Species Diversity And Feeding Habits Of Fish Communities In The Rivers Of Chongming

Fish is one of the most widely distributed organisms in water and it plays an important role in the structure and function of ecosystem.Located in the Yangtze estuary,there are many rivers and lakes in Chongming Island,and the fish resources are rich,which provide sufficient fish resources for Chongming and Shanghai urban area,it is a natural breeding nursery for the inland fish resources in Shanghai.It is of great significance for studying the dynamics of fish community and exploring the structure and function of aquatic ecosystem to study the diversity and feeding habits of fish species and analyze the influencing factors.In this study,fixed sample points were set in the Beiheng canal,the Nanheng canal and the vertical canals of Chongming Island.Trawling survey was conducted in June and November in 2018respectively,and supplementary survey was conducted with cage net for four seasons.Water environmental parameters and habitat characteristics were recorded simultaneously.On this basis,the spatial and temporal differences of species diversity in fish communities were analyzed,and the feeding characteristics of the dominant fishes were analyzed by gastric content analysis combined with stable isotopes,and the main factors affecting fish species diversity and feeding habits were discussed.Here were the main research results and conclusions:(1)Composition and distribution of fish community1.The ecotype of fishes in the rivers of Chongming were diverse,similar to the fish community composition in the common rivers,the fish community composition of Chongming was mainly composed of freshwater fishes.However,under the influence of saltwater invasion,there were also brackish water species,which reflected the typical characteristics of freshwater fish composition in the rivers of islands.During the survey,56 fish species were recorded,belonging to 6 orders and13 families.Among them,38 species were recorded in trawl survey and 42 species in cage net survey.2.In the survey of trawl,there were significant differences in fish communities among different rivers,and the difference between different seasons was greater.There was little difference in the dominant species among different rivers,the main dominant species were Carassius auratus,Pseudobrama simoni,Erythroculter ilishaeformis and Coilia ectenes.There were obvious differences in the dominant species among different seasons.In summer,the dominant species were Carassius auratus,Pseudobrama simoni and Erythroculter ilishaeformis;While in autumn,the dominant species were Coilia ectenes and Pseudobrama simoni.The main fishes in summer were larger in size,and the main fishes were mainly composed of small and numerous species in autumn.The characteristics of body length and body weight of Carassius auratus,Erythroculter ilishaeformis and Pseudobrama simoni were significantly higher in autumn than in summer(p<0.05).The characteristics of body length and body weight of the dominant species showed significant differences in the different rivers and different seasons.The body size of fishes in the Beiheng canal was the largest,the Nanheng canal was smaller,and the vertical canals was in between.Coilia ectenes was an important species affecting the composition of fish communities in different seasons.3.In the survey of cage net,freshwater fish was the main ecotype,and benthic fish accounted for about 48%.Ctenogobius giurinus was the common dominant species of four seasons.The number of fish species,abundance and biomass in spring and summer were higher than those in the other two seasons,and the highest was in summer.The abundance and biomass of fish were the highest in the Beiheng canal and the lowest in the Nanheng canal.Similar to the survey of trawl,seasonal differences in the composition of fish species were greater than the differences among different rivers.(2)Feeding habits of the fishes1.The dominant fishes in the rivers of Chongming had a wide range of food sources,mainly fish,aquatic plants and crustaceans.The feeding intensity and food types were obviously different in different seasons and the different rivers.In the different rivers,the proportion of aquatic plants that fish fed on in the Beiheng canal was largest,the feeding intensity of the dominant fishes was the lowest in the Nanheng canal.Among all species,the feeding intensity of Parabramis pekinensis and Pseudobrama simoni was higher than that of other fishes,and their gastric contents were mainly composed of aquatic plants.Among the gastric contents of Erythroculter ilishaeformis and Erythroculter dabryi,fish and crustaceans accounted for the largest proportion;Coilia ectenes fed mainly on crustaceans.2.The range of ?¹³C values of dominant fishes was slightly larger in summer than in autumn,and the?¹³C values gradually increased from the pelagic fishes to the benthic fishes.The range of?¹⁵N values was significantly different in different rivers,the fishes in the Beiheng canal and the vertical canals were about 1.3 trophic levels higher than those in the Nanheng canal.The?¹⁵N values of carnivorous fishes such as Erythroculter dabryi and Coilia ectenes were higher than those of herbivorous fishes such as Parabramis pekinensis and Pseudobrama simoni.Fishes with various feeding habits occupied an important position in the whole community respectively.3.There were microplastics in the digestive system of the dominant fishes,the characteristics were mainly as follows:the abundance of microplastics took in by the omnivorous fishes Carassius auratus was the highest in different seasons.The abundance of microplastics took in by the benthic fishes was higher than that of the pelagic fishes.There was no significant correlation between the amount of microplastics and the body weight and body length of the dominant species(p>0.05).(3)The main factors affecting the species diversity and feeding habits of fishesThere were spatial and temporal differences in various water environmental factors,and they all showed significant correlation with the abundance and biomass of the dominant fishes(p<0.05).Water environmental factors such as pH,dissolved oxygen,conductivity and salinity were mainly responsible for the distribution differences of fish communities in the different rivers.Temperature mainly affected the variation of fish communities in different seasons.In the Nanheng canal,the activities such as shipping and damming disturbed the growth of aquatic organisms,and the feeding habits of the fishes was also affected.The natural habitat of Beiheng canal was intact,the coverage rate of aquatic plants in the Beiheng canal was higher than in other rivers,and the fishes had more food selectivity.However,the land use and pollutant discharge along the Beiheng canal led to changes in water quality in part of the river,and then had an impact on fish communities.Many factors contributed to the differences in composition,distribution and feeding habits of fish communities in the rivers of Chongming.In general,there were significant spatial and temporal differences in fish communities and feeding habits.Regional human activities and habitat characteristics were the key factors affecting the structure of fish communities;And various water environmental factors acted on the fish communities comprehensively.In the future,in the process of human activities and urbanization,the disturbance of human activities to the fish habitat should be minimized.Meanwhile,in order to enhance the integrity of aquatic ecosystem under different disturbances,we should pay attention to the comprehensive effect of water environment factors on aquatic organisms.