Spatial-temporal distribution of fish density in the Oujiang estuary during summer and autumn

The spatial-temporal distribution of fish in the Oujiang estuary and the impact factors such as dominant species, topography and geography, as well as hydrological factors on the distribution were investigated during two surveys in June and September 2007. Results showed that weight density (total fish weight in a given water area) was 150.54 (kg/km2) and individual density (total fish number in a given water area) was 29.11 (103 ind./ km2) in June, and 271.53 (kg/km2) and 14.99 (103 ind./ km2) in September, respectively. In another word, the biomasses in the estuary were 67923 kg and 122193 kg in June and September, respectively. The dominant fish species was Argyrosomus argentatus in June, and was replaced by Harpodon nehereus in September. Distribution pattern of fish weight and number was the same in the estuary, which was that both fish weight and number were higher in the east part than in the west part. Fish distribution was positively related to water depth, and surface water temperature significantly affected the seasonal distribution of fish in the estuary. Mixture of Taiwan current and Oujiang discharge forms an ideal hydrological environment in the estuary for fish. [Acta Zoologica Sinica 54（6）：981– 987, 2008].