Study Of Fish Diversity In Yueqing Bay Based On Environmental DNA Method

In order to understand the current status of fishery resources in Yueqing Bay under multiple pressures such as overfishing and environmental degradation,the author used environmental DNA and metabarcoding technology to analyze the species composition and spatial and temporal changes of diversity of fish at 10 stations in Yueqing Bay in November 2018 and May 2019 to grasp the fish community structure and the spatial and temporal distribution pattern of Yueqing Bay.At the same time,the traditional fishery resources survey methods are used for comparative analysis,and the application of environmental DNA technology in fish biodiversity research is explored for further optimization.The results show that:1.Mi Fish fish universal primers were used to amplify the total environmental DNA extracted from seawater samples in Yueqing Bay.The total number of fish detected in 20 samples was about 66 species within 29 families,13 orders and two classes.A total of 25 species of fish were detected in autumn within 22 genera,14 families,nine orders,and 59 species of fish were detected in spring within 52 genera,26 families,12 orders and 2 classes.The five species with the highest relative abundance in this sea area in autumn are Cynoglossus bilineatus(15.7%),C.nasus(14.1%),Takifugu fasciatus(9.2%),and Pinjalo pinjalo(7.7%)and Paraparlagusia japonica(6.9%).The five species with the highest abundance in the sea area in spring are Harpodon nehereus(24.9%),Larimichthys polyactis(10.6%),and Lateolabrax maculatus(7.9%),Liza carinata(9.7%)and Trichiurus lepturus(6.9%).2.Four diversity indexes are mainly selected to reflect the alpha diversity of the survey area,including Shannon-wiener diversity index,Margalef richness index,Pielou evenness index,and Simpson diversity index.As a result,the diversity of fish communities in different seasons fluctuate significantly between stations.From the perspective of seasonal changes in fish biodiversity,the diversity index in spring is higher than that in autumn,because fish reproductively migrate from the open sea to the near shore in spring.In addition,due to the influence of the Ou'jiang River runoff and precipitation,a dilute water mass is formed resulting of reproduction ofzooplankton.Therefore,it is a natural breeding place with high fish diversity.Redundancy analysis(RDA)analysis of environmental factor parameters and fish species finds that the C.bilineatus,P.japonica,Butis koilomatodon and Butis melanostigma are skewed to higher salinity while T.fasciatus are distributed in deeper water areas.C.nasus has a negative correlation with chlorophyll a,which is related to eating habits of C.nasus.3.With the combination of the two methods,the identified fish taxa include 85 species within 66 genera,31 families and 14 orders.The trawl catches 42 fish species,belonging to 35 genera,17 families and 10 orders.19 species of fish found only in trawl catches due to loss of information in taxonomic databases and too low DNA abundance.For 44 species of fish are only identified by e DNA metabarcoding,it is speculated that the detected DNA may not originate from the surrounding individuals of fish species that swim too fast.It has been shown that in the waters of Yueqing Bay,more fish species can be detected by environmental DNA than by trawling.4.The comparison of the results of environmental DNA sampling and trawling survey conducted in Yueqing Bay in this paper,sort out the advantages and disadvantages of environmental DNA technology.In terms of advantages,the detection rate of environmental DNA species is higher than that of trawl surveys,and the method is more friendly to the environment and target species results from no direct contact or capture of organisms.Second,the environmental DNA has high sensitivity without taxonomy experts and it reduces field survey time and money.In addition,environmental DNA is degraded and transported in seawater by factors such as temperature,salinity,and water flow.Therefore,relatively accurate biomass and location information cannot be obtained.It is not yet possible to analyze the biological information of the target species through DNA,such as gender,body length,weight,etc.