| The important research contents in this experiment as follows:1. Oyster shellpowder （OP） and sugarcane bagasse （BA） were used as bottom substrates to researchtheir effects on Litopenaeus vannamei intensive culture under zero-water exchangecondition. Parameters including water quality （TAN concentration, NO2-Nconcentration, Chl.a concentration）, bacterial density （total bacterial and nitrogencycle bacterial densities） in the bottom and water, zooplankton densities, and shrimpgrowth performance were investigatedï¼›2. Different nitrogen species assimilated by aVibrio alginolyticus （Z5） strain under different C/N ratiosï¼›3. Ammonia nitrogen andnitrite nitrogen removal in shrimp culture by Vibrio alginolyticus （Z5） strainimmobilized in SA-beads. The pupose of this experiment was provided as referencefor the research of optimization of bottom substrate on shrimp culture, the regulativemechanism of probiotic on water quality, and application of immobilizedmicroorganism technology on shrimp culture. In addition, contribute to reduce thedischarge of wastewater to environment in aquaculture. The significant results werelisted below:1. Effect of optimization of bottom substrate on shrimp culture under zero-waterexchange conditionOyster shell powder （OP）, sugarcane bagasse （BA）, OP and BA mixture （OS）,and fresh soil （FS） were used as bottom substrates to compare their effects onLitopenaeus vannamei intensive culture under zero-water exchange condition.Parameters including water quality, total bacterial and nitrogen cycle bacterialdensities in the bottom and water, zooplankton densities, and shrimp growth performance were investigated. Total ammonia-nitrogen （TAN） in BA was below0.36mg/L which was significantly lower than those in other treatments at the end of theculture （P <0.05）. NO2-N concentrations in OS were below0.50mg/L which wassignificantly lower than those in other treatments （P <0.05）. This result wasconsistent with the relatively higher ammonia-oxidizing and nitrite-oxidizing bacterialdensities, respectively. The Chl.a concentrations in OP, BA, and OS exhibited a slowincreasing trend during the entire period, whereas these in FS kept a low level and didnot increase significantly. The bacterial densities in the bottom substrates of OP, BA,and OS were one order of magnitude greater than those in FS. The zooplanktondensities in treatments containing the substrate of BA （BA and OS） were significantlyhigher than those without BA （FS and OP）（P <0.05）. These increased bacterial andzooplankton generated synergistic effects along with improved water quality usingBA and OS on shrimp growth performance, which was demonstrated in highersurvival rates and yields, and lower feed conversion rates. We first demonstrate thebeneficial effects of using appropriate bottom substrates, indicating that BA and OSare effective for improving the performance of L. vannamei intensive culture withoutwater exchange.2. Effect of sugarcane bagasse as bottom substrates at different amounts onLitopenaeus vannamei intensive cultureDifferent amounts of bagasse （0.5kg/m2,1kg/m2,1.5kg/m2and2kg/m2,bagasseshort for BA） mixing with oyster shell powder（5kg/m2, oyster shell powder short forOP） were added as bottom substrates into Litopenaeus vannamei intensive culture toestimatethe effect on the aquaculture environment and shrimp by investigating waterquality, total bacterial and nitrogen cycle bacterial densities in the bottom and water,zooplankton （>160μm） densities and shrimp growth performance. The groups wereBA0.5, BA1, BA1.5and BA2, respectively. Result showed that there were somesignificance differences in water quality and bacterial density in water and bottomsubstrates with different amounts of bagasse. BA could promote the growth ofzooplankton strongly; nevertheless, there were no significance difference with addition different amounts of BA. In addition, BA suspended in water couldcontribute to improve the utilization of nutrient substance in aquacultureenvironment.However, addition excessive BA would cause the environment pressure,so it was good the amount of BA added between0.5-1kg/m2.3. Different nitrogen species assimilated by a Vibrio alginolyticus （Z5） strain underdifferent C/N ratiosNitrogen assimilation characteristics of a Vibrio alginolyticus （Z5） wereinvestigated under single nitrogen source （organic nitrogen, NH4-N, or NO2-N） andmixed nitrogen source （organic nitrogen and NH4-N, organic nitrogen and NH4-N, orNH4-N and NO2-N） at different C/N ratios. The activities of protease, glutaminesynthetase and nitrite reductase involved in nitrogen metabolism were also determined.The results showed that the assimilation rates of both organic nitrogen and inorganicnitrogen of Vibrio alginolyticus （Z5） were affected by C/N ratio. The assimilationrates of NH4-N and NO2-N under C/N ratio of20were3.39times and2.25timeshigher than those under C/N ratio of5. There were no significant differences in theassimilation of NH4-N and NO2-N between C/N of15and C/N of20（P>0.05）. Theassimilation processes of NH4-N and NO2-N were NH4-Nâ†'bacterial protein andNO2-Nâ†'NH4-Nâ†'bacterial protein, respectively. The assimilation rates of inorganicnitrogen （NH4-N and NO2-N） increased with higher C/N; and the protein nitrogencontent of the bacteria enriched from NH4-N and NO2-N increased from25.0%and19.4%under C/N of5to41.3%and43.0%under C/N of20, respectively. Moreover,Vibrio alginolyticus （Z5） preferred to assimilate NH4-N than NO2-N. Additionally, theactivity of glutamine synthetase was regulated significantly by NH4-N while theactivities of protease and NiR were not regulated significantly by the nitrogen species.4. Ammonia nitrogen and nitrite nitrogen removal in shrimp culture by Vibrioalginolyticus （Z5） immobilized in SA-beadsIn this study, SA-beads which formed of the Vibrio alginolyticus （Z5）, sodiumalginate and sugarcane bagasse were studied for the ammonia nitrogen （NH4-N） and nitrite nitrogen （NO2-N） removal in shrimp cultrue. In addition, the variation ofbacterial density embedded in SA-beads was evaluated. The results indicatedSA-beads might have a maximum capacity of1.06×108cfu/bead. However, optimuminitial bacteria density embedded in SA-beads should be104cfu/bead-105cfu/bead.The maximum NO2-N degradation rate of SA-beads could reach to8.44mg/L·day,and the average NO2-N degradation quantity of each bead was0.06mg. The additionof carbon source could accelerate the degradation of NH4-N and NO2-N for-beads. Inorder to evaluate activity of SA-beads in shimp culture,50days cultivationexperiment was carry out in aquariums. The NH4-N and NO2-N concentrations whichwater treatment with SA-beads were below1.55mg/L and1.62mg/L at later period,repectively, which were lower than those in control treatment （P <0.05）. There wasno significant difference in NH4-N and NO2-N concentrations which water treatmentwith SA-beads and exchanging water （P>0.05）, and the yield which water treatmentwith SA-beads could reach about70%of those which water treatment withexchanging water. Moreover, POC and DOC concentrations in water were enhancedby SA-beads added. In late period, even though some SA-brads broken, the sugarcanebaggse contained in SA-beads might be suspend in water to continue to keep goodwater quality. |
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