Ecological Study Of Large-size Yangtze River System Chinese Mitten Crab In Ningxia

Ningxia’s yellow irrigation area is an important national production base for integrated rice-crab co-culture,with a total pond farming area of 216,000 mu in Yinchuan City in 2016,of which 32,000 mu is for rice-crab co-culture,ranking first in the northwest.The national 13th Five-Year Plan is promoting effective rice-fishery co-culture models across the country,and a variety of rice-fishery production models such as rice-shrimp co-culture（Qianjiang’s"shrimp-rice co-culture"）and rice-crab co-culture（Liaoning Panjin’s rice-crab co-culture model）have emerged nationwide.But how does Ningxia,there is an urgent need to adopt a new form of agriculture to achieve integrated ecological and economic benefits.One of the reasons limiting the development of crab industry in Ningxia area is the crab fry,which has problems such as late introduction of fry,low survival rate,small size of adult crab and poor fertility in the breeding process.The lack of suitable hydrophytes,excessive feeding,and too close spacing of rice are the current situation of the culture environment of the river crab industry in Ningxia.In this study,we investigated the growth performance of Chinese mitten crab in Ningxia in the rice crab symbiosis mode and pond culture mode,analyzed the most optimal species of river crab suitable for cultivation in Ningxia,and analyze the carapace morphology using the landmark point method to provide theoretical reference for the artificial selection and breeding of Chinese mitten crab,analyze the microbial community structure in water bodies of different aquatic grass culture modes provides a reference for improving the culture environment of paddy fields and ponds.The study provides a reference for the ecological study of Chinese mitten crab culture in Ningxia region.1.In terms of selection and breeding,the correlation analysis showed that each trait of Jinyuan crab,Shuiyang crab and Noah crab showed highly significant correlation（P<0.01）.The correlation coefficients were r_1y>r_2y>r_3y for Jinyuan crab,r_1y=r_2y>r_3y for Shuiyang crab,and r_2y>r_1y>r_3y for Noah crab,all of which were positively correlated.Path analysis showed that carapace length had the greatest direct effect on body weight of Jinyuan crab and Shuiyang crab,and carapace width had the greatest direct effect on body weight of Noah crab.Carapace length and carapace width were the key traits affecting body mass.The multiple regression equations established by stepwise linear regression were Y _Jinyuan=-76.845+2.094X₁+0.827X₂,Y _Shuiyang=-64.218+1.374X₁+1.489X₂,and Y _Noah=-117.958+3.051 X₂-1.478X₃.From the coefficients of the regression equations fitted linearly for carapace length and carapace width,it was obtained that both the shell length/shell width were close to 1.The carapace of Jinyuan crab was closer to square than the other two crabs.The results of the grid deformation diagram showed that the morphological features that differed among the three groups were mainly the lateral teeth of the carapace,the M-shaped pattern and the position of the concave point on the posterior lateral margin.The carapace of the artificially selected Chinese mitten crab was wider,and the carapace of the Jinyuan crab was wider than that of the other two selected Chinese mitten crabs.The width of the carapace of Chinese mitten crab may be a reliable selection indicator.2.The relationship between body mass,carapace length and carapace width was a power function with the curvilinear regression equation y=ax^b;the relationship between carapace length and carapace width was a linear function with the curvilinear regression equation y=cx+d.In the rice-crab co-culture model in 2021,the average body mass of Noah crab was higher than that of other crab species.The average body mass of Noah crab was highest in the growth cycle of June-September,and the growth rates of both Noah male and female crabs in August-September were higher than those of other crab species.The specific growth rates of both male and female crabs of Liao crab were higher in June-August.The gonadosomatic index of female crabs was higher than that of male crabs in both Yangtze River system and Liaohe River system,and the hepatosomatic index of female crabs was higher than that of male crabs,and the gonadosomatic index of Noah’s crab was the highest.In the rice-crab co-culture model in 2022,from July-September,the average body mass of Nicha crab increased significantly than Noah crab.the