Study On The Application Of Biofloc System In Shrimp Culture

Bioflocs technology(BFT)is a new technology that has the effect of reducing feed coefficients,increasing the survival rate of farm animals,reducing feed costs and reducing environmental pollution.Bioflocs technology was developed on the basis of zero-water-exchange farming technology and activated sludge water treatment technology.The application of bioflocs technology to practical aquaculture is not yet mature and more research is needed.In this paper,we investigated the application effects of bioflocs systems in shrimp farming under different environments and the dynamic changes in microbial community structure and function of the farming system.The main results are as follows.1.Construction of bioflocs shrimp farming system.The pond size was 3.0 m×4.0 m,and the depth of the water was 1.0 m.The bioflocs system was constructed by inoculating the bioflocs and adding nitrogen and carbon sources to the water.Biological flocculation systems The ammonia nitrogen in the water of the shrimp farming system was 0.02±0.005 mg/L,nitrite nitrogen was 0.11±0.046 mg/L,and nitrate nitrogen was 0.25±0.083 mg/L,the water quality was stable.The results indicated that the nitrogen conversion effect in the constructed bioflocs system was stable and the concentration of trinitrogen decreased to a lower level,which could be used for shrimp culture.2.The bioflocs shrimp culture system was used to culture Japanese sac shrimp(Marsupenaeus japonicus)and compare the differences between the semi-closed culture model(the control group)and the bioflocs culture model(the experimental group).The results show that the concentration of ammonia nitrogen in the experimental group reached the maximum(2.99 mg/L)on day 5,and it reached a maximum(7.51 mg/L)in the control group on day 9.The results of high-throughput sequencing showed that a total of 549 genera in 23 phylum of microorganisms were identified in the bioflocs system.At the phylum level,the relative abundance of Proteobacteria decreased with increasing time(from 67.72% to 44.45%)and Bacteroidetes and Chloroflexi increased with increasing time(from 5.99% and 6.68% to 16.06% and 19.02% respectively).The results indicated that the bioflocs system had a significant ability to eliminate ammonia nitrogen and nitrite nitrogen,and the rate of nitrogen conversion was higher in the experimental group than in the control group.Aqueous flora in cultured stable Bioflocs systems showed a decrease in diversity and an increase in abundance,and the key genera involved in nitrogen conversion had significant changes in flora at different times.3.The bioflocs shrimp culture system was used to culture M.japonicus and investigate the efficiency and stability of nitrogen conversion in the biofloc system during abrupt temperature changes.The results show that there was no significant effect of abrupt temperature changes on the nitrogen conversion pathway in the biofloc system during the experiments,and the nitrate nitrogen in the experimental group showed an increase after abrupt temperature change,from 19.65 mg/L at experiment 5 d(before abrupt temperature changes)to 31.54 mg/L at experiment 10 d(after abrupt temperature changes),and the cumulative rate was greater in the experimental group than in the control group.High-throughput sequencing revealed that a total of 4219 OTUs were obtained in both experimental and control aqueous organisms.The abundance and diversity indices were greater in the experimental group than in the control group,and greater before than after abrupt temperature changes.Microbial communities in the water and gut after temperature mutation were lower in abundance and diversity than before abrupt temperature changes.Bioflocs systems performed better than semi-closed culture systems in coping with abrupt temperature changes,with higher stability in both abundance and diversity of microbial communities.4.In this study,The bioflocs shrimp culture system was used to culture Litopenaeus vannamei under different salinity conditions and investigate the effects of salinity on the Bioflocs system and shrimp growth.The results showed that the body mass growth rates were largest(70.73 %)in the salinity 15 group and the salinity 20 group.The total alkalinity and p H in the water decreased continuously during the experiment.The higher the salinity,the faster the ammonia nitrogen accumulation.The ammonia nitrogen concentration in the salinity 30 group reached a maximum(8.62 mg/L)at day 6,which in the other groups showed the same trend changes.High throughput sequencing showed that the relative abundance of Chloroflexi decreased with increasing salinity(from 11.3% to 3.5%)at the phylum level,and the relative abundance of Actinobacteria increased with increasing salinity(from 4.4% to 6.6%).The rate of generation and the rate of removal of nitrite nitrogen at lower salinities were higher than those at higher salinities,however,the desired results were achieved.Later in the experiment,as the salinity increased,the significant functional classification of the flora increased,and the abundance of functions also increased.At the same time,however,there were no significant differences in the performance of bioflocculent colony diversity and abundance differences,and the key genera involved in nitrogen conversion were not significantly different at different salinities.In this paper,the changes in water quality,microbial community,shrimp growth and physiology in the biofloc farming system were studied by constructing a biofloc farming system for shrimp,and the results show that the biofloc system can improve the water quality of the shrimp farming system and optimize the microbial community in the farmed water body,which has great potential for application in aquaculture production and provides a reference for the promotion of the biofloc seawater culture model for shrimp.