Spatial dietary differentiation and trophic variation in <i>Gymnocypris chilianensis</i> across three watersheds of the Hexi Corridor

Gymnocypris chilianensis is an endemic cyprinid fish distributed across three major watersheds – Shiyang, Heihe and Shule Rivers – within the Hexi Corridor on the northeastern Qinghai-Tibetan Plateau. Understanding its dietary ecology is essential because trophic interactions influence energy flow, ecological niche differentiation, adaptive responses to environmental change and the management of freshwater biodiversity. We employed a dual-method approach combining stable isotope analysis and metabarcoding of gut contents to characterize dietary composition and trophic variation. Stable isotope results revealed significant spatial differences in δ1³C and δ15N values (MANOVA, p < 0.05), indicating watershed-specific trophic differentiation and variation in carbon source usage. Metabarcoding identified 95 plant genera and 40 animal genera across all samples, including both shared and watershed-specific taxa. Plant-derived dietary patterns exhibited clear geographic structuring and strong ecological coherence, potentially reflecting differences in water resource management and anthropogenic disturbance among watersheds. This study provides integrated insight into the trophic ecology of G. chilianensis and underscores the role of regional environmental context in shaping freshwater food webs, with implications for conservation and management of alpine river ecosystems.