Study On The Ecological Culture Model Of Larimichthys Crocea And Ulva Prolifera

In order to solve the problem that Larimichthys crocea cage aquaculture caused serious pollution and frequent disease in offshore sea area,an indoor recirculating aquaculture system was established to explore the key factors of indoor recirculating aquaculture system.The nutrient release of large yellow croaker was monitored in an indoor independent circulating water system and the effects of metabolic activities on water quality of large yellow croaker were studied.Ulva prolifera has a wide range of suitable temperature,strong adaptability to Ulva prolifera,high absorption rate of nutrients,and high nutritional value and biological application value.It is an excellent ecological restoration material.In this study,Ulva prolifera was used as an ecological restoration species in Larimichthys crocea culture system to seek a suitable breeding pattern and provide data for the application of Larimichthys crocea-Ulva prolifera ecological culture pattern.The specific results are as follows:1.Construction of indoor recirculating aquaculture system for Larimichthys crocea and monitoring of nutrient release during growth and metabolism of Larimichthys croceaThe constructed indoor circulation culture system can be used for indoor culture research of Larimichthys crocea.The water flow of the circulation system can ensure that dissolved oxygen is in a stable numerical range,so as to ensure that organisms in the circulation system will not appear hypoxia.The results showed that the p H value and nitrogen and phosphorus content of water body were obviously changed by the food residue.The growth of Larimichthys crocea will significantly change the water quality environment,thus affecting the survival rate of Larimichthys crocea.The survival rate of Larimichthys crocea without food was 54%in the indoor recycling system.The amounts of DIN and DIP released by dissolving artificial supplemented bait in water are as follows.The amounts of DIN and DIP metabolized by Larimichthys crocea under the condition of1%daily feeding amount are as follows:PO₄^3—P-19.2μmol·g·d^-1and NO₂^—N-42.8μmol·g·d^-1.2.Study on inorganic nitrogen absorption kinetics and removal effect of Ulva proliferaThe absorption kinetics characteristics of NO₂^--N,NH₄⁺-N and NO₃^--N of Ulva prolifera were measured and compared under the nitrogen starvation state,and the effects of different initial concentrations of NO₂^--N,NH₄⁺-N and NO₃^--N on the absorption rate were determined.The experimental results are as follows:The maximum absorption rates of NO₂^--N,NH₄⁺-N and NO3--N reached the highest values in 1h,which were 41.45μmol·g^-1·h^-1,60.59μmol·g^-1·h^-1 and 174.51μmol·g^-1·h^-1,respectively.The removal rates of NO₂^--N at the highest concentration of 30μmol·L-1,NH₄⁺-N at 25μmol·L-1 and NO₃^--N at 90μmol·L-1 reached 100%within 6 h.According to the calculation and analysis of Mi’s constant,the preferred absorption order of Ulva prolifera was NH₄⁺-N>NO₂^--N>NO₃^--N when the three combinations of N existed simultaneously.3.Study on the construction and stability of Larimichthys crocea-Ulva prolifera integrated culture systemIn the integrated culture system of Larimichthys crocea and Ulva prolifera,the mortality rate of Larimichthys crocea was effectively reduced by Ulva prolifera added into the system of Larimichthys crocea circulating culture,and the nutrient salt in water was absorbed by Ulva prolifera,which effectively improved the deterioration of water quality in the system of Larimichthys crocea circulating culture.The stability of water quality can affect the immunity and resistance of fish,thus improving the survival rate.When the ratio of Larimichthys crocea to Ulva prolifera is 1:0.5,the nutrient content in water can be maintained stable,that is,the nutrient released by the growth and metabolism of Larimichthys crocea can be just absorbed by Ulva prolifera,which can maintain the stability of water quality in the process of breeding.In the actual application scenario,the aquaculture area often presents the characteristics of eutrophication.The combination of Larimichthys crocea-Ulva prolifera ratio of 1:1 can be well adapted to the scene.Under the condition of maintaining the absorption of nutrient salt released by aquaculture organisms,it can alleviate the eutrophication of background water quality to a certain extent.It is suggested that the biomass of Ulva prolifera should not exceed the ratio of1:1.5 to ichthyophylla,because excessive density Ulva prolifera population limits the photosynthesis of Ulva prolifera and reduces its ability to absorb nutrients.4.Explored the diversity and composition of bacteria in water bodies with different aquaculture modes,analyzed the changes of microbial community,and analyzed the relationship between microbial community and environmental factors.A total of 46 phyla,119 classes,283 orders,510 families,962 genera,1487 species of microorganisms were detected by high-throughput sequencing,with a total of 2334OTU.Based on the study of plankton in Larimichthys crocea-Ulva prolifera integrated culture system,it was found that the intestinal microbial community of Larimichthys crocea cultured in circulating water system with single baiting showed low diversity and low evenness,and the richness also decreased to a certain extent.The microbial diversity in the water body was higher than that in the fish gut,and that in the baited group was higher than that in the untreated group.The richness data showed that the richness of intestinal microorganisms in fish was higher than that in water.In the integrated culture system,Bacteroidetes were the first dominant phylum,Proteobacteria and greencurved phylum were the second and third dominant phylum.In the integrated culture system of Larimichthys crocea and Ulva prolifera,Proteobacteria was the first dominant phylum,Bacteroidetes and Spirochaeta were the second and third dominant phylum.In the integrated culture system of Larimichthys crocea and Ulva prolifera,both chemoheterotrophy and aerobic heterotrophy were predicted to have high species abundance.