Abstract: Spatial and temporal variation of fish assemblage structure in the adjacent sea area of the Yangtze River estuary and its relationship with environmental factors were studied based on fish abundance data sampled from 1998 to 2001. Multivariate methods were adopted including both hierarchical classification and constrained ordination. Rare species were excluded, the remaining 48 species fishes belong to 10 orders, 28 families. Among them, the species number of Perciformes was highest, and three most abundant orders contributed 99.81% of the total count: Myctophiformes, Perciformes and Clupeiformes. Dominant species were different between the seasons: Harpodon nehereus, Benthosema pterotum and Setipinna taty were dominant species in autumn; while Pampus argenteus and Johnius belengeri in spring. The interannual differences during same season were not significant, but the seasonal differentiation was found between autumn and spring. The canonical correspondence analysis(CCA) show that fishes were separated into four ecological assemblages: hypsithermal-saline, hypsithermal-brackish, hypothermal-brackish, and hypothermal-saline group. The nearshore area represented an abundance peak of fish community in the adjacent sea of the Yangtze River estuary. Significant dissimilarities of assemblage structure and habitat environment were found in four ecological assemblages. The influence degree of environmental factors on the fish community was especially discussed. The analyses results showed that environmental factors influencing fish assemblage structure include bottom temperature, water depth, bottom and surface pHs, surface total phosphorous and bottom dissolved oxygen.

Key words: Yangtze River estuary  , fish assemblage ,  , environmental factor