Research And Application Of Key Technology For Shrimp Litopenaeus Vannamei Pond Aquaculture Environment Remediation

The white shrimp（Litopenaeus vannamei）is one of the most important and valuable industrial marine aquaculture species,and pond farming is the main way of shrimp culture.High economic benefits promote the rapid development of shrimp industry,but it also brings serious ecological problems,including water pollution,disease epidemic and security of aquatic product.Developing countries are trying to explore new technologies for healthy shrimp culture.With the continuous high pressure of environmental protection policies in China,the utilization of solid waste from aquaculture and wastewater ecological treatment will also become urgent technologies for aquaculture sustainable development.To accelerate the green development of aquaculture industry,solve the shrimp pond aquaculture non-point source pollution and achieve a balance between the economy and ecology,this paper studied shrimp pond culture in situ remediation technology,ex situ remediation and abandoned shrimp pond remediation technology to realize the purpose of water saving,emissions reduction and waste recycling.These technologies will promote shrimp aquaculture industry transformation and upgrading of technology.The main research results of the paper are as follows:（1）Shrimp pond culture in situ remediation technology mainly studies the polytrophic integrated culture mode,mullet（Mugil cephalus）was selected for feeding and utilization of shrimp culture sediment.Intensive pond shrimp aquaculture produces a large quantity of organic deposits due to uneaten food and fecal matter.The study consisted of two complementary parts.The first part was a laboratory feeding trial conducted under controlled conditions to measure the ingestion and absorption by M.cephalus of organic deposits collected from an L.vannamei aquaculture pond.The second part was a polyculture experiment with L.vannamei and M.cephalus designed to investigate the viability of introducing the bottom-feeding M.cephalus to shrimp pond culture and the effect of the polyculture on the water quality of the system and on the growth performance of shrimp and fish.Polyculture experiment with L.vannamei and M.cephalus was conducted with six different densities of medium sized（18.0±4.1 g/ind）mullets cultured with shrimp（ML-0,ML-1,ML-2,ML-3,ML-4,and ML-5corresponding to ratios of fish to shrimp of 0:300,1:300,2:300,3:300,4:300,and 5:300,respectively）.The results showed that,in the feeding trial,the specific growth rate（SGR）of small and medium mullets was obviously higher than that of large mullets,and SGR was negatively correlated with mullet body weight.Medium mullets had the highest ingestion rate,whereas small mullets had the highest feces production rate.The organic matter and N assimilation efficiency values of medium mullets were highest（60.7%and82.2%,respectively）.The fish removed 0.62 g/ind/d of organic matter and 0.043 g/ind/d of organic N from the enriched sediment.In the polyculture experiment,the survival rate and yield of white shrimp in treatment ML-4（96.4%±0.8%and 5.2±0.2 kg,respectively）were higher than those in the other treatments,and the survival rate was significantly higher than those of the ML-0 and ML-2 groups（P<0.05）.During the polyculture experiment,mullet density significantly affected the water environment.Overall,the best survival rate and yield of shrimp were achieved at the density of 4:300.These results indicate that mullets as detritivores can effectively ingest and absorb organic deposits generated by white shrimp culture.Additionally,these findings show that polyculture of mullets at suitable size and density does not lead to decreased yield of white shrimp;instead it increases shrimp survival and food utilization efficiency and improves the water quality of the system.Thus,shrimp-mullet co-culture should be promoted to improve the health and sustainability of intensive shrimp aquaculture.