Seawater Recirculating Aquaculture System Research Articles

Evaluating protein skimmer performance in a commercial seawater recirculating aquaculture system (RAS)

Combining protein skimming with ozone (O3) is a common method for removing microparticles in recirculating aquaculture systems (RAS). Nevertheless, there is a limited number of studies that have validated protein skimming's performance at a commercial scale. Additionally, variations in protein skimmer designs and operational variables may yield different performance outcomes. In the present study, the performance of two types of full-scale protein skimmer (S1 and S2) were compared and evaluated under two levels of hydraulic retention time (HRT) (1.8 and 2.2 min) and three levels of O3 doses (0, 7, and 14 g O3/kg feed) in a commercial seawater RAS facility. Samples from the inlet and outlet of the protein skimmers were collected at each combination of operational variables. They were analysed for several relevant water quality parameters to quantify the treatment efficiency. O3 dose significantly improved water quality and reduced the numbers of microparticles and bacterial activity in a single pass. Besides that, doses as high as 14 g O3/kg feed significantly increased total residual oxidant (TRO) concentration. Additionally, an increase in HRT exerted a moderate effect on removing microparticles and a strong effect on redox potential (ORP) and TRO. Finally, the type of protein skimmer only affected the ORP, causing no significant changes to other water quality metrics. The correlations between the investigated water quality parameters defined a clear pattern of the ongoing processes and particle characteristics. Overall, the results demonstrated that protein skimming combined with carefully selected O3 doses can improve general water quality and control critical factors such as bacterial activity and microparticles under commercial operations.

Impact of temperature and dietary replacement of fishmeal on cardiovascular remodelling and growth performance of adult Atlantic salmon (Salmo salar L.)

The development of pathophysiological cardiac alterations in farmed salmonids is a recurrent and widespread welfare issue. Although the aetiology of such cardiac alterations is still unclear, several factors, including rearing temperature, selective breeding programs, and feeding strategies, could induce a morpho-physiological remodelling of cardiac structure. This maladaptive cardiac remodelling could impair cardiac function and health of farmed salmonids leading to premature mortality and production losses. In this study, we aimed to better understand the impact of suboptimal elevated temperature, resembling a typical summer temperature in Tasmania, and different feed formulations with low inclusion of fishmeal on cardiovascular remodelling and growth performance of adult Tasmanian Atlantic salmon. Fish were reared in a seawater recirculating aquaculture system and fed one of three diets with different fishmeal contents (6, 12, and 18%), while exposed to a temperature profile characterised by an incremental increase (1 °C per day) from 15 to 19.5 °C, 84 days at 19.5 °C (elevated temperature), and finally 34 days at 15 °C (optimal temperature). In terms of cardiac morphometric parameters, ventricular roundness (measured as height:width ratio) was not affected by temperature or dietary treatment. Conversely, the angle between the bulbus arteriosus and the ventricle significantly increased after the elevated temperature phase, along with relative ventricular mass, showing signs of maladaptive remodelling compared to initial conditions. However, these cardiac parameters were not different between the elevated and optimal temperature phase, which was associated with no changes in transcript abundance of molecular markers of pathological hypertrophy and remodelling, such as, atrial natriuretic peptide (anp) and b-type natriuretic peptide (bnp). Collectively, standard growth rate (SGR) and temperature growth coefficient (TGC), along with feed conversion ratio (FCR), were significantly elevated following exposure to suboptimum elevated temperature relative to optimal temperature. However, no differences in growth rate were observed in fish fed distinct dietary treatments at both elevated and optimal temperatures. These results imply that feeds with low levels of fishmeal can be used under challenging Tasmanian summer conditions without detrimental effect on salmon growth performance. Furthermore, our findings suggest that suboptimal elevated temperatures may induce remodelling of cardiac structure in adult Atlantic salmon, thereby potentially compromising cardiac function and overall health. Future efforts to manage Atlantic salmon susceptibility to climate change will require further research on the effect of challenging environmental conditions on cardiac physiology and performance in an attempt to prevent cardiac pathology, thereby improving health and welfare of farmed salmonids.

