Construction And Regulation Of Culturing Tilapia(Oreochromis Niloticus) Aquaculture Systems With Algal-bacterial Biofloc Technology

With the shortage of land resources and serious pollution of farming environment in recent years,high-density intensive farming is increasingly sought after by the aquaculture industry.Biofloc technology（BFT）has become a new research hotspot with high breeding density,improved protein utilization efficiency,and enhanced immunity of cultured subjects.However,it is mainly used in factory farming.It is dominated by bacteria and rarely used in sunlight,that is algae coexisting biofloc culture system.This paper mainly explores the construction and regulation of tilapia（Oreochromis niloticus）algal-bacterial biofloc technology from the following three parts.1.Preliminary study of culturing tilapia（Oreochromis niloticus）with algal-bacterial biofloc technologyIn order to explore the establishment of an efficient and economical tilapiacoexisting biofloc culture system,an algal coexisting biofloc（experimental group）and a whole-bacterial biofloc（control group）were used to culture tilapia（GIFT,Oreochromis niloticus）114 d,by studying water quality,growth and non-specific immunity in culture systems.The experimental group provided light,the intensity was（9056.67±89.63）lx,the circadian rhythm was 12L:12D;the control group had no light.After data analysis,the chlorophyll a in the experimental group was significantly higher than that in the control group（P<0.05）,and the concentrations of TAN and NO₂^--N were suitable for the growth of tilapia.The nitrate NO₃^--N in the experimental group was lower than that in the control group and higher in the later stage than in the control group.The experimental group of PO₄^3--P and TSS were lower than the control group.Survival rate,feed coefficient,final mass,terminal density,weight gain,protein efficiency and specific growth rate of the experimental group tilapia There was no significant difference from the control group（P>0.05）.However,the phenomenon of algal extinction occurred in the experimental group.During this period,except for serum alkaline phosphatase activity and hepatic pancreatic lysozyme were significantly lower than the control group（P<0.05）.There was no difference in serum total superoxide dismutase,LZM and AKP and T-SOD in hepatopancreas compared with the control group（P>0.05）.In the 16S rDNA analysis results,the experimental group and the control group were significantly higher in the early stage than in the control group（P<0.05）,both at the level of the door and at the level of the control group,and the latter were all Chloroflexi.Mainly,the experimental group Cyanobacteria showed a trend of more first and then less;in the analysis of 18S rDNA results,the experimental group Chloroplastida increased first and then decreased,Gastrotricha and rotifers increased significantly,while the control group had no algae.The results show that the algal coexisting biofloc culture system is beneficial to control water quality,inhibit the growth of cyanobacteria,reduce feed cost,and is suitable for tilapia growth.2.Effects of different concentrations of algal-bacterial biofloc technology on cultured tilapiaIn this experiment,four groups of TSS different concentration gradient algae coexisting bioflocs were established,which were group A（TSS 200-300）mg/L,group B（TSS 300-500）mg/L,group C（TSS 500-700）mg/L and group D（TSS not adjusted）,explore the effects of different TSS algae coexisting bioflocs on cultured tilapia,and screen the optimal growth concentration.The results showed that the water quality was unstable due to long-term regulation of TSS in group A.The average NO₂^--N was（1.34±0.91）mg/L,which was significantly higher than other groups（P<0.05）.Groups C and D of TAN and NO₂^--N are very stable.At the end of the experiment,the concentrations of NO₃^--N in the four groups were accumulated to（202.82±45.05）mg/L,（241.20±175.35）mg/L,（266.42±200.43）mg/L,and（292.88±232.47）mg/L,respectively.At the end of the experiment,the serum levels of AKP,T-SOD,LZM,T-SOD and AKP in the head and kidney were significantly higher in the B group than in the other groups（P<0.05）.In summary,TSS has stable water quality in（300-500）mg/L,TAN is less than 0.1 mg/L,and NO₂^--N is lower than 1 mg/L,which is beneficial to tilapia LZM,AKP and T-SOD.Increased specific immune activity enhances the resistance of tilapia.3.Study on the removal rate of TAN and NO₂^--N by algal-bacterial biofloc technologyIn this experiment,based on the experimental two TSS（500-700）mg/L algaecoexisting biofloc group,the light group（L）,the dark group（D）and the bacterial predator group（AC）were separately investigated for TAN,The removal rate of NO₂^--N.The results showed that in the TAN removal rate experiment,the initial TAN concentration was 10 mg/L,and the AC group removal rate was（1.03±0.07）mg/（L·h）,which was significantly higher than that of L group and D group（P<0.05）,eventually decreased to（3.52±0.25）mg/L after 12 hours,followed by L group（4.63±1.04）mg/L,D group（6.07±0.48）mg/L,NO₃^--N The concentration was significantly lower in the L group than in the other groups.In the NO₂^--N removal rate experiment,the initial NO₂^--N concentration was 10 mg/L,and there was no significant difference in the removal rate of the three groups,but the AC group was higher than the other groups,and eventually fell to（5.17±0.46）mg/L,followed by L group decreased to（5.88±1.02）mg/L,D group decreased to（5.18±0.45）mg/L,NO₃^--N concentration was significantly lower in the L group than the other groups.Microbial community structure was sequenced by high-throughput.In the 16S rDNA analysis results,there was no significant difference in the structure of the three groups of bacteria;in the 18S rDNA analysis results,the rotifers in the AC group were significantly higher than the other groups.The results showed that the same concentration of TAN and NO₂^--N were placed in the culture environment.The removal rate of TAN and NO₂^--N in the AC group was the highest,that is,the removal of some bacterial predators at an appropriate degree was beneficial to the growth of bacteria and had a positive impact on the purification of water.And it proves that the algal symbiotic nitrifying biofloc system can optimize the water quality.