Abstract: Rugao section at the lower reaches of the Yangtze River is located near estuaries and strongly affected by tides. Changqingsha and Minzhusha located in Rugao section have a typical stream-sandbank habitat with special hydrological condition. In order to understand the assemblage characteristics of larval and juvenile fish and the influencing factors in this special habitat, we conducted ichthyoplankton surveys in Changqingsha and Minzhusha from May to August each year between 2018 and 2020. A total of 17776 larval and juvenile fish were collected during the survey, belonging to 6 orders, 8 families and 34 species, with Cyprinidae being absolutely dominant. Hemiculter leucisculus, Hemiculter bleekeri and Coilia nasus were the predominant species in Changqingsha and Minzhusha. The mean abundance of larval and juvenile fish in June and July at each section was significantly higher (P<0.05) than other months, with the highest abundance in July 2019 and H. leucisculus as the most dominant species (S3#, 204.75 ind·100 m^-3). The total abundance of larval and juvenile fish in the north branch was higher than the south branch in Rugao section. The clustering analysis based on the abundance of dominant and common species at 14 sites showed that they could be divided into three groups at a similarity level of 84.60, showing significant differences in assemblage structure of larval and juvenile fish in different groups (R=0.76, P<0.05). Results of MDS analysis showed stress=0.14<0.2, indicating a meaningful interpretation of the clustering results for each site. Results of RDA analysis showed that the abundance of larval and juvenile fish was positively correlated with temperature and turbidity and negatively correlated with transparency. Overall, our results indicated that the stream-sandbank habitat affects the assemblage structure of larval and juvenile fish. The north branch with a weaker diversion effect in the surveyed section is more suitable for reproduction of most fish species, and the survival and development of larval and juvenile fish. It is recommended to strengthen protection and monitoring in the branch waters of Yangtze River, which would play an important role in the replenishment of fish resources.

Key words: Rugao section of the Yangtze River, main stream-sandbank habitat, larval and juvenile fish, assemblage structure, environmental factor.