Research And Application Of Functional Effects Of Biofloc In Zero-water Exchange Litopenaeus Vannamei Culture System

The drive force of zero-exchange shrimp culture system is biofloc, which playimportant roles in controlling water quality, recycling feed nutrients, and improving shrimphealthy growth. This thesis include experimental and field studies on Litopenaeus vannameiculture in zero-water exchange systems under control conditions. Experiments wereconducted to investigate the technology of controlling water quality by promoting bioflocthrough carbohydrate addition in intensive shrimp culture systems, the mechanism ofenhancing protein nutrition and growth performance of cultured shrimp by promotedbiofloc, functional regulating effects in immune and antioxidant defense systems of culturedshrimp by promoted biofloc. Field studies were also conducted to explore the applicationmethods of biofloc technology for shrimp intensive culture in closed ponds. The aim ofthese studies is to provide scientific basis and technical support for establishingbiofloc-based efficient and healthy shrimp culture system. Experimental design and themain research results are as follows.1) The effects of two biofloc levels promoting by different amounts of sucroseaddition on water quality, and shrimp digestive enzymes activity and growth performance inzero-water exchange culture tanks. The control group was operated with water exchange,and the experiment lasted for30d. The results show that TAN and NO2-N concentrationswere maintained at very low levels; protease, amylase, cellulase and lipase activities inhepatopancreas and stomach, weight gain rate and special growth rate of the shrimp tendedto increase in the bioflocs treatments compared to those in the control.2) A2×2factorial design experiment with two dietary protein levels (35%vs.25%)and two C/N ratios (20vs.15) was conducted to evaluate biofloc composition and shrimpperformance in zero-exchange culture tanks for a period of30d. The results show that both dietary protein level and C/N ratio have significant effects on crude protein, crude lipid andash contents, and extracellular protease and amylase activities of biofloc while nosignificant effects on shrimp survival, growth and protein efficiency ratio. Meanwhile,treatments fed with35%protein feed had significant lower feed conversion rates than thosefed with25%protein feed.3) The effects of two input C/N ratios (15,20) through manipulation with sucroseaddition on biofloc development, and shrimp digestive enzymes activity, physiologicalhealth, growth performance and body composition in zero-water exchange culture tanks.The control group was operated with water exchange, and the experiment lasted for30d.The results show that the biofloc developed under two input C/N ratios had appropriatecrude protein, crude lipid and ash contents, and extracellular protease and amylase activities.Compared to the control, protease and amylase activities in hepatopancreas and stomach ofthe shrimp tended to increase; total haemocyte count in haemolymph, phagocytic activity ofhaemocyte, total antioxidant capacity and reduced/oxidized glutathione ratio in plasma andhepatopancreas, superoxide dismutase activity in plasma, and growth performance of theshrimp significantly increased; crude lipid and ash contents of the whole shrimp tended toincrease.4) The effects of different dietary protein levels (35%,30%,25%,20%) on digestiveproteinases activity, feed utilization, protein retention, physiological health and growthperformance of the shrimp in biofloc-based zero-water exchange culture tanks. The controlgroup was operated with water exchange and fed with35%protein feed, and the experimentlasted for7weeks. The results show that the biofloc treatments had higher total proteinasesand trypsin activities in hepatopancreas of the shrimp, protein efficiency ratio, and proteinproductive value, compared to the control. For biofloc treatments, the dietary protein levelcan be reduced from35%to25%without effecting digestive proteinases activity, feedconversion rate, protein efficiency ratio, protein productive value, immune defense activity(in terms of total haemocyte count in haemolymph, phagocytic activity of haemocyte,antibacterial activity and bacteriolytic activity in the plasma), antioxidant status (in terms oftotal antioxidant capacity, superoxide dismutase activity, reduced glutathione level, reduced/oxidized glutathione ratio in plasma and hepatopancreas), and growth performanceof the shrimp.5) Using land-based enclosures experimental ecology method to investigate theeffects of different input C/N ratios (12,16,20) and stocking densities (80,120,160ind m2)on water quality, shrimp growth performance and feed coefficient in a closed earthen pondfor a period of11weeks. The results show all treatments had very low TAN and NO2-Nconcentrations during the culture period. As C/N ratio increased (12â†'16â†'20), the growthof the shrimp tended to increase while feed coefficient tended to decrease. As stockingdensity increased (80â†'120â†'160), the growth and survival of the shrimp tended todecrease while yield tended to decrease.