gonadosomatic index and hepatosomatic index of female crabs were higher than that of male crabs in Liaohe River system,and the gonadosomatic index of male crabs was the highest at 2.25%,the gonadosomatic index of female crabs was the highest at 5.57%.The highest hepatosomatic index of male crabs was 7.95%and 9.57%in female crabs.The fertility of male crabs in the Liaoning River system was higher than that of female crabs,and the fertility of male and female crabs could reach 0.8 and 0.75,respectively.In 2022 in the pond finishing mode,the weight gain rate and specific growth rate of Nicha crab males in July-September were greater than those of Noah crab males.The gonadosomatic index and hepatosomatic index of both Nicha crab males and females were higher than those of Noah crab,and the gonadosomatic index of Nicha crab males and females were 3.26%and 1.52%,and the hepatopancreas index was 9.94%and 8.8%.The gonadosomatic index of Noah crab was 1.85%and 1.28%for male and female,and the hepatopancreas index was 7.88%and 6.08%.The Noah crab of the Yangtze River system or Liao crab can be selected in the rice-crab co-culture mode,and the Nicha crab of the Yangtze River system can be selected in the pond culture mode.3.Illumina Miseq high-throughput sequencing technology was used to study the differences in microbial community structure of the aquaculture environment in the rice-crab co-culture and pond finishing in the aquatic plant culture mode,the non-aquatic plant culture mode and the aquatic plant fertilization culture mode,respectively.The result of the study showed that the microbial community diversity in the water column of the aquatic plant mode was lower than that of the non-aquatic plant mode.The dominant phyla of microbial community in the water column of both models were similar.The higher relative abundance of microorganisms in the water column in the phylum were Proteobacteria,Actinomycetes,Firmicutes,Bacteroidetes,Cyanobacteria and Verrucobacteria.The dominant microbial genera in the water column of the aquatic plant culture model were Acinetobacter,Domibacillus,hgcl＿clade and Exiguobacterium.The dominant microbial genera in the water column in non-aquatic plant culture mode were Domibacillus,Exiguobacterium and hgcl＿clade.The abundance of Proteobacteria in the aquatic plant culture mode was significantly higher than non-aquatic plant culture mode in the phylum（P<0.05）.The phylum whose abundance was highly significantly higher in the non-aquatic plant culture mode than aquatic plant culture mode were Cyanobacteria and Verrucomicrobiota.In the pond finishing mode,the diversity of the water column microbial community was lower in the aquatic plant culture mode than non-aquatic plant culture mode,and the community species richness was higher.At the genus level,the higher relative abundance of microorganisms in the water column in the aquatic plant culture was Hydrogenophaga,Polynucleobacter and Mycobacterium.The higher relative abundance of microorganisms in the water column under the non-aquatic plant mode was Cyanobium＿PCC-6307,Acinetobacter and Mycobacterium.The results of the significance test for differences between groups showed that there were no significant differences in species between the two culture modes.The water quality analysis showed that the content of ammonia nitrogen,phosphate and nitrite in the water was reduced after the aquatic plant fertilization recirculation aquaculture system.The results of microbial community diversity analysis in the water column of the aquatic plant fertilization culture mode showed that the Actinobacteriota was the dominant phylum in the pond water column and the Proteobacteria was the dominant phylum in the ring ditch water column.The dominant genus in the ring ditch water body was Acinetobacter,the dominant genus in the water body of the aquatic plant fertilization pond was Cyanobium＿PCC-6307,and the dominant genus in the water body of the aquatic plant yellow river water was undefined Pe M15.The results of the significance test for differences between groups indicated that there was no significant difference in species between the aquatic plant fertilization pond and the aquatic plant yellow river water culture pond.Salinity explained a high degree of community variation and was the main environmental driver of community variation in the water body factors.The insignificant effect of temperature on the microbial community in the water column may be due to the small size of the test ponds and paddy culture water column.