Study on modified SA-H3BO3 immobilization microorganism method for wastewater treatment in seawater recirculating aquaculture system

The sodium alginate-H3BO3 (SA-H3BO3) is traditionally used as bioremediation method for wastewater treatment in recirculating aquaculture system. Even though this method has many advantages (e.g., high cell loading) for immobilization, the remove of ammonium is not very effective. In this study, a modified method was built by adding polyvinyl alcohol and activated carbon into SA solution, and then crosslinked with saturated H3BO3–CaCl2 solution for creating new beads. Moreover, response surface methodology was utilized for optimizing the immobilization based on Box-Behnken design. The removal rate of ammonium in 96 h was taken as the primary performance criterion to characterize the biological activity of immobilized microorganisms (i.e., Chloyella pyrenoidosa, Spirulina platensis, Nitrifying bacteria, and Photosynthetic bacteria). Based on the results, the optimal parameter of immobilization as follows: the concentration of SA was 1.46%, the concentration of polyvinyl alcohol was 0.23%, the concentration of activated carbon was 0.11%, the crosslinking time was 29.33 h, and the pH was 6.6.

Rasiella rasia gen. nov. sp. nov. within the family Flavobacteriaceae isolated from seawater recirculating aquaculture system.

A novel bacterium designated RR4-40T was isolated from a biofilter of seawater recirculating aquaculture system in Busan, South Korea. Cells are strictly aerobic, Gram-negative, irregular short rod, non-motile, and oxidase- and catalase-negative. Growth was observed at 15-30°C, 0.5-6% NaCl (w/v), and pH 5.0-9.5. The strain grew optimally at 28°C, 3% salinity (w/v), and pH 8.5. The phylogenetic analysis based on 16S rRNA gene sequences showed that strain RR4-40T was most closely related to Marinirhabdus gelatinilytica NH83T (94.16% of 16S rRNA gene similarity) and formed a cluster with genera within the family Flavobacteriaceae. The values of the average nucleotide identity (ANI), digital DNA-DNA hybridization (dDDH), and average amino acid identity (AAI) between genomes of strain RR4-40T and M. gelatinilytica NH83T were 72.91, 18.2, and 76.84%, respectively, and the values against the strains in the other genera were lower than those. The major fatty acids were iso-C15:0 (31.34%), iso-C17:0 3-OH (13.65%), iso-C16:0 3-OH (10.61%), and iso-C15:1 G (10.38%). The polar lipids comprised phosphatidylglycerol, diphosphatidylglycerol, aminophospholipid, aminolipid, glycolipid, and sphingolipid. The major respiratory quinone was menaquinone-6 (MK-6) and the DNA G + C content of strain RR4-40T was 37.4 mol%. According to the polyphasic analysis, strain RR4-40T is considered to represent a novel genus within the family Flavobacteriaceae, for which the name Rasiella rasia gen. nov, sp. nov. is proposed. The type strain is RR4-40T (= KCTC 52650T = MCCC 1K04210T).

Removal of microparticles and bacterial inactivation in freshwater RAS by use of foam fractionation, H 2 O 2 and NaCl

Foam fractionation (FF) is an effective water treatment technology used to remove fine particles in seawater recirculating aquaculture systems (RAS). However, there is only limited available information on the operation and efficiency of FF in freshwater. This study investigated the treatment efficiency of FF by measuring changes in bacterial activity and microparticle densities in freshwater from RAS. Thirty-six separate batch tests were performed with FF separately and in combination with addition of hydrogen peroxide (H2O2) and salt (NaCl). Both chemicals are commonly used for water treatment in freshwater aquaculture. The experiment was a 2 × 2 × 3 factorial design with 3 factors: FF (present or absent), H2O2 (0 or 10 mg L⎻1) and NaCl (0, 3, or 10 ppt). FF reduced the concentration of microparticles and turbidity in freshwater by 58.7 ± 5.4% and 27.5 ± 3.8% respectively. H2O2 had a significant antimicrobial effect, and the combination of H2O2 and FF resulted in an 80% reduction in bacterial activity in freshwater. Addition of NaCl improved the efficiency of FF by further reducing particle concentration and turbidity two-fold at 10 ppt compared to 0 ppt. This study provides new knowledge on the potential use of FF to improve the water quality in freshwater RAS, and this was further enhanced by the addition of H2O2 or NaCl.

