Study On Temporal-spatio Characteristics Of The Fish Community Diversity In Hechangzhou Section Of The Lower Yangtze River And Its Influencing Factors

With slow-flow water,rich aquatic vegetation and abundant nutrients,the shoal provides an excellent spawning grounds for many fishes producing viscid eggs,and also provides an indispensable feeding ground for almost all fishery larvae.It is the key habitat for maintaining the aquatic biodiversity and sustainable development of fishery resources in the Yangtze River.In order to understand the current status of fish community structure and grasp the ecological environment of fish growth in the lower reaches of the Yangtze River,fish survey using set nets and cages to catch fishing and determination of water environmental factors was carried out in Hechangzhou from November 2016 to October 2017.during the data analysis,we apply the redundancy analysis,percentage analysis of similarity,hierarchical clustering,Pearson test of significance,and multidimensional sorting to analyze the spatial-temporal characteristics of fish community diversity in the waters of the Hechangzhou,and explore the environmental factors which impacts the fish community and dominant species.1.Based on the data analysis of the annual survey about the spatial and temporal characteristics of fish community diversity in Hechangzhou waters,the results showed that a total number of 78 fish species belonging to 57 genera,17 families and 9 orders were collected and identified,the dominant fishes belonging to Cyprinidae account for 57.69% of the species.The number and quantity of catch species were both higher in summer and autumn than in spring and winter;the species of fish located in the habitat of the Yangtze River were higher than those in the harbor,and most fishes appear at site which were not navigable and closer to the beach in the Yangtze River.In various ecological types,the freshwater settled fish,omnivorous fishes and middle and lower fishes were dominant,and the species composition regularity of various ecological types in spatial and temporal are similar,indicating the community structure is relatively stable in Hechangzhou waters.The dominant species are Hypophthalmichthys molitrix,Parabramis pekinensis,Aristichthys nobilis,and Pseudobrama simoni,The important species are Culter alburnus,Ctenopharyngodon idellus,Xenocypris argentea,Carassiusauratus,Coilia macrognatho,Pseudobagrus vachellii.The number and the weight of dominant species and important species accounted for 84.93% and 92.36% respectively,indicating that the ecological dominance of the community was relatively concentrated in the survey.Based on the analysis of the annual catch numbers,the Shannon-wiener index(H')is 2.53,the Pielou's index(E)is 0.21,the Margalef's index(R)is 6.36,and the Dominance index(D)is 0.15,the diversity level is lower than previous years,and shows a certain spatial and temporal difference.The fish specifications are dominated by those below 50 g single tail,and the proportion increased compared with previous years.Cluster analysis based on catch quantity shows that the 12 months were divided into 2 groups at 61.39% similarity levels,1-3 months were group A,the rest of the month was group B;Five points are divided into 2 groups at 75.60% similarity level,class I to III were group X,the other sites were group Y.Indicating that there are certain differences in the spatial and temporal structure of fish community structure in Hechangzhou waters,especially in temporal differences.2.Based on the data from the annual survey,the fish community structure and main influence factors were analyzed by the redundancy analysis(RDA).The results showed that only orthophosphate concentration,water temperature and depth were significantly associated with the fish community.Among them,the correlation between Ctenopharyngodon idellus,Carassiusauratus and orthophosphate concentration,the correlation between Elopichthys bambusa,Hemiculter bleekeri and depth,the correlation between Culter mongolicus,Mylopharyngodon piceus and water temperature,were greatest positive.Besides,the tide also had certain influence on fish community structure,In general,the number of species and quantity of fish of spring tide is more than that of neap tide.3.The analysis results about spatial-temporal characteristics of relative abundance and specifications of the main dominant species showed that the average weight of the Hypophthalmichthys molitrix was 365 g,the minimum and maximum weight was 4.24 g and 4811 g;respectively,the average weight of the Parabramis pekinensis was 63.53 g,the minimum and maximum weight was 0.85 g and 1163 g.respectively,The exponent function analysis showed that the b values the length and weight of Hypophthalmichthys molitrix and Parabramis pekinensis were close to 3,all of which were similar to uniform growth.The results showed that there were spatial and temporal differences in relative abundance of Hypophthalmichthys molitrix and Parabramis pekinensis,and the size of Hypophthalmichthys molitrix was relatively homogeneous than that of Parabramis pekinensis.the Pearson significance analysis showed that all the environmental factors had no significant influence on the tail number of the Hypophthalmichthys molitrix,additionally,among various environmental factors,only the water depth and temperature had a positive correction with the catch number of Parabramis pekinensis.