To explore the nutritional structure and subsequently construct a brief food network of fish communities in the Wanshan Islands, this study analyzed the main nutritional characteristics of the key fishery organisms using stable isotope technology in autumn (September) of 2021, while simultaneously calculating various quantitative indicators. As a result, the δ¹³C value of fish from the Wanshan Islands ranged from –21.23‰ (Mugil cephalus) to –14.00‰ (Eubleekeria splendens), with a mean value of (–16.96±0.41)‰. Additionally, the δ¹⁵N value ranged from 9.93‰ (Trachinotus ovatus) to 14.83‰ (Pennahia anea), with a mean value of (12.52±0.34)‰. The trophic levels of these fish varied from 2.54 to 3.98, with an average trophic level of 3.30. Furthermore, the δ¹³C range (CR), δ¹⁵N range (NR), total area (TA), standard ellipse area (SEAc), mean distance to centroid (CD), mean nearest neighbor distance (MNND), and standard deviation of nearest neighbor distance (SDNND) of the fish were 7.23, 4.90, 23.64, 3.73, 1.30, and 0.24, respectively. Based on the stable isotope values of carbon and nitrogen, the fishes in the Wanshan Islands could be divided into three main groups: 4 species (3.57%) of planktivorous fishes, 7 species (6.25%) of benthic fishes, and 101 species (90.18%) of low-grade carnivorous fishes. According to the Bayesian mixed model, the main food source of fish in the Wanshan Islands is zooplankton with contribution rate of 62.54%, followed by algae with a contribution rate of 25.28%. This study constructed a novel continuous trophic spectrum of the fishes in the Wanshan Islands that was of great significance in examining the characteristics of food web and trophic structure and could provide strong data support for the protection and management of the Wanshan Islands ecosystem.