Effects Of Different Densities Of Macrobrachium Rosenbergii On Water Quality,Growth Performance,Nutritional Flavor,Intestinal Microflora Of Chinese Mitten Crab(Eriocheir Sinensis)Ponds

In recent years,the consumption scale of crab has increased continuously.The market prospect is good.At present,there are some shortcomings in the pond culture of crab,such as high risk of single breed breeding,low utilization rate of water,high bait coefficient,fragile pond ecosystem and easy eutrophication.These lead to the problems of "high yield but no harvest" and low breeding efficiency,and hinder the healthy development of crab industry.The nesting mode of crab has many advantages,such as mutually beneficial coexistence of organisms,growth of breeding varieties,improvement of ecological environment and avoidance of market risks.In recent years,the model of crab nesting with Macrobrachium rosenbergii had received more and more attention.However,the aquaculture model is still a summary of production experience and lack of systematic research.Density is the main factor affecting the growth,survival and yield of crustaceans.Density is the key to success in the culture of crab nesting with Macrobrachium rosenbergii.In order to explore the appropriate density in the model of crab nesting with Macrobrachium rosenbergii,we set three low,medium and high density groups.We analyze the effects of different density on pond water environment,intestinal flora,growth performance,antioxidant capacity and nutritional quality of cultured objects.These results are as follows:1.Effects of different densities of Macrobrachium rosenbergii on pond water environment and intestinal microfloraWe collected water samples three times at different molting stages of crab.Water quality experimental indexes include temperature,dissolved oxygen,ammonia nitrogen,nitrite,total nitrogen and total phosphorus.They were determined in the three groups.At the beginning of nesting,the contents of ammonia nitrogen and nitrite nitrogen in the medium and high density groups were significantly higher than those in the low density group,while the contents of total nitrogen and total phosphorus in the medium and high density groups were lower than those in the low density group.At the middle stage of interbreeding(July),there were no significant differences in other indexes among the three groups.The nitrite nitrogen content in medium density group was significantly lower than that in other groups(P < 0.05).In the later stage(October),the content of nitrite nitrogen in the medium and high density groups was significantly lower than that in the low density group.The content of total phosphorus was higher than that in the low density group.On the whole,the water quality indexes were all in the range suitable for the growth of crab.In this study,We used 16 Sr DNA sequencing technology to analyze the water and intestinal microflora.We found that Proteobacteria and Firmicutes were the dominant phyla in the water and intestinal microorganisms of crab among the three density groups.At the genus level,the dominant genera were Exiguobacterium and Acinetobacter.Candidatus Bacilloplasma was the dominant bacterium in the three density groups of intestinal microorganisms of crab.In the correlation analysis of water microflora and water quality indexes,nitrite nitrogen and total nitrogen were the main controlling factors of community composition difference.In the analysis of intestinal microbial function prediction,the three density groups were consistent in 45 functional prediction analyses,such as cytoskeletal structure,immune mechanism,RNA processing and modification,and energy conversion.2.Effects of nesting Macrobrachium rosenbergii with different densities on growth and antioxidant capacity of Chinese Mitten crabThe results of growth indexes showed that the body weight and Carapace length of female and male crabs in high density group were significantly higher than those in other groups(P < 0.05).In terms of economic benefits,the medium density group had the highest total output value.The total profit of medium density group was significantly higher than that of low density group(P < 0.05).It was 32% higher than the low density group and 24% higher than the high density group.When the density of Macrobrachium rosenbergii was the medium group,the pond culture efficiency was the highest.The results of antioxidant capacity showed that the contents of superoxide dismutase and total antioxidant capacity of female crabs in medium density group were significantly higher than those in other groups(P < 0.05)at the early stage of nesting(June),and the contents of superoxide dismutase of female crabs in medium density group decreased with the increase of nesting time.The contents of glutathione peroxidase and phenol oxidase in medium density group were lower than those in high density group(P < 0.05).At the end of nesting(October),the catalase activity of female crabs in medium density group was significantly lower than that in low density group(P < 0.05).Compared with the early stage of nesting(June),the catalase activity of female crabs in the three density groups showed an increasing trend.There was no significant difference in malondialdehyde content among all density groups in the whole nesting time(P > 0.05).There were no significant differences in the contents of catalase,glutathione peroxidase,total antioxidant capacity and phenol oxidase of male crabs in the three density groups during the whole nesting time(P > 0.05),but the content of superoxide dismutase of male crabs in medium density group decreased gradually with the increase of nesting time.The malondialdehyde content of male crabs in medium density group was lower than that in low density group(P < 0.05)at the metaphase of nesting(July).In conclusion,in terms of oxidative stress,the antioxidant capacity of crab in the three density groups fluctuated with the change of nesting density and time.3.Effects of different densities of Macrobrachium rosenbergii on nutritional quality of Chinese Mitten crabThere were no significant changes in the four basic nutrients(crude fat,crude protein,moisture and ash)of female crabs(P > 0.05).The stearic acid in medium density group was significantly higher than that in high density group(P < 0.05).The polyunsaturated fatty acid content in medium density group was significantly higher than that in other groups(P < 0.05),and the docosahexaenoic acid content in medium density group was significantly higher than that in low density group(P < 0.05).The myristic acid content of male crab medium density group was significantly higher than that of high density group(P < 0.05).The contents of erucic acid and methyl octadecadienoate in medium density group were the highest and significantly different from those in other groups(P < 0.05).In addition,the contents of eicosapentaenoic acid and docosahexaenoic acid in medium density group of male crab were higher than those in high density group,but the difference was not significant(P > 0.05).The contents of polyunsaturated fatty acids,methyl octadecadienoate,eicosapentaenoic acid and docosahexaenoic acid were higher in the medium density group of male and female crabs.The contents of aspartic acid and glutamate in female crab medium density group were significantly higher than those in low density group(P < 0.05).These amino acids fluctuated in male crabs with different densities of Macrobrachium rosenbergii.The content of inosinic acid in medium density group was higher than that in other groups(P > 0.05),which indicated that rearing medium density Macrobrackum rosenbergii could improve the umami flavor of crab.In conclusion,different densities of Macrobrachium rosenbergii cultured had certain effects on the growth,antioxidant enzyme activity,nutritional flavor quality,water and intestinal microorganisms of crab.Considering the growth and economic benefits comprehensively,the total output value and the total benefit of medium density enculturated Macrobrachium rosenbergii ponds were the largest.