Study On The Probiotic Effect And Aquaculture Wastewater Purification Of Crucian Carp(Carassius Auratus Gibelio)by The Luteovulum Azotoformans And Chlorella Vulgaris Association

Aquatic products have a very promising future in solving the food shortage,aquaculture production is gradually exceeding natural harvesting worldwide.However,many problems restrict the development of the aquaculture industry,such as environmental pollution,diseases,and so on.Therefore,a green and healthy ecological aquaculture model is an inevitable requirement for aquaculture sustainable development,ecological environment protection,and human health maintenance.Nowadays,how to efficiently treat wastewater and healthily increase the production of aquatic animals are still bottlenecks that need to be addressed urgently.Bacteria and macroalgae,as the basis of natural water purification,are efficient,economical,and easy-to-operate.Meanwhile,mutually beneficial symbiosis exists between them which can not only form a stable community structure but also maintain sustainable ecological functions.Thus,crucian carp were used as experimental subjects in this research to assess the water purification and probiotic effect of the photosynthetic bacteria,Luteovulum azotoformans EBL0706,and a bacteria-microalgae ecological aquaculture system based on L.azotoformans EBL0706 and Chlorella vulgaris association was designed and constructed.The relationships among production,water quality,and fish health were investigated by laboratory trials and outdoor pilot-scale fish ponds,main results were shown as follows:1.In the lab,L.azotoformans EBL 0706 could convert ammonia-N and nitrite-N which are toxic to aquatic animals into nitrate-N which is relatively non-toxic in both medium and actual wastewater.Meanwhile,it has the potential to promote the growth of microalgae,the production of indoleacetic acid in the medium was 38.3 ± 0.7 mg/L.2.Daily supplementary L.azotoformans EBL 0706 could significantly increase fish final weight by 21.5% compared with traditional culture,and improve the liver antioxidant capacity.The catalase activity was increased by 48.9% and superoxide dismutase activity was increased by 32.3%,and malondialdehyde content was reduced by 119.5%;the results of liver morphology proved that the inflammation was significantly improved.The intestinal health was also improved and the diversity and richness of intestinal microbiota were increased,the cumulative mortality rate after intraperitoneal injection of pathogenic bacteria was also reduced by 50%.3.The bacteria-microalgae association could purify ammonia-N and nitrite-N in the rearing water,the average concentrations in 8 weeks were reduced by 95.0% and 84.2%.The intestinal amylase activity of crucian carp was increased by 56.3% and lipase activity by 63.9% in this rearing pattern,and the morphological structure of the intestine was significantly improved,the diversity and richness of intestinal microbiota were enhanced.The number and density of muscle fibers and muscle hardness were improved.Liver antioxidant capacity was significantly increased and the survival rate after intraperitoneal injection of pathogenic bacteria was also increased.The bacteria-microalgae association improved water quality and then improved intestinal health,eventually increased fish production.4.In the scale ecological aquaculture system,the crucian carp production increased by 13.3%,and the rearing water quality was significantly improved,total ammonia-N and nitrite-N reduced by 29.2%,51.3%,and 33.5%,and nitrogenous compounds in the ecological aquaculture system was the microalgae assimilation at the beginning and the nitrogen cycle gradually became dominant gradually as the experiment progressed.The abundance of nitrogen cycling functional genes amo A and nir K in the aquatic environment was higher than that in the traditional culture system,and some functional microorganisms unique to the ecological aquaculture system such as Prosthecobacter,Candidatus,ethylacidiphilum,Arenimona,and Silanimonas arose.In summary,the photosynthetic bacterium L.azotoformans EBL 0706 has the potential to safely improved the rearing water quality,the bacteria-microalgae system constructed with Chlorella vulgaris can efficiently improve the rearing water quality and promote the health of crucian carp finally increasing production.This study demonstrated the biological mechanism of the operation process of the ecological aquaculture system from the perspective of the intestinal health and microbial community changes,furthermore,the relationships among water quality,crucian carp health,and the fish production were proved which is conducive to the construction of the ecological aquaculture system for both efficient wastewater purification and healthy yield increasing.