Abstract: To explore the feeding characteristics and trophic structure of fish in the middle route of South-North Water Diversion Project (MSNWDP), we analyzed food composition, isotope characteristics, trophic level, niche breadth, niche overlap, and organic carbon sources of the main fishes in Henan section of the MSNWDP through stomach content analysis and carbon and nitrogen stable isotope techniques. The results showed that fishes in Henan section mainly relied on endogenous carbon sources, with planktonic algae being the most important endogenous carbon source and terrestrial insects being important sources of exogenous carbon. The trophic level of fish ranged from 2.00 to 3.59 based on stomach content analysis, and ranged from 2.66 to 4.39 based on δ15N stable isotopes, indicating that the length of food chain was relatively long. The results of ecological niche spatial structure analysis showed that omnivorous fish had the widest niche breadth, while other types of fish had the narrow niche breadth. There were some differences in the results of niche overlap between stomach contents and isotope analysis, which may be related to the technical characteristics of the two methods. The total area (TA) of the convex hull, corrected standard ellipse area (SEA), δ¹³C range (CR), and the mean distance to the centroid (CD) of the main fish species were relatively small. The mean nearest neighbor distance (MNND) and the standard deviation of nearest neighbor distance (SDNND) were relatively high, indicating that food diversity and trophic redundancy were small and the ecosystem stability was low. This study could provide technical supports for fish resources regulation and aquatic ecosystem management of the MSNWDP.

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