Study On The Reproductive Performance And Changes In Fatty Acid Composition Of Coilia Nasus In The Yangtze River Estuary

Coilia nasus is a species of anadromous migratory fish that lives in estuaries or near the sea.During the breeding season,it enters the Yangtze River from the ocean to reproductive migration.The Yangtze River Estuary has always been considered a channel for the reproductive migration of C.nasus.In early February of each year,a large number of C.nasus gather in groups to form a fishing season,which is most prosperous around the Qingming Festival.It is generally believed that when C.nasus enters the waters of the Yangtze River Estuary,its gonadal development stage is still in stage II.However,this study conducted a survey and sampling of the population of C.nasus migrating to the Yangtze River Estuary from April to June 2021.The population composition of C.nasus during the breeding period in the Yangtze River Estuary was analyzed,and it was found that the ovarian development stages of C.nasus in the Yangtze River Estuary waters were distributed between stages II to V.Among them,the breeding population of the first cichlid fish to migrate to the Yangtze River Estuary is mainly composed of large-sized female individuals with gonadal development to stage II.Afterwards,it needs to undergo a long upward migration process and breed at the spawning ground after the gonadal development is mature.The individual size of C.nasus that later migrated to the Yangtze River Estuary is relatively small,but its gonads are more mature.After passing through the Yangtze River Estuary,it can migrate for a short time to a spawning ground closer to the mouth for breeding.In summary,the size and gonadal maturity of the breeding population of C.nasus migrating to the Yangtze River Estuary at different times are consistent with their position and migration patterns.Through the analysis of the sex body index,condition factors and fecundity of the breeding population of C.nasus migrating to the Yangtze River Estuary,it is found that their reproductive performance and health status are good.This study selected wild female reproductive period C.nasus from the natural waters of the Yangtze River Estuary as the research object.The fat content and fatty acid composition in its muscles,liver,and ovaries were measured using national standard methods,and the differences in corresponding components among the three tissues were analyzed.The results showed that the fat,PUFA,EPA,DHA,n3-PUFA content,as well as UFA/SFA,n3-PUFA/n6-PUFA ratio,were the highest in the ovaries during the reproductive period of C.nasus.The distribution patterns of corresponding components between different tissues were closely related to the reproductive habits of female adult C.nasus during that period.The accumulation of rich lipids and reasonable essential fatty acid nutrition in the ovaries can improve the reproductive performance of C.nasus during that period,and provide sufficient nutrition and energy for the later development of eggs and larvae.Due to the fact that the essential fatty acids of fish can only be obtained from their diet through feeding,it is necessary to obtain the necessary nutrients such as fatty acids through feeding on external bait.In this study,the fatty acid composition and changes in fatty acid content of different tissues during the development process of the breeding population of C.nasus were analyzed.The research results can lay a foundation for further exploring the relationship between ovarian fatty acid content at different developmental stages and its relationship with gonadal development and egg quality.The relevant data can enrich the knowledge of the breeding biology of C.nasus and provide theoretical guidance for the protection of the breeding population in the Yangtze River Estuary.In order to find out the source of fatty acids in the breeding population of C.nasus in the Yangtze River Estuary,this study analyzed the food species contained in the stomach of C.nasus,used high-throughput sequencing as an auxiliary means to identify the food species,and preliminarily explored the feeding habits of C.nasus during the breeding period in the Yangtze River Estuary.Research has found that the diet of C.nasus includes fish such as juvenile C.nasus,Odontamblyopus rubicundus,Hemiculler leucisculus,as well as shrimp such as Macrobrachium nipponense and Exopalaemon annandalei,indicating that the main diet for the breeding population of C.nasus is juvenile fish and shrimp.During its migration process,it will choose nearby bait organisms distributed in the waters of the Yangtze River Estuary.The abundant bait organisms in the Yangtze River Estuary can meet the energy required for the spawning and reproduction of C.nasus.In summary,this study investigated the reproductive performance of C.nasus in the Yangtze River Estuary and explored the reproductive potential of the population.It was found that the size and gonadal maturity of C.nasus that migrated to the Yangtze River Estuary at different times were closely related to their position and migration patterns.The good reproductive performance and health status of the C.nasus in the Yangtze River Estuary also reflect that its energy needs during migration can be well met.Due to the fact that the level of fatty acids in the parent fish is a key factor affecting their reproductive performance,this study analyzed the fatty acid composition of the breeding population of C.nasus and found that the ovaries can accumulate rich lipids and reasonable essential fatty acid nutrients,which is an adaptation to the reproductive activities of C.nasus during the breeding period.In addition,in order to explore the source of fatty acids in the breeding population of C.nasus,this study also conducted a preliminary exploration of the feed composition of the breeding population of C.nasusa in the Yangtze River Estuary.The results indicate that during the migration process,the breeding population of C.nasus will choose young fish and shrimp distributed in the nearby waters of the Yangtze River Estuary for feeding,and the abundant feed organisms in the Yangtze River Estuary can meet the energy requirements for its spawning and reproduction.Overall,this study has explored the reproductive performance and changes in fatty acid composition of C.nasus,providing theoretical guidance for protecting the breeding population and thus protecting C.nasus resources.