PCR, in-situ hybridization, and phylogenetic analysis suggest that 'big belly' disease in barramundi, Lates calcarifer (Bloch), is caused by a novel Vibrio species.

'Big belly' disease is a chronic, granulomatous bacterial enteritis and peritonitis, first reported in 3- to 4-week-old Asian seabass or barramundi, Lates calcarifer Bloch fry. Affected fry are emaciated and have a swollen abdomen, and the condition is referred to as 'skinny pot-belly' or 'big belly' disease. In this study, histopathological examinations of diseased fish from a batch of 2-month-old, 6- to 8-cm L.calcarifer fingerlings, kept in seawater recirculating aquaculture systems, showed pathology resembling 'big belly' disease. Ethanol-fixed tissues were tested positive using specific PCR primers based on 16S rRNA genes. In situ hybridization using dioxygenin-labelled positive PCR products on formalin-fixed paraffin-embedded tissues showed positive reactions with intralesional, clusters of the large, 'big belly' coccobacilli. A phylogenetic tree constructed based on analyses of these 16S rRNA gene PCR products from five positive fish suggests that the 'big belly' bacterium is most likely a novel Vibrio species.

Pikeienuella piscinae gen. nov., sp. nov., a novel genus in the family Rhodobacteraceae.

A novel bacterium, designated strain RR4-56T, was isolated from a biofilter of a seawater recirculating aquaculture system. The 16S rRNA gene sequence analysis showed that the isolate was closely related to Halovulum dunhuangense YYQ-30T (92.6%), Albimonas donghaensis DS2T (91.3%), Pontivivens insulae GYSW-23T (91.3%), and Monaibacterium marinum C7T (90.9%), belonging to the family Rhodobacteraceae. The strain was aerobic, Gram-negative, rod-shaped, oxidase-positive, and catalase-negative. Its optimum temperature, pH, and salinity for growth were 25-30°C, pH 8.5, and 2-3% NaCl (w/v), respectively. Its growth occurred at 15-35°C, pH 5.0-9.5, and 0-7% NaCl (w/v). It contained ubiquinone-10 (Q-10), a respiratory quinone, and the major cellular fatty acids were 11-methyl C18:1 ω7c (31.9%), C18:1 ω6c (30.4%), and C19:0 cyclo ω8c (16.1%). The polar lipids present in the strain were phosphatidylglycerol, an unidentified phospholipid, and an unidentified aminolipid. The strain had one 4,373,045 bp circular chromosome with G + C contents of 65.9 mol% including 4,169 genes, 4,118 coding sequences (CDSs), 3 rRNAs, and 45 tRNAs. Genome annotation predicted some gene clusters related to the degradation of several types of organic matter such as protocatechuate, catechol, and phthalate. Based on the polyphasic characteristics, RR4-56T represents a novel genus and species in the family Rhodobacteraceae, for which the name Pikeienuella piscinae gen. nov., sp. nov. was proposed. The type strain is RR4-56T (= KCTC 52648T = DSM 107918T).

Optimized energy consumption in electrochemical-based regeneration of RAS water

The rapid expansion of the aquaculture industry and seawater recirculating aquaculture systems (SW-RAS) parallel to the human growth require more efficient water consumption while preserving water resources. Cost-effective purification technologies to remove the highly toxic ammonia nitrogen (TAN), whose accumulation is produced by the fish metabolism, are fundamental to this goal. The high chloride concentration in seawater is at the same time an obstacle to conventional biological technologies and an opportunity to apply the chlorine-based oxidation of TAN. Thus, this work focuses on TAN oxidation by electrogenerated chlorine and considers alternative process configurations, (i) one-step electrochemical oxidation and, (ii) two-steps breakpoint oxidation after chlorine electrogeneration.The experimental assessment highlights that both process alternatives are effective in the total removal of ammonia and combined chlorine, when model SW with TAN concentration of 10 mg NH4+/L is treated. The specific energy intensity defined as kWh/mg NH4+ has been calculated for both configurations; being the two-stage process 2 times more energy efficient. Thus, this work provides the guidelines for the design of optimized electrochemical RAS water remediation with minimum energy consumption.

