Investigation And Study On Early Fish Resources In Mudong Section Of Three Gorges Reservoir Area

The upper reaches of the Yangtze River are rich in fish resources,which is one of the main fish germplasm resources in China.In recent years,due to the increasing human activities,such as overfishing and the construction of water conservancy projects,the fish resources in the upper reaches of the Yangtze River have shown a significant downward trend.To clarify the distribution of early fish resources and spawning grounds is beneficial to the conservation of fish resources.The primary work of early investigation and research on fish resources is the identification of fish eggs and larvae,but the traditional investigation methods are complicated.Due to its sensitivity,high accuracy,high speed and high efficiency,DNA barcoding technology is widely used.Based on the DNA barcoding technology and traditional cone net.this study investigated the early fish resources in Mudong section of the upper reaches of the Yangtze River were investigated from April to July,2022.By identifying the early fish resources and their relationship with environmental factors,the present situation of fish resources,diversity and spawning ground distribution were explored,in order to provide data for the follow-up investigation and research of fish resources in the upper reaches of the Yangtze River.The main results are as follows:1.Based on the DNA barcoding technology,using Cyt b gene as a marker gene,fro m April to July,2022,a total of 56 species of early fish resources,belonging to 4 orders a nd 10 families,were collected in the Mudong section in the upper reaches of the Yangtze River,Cypriniformes had the largest number of species,with 46 species,accounting for 82.14%of the total species.Followed by Siluriformes and Perciformes,with 5 and 4 specie s,accounting for 8.93%and 7.14%,respectively;Salmoniformes had only 1 species,acco unting for 1.79%.The dominant species are Coreius heterodon、Rhinogobio cylindricus、Ctenopharyngodon idellus、Hemiculter bleekeri、Hypophthalmichthys molitrix、Pseud olaubuca engraulis.2.During the monitoring period,the total runoff of fish eggs flowing through the section of Mudong was 32.29×108ind.Among them,the reproductive scale of Hemiculter bleekeri is the largest,which is 8.45×10~8ind.,accounting for 26.17%of the total flow during the sampling period;Followed by Coreius heterodon,4.99×10~8ind.,accounting for 15.44%.Then,Coprinus cylindrica and Ctenopharyngodon idellus,with runoff scales of 4.72×10~8ind.and 3.48×10~8ind..Respectively,were the next.The egg runoff scales of the four major domestic fishes and the endemic fishes in the upper reaches of the Yangtze River,such as Rhinogobio cylindricus and Leptobotia rubrilabris,were relatively large,while the egg runoff of the other endemic fishes in the upper reaches of the Yangtze River,such as Xenophysogobio boulengeri,Rhinogobio ventralis and Jinshaia sinensis,also has a certain quantitative scale.The flow of Mudong cross-section ranged from 8540 to 29600m~3/s,with an average value of 13749 m~3/s.The water temperature ranged from 18.7 to23.1℃,with an average of 21.0℃.Transparency varied from 24 to 180 cm,with an average of 95 cm.The dissolved oxygen ranged from 3.26 to 8.15μmol/L,with an average of 5.96μmol/L.The p H value ranged from 7.98 to 8.88,with an average of 8.41.There is a positive correlation between these five indicators and water temperature,but it is not obvious,a positive correlation with flow rate,and a negative correlation with dissolved oxygen and transparency.3.Based on the development period,embryo development time and cross-sectional velocity of fish eggs collected from the Mudong section of the main stream,it is estimated that there are 11 fish spawning grounds in the upper reaches of Mudong section,among which there are 5 main spawning grounds,namely Cuntan Bridge spawning grounds,Jialing River Estuary spawning grounds,Egongyan Bridge spawning grounds,Luohuang Town Bridge spawning grounds and jiangjin district Longmen Town spawning grounds.