Abstract: The community structure and species diversity of fishes in the Jiulong Estuary were evaluated based on two trawling surveys conducted in May and November, 2009. Totally 35 fish species were identified, belonging to two classes, 12 orders and 22 families. According to their habitats, three species are pelagic fish, seven near-demersal fish and 25 demersal; and 10 species are estuarine and 25 marine. Based on their temperature adaptions, 22 species are warm water fish, and the rest 13 are temperate warm water fish. According to their feeding habits, seven species are lower carnivorous fish and 28 middle carnivorous fish. Arius sinensis, Coilia mystus and Odontamblyopus rubicundus were dominant species in the samples of May, and A. sinensis, C. mystus and Johnius belengerii were dominant species in the samples of November. The weight densities were 471.53 and 143.97kg?km^-2, and the individual densities were 40811 and 3804ind?km^-2 in May and November, respectively. The Shannon-Wiener index, Pielou index, Margalef index and Trophic index of the fishes in the Jiulong Estuary were 1.20, 0.39, 3.11 and 3.55, respectively. Compare to the survey data conducted in the same periods in 1985, the fish community structure and species diversity changed largely, and the trophic index deceased significantly in the Jiulong Estuary. Overfishing, environmental pollution and habitat loss are suggested to be the main factors contributing to the decline of fish diversity in the Jiulong Estuary.

Key words: fish, biodiversity, trophic index, Jiulong Estuary