Salaquimonas pukyongi gen. nov., sp. nov., a novel bacterium within the family Phyllobacteriaceae.

A novel aerobic, Gram-negative bacterial strain, RR3-28T, was isolated from a seawater recirculating aquaculture system in Busan, Republic of Korea. Cells were rod-shaped, non-motile, oxidase-positive, catalase-negative and grew optimally at 25-30 °C, pH 8.5 and 3 % (w/v) NaCl. Based on the results of phylogenetic analysis, strain RR3-28T was most closely related to Zhengella mangrovi X9-2-2T within the family Phyllobacteriaceae with 95.97 % 16S rRNA gene sequence similarity. The major cellular fatty acids were summed feature 8 (C18 : 1ω7c and/or C18 : 1ω6c, 71.1 %) and 11-methyl C18 : 1ω7c (14.4 %). The major polar lipids were phosphatidylglycerol, phosphatidylethanolamine, phosphatidylmonomethylethanolamine, phosphatidylcholine and unidentified aminolipids. The predominant quinone was ubiquinone Q-10 and the DNA G+C content was 58.6 mol%. On the basis of its phenotypic and genotypic characteristics, strain RR3-28T represents a novel genus and species belonging to the family Phyllobacteriaceae, for which the name Salaquimonas pukyongi gen. nov., sp. nov. is proposed. The type strain of the species is RR3-28T (=KCTC 52649T=DSM 107947T).

Microbial valorization of solid wastes from a recirculating aquaculture system and the relevant microbial functions

This study was performed to establish valorization technology for solid wastes from a seawater recirculating aquaculture system (RAS) by using beneficial microorganisms. An efficient microbial agent (KBM-1) was selected based on the degradation activity of the RAS solid wastes (20% slurry) in a lab-scale reactor system considering the removal rates of chemical oxygen demand, solid material, total nitrogen, ammonium-N, and nitrate-N and the production of organic acids as electron donors for denitrification. The microbial consortium KBM-1 was particularly efficient in the removal of ammonium-N and nitrate-N with removal efficiencies of 42% and 50%, respectively, in eight days and in the rapid production of organic acids (230 mg L−1, 3.5 mM, 0.018 kg m−3 d−1) after two days. There was a concomitant removal of NO3--N (41%, 0.005 kg N m−3 d−1) after two days when a significant production of organic acids occurred. Comamonas sp. was a dominant genus after eight days in all treatments. The level of nitrate-N in the treatments with KBM-1 decreased by 50.4% after eight days, as opposed to that of the control sample (27.7%), indicating the potential denitrification activity of Citrobacter freundii and Comamonas sp. The bioaugmented species (Sporolactobacillus inulinus, Lactobacillus mali, Lactobacillus casei, and Clostridium tyrobutyricum), constituting 41% of the total communities, appeared to facilitate the growth of indigenous microbial communities that were involved in the degradation (hence valorization) of solid wastes (mostly remaining fish feed and fish feces) into simple metabolites (organic acids and inorganic materials such as ammonium, nitrite, nitrate, and CO2). The simultaneous generation of organic acids through the valorization of solid wastes and their subsequent reuse in the denitrification of an RAS biofilter system can provide a significant contribution to the eco-friendly management of RASs and provide meaningful economic merit to the solid wastes of RASs.

Chlorine-based disinfection for controlling horizontal transmission of VNN in a seawater recirculating aquaculture system growing European seabass

