A Primary Study On The Application Of Bioflocs Technology To Seawater Polycultureponds Of Portunus Trituberculatus And Litopenaeus Vannamei

Bioflocs is organic detritus in water body composed of algae, heterotrophic bacteria, protozoon and un-consumed and non-digested feed. Biofloc technology is considered as an efficient means ofimproving water quality, decreasing the feed coefficient and ecological control in health aquaculture system by controllingC/Nsince nutrients could be continuously recycled and reused. In this thesis, we try to apply the biofloc technology based on the C/N control by addition molasses and coupled with additional living bacteria agent to the polyculture system ofPortunus trituberculatus and Litopenaeus vannamei to study the comprehensive biological consequence including the growth performance of aquaculture animals, water and sediment environment and so on.Three experiments are involved in this paper. The detailed experiment process is below:1.Effects of C/N ratio on culture environment and growth performance of Portunus trituberculatus and Litopenaeus vannamei in polyculture systems.During July to October in 2013, land-based enclosures were adopted to study effects of different C/N ratio levels on culture environment and growth performance of Portunus trituberculatusandLitopenaeus vannamei in polyculture systems. The control was feed with clam and compound feeds, while four treatments (C1、C2、 C3 and C4) were raised the C/N ratio to 10,15,20,25 respectively by addition of molasses to water column.The results showed that when the C/N ratios were 10、15 and 20, the concentration of ammonia in water was significantly lower than the control (P<0.05); Similarly, the concentrations of nitriteand reactive phosphorus reducedsignificantly in the late stage of cultivation(P<0.05); When the C/N ratio was 10 or 15, the accumulation of the total nitrogen in the sediment was remarkably lower than the control (P<0.05); When the C/N ratio was 15, the yield of Portunus trituberculatus and Litopenaeus vannamei reached the highest point with 2554.93± 190.11 kg hm-2 and 2753.17±75.12 kg·hm-2 respectively, which were obviously higher than the control with 2112.92±246.61kg·hm-2 and 2121.99±77.19kg hm-2 (P<0.05); The highest survival rate of Litopenaeus vannamei resulted in the treatment group of C/N=15, which was significantly higher than the control (P<0.05). To summarize, when C/N was optimum, the bioflocs could reduce the concentration of ammonia and nitrite effectively,utilize the reactive phosphorus efficiently and decrease the accumulation of the total nitrogen and total phosphorus in the sediment. When the C/N was 15, it could effectively improve the environment of culture systems and the growth performance as well as the yield of Portunus trituberculatus and Litopenaeus vannamei.2.Effects of adding molasses and different kinds of probiotics on culture environment and growth performance of Portunustrituberculatus and Litopenaeus vannamei in polyculture ponds.During July to October in 2014, land-based enclosures were adopted to study effects of C/N control and adding different kinds of probioticss on culture environment, the number of the bacteria in water body and growth performance of Portunus trituberculatusandLitopenaeus vannamei in polyculture systems. Keep the C/N at about 15 by adding molasses, and making the bacterias have a concentration about of 104cfu/ml in’water body after using different kinds of probioticss.The results show:in five kinds of the cultivation of biofloc, the treatment C3 (Bacillus cereus and C/N=15) and C5 (EM bacteria group and C/N= 15) show optimal comprehensive effects;Followed by treatment Cl (C/N=15);Treatment C2 (Bacillus pumilusand C/N=15), treatment C4 (Nitrifying bacteria and C/N=15) improve the water quality to a certain extent, but the growth performance and yield of Portunus trituberculatusandLitopenaeus vannamei have no significant difference compared with the control group (P>0.05).3.Effects of adding molasses and different kinds of probioticss on sediment of ponds of Portunus trituberculatus and Litopenaeus vannamei in polyculture systems.During July to October in 2014, land-based enclosures were adopted to study effects of using the control of carbon and probioticss technology on sediment environment, the number of heterotrophic bacteria and vibrio in sediment. Results show that all the treatments could significantly reduce the total nitrogen and total phosphorus concentration, and maintain the C/N of sediment of the pond at a high level. The treatment C5 shows the optimal comprehensive effects in five treatments.Treatment C1 (C/N=15), treatment C3 (Bacillus cereus and C/N=15), treatment C4 (Nitrifying bacteria and C/N=15) and treatment C5 (EM bacteria and C/N=15) could effectively improve the total number of heterotrophic bacteria in sediment, while treatment C2(Bacillus pumilusand C/N=15) and C4 could keep the vibrio at lower levels in sediment.Overall, treatment C1, C3 and C5 could keep the number of heterotrophic bacteria and vibrio at an appropriate level in sediment.The technology of application of living bacteria agents and control of C/N, can maintain a relatively stable C/N in sediment, promote the development of heterotrophic bacteria, and accelerate the utilization of nitrogen, phosphorus and other nutrients which could do some help to reduce the excessive accumulation of them; and it also could decrease the number of vibrio and then improve the sediment environment of the pond.