| During the culture process of black tiger shrimp,decomposition of residual diets,shrimp excrement,and dead shrimp bodies could easily lead to excessive concentration-s of ammonia and nitrite in the cultured water,and these toxic substances could affect the growth of black tiger shrimp.Therefore,the removal of ammonia and nitrite in aqua-culture system was crucial.Pond and high-level pond aquaculture modes maintained the water environment by changing a large amount of water,resulting in problems such as the waste of water resources,surrounding environmental pollution,and the spread of viral and bacterial diseases.Although recirculating aquaculture system could improve the utilization rate of water resources,the investment and operating costs of this aqua-culture mode were too high,making it difficult to popularize in a large area.Biofloc technology(BFT)and internal circulation mode(ICM)were considered to have eco-nomic,environmental,and social benefits.BFT had the advantages of purifying water quality,reducing water exchange,promoting nutrient circulation,reducing feed conver-sion ratio,etc.ICM had the advantages of saving water and energy,stable water quality,preventing the invasion of exogenous pathogens,reducing the incidence rate of shrimp,etc.This experiment took black tiger shrimp as the research object,and compared wa-ter quality characteristics and shrimp growth of BFT and ICM systems in the inter-mediate rearing stage and culture stage,the effects of different stocking densities(400tails/m3and 600 tails/m3)on water quality and shrimp growth were also researched.Besides,the bacterial community structure and diversity of different samples in BFT and ICM systems were compared based on Illumina Miseq high throughput sequencing technology.The main conclusions were as follows:(1)During the intermediate rearing period,the concentration of ammonia nitrogen in BFT system was significantly higher than that in ICM system(P<0.05),but there was no significant difference in nitrite nitrogen between the two aquaculture systems(P>0.05).During the culture period,the concentrations of ammonia nitrogen and ni-trite nitrogen in BFT system were significantly higher than those in ICM system(P<0.05).With the increase of stocking density,the increases in concentrations of ammonia nitrogen and nitrite nitrogen in BFT system were higher than those in ICM system.The concentrations of nitrate nitrogen,total phosphorus and chemical oxygen demand in the two aquaculture systems increased with the extension of the experimental period and the increase of stocking density.The concentration of nitrate nitrogen in BFT system was significantly lower than that in ICM system during the whole experimental period(P<0.05),but the concentration of chemical oxygen demand was significantly higher than that in the latter(P<0.05).There was no significant difference in total phosphorus between the two aquaculture systems during the whole experimental period(P>0.05).(2)The mean value in body length and body weight of black tiger shrimp in the two aquaculture systems were not significantly different during the whole experimental period(P>0.05).The unit yield of shrimp in ICM system was significantly higher than that in BFT system during the whole experimental period(P<0.05).With the increase of stocking density,the increase in unit yield of shrimp in ICM system was higher than that in BFT system.The specific growth rate,protein efficiency ratio,and survival rate of shrimp in ICM system were significantly higher than those in BFT system during the whole experimental period(P<0.05),while the feed conversion ratio was significantly lower than that in the latter(P<0.05).The specific growth rate,protein efficiency ratio,and survival rate of shrimp in the system with a stocking density of 400 tails/m~3 were significantly higher than those in the system with a stocking density of 600 tails/m~3(P<0.05),while the feed conversion ratio was significantly lower than that in the latter(P<0.05).(3)The bacterial community richness and diversity in BFT system were higher than those in ICM system,and the bacterial community richness and diversity in bottom sand of the same aquaculture system were higher than those in water and biofilm.The bacterial community composition of samples from different aquaculture systems was significantly different.The bacterial community composition of different samples from the same aquaculture system was relatively similar,but the relative abundance of bac-terial community was significantly different.A total of 44 phyla,98 classes,and 599genera were detected in the two aquaculture systems,among which 39 and 36 phyla,84 and 77 classes,418 and 400 genera were detected in BFT and ICM systems,respect-tively.There were no common dominant bacterial genera in the two aquaculture sys-tems.The dominant bacterial genera in BFT system were norank＿f＿＿norank＿o＿＿Chlo-roplast,unclassified＿f＿＿Microbacteriaceae,Draconibacterium,unclassified＿f＿＿Rho-dobacteraceae,Lutibacter,etc.The dominant bacterial genera in ICM system were norank＿f＿＿norank＿o＿＿PB19,Marinicella,norank＿f＿＿Flavobacteriaceae,Oceanospi-rillum,Halarcobacter,etc.(4)There were 9,10 and 12 functions related to carbon,sulfur and nitrogen cycles in the two aquaculture systems,respectively,including fermentation,methylotrophy,hydrocarbon＿degradation,respiration＿of＿sulfur＿compounds,sulfate＿respiration,sul-fite＿respiration,nitrate＿reduction,nitrate＿respiration,nitrite＿respiration,nitrate＿de-nitrification,nitrite＿denitrification,nitrification,etc.The bacteria related to carbon and sulfur cycle accounted for a high proportion in the two aquaculture systems.The bac-teria related to carbon cycle mainly existed in water of BFT and ICM systems.The bac-teria related to sulfur cycle were mainly distributed in bottom sand of BFT system,and biofilm,water and bottom sand of ICM system.The bacteria with denitrification mainly existed in water of BFT system,and water and biofilm of ICM system.The bacteria with nitrification were mainly distributed in bottom sand and biofilm of ICM system. |
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