An innovative physicochemical approach for treating the recycled water within a seawater recirculating aquaculture systems (RAS) has been recently developed, which includes inherent disinfection within the ammonia electro-oxidation cycle. The efficiency of the inherent disinfection was tested in comparison to a RAS consisting of a bio-treatment unit (which did not include a disinfection component), both systems operating under similar fish densities and makeup water flow rates. Neural necrosis virus (NNV) was chosen as a model pathogen, due to its pathogenicity to sea bass (Dicentrarchus labrax) and many other aquaculture species. The course of infection (exposure → immune response → infection) was monitored in a cohabitation experiment, testing the horizontal transmission of NNV using immunological and molecular methods, in addition to recording clinical signs. Results indicate that under the conditions prevailing in the RAS in which the physicochemical method was applied, the NNV horizontal transmission pathway was blocked. No immune response to viral neural necrosis (VNN) was detected in the fish sampled during the experiment, in contrast to a significant and classic immune response observed in the fish held in the RAS based on bio-treatment. Challenged fish in both systems showed typical outbreak profile, however in the bio-treated RAS, a slow disease course was observed, hypothesized by us to be the result of a high concentration of humic substances present in the water. The results indicated that the off-host phase of the NNV can be controlled by effective chlorine-based disinfection. The disinfection effect in the physico-chemically-treated RAS and C∙t (chlorine concentration times the retention time) value quantified in the present work are most likely sufficient to reduce infection of a wide range of other aquaculture pathogens.

Hematological and histological changes of black porgy Acanthopagrus schlegeli in ozonated recirculating systems

This study evaluated hemato-histological changes of black porgy in recirculating aquaculture systems (RAS) with three different ozone doses (no ozone, 20 g, and 40 g ozone/kg feed day−1). During the 44-day study, black porgy did not show significant behavior changes or mortalities in both the ozonated systems displaying average total residual oxidants concentrations of 0.12 and 0.25 mg/L. There were no differences in growth and blood parameters among the systems. However, histological alterations on gills and livers were observed in both the treatment systems. In the higher ozone dose, signs of cellular damage were more apparent. Although the ozone doses did not manifest a serious adverse effect on growth and hematological observations in this short-term study, an ozone dose should not exceed 20 g ozone/kg feed day−1 for black porgy based on the histological result. In order to use ozone in a seawater RAS, further studies will be needed to evaluate long-term effects of total residual oxidants.

해수순환여과양식시스템에서 분리된, Nitratireductor 속과 관련된 균주 RR3-28의 유전체 서열

해수순환여과양식시스템에서 분리된, Nitratireductor 속과 관련된 균주 RR3-28의 유전체 서열

순환여과양식시스템으로부터 분리된 Halioglobus sp. RR3-57의 유전체 분석

순환여과양식시스템으로부터 분리된 Halioglobus sp. RR3-57의 유전체 분석

Electrooxidation for simultaneous ammonia control and disinfection in seawater recirculating aquaculture systems

A new operational approach for seawater recirculating aquaculture systems (RAS), which is based solely on physicochemical water treatment techniques, is described. Within this concept the fish are grown at very high TAN concentration and slightly acidic pH, the latter calculated to maintain the NH3 concentration lower than a predetermined threshold (typically <0.1mgN/l). The inherently high Cl− concentration in seawater enables efficient electro-generation of Cl2(aq) species and consequent electrooxidation of ammonia directly to N2(g). Fish pond water is constantly recycled between electrolysis tanks and the pond, supplying both disinfected water and most of the acidity required to maintain the necessary low pH in the fish pond. For establishing proof-of-concept gilthead seabream (Sparus aurata) was grown at the pilot scale for 133 consecutive days. Throughout this period the fish showed excellent growth rate and survival, along with excellent general health condition. 88% of the NH3 mass excreted by the fish was electro-oxidized in the pilot system, while at the same time the pond water was efficiently disinfected. The high TAN concentrations in the rearing water resulted in high current efficiency in the electrooxidation step, reduced water treatment units volume and generation of very low trihalomethane (THM) concentrations, attributed to the low pH allowed to develop during the electrolysis stage. The pilot system was operated in two stages differing in TAN concentration (30 and 65mgN/l) and pH (6.7 and 6.4, leading to NH3(aq) concentrations of 0.047 and 0.052, respectively). Average current efficiency in the TAN electrolysis step was 68%. Cost analysis showed that both capital and operational costs were highly competitive, as compared with conventional RAS operation. Specifically, the cost of the water treatment component within the pilot operation (TAN removal to N2(g) and water disinfection) was estimated at ∼$0.205per kg feed, out of which $0.079 was attributed to electricity costs.

Uncultured bacterial diversity in a seawater recirculating aquaculture system revealed by 16S rRNA gene amplicon sequencing.