（2）The mullet could ingest uneaten food and fecal matter produced by shrimp culture,greatly reduce culture water solid particles,but many dissolved organic matter and inorganic nitrogen have not been absorbed and transformed.Sesuvium portulacastrum ecological floating beds could markedly decrease nitrogen and phosphorus in culture water.The part mainly focus on growth and relationship between S.portulacastrum and nutrient.Hydroponic S.portulacastrum period was 82 d.Five salinity treatment groups（0,10,20,30 and 35）were designed to study the plant wet weight,dry weight,height and nutrient accumulation rate.Variation in ammonium nitrogen（NH₄⁺-N）,nitrate nitrogen（NO₃^--N）,phosphate(PO₄^3-)and tryptophan（Trp）by S.portulacastrum rhizosphere were measured under bacteriostatic and non-bacteriostatic conditions.The results showed that dry matter content and nutrient element accumulation rate in S.portulacastrum was the highest under hydroponic culture when the salinity is 10.The accumulation rates of organic carbon,organic nitrogen and organic phosphorus were5.572±1.611 mg/d/ind,0.313±0.058 mg/d/ind,0.057±0.013 mg/d/ind,respectively.High salinity 35 brings pressure on the growth of S.portulacastrum.Under different salinity conditions,S.portulacastrum preferentially use organic nitrogen and nitrate nitrogen as nitrogen sources,however the absorption of organic nitrogen was inhibited at the high salinity 20-35.The study provided scientific data for Mullet-Shrimp-Sesuvium multi-trophic culture model establishment.（3）Shrimp pond ex situ restoration technology mainly included solid waste collection facilities,efficiency and tail water treatment effect.The aquaculture waste collection facilities are mainly composed of sedimentation tower for solid waste collection,three-stage series biological tank for tail water treatment.The results showed that solid waste collection efficiency of the sedimentation tower was 10.6%±1.8%,31.1%±5.7%and 52.2%±5.2%,respectively,in the early,middle and late stage of shrimp culture.The total nitrogen collection ratio were 1.4%±0.2%,3.4%±0.6%and 9.1%±0.1%,respectively.The extraction time of aquaculture wastewater should not exceed 1 min,and the precipitation time of solid waste was less than 2 h.Three stage purification tank filled with biological brush under wastewater flowing condition for 60 d.After 30 days of aeration and anaerobic treatment,dissolved oxygen content range remain 1.11-1.98 mg/L,0.27-0.45 mg/L and 4.60-5.82 mg/L,respectively.After determination and analysis,the removal rates of total nitrogen and ammonia nitrogen in the tail water after solid waste collection could reach to 45.5%and 93.6%.High-throughput sequencing analysis was conducted on the biological brush in the three-stage purification tank,and it was found that the abundance of nitrifying bacteria in the third-stage biological tank was the highest.They mainly include Nitrosomonas,Nitrosospira and nitrite oxidizing bacteria,which can well explain the effect of three-stage nitrification.（4）Abandoned shrimp pond remediation technology guided by the theory of ecosystem succession,comprehensive utilized ecological engineering,biological restoration and ecological aquaculture.Abandoned shrimp pond environment was reconstructed by simulating natural mangrove habitat.The abandoned shrimp pond mainly planted with Guangxi native mangrove plants,such as Rhizophora stylosa,Avicennia marina（Forsk.）Vierh.,and Aegiceras corniculatum（L.）Blanco,which grow well after one year.Natural hydrodynamic recovery and submergence duration are the most important factors for the healthy growth of mangrove plants in shrimp pond.On the basis of the improvement of the substrate and the construction of plant community,the macrobenthos community was reconstructed,and the dominant species were the Sermyla riqueti and Cerithideopsilla cingulata.The L.vannamei,M.cephalus and Scylla paramamosain were the main breeding objects,overall profit could reach to 33000RMB/a,while the mangrove value in the shrimp pond ecosystem can reach 271200RMB/a.The study brings great impetus for abandoned shrimp pond restoration,and provide practical reference for emissions reduction technology research.（5）The three shrimp pond restoration technologies both improved organic water in residual bait and feces produced by shrimp culture,reduces the pollution to the ecological environment,increased carbon sink breeding technology,finally achieved economic benefit and ecological benefit.Therefore,the study result of the paper can provide referential demonstration and guidance for the actual situation of shrimp ponds at different regions.