Fish Diversity Of The Yangtze River-Shijiu Lake Connected System Based On EDNA Technology

The Yangtze River and its lake ecosystem are one of the most important wetland areas in the world with abundant water resources and biodiversity.Shijiu Lake is one of the few Yangtze River-connected lakes in the middle and lower reaches of the Yangtze River.It is connected with Dangtu section of the Yangtze River,and its water level is affected by seasonal flooding.Shijiu Lake and The Yangtze River form the Yangtze River-Shijiu Lake connected system.In order to monitor the fish diversity of the Yangtze River-Shijiu Lake connected system,eDNA can be regarded as a time-saving and resource-saving method.The objectives of this study are as follows:(1)The fish composition of the Yangtze River-Shijiu Lake connected system was analyzed based on eDNA technology.(2)The spatial differences of fish community structure of the Yangtze River-Shijiu Lake connected system in the lake area,the channel and the river section were analyzed to reflect the connectivity of the whole system.(3)In the case of seasonal flooding of the Yangtze River-Shijiu Lake connected system,the distribution of fish driven by seasonal water flow was studied.In this study,water samples were collected in October 2020(autumn),January 2021(winter),April(spring),and July 2021 in the Yangtse-Shijiu Lake connection system.A total of 180 eDNA samples were collected at 15 survey sites,with 3 parallel water samples collected at each site.Then theDNA in the water sample was filtered to the filter membrane,and theDNA on the filter membrane was extracted by sampling DNA extraction kit.Mifish primers were used for PCR amplification twice,and highthroughput sequencing was performed on Illumina Miseq platform.Bioinformatics analysis was performed to obtain the final FISH OTU classification information.The main results of this study are as follows:1.Using eDNA technology to study the Yangtze River-Shijiu Lake connected system,the filtration process of eDNA technology was optimized from the number of filtration membrane and filtration time.All theDNA of 180 samples collected from the Yangtze River and Shijiu Lake connected system were amplified by PCR,156 fish OTU were obtained and 66 fish taxa were annotated.The composition of fishes is as follows:34 Species at the Species level,20 Species at the Genus level,9 at the Subfamily level,2 at the Family level,and 1 at the Order level,belonging to 34 Species,42 genera,21 families,9 orders.Cypriniformes(79.98%)were the most common,among which Cyprinidae(77.44%)were the most important,followed by Cobitidae.There were false positives in the survey results,including fish of Scomber,Schizothoracinae,Pseudosciaeninae,and Lefua costata.2.The Yangtze River-Shijiu Lake connected system was divided into three areas according to its flow characteristics,and the spatial characteristics of fish diversity were analyzed.The results showed that the maximum values of fish taxa and OTUs appeared in the river section,and the fish taxa and OTU were abundant in the river section.The composition of fishes in lake area,river channel and river section overlapped considerably,with 50 species occurring in all three types of waters.Shannon-wiener diversity index(H ’)ranged from 2.88-5.02,Pielou evenness index(D)ranged from 0.64 to 1.11.ANOSIM test showed that there was no significant difference in diversity index among different types of waters.Ten species of migratory fishes were classified,and these migratory fishes were distributed in different types of waters.Non-metric multidimensional scaling analysis based on Bray-Curtis distance index and PERMANOVA Adonis test Pr(>F)= 0.008(<0.05)showed that there were significant differences in relative fish abundance in lake area,river channel and river section.According to the relative abundance,Carassius auratus,Cyprinidae and Culter mongolicus are distributed in each region and each site,while other species are scattered in some sites.The Yangtze River-Shijiu Lake connected system drives the exchange and replenishment of fish resources in lake area,river channel and river section under the state of natural river passage,and promotes the similar fish composition in all study areas.The change of water level and the connected state regulate the habitat conditions and form microhabitat patches,which indirectly affect the spatial pattern of fish.3.There were 22,33,35 and 37 fish taxa in autumn,winter,spring and summer,respectively.The fish taxa were the least in autumn and the most in summer.The number of OTU(OTUs)detected in different seasons were different,with the maximum values in summer and the minimum values in autumn,and there was no significant difference between spring and winter.The overlap of OTUs between seasons was 0,and the overlap of fish taxa between seasons was 13.The Richness index and Shannon-Wiener diversity index were significantly higher in summer than in other seasons,similar in winter and spring,and the lowest in autumn(Richness index,P<0.05;Shannon-wiener diversity index,P<0.05).Pielou evenness index had no significant difference among different seasons(P>0.05).In addition,the seasonal distribution of three species of characteristic fish with unique life history strategies in the middle and lower reaches of the Yangtze River,Hypophthalmichthyinae,Ctenopharyngodon idella,and Elopichthys bambusa,are in line with the life history of the migratory fish.To sum up,this study explored the effectiveness and feasibility of eDNA technology in the study of fish diversity in the composite ecosystem,and initially analyzed the fish composition of the Yangtze River-Shijiu Lake connected system.On this basis,the spatial differences of fish community structure in the Yangtze River-Shijiu Lake connected system in the lake area,river channel and river section were investigated,and the distribution of fish in the complex ecosystem driven by seasonal water flow was also studied.Under the background of Yangtze River protection,this paper provides background data for evaluating the effect of fishing ban in Shijiu Lake and the impact of fishing ban in Yangtze River on connected lakes.