Comparative Study On Water Quality,Growth,Immunity And Microbial Community Structure Of Tilapia Cultured In Heterotrophic And Nitrifying Biofloc

1.The effects of two biolfloc culture models on the growth and immunity of tilapiaIn order to study the influence of biofloc on the growth of tilapia seedlings,two types of biofloc breeding models were established,namely group A autotrophic nitrifying bioflocs,and no additional carbon source was added during the entire breeding cycle;group B Heterotrophic bioflocs are added to the aquaculture system with glucose as a carbon source to maintain a carbon/nitrogen ratio of 15.Tilapia seedlings were cultured for 51 days,and their effects on water quality changes,seedling growth,and the effects of seedlings on immune function,digestion and antioxidant capacity were compared.The results showed that the toxic nitrogen compounds in group A and group B were maintained at safe concentrations throughout the breeding cycle.Among them,the concentration of TAN in group A reached a peak of 1.43 mg/L on the third day,and dropped to 0.019 mg/L on the seventh day,and has remained at the lowest level since then.The TAN of group B decreased to 0.045 mg/L on the 5th day.The NO₂^--N in group A reached its peak on the 5th day,and the concentration has been maintained at a low level since then.The concentration of NO₃^--N in group B was always lower than that in group A,and there was a significant difference after the 7th day（P<0.05）.The survival rates of tilapia in group A and group B were（86.67±0.02）%and（88.00±0.04）%,respectively,and there was no significant difference.Feed coefficient（FCR）,terminal weight（FW）,terminal density（FD）and specific growth rate（SGR）were not significantly different（P>0.05）.The average final weight of group B was 17.68%higher than that of group A.At the end of the experiment,the weight gain rates of group A and group B were（424.07±50.93）%and（436.83±57.88）%,respectively,with no significant difference（P>0.05）,but the weight gain rate of group B was greater than that of group A.Generally speaking,the breeding effect of heterotrophic bioflocs is better than that of nitrifying bioflocs.The protease activity of tilapia intestines in group B was 14.02%higher than that in group A,and there was a significant difference（P<0.05）.However,the activities of amylase and lipase in the intestine of tilapia in group A were significantly higher than those in group B（P<0.05）.Lactate dehydrogenase（LDH）,NADP-malate dehydrogenase（MDH）,fructose 1,6bisphosphatase（FDPase）,reduced glutathione（GSH）,and glycerin（MDA）are the antidote to the liver Oxidation indicators,the activities of LDH,MDH,FDPase,and GSH in group B were higher than those in group A（P&0.05）.Among them,the activity of FDPase in group B was 50.39%higher than that in group A.Only the activity of MAD in group A was higher than that in group B（P&0.05）.The serum levels of cortisol（cortisol）,lysozyme（LZM）,immunoglobulin M（lg M）,and peroxidase activity of tilapia in group B were significantly higher than those in group A（P<0.05）.2.Effects of two biofloc culture models on tilapia gut microbesThe number of OTUs obtained by group A and group B in fish intestines were1197 and 1070,respectively.The number of OTUs obtained by group A and group B in the aquaculture water body were 713 and 579,respectively.Among them,the number of unique OTUs in the GA group is 115,accounting for 21.8%of the number of OTUs in the GA group,and the unique number of OTUs in the GB group is 59,accounting for 10.2%of the number of OTUs in the GB group.The number of OTUs shared by the GA group and the GB group is 57,accounting for 8%and 9.8%of the OTUs of the GB group in the GA group,respectively.The GA group and the WA group share 67OTUs,accounting for 9.4%of the GA group OTUs,and the GB group and the WB group share 54 OTUs,accounting for 9.3%of the GB group OTUs.Through principal coordinate analysis（PCo A）based on the Bray-Curtis distance algorithm,you can see the differences in the aquaculture water environment and the composition of the intestinal bacterial community.The analysis shows that the tilapia gut microbial community has a clear division among different culture environments.According to the results of the test annotations,a total of 32 phyla,69 classes,181orders,325 families and 584 genera were detected in all samples in this sequencing.LDA discriminant analysis and distribution.The bacteria in the intestines of tilapia in group A are Desulfovibrio,Chitinophagaceae,and Nocardioides;in group B tilapia intestines are rich There are Micropruina,Propionibacteriales,Propionibacteriaceae,Nakamurellaceae,Nakamurella,Frankiales and so on.Mycobacterium is the most important potential pathogenic bacteria in water and intestines,while Diplorickettsiaceae and Plesiomonas are kept at a low level.Except for Clostridium,other potential pathogenic bacteria such as Aeromonas and Flavobacterium in the water and intestines were higher in the nitrifying group than in the heterotrophic group.3.Study on the effect of two biofloc models on Tilapia liver transcriptomeA total of 35841 expressed genes were detected in this analysis,including 32,640known genes and 3201 new genes;a total of 68,077 expressed transcripts,including54681 known transcripts and 13,396 new transcripts.The effective sequencing amount obtained is 87.73%of the original sequencing amount,and the GC base content range is 49.20%-50.03%.According to the analysis of the KEGG metabolic pathway,the differential genes can be divided into five major categories,namely metabolism,genetic information processing,environmental information processing,cellular processes and biological systems.Among them,the number of genes in the biological system accounts for the largest proportion,reaching 312.Within this category,the immune system contains the most genes（101）,and the rest are the Endocrine system（56）.Digestive system,Nervous system,etc.KEGG PATHWAY enrichment analysis of the genes in the differential gene concentration analysis showed that the KEGG pathway enrichment analysis showed that the differentially expressed genes in the liver of tilapia cultured in heterotrophic bioflocs were mainly enriched in drug metabolism-cytochrome P450,Metabolism of xenobiotics by cytochrome P450,Steroid hormone biosynthesis,etc.