Trophic niche overlap in native and alien fish species can lead to competitive interactions whereby non‐native fishes outcompete indigenous individuals and eventually affect the viability of natural populations. The species Erythroculter mongolicus and Erythroculter ilishaeformis (belonging to the Culterinae), which are two commercially important fish species in the backwater bay of the Pengxi River in the Three Gorges Reservoir (TGR), were threatened by competition from the non‐native Coilia ectenes (lake anchovy). The latter is an alien species introduced into the lower reaches of the Yangtze River in China and now widespread in the TGR. The trophic consequences of non‐native lake anchovy invasion for E. mongolicus and E. ilishaeformis were assessed using stable isotope analysis (δ13C and δ15N) and associated metrics including the isotopic niche, measured as the standard ellipse area. The trophic niche of native E. mongolicus had little overlap (<15%) with the alien fish species and was significantly reduced in size after invasion by lake anchovy. This suggests that E. mongolicus shifted to a more specialized diet after invasion by lake anchovy. In contrast, the trophic niche overlap of native fish E. ilishaeformis with the alien fish species was larger (>50%) and the niche was obviously increased, implying that fish in this species exploited a wider dietary base to maintain their energetic requirements. Thus, marked changes for the native E. mongolicus and E. ilishaeformis were detected as the trophic consequences of invasion of non‐native lake anchovy.

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Abstract-JiuquwanReservoir is the only drinking water source supplied for Xunwu county residents. It is located in the middle reaches of Mati River belongs to the East River upstream tributary of the Pearl River basin. The ecological management projects of cyanobacteria bloom in Jiuquwan Reservoir was described. And the influence of ecological projects of the reservoir for algae and other biological compositions and nutrient levels was analyzed. The results showed that the ecological management projects played an active role in management cyanobacteria bloom and eutrophication and had played a positive role in the optimization of water ecosystem. These projects have had desired ecological effects in Jiuquwan Reservoir.