The dissolution of total suspended solids and treatment strategy of tailwater in a Litopenaeus vannamei recirculating aquaculture system

In recirculating aquaculture systems(RASs),the effective treatment of aquaculture tailwater is essential to maintain the health of the RAS.This study investigated the optimal time and method for tailwater treatment during three periods of the aquaculture of the Litopenaeus vannamei:nursery(0–26 d),middle(27–57 d),and later(57–104 d).The variation of several water parameters during the dissolution of total suspended solid(TSS)in tailwater,applied with the effects of ozone on the microorganism and water quality parameters were investigated.Results showed that the TSS concentrations in tailwater decreased with time,although not significantly(P>0.05),whereas total ammonia nitrogen(TAN),nitrite(NO-2-N),and nitrate(NO_(3)^(-)-N)increased significantly(P<0.05).Therefore,TSS should be removed from the tailwater as early as possible,being most optimal within 4 h.Ozone removed 38.24%–48.95%of TSS,17.78%–90.14%of TAN,and 87.50%–98.90%of NO-2-N after 4 h of treatment.However,it resulted in the significant accumulation of NO_(3)^(-)-N.Moreover,the total number of Vibrio and bacterial counts in aquaculture tailwater was reduced completely by ozone within 4 h.Thus,these results provided technical details and data support for the effective treatment of tailwater from shrimp RAS.

Intestinal microbiota of healthy and unhealthy Atlantic salmon Salmo salar L. in a recirculating aquaculture system

The present study sampled the intestinal content of healthy and unhealthy Atlantic salmon( Salmo salar L.), the ambient water of unhealthy fish, and the biofilter material in the recirculating aquaculture system(RAS) to understand differences in the intestinal microbiota. The V4–V5 regions of the prokaryotic 16 S r RNA genes in the samples were analyzed by Mi Seq high-throughput sequencing. The fish were adults with no differences in body length or weight. Representative members of the intestinal microbiota were identified. The intestinal microbiota of the healthy fishincluded Proteobacteria(44.33%), Actinobacteria(17.89%), Bacteroidetes(15.25%), and Firmicutes(9.11%), among which the families Micrococcaceae and Oxalobacteraceae and genera S phingomonas, Streptomyces, Pedobacter, Janthinobacterium, Burkholderia, and Balneimonas were most abundant. Proteobacteria(70.46%), Bacteroidetes(7.59%), and Firmicutes(7.55%) dominated the microbiota of unhealthy fish, and Chloroflexi(2.71%), and Aliivibrio and Vibrio as well as genera in the family Aeromonadaceae were most strongly represented. Overall, the intestinal hindgut microbiota differed between healthy and unhealthy fish. This study off ers a useful tool for monitoring the health status of fish and for screening the utility of probiotics by studying the intestinal microbiota.

Characterization of Bacterial Community,Ammonia-Oxidizing Bacteria,and Nitrospira During the Operation of a Commercial-Scale Recirculating Aquaculture System for Culturing Pufferfish Takifugu rubripes

We investigated the changes in communities of bacteria,ammonia-oxidizing bacteria,and Nitrospira during the operation of a pufferfish Takifugu rubripes recirculating aquaculture system by using high-throughput DNA sequencing.Differences in bacterial communities were observed at days 1-32,47-62 and 78-93 of biofilm development by using 16S rRNA gene pyrosequencing.The relative abundance of Proteobacteria(Gammaproteobacteria)increased,while that of Bacteroidetes(Flavobacteria)decreased.The proportions of Nitrosomonas and Nitrospina ranged from 0.02%to 0.30%and from 0.02%to 0.83%,respectively.Ammonia monooxygenase gene pyrosequencing revealed that the top three operational taxonomic units were related to Nitrosomonas aestuarii(17.5%-61.1%),uncultured beta proteobacterium clone B67S-54(1.9%-45.2%),and uncultured bacterium clone AZPa8(3.6%-24.7%).Nitrite oxidoreductase gene pyrosequencing revealed that the relative abundance of the dominant strain Nitrospira sp.Ecomares 2.1 increased,but that of the abundant species Nitrospira marina decreased.Our results demonstrated that the communities of bacteria,ammonia-oxidizing bacteria,and Nitrospira were changing during the operation of the pufferfish recirculating aquaculture system.

