Study On The Fish Diversity In Fluctuating Backwater Area Of The Three Gorges Reservoir Based On EDNA Metabarcoding

The waterway development of the upper reaches of the Yangtze River,known as the "golden waterway",is the foundation to promote the development of the Yangtze River economic belt.Since the impounding of the Three Gorges Reservoir,the waterway conditions in the fluctuating backwater area of the Three Gorges Reservoir have been greatly improved.However,during the water-leveling period,some reefs obstructing navigation surface,leading to frequent ship grounding accidents,which seriously affect the waterway development of the Yangtze River.Therefore,the Yangtze River waterway regulation is included in the key project in the "13th Five-Year Plan" development plan of Yangtze River Water transportation.However,this section is an important distribution area of rare endemic fishes and economic fishes in the upper reaches of the Yangtze River,and its fish germplasm resources and living environment are of high conservation value.The contradiction between Yangtze River waterway regulation and fish resource protection has become the key to hinder the development of Yangtze River shipping.Therefore,it is of positive significance for the protection of Yangtze River fish resources and the construction of Yangtze River waterway to clarify the status quo of fish resources and distribution characteristics of fish communities in the study area.With the introduction of the Yangtze River fishing ban in 2020 and the Yangtze River Protection Law in 2021,traditional methods,including net fishing,electric fishing and gill nets,have been limited due to the damage they cause to fish and their habitats in the Yangtze River.In addition,because of the complex hydrological situation and the changeable underwater terrain in the fluctuating backwater area of the Three Gorges Reservoir,the traditional survey methods for the rare and endemic fish monitoring are not enough.In this study,eDNA metabarcoding was applied for the first time to investigate fish diversity in the fluctuating backwater of the Three Gorges Reservoir during 2021 to2022,to explore the differences in the distribution of fish communities under different seasons,and to explore new methods suitable for the monitoring and conservation of fish diversity in this region.It provides scientific basis for the health assessment of Yangtze River water ecosystem and the waterway regulation of Yangtze River.The main research results are as follows:(1)According to the eDNA metabarcoding fish diversity monitoring in the three seasons from 2021 to 2022,a total of 138 fish species were detected,belonging to 8 orders,24 families and 91 genera,including 96 species in 4 families of 63 gnenra in Cypriniformes,18 species in 4 families of 9 genera in Siluriformes,15 species in 9families of 10 genera in Perciformes,3 species in 3 families of 3 genera in Cyprinodontiformes,3 species in 1 families of 3 genera in Salmoniformes,and 1 species in 1 families of 1 genera in Acipenseriformes,Synbranchiformes and Clupeiformes.There are 1 species of national first class key protected fish,9 species of national second class key protected fishes,34 species of rare and endemic fishes in the upper reaches of the Yangtze River,10 species of key protected fishes in Chongqing,and 4 species of exotic fishes.O.bidens,C.idellus,H.molitrix,A.nobilis,A.wangi,H.bleekeri,R.cylindricus,C.carpio,C.auratus,S.sichuangensis,S.asotus,P.nitidus and R.giurinus have high abundance OTU sequence and the dominant species.The results are generally better than the traditional survey results,especially for rare protected fish and invasive fish,eDNA metabarcoding has a significant advantage.At present,the application of eDNA metabarcoding in the Yangtze River is in the development stage,and its technical standardization analysis process still needs to be optimized and perfected to quickly,efficiently and accurately evaluate the fishery resources in the Yangtze River.(2)By analyzing and comparing the distribution and composition of fish community in the three seasons and exploring the influence of environmental factors on the distribution of fish community,it was found that there were significant differences in the structure of fish community in the three seasons.In summer flood season,fish drifted along the current to the slow flow area to complete their early life history.During the winter storage period,fish overwintered in the lower reaches of the reservoir where the water flow was slow and the water depth was large.In spring,fish whirled back to Jiangjin,Changshou,Fuling and other places in the upper reaches of the reservoir to spawn.Combining p H,temperature and dissolved oxygen,it was found that p H had no significant effect on fish distribution,while temperature and dissolved oxygen had significant effect on fish distribution.The results show that eDNA metabarcoding can be used to monitor fish diversity and explore the distribution characteristics of fish communities in the fluctuating backwater area of the Three Gorges Reservoir,and can be used as a key technology to establish a non-invasive fish resource monitoring system.