Abstract:To understand the status of early-stage fish resources in the Yibin Section in the upper reaches of the Yangtze River and guide the protection of fish resources in this section, surveys were carried out from April to July in the years of 2017~2019. The results showed that there were 22 species of eggs and larvae in five families and three orders, and the largest proportion was in the Cyprinidae. Among these, 13 species produced drifting eggs, and six species were endemic to the upper reaches of the Yangtze River. The breeding time of different fish had obvious annual differences, but the peak of fish breeding occurred in June. From 2017 to 2019, the number of drifting eggs was estimated to be 12.10×106, 70.42×106, and 35.77×106 for each year, respectively. The number of larvae was estimated to be 30.95×106, 41.47×106, and 39.44×106, respectively. The number of eggs of endemic fish in the upper reaches of the Yangtze River was estimated at 15.91×106 over three years. According to the calculation, there were many spawning sites of fish drifting upstream of the Yibin Section, and the larger spawning sites were mainly located in the reaches of Zhouba, Peachwan, and Hualong Wharf. The spawning sites of Rhinogobio typus were distributed from Dongyuemiao to Xiangjiaba, with the largest cumulative spawning amount in three years, up to 40.93×106. The spawning grounds of R. typus tended to migrate downstream. The spawning grounds of Ctenopharyngodon idellus are mainly distributed in the Mamingxi Wharf and Peachwan areas. The results of the canonical correlation analysis showed that environmental factors such as water level, water temperature, and water discharge had different effects on the density of drifting fish eggs. Lepturichthys fimbriata and Parabotia fasciata lay eggs when the water temperature and water discharge are high. The reproductive conditions of C. idellus and Leptobotia microphthalma were similar to each other, and they were highly correlated with the water level, water discharge, and velocity. The spawning of R. typus and Coreius heterokon was significantly affected by changes in dissolved oxygen and transparency. Although affected by many factors, such as the development of cascade hydropower in the Jinsha River, the Yibin Section, as an important part of the mainstream national nature reserve of rare and endemic fish in the upper Yangtze River, is still a crucial distribution area for the spawning and breeding of many fish species, and the fish populations have slowly recovered in recent years. Therefore, we should strengthen the early resource research in this section, carry out habitat conservation and remediation, and implement a “10-year Fishing Ban” to promote resource recovery.
