Effects Of Bait And Culture Mode On Water Quality,Water And Intestinal Bacteria In The Culture Of Hyriopsis Cumingii

China is the world’s largest producer and exporter of freshwater pearls,but the quality of pearls produced under the traditional culture model is mostly uneven,but also led to serious water pollution.With the promulgation of the government’s related restrictions on breeding,the industrial characteristics of pearl breeding with large output and low quality need to be improved,and a breeding model that is more friendly to the ecological environment must be established.In aquaculture,aquaculture water quality and bacteria play a vital role in the growth and development of aquatic organisms and disease control.In this study,we investigated the effects of bait microalgae,exogenous calcium ions,cultivation methods and probiotics on water quality（pH,ammonia nitrogen,nitrite nitrogen,nitrate nitrogen,total phosphorus,calcium ions and magnesium ions）,bacterial communities of water and intestines,as well as the effects of probiotics on growth,non-specific immune system and digestive capacity of the mussels（Hyriopsis cumingii）.The results were analyzed by high-throughput sequencing and bioinformatics to provide a theoretical basis for optimizing the breeding pattern.The main findings are as follows:Monora phidiumcontortum and Cyclotella sp.were fed separately to H.cumingii for 4 weeks,with water quality measured weekly and intestines and water collected for bacterial communities on days 0,7,14 and 28.The results showed:Both groups had maximum values of ammonia nitrogen and nitrite nitrogen on day 7 and 14,respectively,while nitrate nitrogen and total phosphorus both had maximum values on day 28.The dominant phyla（relative abundance>5%in at least one sample）were similar in bacterial communities of water and intestines,with both Actinobacteria,Bacteroidetes,Firmicutes,Proteobacteria and Verrucomicrobia,but there were significant differences in the abundance of bacteria.At the genus level,the composition of the intestinal and water bacterial communities was clearly different,but both Polynucleobacter and Reyranella of Proteobacteria were the dominant genera.From the redundancy analysis（RDA）,it was clear that pH was the most influential hydration indicator on water bacterial communities and NO₂^--N was the hydration indicator most closely related to intestinal bacterial communities.The functions of the intestinal and water bacterial communities were obviously different,but both were mainly related to energy production and biosynthesis.Comprehensive analyses such as principal component analysis（PCoA）and permutation multivariate analysis of variance（PERMANOVA）showed that both Monora phidiumcontortum and Cyclotella sp.had no significant effect on the changes of both water quality and bacterial communities,while time had a significant effect on water and intestinal bacterial communities.Calcium ions（1 m M）were added to the water of H.cumingii culture and rotating Monora phidiumcontortum and Cyclotella sp.were mixed and fed for 4 weeks,water quality was measured weekly,and the intestines and water were collected for bacterial communities on days 0,7,14 and28.The results showed:Both groups had maximum values of ammonia nitrogen and nitrite nitrogen on day 7 and 14,respectively,while nitrate nitrogen and total phosphorus both had maximum values on day 28.Ca²⁺was significantly absorbed by H.cumingii,with an average weekly uptake of 13.51±0.71 mg/L.The dominant phyla were similar in bacterial communities of water and intestines,with both Actinobacteria,Bacteroidetes,Firmicutes,Proteobacteria and Verrucomicrobia,but there were significant differences in the abundance of bacteria.At the genus level,the composition of the intestinal and water bacterial communities was clearly different,but both Chryseobacterium of Bacteroidetes and norank＿f＿＿Rhizobiales＿Incertae＿Sedis of Proteobacteria were the dominant genera.From the RDA analysis,it was clear that NH₄⁺-N was the most influential hydration indicator on water bacterial communities and pH was the hydration indicator most closely related to intestinal bacterial communities.The functions of the intestinal and water bacterial communities were obviously different,but both were mainly related to energy production and biosynthesis.Comprehensive analyses such as PCoA and PERMANOVA showed that Ca²⁺had no significant effect on the changes of both water quality and bacterial communities,while time had a significant effect on water and intestinal bacterial communities.The mussels were respectively cultured for 40 days in two ways,substrate silt and mesh hanging,with a mixture of Scenedesmus dimorphus and Cyclotella sp..Water quality was measured every 5days and the intestines and water were collected for bacterial communities on days 0,5,10,20 and40.The results showed:At the end of the experiment,NH₄⁺-N and TP concentrations were significantly higher in the mesh-hanged group than in the substrate silt group,while NO₂^--N,NO₃^--N,Mg²⁺concentrations and pH were significantly lower than in the substrate silt group.The dominant phyla were similar in bacterial communities of water and intestines,with both Actinobacteria,Bacteroidetes and Proteobacteria,but there were significant differences in the abundance of bacteria.At the genus level,the composition of the intestinal and water bacterial communities was clearly different,but Mycobacterium of Actinobacteria was the dominant genera.From the RDA analysis,it was clear that TP was the most influential hydration indicator on water bacterial communities and NH₄⁺-N was the hydration indicator most closely related to intestinal bacterial communities.The functions of the intestinal and water bacterial communities were obviously different,but both were mainly related to energy production and biosynthesis.Comprehensive analyses such as PCoA and PERMANOVA showed that the cultivation method was able to change the nitrogen and phosphorus content of water,thus causing some effects on the bacterial community structure.The bacterial communities were affected by the hydration indexes that varied greatly with culture time.Different probiotics（photosynthetic bacteria and Bacillus）were added to the water of H.cumingii culture,and Scenedesmus dimorphus and Cyclotella sp.were mixed and fed for 7 weeks.Water quality was measured weekly,and at the end of the culture,the growth status and pearl quality of the mussels were measured,plasma,hepatopancreas and intestine were collected to determine antioxidant,immune and digestive enzymes,and water and intestine were collected for bacterial communities.The results showed:The two probiotics had no significant effect on the growth,inner shell color and pearl quality of H.cumingii,but a significant effect on pearl shape.Both probiotics were effective in enhancing antioxidant,immune and digestive enzyme activities as well as significantly reducing NO₂^--N and pH.The dominant phyla were similar in bacterial communities of water and intestines,with both Actinobacteria,Bacteroidetes and Proteobacteria,but there were significant differences in the abundance of bacteria.At the genus level,there was a clear clustering distinction between the water and intestinal bacterial communities,with the control and Bacillus groups having more similar water bacterial communities and the control and photosynthetic bacteria groups having more similar intestinal bacterial communities.From the RDA analysis,it was clear that the hydration indicator most closely related to both the bacterial communities of water and intestines was NH₄⁺-N.The functions of the intestinal and water bacterial communities were obviously different,but both were mainly related to energy production and biosynthesis.Comprehensive analyses such as PCoA and PERMANOVA showed that probiotics had significant effects on pearl shape,non-specific immune and digestive systems and cultured water quality of H.cumingii,but not on growth and bacterial communities.