Effects Of Enriched Nitrifying Bacteria On The Growth,Immunity And Cultivation Water Body Of Sea Cucumber

The aquaculture scale of aquatic products in China has been the first in the world for many years.The high-density and intensive aquaculture mode is easy to cause problems such as pollution of aquaculture water and frequent disease.Nitrifying bacteria has advantages in the treatment of aquaculture wastewater,and its viable agents have achieved positive results in aquaculture.In this study,enrichment medium was used to obtain enriched nitrifying bacteria by controlling the concentration of NH₄⁺in the growth environment of nitrifying bacteria.Objective to explore the nitrification ability of nitrifying bacteria enriched bacterial solution,its water purification ability on artificial sewage and aquaculture water body,the growth of sea cucumber,aquaculture water body and intestinal flora and immune function.Firstly,after 90 days of enrichment,the enrichment solution of nitrifying bacteria with relatively stable flora structure was obtained.The enriched nitrifying bacteria were sequenced by high-throughput sequencing,and the composition of their flora was analyzed.After domestication and enrichment,the dominant bacteria in the enriched solution of nitrifying bacteria were Proteobacteria at phylum level,and Pseudomonas at genus level.The concentration of nitrite in fresh water medium was0.028 mg/ml,and that in seawater medium was 0.026 mg/ml.The initial ammonia nitrogen content of artificial seawater wastewater and artificial fresh water wastewater were 3.59 g/L and 3.51 g/L respectively,which were reduced to 1.16 g/L and 1.62g/L respectively after adding nitrifying bacteria.The ammonia nitrogen content of EG and CG was 0.17 mg/L and 0.39 mg/L respectively.In sea cucumber culture water,the initial chemical oxygen demand of control group（CG）and experimental group（EG）was 0.60 mg/L and 0.70 mg/L respectively.After 5 days,the chemical oxygen demand of control group（CG）and experimental group（EG）was 3.53 mg/L and 2.25 mg/L respectively.The enrichment solution of nitrifying bacteria can promote the growth of Apostichopus japonicus.After 60 days of feeding,except for the activity of catalase,the activities of acid phosphatase（ACP）,alkaline phosphatase（AKP）,nitric oxide synthase（NOS）and other immune related enzymes increased.The results showed that Proteus and Bacteroides were dominant at phylum level,but Proteus and Bacteroides were dominant at middle stage（SS.M）and middle stage（CS.M）.After adding enriched nitrifying bacteria,the flora structure in the intestine and water body of sea cucumber changed,the abundance of beneficial flora increased and the abundance of harmful flora decreased,which made the ecological balance of sea cucumber body and water body more stable.After the enrichment of nitrifying bacteria solution,the structure of bacteria in the intestine and water of sea cucumber changed,the abundance of beneficial bacteria increased,and the abundance of harmful bacteria decreased,which made the ecological balance of the body and water more stable.The gene expression levels of TLR,My D88,IRAK4,NFκB,Akt,P38 and JNK in the experimental group（CLE）and the control group（CLC）were analyzed.Compared with the control group（CLC）,there was no significant difference in the gene expression of intestinal cells in the experimental group.