Fish Species Composition And Diversity In The Northern And Southern Foothills Of The Qinling Mountains Based On Environmental DNA High-throughput Barcoding Technology

In the 13 th Five-Year Plan for Fisheries Science and Technology Development released by the Ministry of Agriculture in 2017,"Assessment and Management of Fishery Resources in Important Waters" was listed as one of the top scientific and technological tasks.With the commencement of the 10-year fishing ban on the Yangtze River in 2020,the conservation of fish resources and ecological diversity of inland rivers,especially the Yangtze and Yellow rivers,our mother river,and their important tributaries,has become the primary research target.The Qinling Mountains are the geographical north-south dividing mountain range in China,and their elevation is staggered,with abundant water resources,giving fish a unique living environment.The Qinling Mountains are naturally divided into two basins: the Han,Jialing,and Dan River basins,which flow to the southern part of Shaanxi Province,and the Wei River basin,which flows to the Guanzhong Plain in the north.The intricacies of the watersheds within the Qinling Mountains have led to an uneven distribution of species within the watershed.Earlier,fish resource surveys in the Qinling waters were mostly conducted by traditional methods such as manual fishing and walk-in surveys.The shortcomings of these methods are time consuming,high labor cost,and insensitive to rare species.Therefore,this paper adopts environmental DNA highthroughput barcoding technology to survey fish diversity in the north and south foothills of the Qinling Mountains,which has been widely used in watersheds with complex hilly landscapes and has a high degree of feasibility.Environmental DNA high-throughput sequencing technology is a new monitoring method that collects,extracts,amplifies and sequences DNA fragments released into the environment by secretion and excretion,and then compares them with species databases to obtain species-specific information.The aim of this study is to obtain a comprehensive survey of fish resources and diversity in the north and south of the Qinling Mountains and in different watersheds,to complement the traditional survey results,to optimize the environmental DNA technique,and to assess the impact of dams on fish diversity in this watershed.In this study,137 sampling sites were set up in the northern and southern foothills of the Qinling Mountains,including 94 in the southern foothills and 43 in the northern foothills.In the sampling,we selected five different migratory bays near the sampling sites for repeated sampling and obtained a total of 685 water samples,which were extracted to environmental DNA through filtration and other steps and then sequenced to obtain fish species composition and diversity data.The main results of this study are as follows.1.In this survey,a total of 12,939 OTUs were obtained,and the data were filtered and processed to assign the obtained OTUs to 102 species such as Brachymystax lenok,Hucho bleekeri,Onychostoma macrolepis,Gobiocypris rarus,Leptobotia elongata,etc.Due to the lack of species information in the database,10 species such as Trilophysa bleekeri were selected as reference data by comparing with the previous survey results and the database.These 102 species belonged to 12 orders,22 families and 70 genera.2.A total of 99 species in 12 orders,22 families and 70 genera exist in the southern foot of the Qinling Mountains,and 88 species in 12 orders,21 families and 65 genera exist in the northern foot.The fish species found in the southern side of the Wei River basin belong to 65 genera and 88 species in 12 orders and 21 families;the fish species found in the Han River basin belong to 87 species in 64 genera and 21 families in 12 orders;the fish species found in the Jialing River basin belong to 64 species in 53 genera and 18 families in10 orders;and the fish species found in the Dan River basin belong to 69 species in 53 genera and 16 families in 11 orders.3.The relative abundance of Carpiformes was the highest in different basins of the Qinling Mountains,followed by Catariformes.Among the rivers in the southern side of the Wei River at the northern foot of the Qinling Mountains,the genus Triplophysa accounted for 4.55%;the Han River basin had a relative dominance of the genus Opsariichthys with4.60%;for the Jialing River basin,the Hemibarbus had the highest percentage of 4.69%;and the genus Sarcocheilichthys and Carassius in the Danjiang River basin accounted for4.35%.The genera Schizothorax,Rhinogobio and Leptobotia are only present in the Han River basin;the genera Romanogobio and Sinibotia are only present in the Dan River basin.Compared with the other three basins,the number of species of the genus Onychostoma was higher in the Jialing River;while the number of species of the genus Triplophysa in the Wei River was significantly higher than those in the other three basins.4.Among the 40 dam-blocked rivers,the diversity of fish species was higher in the lower reaches of most rivers than in the upper reaches,and the dams may have had a negative impact on fish species diversity.Some species such as Phoxinus oxycephalus and Triplophysa siluroides had significant differences in relative abundance between the upstream and downstream reaches,and the dams produced a certain degree of species isolation between the upstream and downstream reaches.The results of this study demonstrate the feasibility of environmental DNA techniques for surveying fish species diversity in large,geomorphologically complex waters.The study provides a more comprehensive monitoring of fish species diversity in the northern and southern foothills of the Qinling Mountains,which can be a reference for other studies of the same type.