Present Situation Of Shrimp Community Diversity And Population Characteristics Of Dominant Species In The Lower Reaches Of Yangtze River

Shrimps are an important part of aquatic ecosystem.They can absorb organic matter in water to reduce nutrient load in water and provide food for carnivorous fish.They occupy an important position in the food chain and play an important role in regulating material circulation and energy flow.There is a lack of investigation and research on shrimp status in the mainstream of the Lower Reaches of the Yangtze River A systematic sampling survey on shrimp community in this section will be carried out to grasp the current situation of shrimp community diversity and the population characteristics of dominant species,so as to support the protection of shrimp resources in the Yangtze River Basin and provide basic data for the evaluation of the effect of fishing ban in the Yangtze River basin.This paper mainly consists of two parts.In the first part,shrimp samples were collected from September 2020 to August 2021 in Anqing,Dangtu,Zhenjiang and Changshu of the Lower Reaches of the Yangtze River,and the community parameters,such as species,quantity,biomass and dominant species,were analyzed statistically.Hierarchical clustering analysis and multidimensional scale ordination analysis were used to analyze the similarity and stability of shrimp communities.The second part is the morphological and genetic study of the dominant species Macrobrachium.nipponense.Path analysis and stepwise multiple regression were used to explore the relationship between 22 morphological traits and body weight of Macrobrachium nipponense population in the lower Reaches of the Yangtze River.The population genetics of 480 Macrobrachium nipponense populations from 4 river sections were studied by using d-loop gene sequences of mitochondrial DNA.The main research results of this paper can be summarized as follows:1.A total of 10 species of shrimps were collected,with 34922 shrimps and 62.57kg biomass,respectively.They belong to 6 genera and 3 families respectively,among which the genus Macrobrachium has 5 species at most,and the other 5 genera have 1 species.Two exotic species,Macrobrachium Rosenbergii and Procambarus clarkii,were collected.The results showed that shrimp communities in the lower reaches of the Yangtze River showed obvious spatio-temporal characteristics:The number of species collected in The Anqing River section was 10,and the number and biomass were 17815 and 32.55kg,respectively,which were significantly higher than those in Dangtu,Zhenjiang and Changshu River sections(P<0.05).The main diversity indices(H)and(E)of the four river sections were significantly different(P<0.05).The number of species collected in summer was 9,and the number and biomass were 15748 and 26.23kg,respectively,which were significantly higher than those in spring,autumn and winter(P<0.05),but the main diversity indexes(H)and(D)of the four seasons were not significantly different(P>0.05).2.Gender characteristics.Path analysis was used to calculate the path coefficients and determination coefficients of main morphological traits and body weight of male and female population of Macrobrachium nipponense in the lower reaches of the Yangtze River,and the effects of each trait on body weight were analyzed.The second step length(P2L)had the most direct effect on body weight of male Macrobrachium nipponense population,and the width of head and breastplate(CW)had the most direct effect on body weight of female Macrobrachium nipponense population.Multiple regression equations of male and female population were established as follows:Y♂=-3.688+0.035X1+0.181X2+0.081X3-0.134X4+0.060X5Y♀=-1.899+0.132X1+0.018X2+0.129X3+0.014X43.Spatial characteristics.The second step foot length(P2L)and body weight(W)had the largest direct effect in Anqing,Dangtu and Zhenjiang populations,with diameter coefficients of 0.353,0.481 and 0.368,respectively.The head and chest armor width(CW)and body weight had the largest direct effect in Changshu population,with diameter coefficients of 0.318.The regression equations of population morphological traits to body weight of Macrobrachium nipponense in Anqing,Dangtu,Zhenjiang and Changshu river sections were as follows:Y 安庆=-2.570+0.026X1+0.174X2+0.081X3+0.094X4Y当涂=-3.234+0.044X1+0.241X2+0.080X3-0.174X4-0.105X5Y 镇江=-2.210+0.225X1+0.034X2+0.051X3Y常熟=-1.810+0.186X1+0.022X2+0.141X34.Seasonal characteristics.In summer,autumn and winter,the second step foot length(P2L)had the greatest direct effect on body weight(W),and the path coefficient was 0.419,0.363 and 0.491,respectively.In spring,the whole length(TL)had the greatest direct effect on body weight(W),and the path coefficient was 0.325.The regression equations of population morphological traits to body weight in spring,summer,autumn and winter are as follows:Y春季=-3.357+0.035X1+0.109X2+0.104X3+0.011X4Y 夏季=-3.776+0.035X1+0.083X2+0.153X3-0.245X4+0.070X5Y秋季=-2.162+0.030X1+0.143X2+0.143X3-0.026X4Y 冬季=-2.237+0.05 1X1+0.237X2+0.082X3-0.118X45.Genetic characteristics.The population genetics of 480 Macrobrachium nipponense from 4 populations were studied using mitochondrial DNAD-loop gene sequences,and 938bp sequences were obtained for further analysis.The average haplotype diversity(Hd)and nucleotide diversity(7r)of Macrobrachium nipponense populations were 0.343 and 0.00054,respectively.The average genetic diversity of Macrobrachium nipponense populations was the lowest in Dangtujiang River,and the highest in Zhenjiang River.All populations showed low Hd and low π.AMOVA analysis showed that 74.69%of the genetic variation came from within the population and 25.48%from among the population.Neither the haplotype phylogenetic tree nor the haplotype network diagram showed obvious drainage differentiation.Neutral test and mismatch distribution analysis showed that the population of Macrobrachium nipponense had recently expanded.