A Preliminary Study On The Early Resource Dynamics And Utilization Of Different Types Of Habitats In The Hejiang Section Of The Yangtze River

In the early life history of fish,habitat environment is a crucial factor affects the feeding,growth,development and survival.As the largest river in China,the Yangtze River is rich in natural resources.However,the construction of projects such as hydroelectric terracing has significantly altered the water flow environment and aquatic habitats in the adjacent waters,so habitat restoration is a major challenge of the Yangtze River.A survey was conducted during the 2021-2022 peak fish breeding season in different habitat types(floodplain:Baita,steep riverbank:Guchuanshi,estuarine area:Hekou:intersection of Chishui River)to understand the dynamics of fish early-stage resources in different types of habitats.The study focused on the dominant species,Rhinogobius cliffordpopei,and carried out feeding and growth analyses of individuals in early life history stages in different types of habitats.The research provides crucial data for understanding the use of different types of habitats and their influencing factors during the early life history stages of fish in the upper reaches of the Yangtze River.It has significant theoretical implications.At the same time,the key factors affecting the early survival and habitat distribution of fish are determined,which can provide targeted measures and suggestions for riverine fish habitat restoration.The main results are as follows:1.In the two years of resource survey,57 taxa of larvae and 23 species of eggs were monitored in the Hegiang section of the Yangtze River,including 18 species of endemic fish.Larvae densities in 2021 were 17.78±19.42ind./1000m~3,14.39±12.88ind./1000m~3 and 8.47±7.95 ind./1000m~3 in estuaries,floodplain and steep river banks respectively,The number of larvae species was 27,19and 21,of which the number of endemic fish species was 4,5 and 4,respectively;in2022,Larvae densities in the three habitats of the estuary,floodplain and steep river banks were 33.28±100.8 ind./1000m~3,21.76±50.73 ind./1000m~3,13.59±26 ind.1000m~3,13.59±26.12 ind./1000m~3;the number of larvae species were 33,47 and 37respectively,among which the number of endemic fish species were 7,11 and 9respectively.The results show that the Hejiang section is an important distribution area for fish eggs and larvae,providing spawning environment for a variety of endemic fish species and satisfying the nursery needs of many fish species;habitat protection in the early stages of fish in the Hejiang section is particularly important,especially for the habitat protection of floodplain and estuarine area.2.Correlation analysis of the density of smolts collected at the three sampling sites in 2021 and 2022 with environmental factors showed that there was a strong correlation between larvae density,number of species and environmental factors at the three sites.ANOSIM similarity analysis between the two years of sampling showed a significant effect of location on larvae aggregation(Global R=0.143,p<0.05),while there were no significant differences in aggregation structure between the two years at the same sites(p=0.431 for estuaries,p=0.84 for rocks,and p=0.08 for steep banks).The main species responsible for differences in the aggregation of pupfish between habitat types were all broadly adapted fish,including the genus Rhinogobius spp.,Neosalanx taihuensis and Pseudolaubuca sinensis.It can be concluded that environmental changes between the two years had little effect on the aggregation of larvae,and the habitat had a greater influence on the aggregation structure of larvae,which was the main factor affecting the aggregation structure.3.Both the Baita and Guchuanshi gobies are mostly made up by the Rhinogobius cliffordpopei.The developmental process of early Porites gobies was divided into four developmental periods:yolk sac stage,anal fin development,ventral fin development and juvenile stage.In the yolk sac stage,the age range was 2-11 days old,with an average body length of 3.7±0.54mm;the age range from anal fin development to ventral fin emergence was 9-22 days old,with an average body length of 5.49±0.72mm.In the early stage,the feeding of the Rhinogobius is mainly on cladoceran first,and as larvae develop,they gradually feed on larger species like copepods and Chironomus riparius.