Abstract: To reveal the current status of fish resources and the changing trend of trophic levels in the western Xiamen Bay, and to provide a scientific basis for the management of fishery resources. Based on the results of bottom trawl surveys conducted in the western Xiamen Bay during 8 sampling cruises from 2023 to 2024, we analyzed the fish species composition, community structure, and carbon and nitrogen stable isotope characteristics of dominant species in this area. Results of diversity indices show that the Margalef's species richness index (D) ranged from 1.00 to 5.23, with a mean of 2.70±0.47; the Shannon-Wiener diversity index (H') ranged from 0.65 to 2.48, with a mean of 1.77±0.18; and Pielou’s evenness index (J') ranged from 0.23 to 0.99, with a mean of 0.67±0.05. The values of D, H', and J' were generally higher during the wet season (Spring and summer) than during the dry season (Autumn and winter). Cluster analysis (CLUSTER) and non-metric multidimensional scaling (NMDS) indicate that the fish community in the western waters of Xiamen Bay could be broadly divided into five groups, with distinct characteristics between the wet and dry seasons. Stable isotope analysis of carbon and nitrogen in dominant fish species indicates that the current trophic levels of these species are relatively concentrated. Compared with the levels observed in the 2010s, the average trophic level has declined, suggesting a shift in the community structure toward lower-trophic-level groups. This shift may be attributed to the replacement of high-trophic-level dominant species or the miniaturization of individuals. The findings provide stable isotopic evidence for the degradation of food-web trophic structure driven by fishing pressure and other human activities.