Characterization of the bacterial communities associated with biofilters in two full-scale recirculating aquaculture systems

Bacteria play a major role in metabolizing ammonia and other metabolites in recirculating aquaculture systems(RASs).To characterize and compare the bacterial communities in the biofilters of two full-scale RASs for the culture of puffer fish,Takifugu rubripes,at different ages and densities were studied.In overall,47807 optimized reads of the 16 S rRNA gene with V4-V5 region were obtained from four biofilm samples collected after biofilm maturation.At 97%cut-off level,these sequences were clustered into 500 operational taxonomic units,and were classified into 19 bacterial phyla and 138 genera.At the phylum level,Proteobacteria and Bacteroidetes were the most abundant,followed by Nitrospirae and Planctomycetes.At the genus level,Colwellia,Marinifilum,Oceanospirillum,Lutibacter,Winogradskyella,Pseudoalteromonas,Arcobacter,and Phaeobacter were the top members.Nitrosomonas and Nitrospira were main ammonia-and nitrite-oxidizing bacteria.Differences in bacterial communities at different sampling dates and similarities of both biofilters were revealed in the Venn diagram and cluster analysis.Maintaining a good water quality and health offarmed fish in RASs depended on the correct management of the bacterial communities.This study provides more accurate information on the bacterial communities associated with the bifilters of both RASs.

Effects of light intensity and photoperiod on the growth and stress response of juvenile Nile tilapia(Oreochromis niloticus)in a recirculating aquaculture system

Light is an essential natural factor of fish growth and development.A light regime in indoor aquaculture is critical for sustainable fish production.This research aimed to investigate the effect of light intensity and photoperiod on the growth performance and stress response of Nile tilapia(Oreochromis niloticus),which is an important commercial species,in a recirculating aquaculture system(RAS).Fingerlings with an average weight of 5±0.9 g were randomly assigned to nine 1.5 m3 tanks with 145 fish in each tank,cultured under different light intensities(1000,2000,and 3000 lx)and photoperiods(12L:12D,18L:6D,24L:0D),and fed to apparent satiation twice a day for 160 days.The growth of tilapia subjected to 2000 lx was significantly better than that exposed to 1000 and 3000 lx(P<0.05)as indicated by the final weight(351.17±10.59 g),growth efficiency(0.77±0.26),specific growth rate(2.65%±0.21%per day)and feed conversion coefficient ratio(1.30±0.36).No significant difference was observed in the growth rate among different photoperiod groups(P>0.05).Light intensity and photoperiod manipulation did not cause a significant chronic stress response in tilapia.This study demonstrated that light intensity,especially at 2000 lx,and photoperiod manipulation could stimulate the growth of tilapia in the RAS and significantly affect economic profitability.This study also served as an important reference for tilapia indoor aquaculture.

Dynamic simulation based method for the reduction of complexity in design and control of Recirculating Aquaculture Systems

In this work we introduce the“Extensible Fish-tank Volume Model”that can reduce the complexity in the design and control of the Recirculating Aquaculture Systems.In the developed model we adjust the volume of a single fish-tank to the prescribed values of stocking density,by controlling the necessary volume in each time step.Having developed an advantageous feeding,water exchange and oxygen supply strategy,as well as considering a compromise scheduling for the fingerling input and product fish output,we divide the volume vs.time function into equidistant parts and calculate the average volumes for these parts.Comparing these average values with the volumes of available tanks,we can plan the appropriate grades.The elaborated method is a good example for a case,where computational modeling is used to simulate a‘‘fictitious process model”that cannot be feasibly realized in the practice,but can simplify and accelerate the design and planning of real world processes by reducing the complexity.

Effects of flow velocity on water quality and ammonia excretion in recirculating aquaculture system culturing juvenile largemouth bass(Micropterus salmoides)

Flow velocity plays an important role in recirculating aquaculture systems(RAS)and the growing practice of culturing juvenile largemouth bass(Micropterus salmoides).In this study,the effects of flow velocity on the water quality as well as the ammonia excretion were discussed from the perspective of actual production,and a polynomial model of ammonia nitrogen excretion was established,using the juvenile largemouth bass.Results showed that the range of ammonia nitrogen and nitrite nitrogen decreased with flow velocity increasing,while the number and volume share of large particles increased.According to the polynomial model,compared with the medium flow velocity(11 cm/s,2.45 body length(bl)/s),the ammonia excretion of juvenile largemouth bass at high(18 cm/s,4.00 bl/s),and low(4 cm/s,0.90 bl/s)flow velocity changed faster with time,and the excretion rate peaked at the 6th hour after feeding,earlier than that under medium flow velocity.Therefore,it is suggested to increase the flow velocity at the 5th hour after feeding and then decreased it at the 10th hour,to ensure better water quality in RAS culturing juvenile largemouth bass.