Bacterial diversity in a seawater recirculating aquaculture system (RAS) was investigated using 16S rRNA amplicon sequencing to understand the roles of bacterial communities in the system. The RAS was operated at nine different combinations of temperature (15°C, 20°C, and 25°C) and salinity (20‰, 25‰, and 32.5‰). Samples were collected from five or six RAS tanks (biofilters) for each condition. Fifty samples were analyzed. Proteobacteria and Bacteroidetes were most common (sum of both phyla: 67.2% to 99.4%) and were inversely proportional to each other. Bacteria that were present at an average of ≥ 1% included Actinobacteria (2.9%) Planctomycetes (2.0%), Nitrospirae (1.5%), and Acidobacteria (1.0%); they were preferentially present in packed bed biofilters, mesh biofilters, and maturation biofilters. The three biofilters showed higher diversity than other RAS tanks (aerated biofilters, floating bed biofilters, and fish tanks) from phylum to operational taxonomic unit (OTU) level. Samples were clustered into several groups based on the bacterial communities. Major taxonomic groups related to family Rhodobacteraceae and Flavobacteriaceae were distributed widely in the samples. Several taxonomic groups like [Saprospiraceae], Cytophagaceae, Octadecabacter, and Marivita showed a cluster-oriented distribution. Phaeobacter and Sediminicola-related reads were detected frequently and abundantly at low temperature. Nitrifying bacteria were detected frequently and abundantly in the three biofilters. Phylogenetic analysis of the nitrifying bacteria showed several similar OTUs were observed widely through the biofilters. The diverse bacterial communities and the minor taxonomic groups, except for Proteobacteria and Bacteroidetes, seemed to play important roles and seemed necessary for nitrifying activity in the RAS, especially in packed bed biofilters, mesh biofilters, and maturation biofilters.

Effects of two different ozone doses on total residual oxidants, nitrogen compounds and nitrification rate in seawater recirculating systems for black seabream Acanthopagrus schlegelii (Bleeker)

Ozone was applied to seawater recirculating aquaculture systems (RAS) to measure the effects on water quality and biofilter efficiency. Three replicate experimental systems were used in this study. Each system consisted of four rectangular culture tanks, a sump, two settling chambers, a foam fractionator and a trickling biofilter. The control system (CS) was not ozonated, but Treatment 1 (T 20) and Treatment 2 (T 40) were ozonated with 20 and 40g O3/kg feedday−1, respectively. Three hundred twenty black seabream (mean weight±S.D. of 334.5±1.9g) were stocked into each system, and cultured for the entire 44-day study period. During this period, total residual oxidants (TRO), nitrogen compounds (Total-ammonia–N, TAN; nitrite–N, NO2–N and nitrate–N, NO3–N) were measured, and nitrification efficiencies of the trickling biofilters were calculated for each system.Generally, the application of ozone to the seawater systems reduced TAN and NO2–N concentrations in the culture tanks of both treatments. However, the nitrification rate of the biofilter in the T 40 and the CS systems was about 50% lower than the rate of the biofilter in the T 20 system. Therefore, the use of a moderate dose of ozone (20g O3/kg feedday−1) appears to enhance nitrification, possibly through the reduction of dissolved organic matter that may interfere with bacterial activity.However, application of ozone at 40g O3/kg feedday−1 appears to depress microbial activity associated with biofiltration and nitrogen removal efficiency, perhaps through toxicity of associated compounds or directly through residual oxidants. Based on the results of this study, continuous ozonation should not exceed 20g ozone/kg feed (mean TRO 0.15mg/L) in a seawater RAS to avoid negatively affecting the nitrification efficiency of the bio-filters.

