| Biofloc technology(BFT)is more and more widely used in industrial aquaculture.With the increasing pressure of environmental protection,the aquaculture industry needs this "closed zero-exchange water" technology more and more.In the production practice,the industrial BFT culture includes the Runway BFT culture,the Land based cement pond BFT culture,the Ectopic recirculating water BFT culture,the sunshine high level pond BFT culture and so on.Because the cost of BFT culture is higher than that of traditional soil pond culture,it is generally used in intensive high density culture,thus producing higher culture efficiency.In order to ensure the health and stability of aquiculture water in a high density closed water environment,it is necessary to transfer the matter and circulate energy of microbial food loop(MFL)in aquaculture water,so as to achieve the effect of efficient water purification.In this paper,the MFL in the sunshine BFT culture was studied.The sunshine BFT culture was designed as the greenhouse structure with light,and BFT was applied to healthy ecological aquaculture.The content of the experiment is divided into the following parts: 1.Effects of organic carbon sources on bacteria and plankton in aquaculture initial waterIn order to investigate the effect of different addition methods of carbon source on aquaculture initial water,we study the changes of bacteria and plankton by using the method of experimental ecology and the control measure of daily adding different concentration of glucose as the organic carbon source into aquaculture initial water.Experimental groups were added 0.84 mg·C/L·d(L group),1.68 mg·C/L·d(M group),3.36 mg·C/L·d(H group)organic carbon source,respectively,and the control group was not added.The results showed that in the 96 h,the total bacteria in L(451.53±114.50 ×107cells/mL)and M(412.36±21.50 ×107cells/mL)reached the highest and were significantly higher than that in H(79.34±16.09 ×107cells/mL)and control group(10.94±7.55 ×107cells/mL)(P < 0.05).No significant difference was in total phytoplankton biomass of each group,but the phytoplankton community changed greatly.The dominant phytoplankton species in each experimental group were more than that in the control group in the 192 h,so the phytoplankton community structure in the experimental group was more stable.The total zooplankton biomass in L(46.94±12.55 mg/L)was significantly higher than other groups in the 96 h(P < 0.05),and there were eight dominant species of zooplankton(Y?0.02)in L,six of which accounted for absolute advantage(Y?0.1).However,there was no significant difference in total zooplankton biomass between M and H.Except for DOC,the trend of water quality in each group was basically the same.The results showed that adding less organic carbon sources per day was beneficial to the growth of bacteria and plankton,that is to say,it was favorable to the growth of fresh water.2.Study on the control measure of Water in the early stage of Sun-factory biofloc aquacultureIn this part,using the method of experimental ecology,the water in the early stage of BFT aquaculture is used as the experimental material.The effects of bacteria free predators(protozoa et al.,group AC),group with shrimp order supplemented with glucose(group GS)and single dose of glucose(group G)on bacteria and plankton in water were investigated.During the experiment,the total number of bacteria in both experimental group and control group was higher than 5 × 105 cells / ml.AC group has the highest peak value,which reflected the descending effect after bacterial predator removal.At the end of the experiment,the content of chlorophyll-a in the GS group was significantly higher than that of the other groups(P < 0.05),indicating that the large predators of the grazing chain had a significant effect on the growth of microalgae.The change trend of biomass of rotifer in G group was similar to that in control group,and there was no significant difference in quantity(P > 0.05),which indicated that glucose supplementation had no significant effect on the biomass of rotifer.The results are as follows: first,the addition of glucose can promote the growth of bacteria,but adding more glucose at once can only promote the growth of bacteria in a short time.Sequential glucose supplementation can promote the growth of bacteria and achieve the biomass accumulation of zooplankton through the uplink effect and it is favorable to the growth of microalgae because of the symbiotic relationship of bacteria and algae.Second,bacterial predators are beneficial to the growth of bacteria.A single downward pressure must have obvious downside effects.Third,when the uplink effect and the downlink effect exist simultaneously,we need to control the balance between them,otherwise,either the uplink effect is dominant or the downlink effect is dominant.In this paper,the up-going effect of glucose addition is greater than that of the down-going effect of Penaeus vannamei.3.Comparative study on the downlink effect in two kinds of sun-factory aquaculture modelsIn this paper,the effect of predation pressure on bacterial growth and its relationship with water quality change in shrimp culture ponds were compared with those in traditional aquiculture ponds of Penaeus vannamei and those in traditional aquiculture of Penaeus vannamei.The purpose of this paper is to explore the role and status of bacteria in pond material circulation,and to evaluate the operation and ecological function of aquaculture system.This part is divided into two groups: Test I(sunshine BFT aquaculture)and Test II(traditional aquiculture of water exchange).In Test ?and Test II,AC-one group and AC-two group was added Actidione to kill and inhibit eukaryote,CK-one group and CK-two group as control group,respectively.In group CK-one,the total number of bacteria had a substantial reduction in the 18 h,less than the total bacterial AC-one group finally;while the total number of bacteria in AC-one group remained 3.4~4.7×106cells/ml,and the overall also increased,compared with the CK-one group shows that predation pressure have influence on the bacteria in the BFT aquaculture water.And predation pressure with the total number of bacteria was negative related in aquaculture water.It shows that the downward effect in BFT aquaculture water is obvious.In Test I and II,phosphate concentrations in both AC-one and AC-two groups,which inhibit eukaryotes,did not change significantly,while phosphate concentrations in CK-one and CK-two groups decreased to almost 0,and nitrite nitrogen decreased significantly.It can be concluded that the bacteria alone have little effect on phosphate and nitrite nitrogen,but microalgae and bacteria have obvious transformation effect on phosphate and nitrite nitrogen under the combined action of microalgae and bacteria.The results showed that the nutrient level of MFL was more closely related and the descending effect was more obvious in the sunshine BFT aquaculture water,and the sunshine BFT aquaculture water had more advantages in the nitrogen and phosphorus transformation.However,the removal efficiency of nitrate nitrogen was not higher than that of water exchange aquaculture,and there was no significant difference in the conversion of ammonia nitrogen and phosphate. |
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