| In recent years,with the rapid development of industry and agriculture as well as the excessive use of water resources,the water environment and ecosystems have been severely damaged,eutrophication of water bodies has become a major issue urgently to be solved in the current global ecological environment research field.Biofloc technology?BFT?promotes rapid the formation of microbial flocs in aquaculture water by adding organic carbon sources,controlling the appropriate carbon nitrogen ratio?C/N?and continuous aeration,and the conversion of ammonia nitrogen in the water body by microorganisms has become a new breeding technology to increase protein content and feed use.Biofloc technology has the functions of regulating the water environment,improving feed utilization and improving the body's immune capacity.In this study,the indigenous microorganisms in the water body of Yilong Lake were separated and identified,and their water purification ability was experimentally analyzed.The water quality index changes at different C/N levels and the growth status of fingerlings were studied.The ideal conditions for the formation of biofloc systems were explored.The biofloc technology was applied test to the pilot study of lake water quality improvement,and the changes in water quality indicators and the growth of fingerlings were observed and recorded.The purpose is to promote the application of the technology system to the economic and sustainable development of wetlands around Yilong Lake.The main contents are summarized as follows:1.Using 16S rDNA gene sequence analysis to isolate and identify the original microorganisms in the water body of Yilong Lake,more than 85 strains were inoculated.The dominant species are Bacillus cereus?about 24%of the total species?,Rheinheimera mesophila?undetermined,about 17%of the total species?,and Bacillus subtilis?about the total species 7%?.Probiotics Bacillus subtilis?experimental group??,Bacillus licheniformis?experimental group??,Bacillus cereus ?experimental group III?,and three Mixed bacteria?experimental group IV?were placed in the water body.The results show that the pH and DO concentrations were significantly lower than those in the control group?P<0.05?,and the TN,NH3-N,COD,NO3-N,and NO2-N concentrations in each experimental group were significantly lower than those in the control group?P<0.05?.Experimental group?had the best degradation effect on the concentration of TN and COD,which decreased by about15%and 22%compared with the control group.On the 16th day of the experiment,more than 10 bighead carps and silver carps were put into each experimental group and control group respectively.The survival rate of bighead carp and silver carp in experimental group I was 100%,and the mortality rate of bighead carp and silver carp in experimental groups II,III and IV was 75%,80%and 90%,respectively.2.Control the C/N of 15?experimental group??,20?experimental group II?and25?experimental group III?respectively.Culture the bioflocs with molasses as carbon source,and observe the water quality change and the growth of fish species in different treatment groups.On the 19th day of the experiment,bioflocs were basically formed,mainly composed of filamentous bacteria,algae,zooplankton,organic debris,and bacterial communities.There was no significant difference in pH and DO concentration between the control group and each experimental group?P>0.05?.The concentrations of TN,NH3-N,COD and NO2-N in each experimental group were significantly lower than those in the control group?P<0.05?,and the NO3-N concentrations in experimental group I were significantly lower than those in the control group?P<0.05?.The NO3-N concentration of?was not significantly different from that of the control group?P>0.05?.The total solid suspended solids?TSS?of experimental group?was beneficial to the formation of bioflocs and the concentration of water quality indicators.On the 19th day of the experiment,more than 15 catfishes and silver carps were added to each experimental group and control group.The survival rate of the fingerlings in the control group and each experimental group were 100%.The average terminal weight of fingerlings in the control group was significantly higher than that in the experimental groups?P<0.05?,and the fullness of the experimental group?was higher than that in the experimental groups?and??P<0.05?.The specific growth rate of the experimental group?was significantly higher than that of the experimental groups?and??P<0.01?.3.The biofloc technology was applied test in outdoor pilot studies and catfish and silver carp were raised?experimental groups?.The morphological structure of the biofloc in the catfish intestine was observed,mainly filamentous bacteria,algae,zooplankton,organic detritus and protozoa are attached to the surface.During the experiment,the average water temperature of the control group and the experimental group in a day was between 18.6?and 22.6?.The pH and DO concentration of the experimental group were significantly lower than those of the control group?P<0.05?.The experimental group TN,NH3-N,and COD,NO3-N and NO2-N concentrations were significantly lower than those in the control group?P<0.05?.The TSS in the experimental group was significantly higher than that in the control group?P<0.05?.At the beginning of the experiment,more than 40 bigheads and 200 silver carps were injected into the experimental group and control group.The survival rate of bigheads and silver carps in the experimental group and control group were 100%.There was no significant difference in weight,final weight,weight gain rate and fullness?P>0.05?,and the specific growth rate in the control group was significantly higher than that in the experimental group?P<0.05?;The final average weight,weight gain rate and specific growth rate of silver carp in the control group were significantly higher than those in the experimental group?P<0.05?.There was no significant difference between the control group and the experimental group?P>0.05?in fullness. |
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