Abstract:The ecological niche is widely used to study species relationships, biodiversity, and community structures. It is also an important method to evaluate inter-and intra-species competition and the status of a population in the community. To understand the community structure and interspecific relationships of fishes in the saltmarsh wetlands of the Yangtze Estuary (YE), this research examined the IRI (index of relative importance), mean clumping index, niche breadth, and niche overlap in the YE using fyke net data from May to October 2019. Ten dominant fish species were collected in three seasons, among which Liza haematocheila, Lateolabrax maculatus, and Odontamblyopus rubicundus were three co-dominant species. Among the 10 dominant fishes, the temporal niche breadth varied from 0.11 to 1.70; Odontamblyopus rubicundus (1.70) had the highest temporal niche breadth, and Larimichthys polyactis (0.11) had the lowest. The spatial niche breadth varied from 0.57-1.53; Liza carinatus (1.53) had the highest spatial niche breadth, and Larimichthys polyactis (0.57) had the lowest. The temporal niche overlap of the dominant fishes varied from 0 to 0.99; 34 species pairs (75.56%) overlapped, while 6 species pairs (13.33%) did not overlap. The spatial niche overlap varied from 0.20 to 0.98; 36 species pairs (80.00%) overlapped, but 2 species pairs (4.44%) did not. The temporal and spatial niches of the dominant fishes in the salt marsh wetlands had distinct seasonal dynamics. Most of the species pairs had spatiotemporal niche overlap (73.33%), and 48.89% of the species pairs reached significant ecological niche overlap, indicating similarities in the spatiotemporal distributions of the dominant fishes in the saltmarsh wetlands. However, competition for the spatial and temporal resources was not the decisive factor affecting the community structure. In conclusion, this research suggests similar spatial and temporal distributions for the dominant fishes in the saltmarsh wetlands, reflecting the competitive relationships between fishes for the utilization of the temporal and spatial resources. Nonetheless, this competition did not affect the fish community structure. The differences in resource utilization may be related to the individual fishes' habits and environment. Further studies of the trophic niches of fish in the saltmarsh wetlands of the Yangtze Estuary are required to better understand the mechanisms of fish habitat selection and biodiversity maintenance.