hydrological and water quality factors exhibiting mutation characteristics. Niche models calculated species niche breadth and overlap, while grey relational analysis revealed the driving mechanisms behind spatial niche differentiation. Results showed that a total of nine environmental factors with significant mutation characteristics were identified, including water depth, turbidity, electrical conductivity, chlorine, sulphate, ammonium nitrogen, bicarbonate, total nitrogen and chemical oxygen demand for C. auratus Linnaeus and H. leucisculus Basilewsky have higher niche breadth and strong adaptability to environmental changes, whereas R. sinensis Günther shows minimal ecological niche overlap and weaker interspecific competition. Fish distribution exhibits distinct spatial heterogeneity, with high biodiversity in the southern mountainous area, low species abundance in the urban centre area, and pollution‐tolerant species dominating the Huaihe region. Niche spatial differentiation is primarily driven by turbidity, ammonium nitrogen and sulphate, reflecting the adaptive response of fish to complex water environment changes in the urban reaches of the lower Yellow River. This study provides theoretical foundations and methodological insights for fish diversity conservation and ecological restoration in changing environments.