Fish resources of early life in the Jiang’an section in the upper reaches of the Yangtze River

The upper reaches of the Yangtze River, with its special geology, geomorphology, climate and natural ecological environment, has bred a rich diversity of fish. However, in recent years, the fishery resources have been declining significantly due to the development of water conservancy projects and the increase of human fishing intensity. As a buffer zone of the “National Nature Reserve for the rare and endemic fishes in the upper reaches of the Yangtze River”, the Jiangan section in the upper reaches of the Yangtze River is rich in fish resources. Surveys were carried out in the Jiangan section from April to May in 2022 to study the fish resources of early life. The eggs were identified by molecular biology methods. At least 20 species of fish breed in the Jiangan section, including 13 species of drifting eggs and 3 species of endemic fish in the upper reaches of the Yangtze River. During the monitoring period, there were 4 spawning peaks at S1 and S2 sites, and 5 spawning peaks at S3 site. It is estimated the total fish eggs passing through the Jiangan section is 3.94 × 10⁸ ind. The Shannon-Wiener diversity index, Margalef richness index, Pielou evenness index and Simpson index of the Jiangan section ranged 0.306-0.496, 1.636-2.087, 0.108-0.169, and 0.816-0.885, respectively. Environmental factors such as water temperature, pH, dissolved oxygen, transparency, water level and water discharge were found to have different degrees of influence on egg density through redundancy analysis. The research results showed that the Jiang’an section was spawning ground for a variety of fish, and the early resources were large in scale but poor in diversity. The natural reproduction of Acipenser dabryanus, Myxocyprinus asiaticus and Procypris rabaudi was not monitored. The increase and decrease in water discharge had a stimulating effect on fish reproduction. Therefore, it is suggested to continue to carry out breeding and releasing scientifically and appropriately and carry out ecological dispatching research to meet the breeding demand of fish in the upper reaches of the Yangtze River.