Study On The Controlling Model Of Bio-floc In Different Culture Systems

Bio-floc is aggregates formed of organic matter's flocculation in the culture water which is mainly composed of heterotrophic microorganism, which can improve water quality, save feed and promote animal immunity. In this thesis we studied different culture conditions for the bio-floc formation and established appropriate culture models in different culture systems for different animals. It consists of four parts as followed:The first part was about Bio-floc is aggregates formed of organic matter's flocculation which is mainly composed of heterotrophic microorganism, protozoa , algae and so on,it can regulate water quality, save feed and improve animal immunity. In this study, the bio-floc technology was applied in the experimental closed culture system of Litopenaeus vannamei. First the amount of carbon sources for stable bio-floc's formation in the closed culture system was studied, then the optimum organic carbon source and the optimum culture density of L. vannamei in the system was determined . Results showed that: Sucrose was added with 0.77 g /g feed to the culture system of L. vannamei at the density of 150 and 300 PL/m2 without water exchange,the protein content of feed was 42%. In this system, the bio-floc formation could be observed from the fourth day. The ammonia nitrogen and nitrite in the system were kept at very low concentrations during the culture period of 84 days and the survival rate were more than 80%. Which means high production of Litopenaeus vannamei with the culture system.The second part was about the roles of bio-floc technology during metamorphosis of shrimp larvae including nauplius of Litopenaeus vannamei and Fenneropenaeus chinensis .The optimum sucrose concentration for the formation of bio-floc in the shrimp culture system was determined. Then the water quality of the culture system at the optimum sucrose concentration was analyzed. Finally the metamorphosis and survival rates with bio-floc technology used at different stages of shrimp metamorphosis were measured. For the determination of optimum sucrose concentration in the culture system of nauplius Fenneropenaeus chinensis, results showed that different concentrations of sucrose from 20 ppm to 40 ppm had no significant effect on the shrimp metamorphosis at different period. The metamorphosis rates were 13.6% and 7.4% at 20 ppm and 40 ppm respectively which were much lower than the traditional breeding method. While no PL was observed in the tested groups with other sugar concentrations at last. For the analysis of water quality in culture system of nauplius larva of Litopenaeus vannamei added with 20ppm sucrose, results showed that the pH of the culture water fluctuated more sharply than control group of traditional breeding. While after the bio-floc formed, the pH tended to stabilize at 8.05. and concentration of ammonia nitrogen and nitrite were lower than traditional breeding controls. For the study of the bio-floc effection on the metamorphosis and survival rates at different stages of nauplius Fenneropenaeus chinensis metamorphosis, results showed that the survival rates of traditional breeding system, culture system using bio-floc two days before breeding nauplius larva, culture system using bio-floc at breeding and culture system using bio-floc at Zâ…¢period of metamorphosis were 35.8%,13.6%,23.3% and 67.9% respectively. It indicated that using bio-floc at Zâ…¢period is the best way for breeding nauplius larva, by which the survival rate of Fenneropenaeus chinensis can reach to 67.9% and the exchanged water was only 6.25m~3.So bio-floc, as a kind of advanced technology, can improve water quality of the culture system. And if reasonably used in seedling process,the survival rate of breeding can be significantly improved and the volume of water exchanged can be significantly reduced.Marsupenaeus japonicus was used as experimental animals in the third part. The bio-floc technology was studied in Marsupenaeus japonicus industrial culture system with rice hulls layed at the bottom of the pool. we studied the effect on Marsupenaeus japonicus industrial culture system with different ways of bio-floc technology under different shrimp density.. Unfortunately due to the bad qualiry of the Marsupenaeus japonicus seedling we did not achieve satifactory results finally. However during the experiment, the early data about water quality and survival rates in the culture system demonstrated that either formation of bio-floc directly in the culture water or by adding previously fermented microorganism out of the culture water to the culture water had more obvious advantages than the traditional factory culture model with exchanging water. And the culture model with density of 300 shrimp/m~3 in outdoor culture had more advantage than others.Scophthalmus maximus was used as experimental animals in the fourth part, We cultured Scophthalmus maximus in barrel using bio-floc technology to get preliminary data. The survival rates were compared between the culture system using bio-floc technology without water exchange and the traditional culture system using well water. The results show that Scophthalmus maximus can adapt well to the culture condition with bio-floc technology with the high survival rate 70%. And the application of bio-floc in the culture water can stablize the concentration of ammonia and nitrite which is favorable for survival of Scophthalmus maximus. The pH value fluctuated with the formation of bio-floc but can be adjusted by adding chemical reagents. Considering the economic, environmental, product quality factors and so on, the bio-floc technology can be used appropriately to ensure good quality of aquatic products, save cost and reduce emissions of pollutants. Here the experiments performed in small water body is a preliminary exploration and the application of Bio-floc in practical culture water need further study.