Study On The Fish Diversity In The Lower Reaches Of Jialing River Using Environmental DNA Metabarcoding Technology

Environmental DNA metabarcoding(eDNA metabarcoding)technology can be used to monitor aquatic ecosystem biodiversity-is a non-invasive,efficient and highly sensitive approach,which contributes to carry out the ecological protection of aquatic ecosystem and the management of fish resources.The Jialing River is the largest firstclass tributary in the upper reaches of the Yangtze River,breeding extremely rich fish resources.The fish diversity of the Yangtze River Basin,including the Jialing River,is facing a serious crisis due to overfishing,water engineering construction and invasion species.In order to put an end to overfishing,the relevant departments announced the implementation of the "Ten Year Fishing Ban" for the Yangtze River from 00:00 on January 1,2020,during which productive fishing of any natural fishery resources is prohibited.In this study,we used eDNA metabarcoding technology to monitor fish diversity in the lower reaches of the Jialing River for the first time during the fishing ban period.A total of 5 sampling sites were set up for monitoring fish diversity in January2021(winter)and March 2021(spring),and the temporal and spatial distribution of fish community in the lower reaches of Jialing River was further explored in combination with environmental factors.This study successfully monitored fish diversity in the lower reaches of the Jialing River based on eDNA macrobarcoding technology,which explored a new method for fish diversity monitoring in the Yangtze River Basin during the "Ten Year Fishing Ban" period,and provided a scientific basis for the management and protection of the ecological environment and fish resources in the lower reaches of the Jialing River.The results are as follows:(1)Fish diversity composition in the lower reaches of Jialing River.Based on the Tele02 universal primer of fish,a total of 88 species of fish were detected in five locations in the lower reaches of the Jialing River-Dongjintuo,Chengjiang,Yanjing,Jingangbei and Sansheng,including 45 species which were endemic to China and 12 species endemic to the upper Reaches of the Yangtze River.These fishes belong to 7 orders,18 families and 55 genera,including 59 species in 5 families of Cypriniformes,15 species in 4 families of Siluriformes,10 species in 5 families of Perciformes,and 1 family and 1 species in 1 family of Acipenseriformes,Cyprinodontiformes,Beloniformes and Osmeriformes.In general,the number of species of cyprinidae was the most,with 46 species,accounting for 52.27%.In addition,four national second-class protected animals – Leptobotia elongata,Onychostoma macrolepis,Procypris rabaudi and Leptobotia rubrilabris,as well as three exotic species of Gambusia affinis,Neosalanx taihuensis and Micropterus salmoides were also detected.The dominant species in this eDNA detection were Cyprinus carpio,Hypophthalmichthys nobilis,Ctenopharyngodon idella,Rhinogobius brunneus,Carassius auratus,Acheilognathus macropterus,Culter alburnus,Rhinogobius giurinus,Pseudobagrus crassilabris,Chanodichthys mongolicus and Saurogobio dabryi.In comparison with the traditional fish monitoring,the relative abundance of small fish such as Rhinogobius,Gobioninae,and Acheilognathus macropterus has increased significantly,while the relative abundance of larger fish such as Spinibarbus sinensis,Tachysurus dumerili,Silurus meridionalis,Tachysurus vachellii,and Hemibagrus macropterus has decreased significantly.The results also showed that fish in the lower reaches of the Jialing River were mainly carnivorous and omnivorous,and their egg types were mainly sticky egg,and their habitat water layer were mainly benthic.(2)The temporal and spatial distribution of fish community in the lower reaches of Jialing River.This study explored the temporal and spatial distribution of fish community in the lower reaches of Jialing River using eDNA metabarcoding technology.Seasonally,the number of fish species in spring was significantly higher than that in winter,and there were significant differences in fish community structure between spring and winter,showing that the detection probability of fish eDNA in winter was lower than in spring.This indicated that eDNA is easier to catch during the breeding season of fish,providing an effective sampling strategy for the monitoring of fish diversity in the Jialing River based on eDNA technology,that is,sampling during the breeding season of fish could detect more fish species.Spatially,the number of fish species below the Caojie power station dam was significantly higher than that above the dam,and fish composition structure above and below the dam was significantly different.In addition,the species compositon was similar among sampling sites below the dam,while the species compositon was different among sampling sites above the dam,and the distribution of fish species below the dam was more uniform than that above the dam.Therefore,it can be concluded that the construction of Caojie Dam has a significant impact on the composition of fish communities in the lower reaches of Jialing River.Finally,combined with environmental factors,we concluded that water temperature,dissolved oxygen and p H all significantly affected the distribution of fish community in the lower reaches of jialing River,of which dissolved oxygen had the strongest correlation with the distribution of fish community and the greatest degree of influence on it.The above results showed that the feasibility and effeciency of eDNA macrobarcoding technology for fish diversity monitoring in Jialing River,could be used as an effective tool for monitoring fish diversity in Jialing River,and playing an important role in the conservation of fish diversity,sustainable exploitation of fisheries and ecofriendly development of Jialing River.At the same time,this technology also provided certain basic information for the monitoring and conservation of fish diversity during the "Ten Year Fishing Ban" period of the Yangtze River.