Comparison of nitrate-removal efficiency and bacterial properties using PCL and PHBV polymers as a carbon source to treat aquaculture water

Nitrate(NO_(3)^(−))accumulation in recirculating aquaculture systems(RASs)with high stocking densities presents a problem for reared animals and the environment.The use of a biodegradable polymer as organic carbon for heterotrophic denitrification exhibits good performance for NO_(3)^(−)removal from wastewater.A comparison of NO_(3)^(−)–N removal efficiency and bacterial properties using polycaprolactone(PCL)and poly(3-hydroxybutyrateco-3-hydroxyvalerate)(PHBV)as carbon sources to treat aquaculture water was conducted for a 102-day period.The results indicated that the NO_(3)^(−)–N removal rates of 0.27±0.07 and 0.19±0.05 g/L per day,respectively,could be achieved with influent concentrations ranging from 81.1 to 132.75 mg/L and a flow rate of 1 L/h.The removal of NO_(3)^(−)–N versus consumed PCL(1:1 w/w)was significantly higher than that versus consumed PHBV(0.3:1 w/w)(P<0.05).The concentrations of effluent nitrite-nitrogen and total ammonium nitrogen were maintained at an acceptable level.The bacterial community structures between the two types of reactors varied significantly.Acidovorax and Denitratisoma were the top two genera of the bacterial community in the biofilm in the PCL beads with a dominance of 26.83%and 6.67%,respectively.In the PHBV beads,Acidovorax at 17.95%and Bdellovibrio at 6.37%were the top two genera.The PCL-denitrification reactor developed in this study showed better potential than the PHBV-denitrification reactor in removing NO_(3)^(−)from aquaculture water.

Effect of seeding biofloc on the nitrification establishment in moving bed biofilm reactor(MBBR)

In recirculating aquaculture systems,nitrification is usually accelerated by inoculating nitrifier or mature biocarriers.In this study,the performance of the establishment of nitrification in the MBBR according to three different strategies:conventional method(Control group A),inoculation with biofloc recovered from a tilapia biofloc culture system(Group B),and addition with extra nitrite(Group C)in the Moving bed biofilm reactor(MBBR)was compared.Among them,the biofloc-inoculated group considerably accelerated the nitrification process in the MBBR(38 d),which is roughly 18 d faster than the control group(A)(56 d)and 21 d faster than group C(59 d).Less ammonia(8 mg/L NH_(4)^(+)-N,10 mg/L in other groups)and external nitrite(2 mg/L NO_(2)􀀀^(-)N)in the influent caused effluent ammonia to drop more slowly(5 d slower than the control group,8 d slower than the B group),which is detrimental to the nitrification process’development.Notably,the influent’s hydraulic retention time(HRT)was reduced from 12 h to 6 h following the successful establishment of nitrification.During the adaptation to reduced HRT,the MBBR inoculated with biofloc experienced short-term changes in the water quality index of the effluent water,whereas the other groups did not.The biofilm seeded with biofloc had the highest mean gray value ratio(1.42)of live/dead cell fluorescence,which grew better and could cover the entire groove under multiple microscope observations.However,the other groups did not demonstrate a similar trend.In summary,the research found that seeding biofloc use as nitrification bioaugmentation into the MBBR of the recirculating aquaculture system(RAS)to greatly speed up the nitrification process.

Performance of feeding Artemia with bioflocs derived from two types of fish solid waste

The production of bioflocs with the solid waste from recirculating aquaculture systems(RAS)and feeding Artemia results in additional nutrient retention and lowers waste discharged from RAS.The solid waste from the drumfilters of two RAS,which stocked European eel(Anguilla anguilla)and Nile tilapia(Oreochromis niloticus),was used as substrate to produce bioflocs in suspended growth reactors,referred to as E-flocs and T-flocs,respectively.Mono-diets consisting of 100%E-flocs and 100%T-flocs were added to culture Artemia,referred as E-Artemia and T-Artemia,respectively,in a laboratory scale test.The efficiency of this feeding regime was investigated.A significant difference was observed in terms of crude protein content(35.59±0.2%)for E-flocs,(29.29±0.95)%for T-flocs,(70.01±0.92)%for E-Artemia and(65.63±0.89)%for T-Artemia.134 out of the total operational taxonomic units(OTUs)were present in E-flocs and T-flocs from the analysis of high-throughput sequencing data.Most of the shared OTUs belonged to cyanobacteria.C18:1n7 of T-flocs was higher than that of E-flocs(P<0.05).C18:2n6 of E-flocs was significantly higher than that of T-flocs(P<0.05).No significant difference was observed in the other fatty acid compositions(P>0.05).The survival rate of E-Artemia was(22±0.02)%,significantly higher than that of T-Artemia(16%±0.02%)(P<0.05).No significant difference was observed between the average body weight of E-Artemia(2.38±0.40 mg)and E-Artemia(2.91±0.21)(P>0.05).The EPA of Artemia fed with E-flocs was(3.00±0.46)%,significantly higher than that of T-Artemia(1.57±0.19%)(P<0.05).This study offers a method for reusing the aquaculture waste,which will be helpful to achieve a zero-pollution discharge for aquaculture systems.