Ozonation in seawater recirculating systems for black seabream Acanthopagrus schlegelii (Bleeker): Effects on solids, bacteria, water clarity, and color

A 44-day production trial was done in three identically configured pilot-scale seawater recirculating aquaculture systems (RAS) to evaluate the effects of two different ozonation levels on solids, bacteria, water clarity, and color variables. The control system (CS) was not ozonated, while the treatment systems received ozone at either 20gO3/kgfeedday−1 (T 20) or 40gO3/kgfeedday−1(T 40).Solids concentrations in the two treatments receiving ozone were lower and less variable than the concentrations in the CS. Ozonation reduced suspended solids (SS) and volatile suspended solid (VSS) concentrations by 42.0–52.5% and dissolved organic carbon (DOC) by 29.3–30.6%. The ratios of DOC to SS and to VSS decreased significantly (P<0.05). In addition, the amount of solid removed from the radial flow settler increased 27.1% in both ozone-treatment systems. Bacteria counts on different culture media (Marine, TCBS and MacConkey agars) varied considerably during the study period, but were generally lower in the treatments receiving ozone than the CS. Differences in bacteria abundance between two treatments, T 20 and T 40, were not significant (P>0.05). Based on 24-h sampling, bacteria counts in CS gradually increased after feeding during the daytime and declined during the night. Counts of Vibrio spp. in T 20 fluctuated daily in a similar pattern to the Vibrio spp. in the CS, while overall bacteria counts in T 40 remained low throughout the 24-h sampling period.Turbidity fluctuated greatly in all treatments; there were no significant differences between any of the treatments (P>0.05). Apparent water color (AC) and true water color (TC) in the treatment were reduced 70% compared to the CS, but there was no significant difference (P>0.05) between the two ozone treatments.Based on the variables measured, the higher dose of ozone (40gO3/kgfeedday−1) did not improve solid concentrations, bacterial counts or water colors beyond the values found in the T 20 treatment. Thus, the use of ozone at 20gO3/kgfeedday−1 in a seawater RAS appears to be sufficient to improve water quality of these systems without adversely affecting black sea bream (Acanthopagrus schlegelii) growth.

Design of Closed Seawater Recirculating Aquaculture System for Korean Rockfish Sebastes schlegeli Culture

Recirculating aquaculture system (RAS) consists of different treatment compartments that maintain water quality within the ranges commonly recommended for fish cultures. However, common RASs still exert considerable environmental impact since concentrations of organic matter and nutrients in their effluents are high. Compared with the traditional RAS, the model RAS developed here use a sedimentation basin for digestion purposes and then use the released volatile organic matter to stimulate a denitrification process. Different treatment compartments for solids, total ammonia nitrogen, and nitrate removal have been reviewed. This paper provides the basic information on designing different treatment compartments as well as the engineering criteria in closed seawater RAS, consisting of circular tanks for fish cultures; dual drain systems, sedimentation basins and foam fractionators for removal of solids; nitrification biofilters for TAN removal; denitrification biofilters for nitrate removal; and aerators for aeration. The main purpose is to outline a common procedure in designing of closed RAS for marine fish culture with an emphasis on easy management and low expense, as well as reduction of the environmental impact.

Performance of a Lab-Scale Closed Seawater Recirculating System for Korean Rockfish Sebastes schlegeli Culture

Performance of a laboratory scale closed seawater recirculating aquaculture system was evaluated. Twenty-kg of korean rockfish (130 fish) with an average body weight of 153.8g was stocked. Over a 107-day culture period, fish reached final density of <TEX>$51.7kg/m^3$</TEX> (initial density, <TEX>$33.3kg/m^3$</TEX>) on the basis of the culture tank volume. On a daily basis, added water amounted to 3.4% of the total water volume in the system. Total ammonia nitrogen (TAN) concentrations were below 1mg/l and nitrite nitrogen <TEX>$(NO_2-N)$</TEX> concentrations were within the range of 1-3mg/l on most sampling days. TAN was removed from bead and sand filters and it was removed or produced in the sedimentation basin. Basically, <TEX>$NO_2-N$</TEX> was removed in the bead and sand filters, while it was either removed or produced in the sedimentation basin. Nitrate nitrogen <TEX>$(NO_3-N)$</TEX> was produced in the bead filters and removed from the sand filter and sedimentation basin. The foam fractionator performed well in the recirculating system. The maximal daily removal values for total suspended solids (755) and protein were 10.9g and 1.4g, respectively. Whole water quality parameters were within the levels commonly recommended for fish culture on most of the sampling days. However, further studies are needed to evaluate the commercial feasibility of this system because of the smallscale system used in present experiment. At least, the present study still provides some basic information for further studies of this kind of system.