Spatio-temporal Dynamics Of Early Fish Resources In Hukou Section Of The Lower Changjiang River And Calculation Of The Four Major Chinese Carps Spawning Grounds

The Changjiang River is the largest river in my country.Its downstream section is from the mouth of the lake to the estuary.The Hukou section refers to the section of the Changjiang River that is about 40 km up and down the Balikou section of the Changjiang River.In braided river more,many of the same river sandbar.Moreover,human activities are disturbed strongly,and there are many factories along the coast,which has caused the water quality of the Changjiang River to be polluted and the ecological pressure on the waters has increased.In order to have a clearer understanding of the current research status of fishery resources in the Changjiang River estuary,historical data from the department and the early period of April to August during the fish breeding period in 2019 were used to investigate and monitor the early resources of the estuary.Through the Index Relative Importance,redundancy analysis and correlation analysis and other data processing methods,the relationship between early fish resource composition,abundance changes in time and space and environmental factors in the estuary section of the lake is analyzed and explored.At the same time,the location and scale of spawning of the four major home fishes in the middle and lower reaches of the Changjiang River are studied.Below are key research findings:1.A total of 246853 larvae and juveniles were collected in 2016,2018 and 2019,belonging to 49 species,14 families and 8 orders.In the past three years,small fishes such as Hemiculter bleekeri and Rhinogobius giurinus are dominant species,while Parabramis pekinensis,Pseudolaubuca sinensis,Xenocypris argentea and Coilia nasus have also changed between dominant and common species in three years.The abundance of larvae and juveniles has fluctuated in the three years.The highest peak of larval and juvenile abundance in 2016 and 2019 appeared at the end of June and early July,and the abundance of larval and juveniles appeared at the end of July in 2018.During the peak period of three years,the three species of fish,H.bleekeri,R.giurinus,and P.pekinensis,dominated the peak period of larvae and juveniles.The horizontal distribution of larval and juvenile abundance during the three years was right bank>left bank>river center.In 2019,a total of 50 days in the four-section joint sampling,it was found that the larval and juvenile abundance changes were as follows:Section 1(Balijiang)>Section 4(Poyang Lake Tongjiang Waterway)>Section 2(Guiying Village)>3 Section No.(Dawan Chau).The first peak period of section 4 occurred earlier than the peak periods of the other three sections.Sections 1,3,and 4 were all larval abundances on both sides of the strait,and section 2 may have larvae and juveniles due to complicated hydrology.The horizontal distribution of abundance is left bank>river center>right bank.Redundant analysis of the correlation between the average daily abundance of larvae and juveniles belonging to the dominant species and common species and environmental factors shows that the average daily abundance of larvae and juveniles and the daily growth rate of water level,the daily growth rate of water flow and turbidity The degree is extremely significantly positively correlated(P<0.01),and is extremely significantly negatively correlated with transparency(P<0.01).2.From April 19 to August 5,2019,the plankton net was used to conduct daily surveys on the 4 sampling sections set up in the Hukou section.In 2019,a total of 589fertilized eggs were collected in the Hukou River section.The molecular identification results found that they belonged to 3 orders,6 families and 30 species,mainly floating egg-producing fish.There were 19 species,a total of 528 eggs,accounting for 89.64%of the total number of eggs.The average density of drifting eggs in the Hukou section is 1.04±1.27 ind./100m~3.During the collection period,there were three peak periods during the rise of river runoff.In the 38-day joint sampling of four sections in 2019,it was found that the three sections had a peak period in late May,and sections 1 and 2had two peak periods in late June and mid-July.The abundance distribution of drifting eggs among the three sections is section 1>section 2>section 3,and the horizontal distribution of fish egg abundance among the three sections is river center>left bank>right bank.Through Pearson correlation analysis of the daily abundance of drifting eggs and environmental factors in the estuary section of the lake,it was found that the daily average abundance of drifting eggs was significantly positively correlated with the daily rising rate of water level and the daily rising rate of water flow(P<0.01),has a very significant negative correlation with transparency(P<0.01),and a significant negative correlation with temperature and p H(P<0.05).3.In this study.We accordingly collected 93 eggs of the four major Chinese carp resources,the majority of which were the eggs of Hypophthalmichthys molitrix,accounting for 80.65%of the total egg numbers.The fertilized eggs collected during the study period were found to be at one of nine stages of development;the majority of them were at the tail bud appearance,blastula,and early gastrula stages,accounting for32.26%,24.73%and 15.05%of the total number of fish eggs,respectively.Taking into consideration the direction of water flow,we inferred that the locations of the spawning grounds of the four carp species were in the vicinity of three river stretches,namely,the Hukou Jiangzhou,Wuxue Longping,and Huanggang Qizhou sections.Moreover,we estimated that the numbers of eggs at the respective spawning grounds were 0.49×10~8,0.68×10~8,and 0.38×10~8ind.Compared with historical data,there were no obvious changes in the locations of these spawning grounds;however,there was a significant reduction in the numbers of eggs at each spawning location.In chronological order,the four major home fish lay eggs in the order of the bottom-up position of the spawning ground.During the study period,the average daily abundance of the four major family fish eggs in the Hukou section was 1.14±2.80 ind./1000 m~3,and there were three peaks during the collection period,all of which occurred during the increase in river runoff.The average density of fish eggs in section 1 was 1.52 ind./1000 m~3,which was significantly higher than that in sections 2(0.88 ind./1000 m~3)and 3(0.43 ind./1000m~3).The results of Pearson correlation analysis indicated that the abundance of eggs of the four carp species was significantly positively correlated with a daily increase in the rate of water flow(P<0.01),and that there was also a significant positive correlation between the daily increase in water flow rate and water velocity(P<0.05).