Marine Recirculating Aquaculture System Research Articles

Effect of oxidation–reduction potential on performance of European sea bass (Dicentrarchus labrax) in recirculating aquaculture systems

The direct impact of oxidation–reduction potential (ORP) on fish welfare and water quality in marine recirculating aquaculture systems (RAS) is poorly documented. In this study, the effects of the fish size (S1, S2, S3) and ORP level (normal, four successive levels) on the performance of European sea bass (Dicentrarchus labrax) were investigated. Three size fish were distributed into two RAS (RAS and RAS O3). Ozone was injected into RAS O3 to increase the ORP level. The ORP was stabilized to four successive levels: 260–300, 300–320, 320–350, and 300–320 mV in fish tanks during four periods (P1–4). At the last day of each period, the hematological parameters, plasma protein and mortality of sea bass were analyzed. Two-way ANOVA revealed that several hematological parameters, including pH, hematocrit, concentrations of oxygen, carbon dioxide, glucose (Glu), ionized calcium, kalium, and hemoglobin, were significantly influenced by the increased ORP levels over the experimental period. The alteration in blood Glu and plasma protein concentration showed that ORP around 300–320 mV started to stress sea bass. Once the ORP exceeded 320 mV in the tanks during the P3 period, mortality occurred even when total residual oxidants/ozone-produced oxidants was only 0.03–0.05 mg L−1 in the fish tanks. At the same time, plasma protein decreased notably due to appetite depression. After the decrease in ORP during the P4 period, mortality continued. In conclusion, the results strongly suggest that for European sea bass in RAS, the ORP should not exceed 320 mV in the tanks. Once ozonation damaged fish, the effect seemed to be irreversible. However, how ORP affected related hematological parameters still need the further investigations.

Effects of membrane filtration on bacterial number and microbial diversity in marine recirculating aquaculture system (RAS) for Atlantic cod (Gadus morhua L.) production

Abstract Particle accumulation in recirculating aquaculture systems (RAS) are generated from uneaten food and feces, and bacteria tends to proliferate. Small organic particles act as substrate for bacterial growth and may by direct interference with gills cause stress and reduce disease resistance for the cultivated species. Most diseases in aquaculture of marine fish larvae are caused by opportunistic microorganisms that become pathogenic when the fish is under stressed conditions. The present study investigated the potential of using a membrane bioreactor (MBR) as a part of the water treatment in a RAS for production of marine fish larvae, since the small pore size (50 nm) efficiently removes organic particles including the colloidal fraction in the system. The experiment was a 50 day start-feeding experiment with Atlantic cod ( Gadus morhua L.), comparing water quality and larval performance in a conventional RAS (cRAS) with a membrane filtrated RAS (mRAS). In mRAS, 8.5% of the water flow was at any time membrane filtrated. The present study showed that the MBR improved water quality significantly by reducing turbidity and by lowering the total number of bacteria in the rearing water (up to 80% reduction). Microbial communities in water samples were significantly different between cRAS and mRAS already on 5 days post-hatching (dph) and throughout the experiment. The microbial community composition of the rearing water was significantly different from the composition of the larval microbiota during the experiment, although differences between larval samples were different only on 50 dph. The present study showed the potential of using MBR to lower the bacterial carrying capacity (CC) by efficiently removing organic particles and bacteria. In average a 13% higher cod larval growth (weight, %) at 40 dph and a 3.0% higher survival rate at 50 dph were measured in the mRAS scheme.

Membrane performance and fouling behavior of membrane bioreactors installed in marine recirculating aquaculture systems

Accumulation of fine suspended solids and colloids in a recirculating aquaculture system (RAS) can be avoided by integrating a membrane filtration unit into the system, where the inclusion of a membrane bioreactor (MBR) may be an alternative. The main purpose of the study was to identify how the feeding regime affected membrane performance and fouling phenomena caused by dissolved and submicron colloidal particles in the system, and how the membrane impacted general water quality and particle characterization. To be able to evaluate membrane performance and fouling behavior, transmembrane pressure (TMP) was monitored and assessed in relation to changes in rearing conditions and different water quality parameters observed. From this study the positive influence on the chosen water quality parameters was apparent, where an improved water quality was observed when including a membrane filtration in RAS. Selected water quality parameters and TMP changed during the experimental period in response to the feeding regime, where algae paste, decaying rotifers and dry feed seemed to contribute the most to membrane fouling. Analysis of the concentration of submicron particles and particle size distribution (PSD) (particles<1μm) showed both a higher concentration and a more spread distribution in the rotifer/algae paste and dry feed period compared to the Artemia period, which might explain the observed increase in fouling. This study also showed that adapted procedures for concentrate removal are important to prevent hydrolysis of retained particles in the concentrate and leakage of nutrients and organic matter back to the system.

The effect of halophyte planting density on the efficiency of constructed wetlands for the treatment of wastewater from marine aquaculture

The low volume batches of highly-concentrated wastewater discharged from land-based marine recirculating aquaculture systems are ideally suited for treatment by halophyte planted constructed wetlands. To evaluate the role of plants and the effect of planting density on yield and performance in small-scale saline constructed wetlands (CWs), NH4++NO3−+NO2−=total dissolved inorganic nitrogen (TDIN) and dissolved inorganic phosphorus (DIP) were measured at regular intervals over 24h periods. CWs were planted with the halophyte Salicornia europaea at high- and low-densities and were compared to the performance of unplanted controls. S. europaea plants were cropped regularly to assess potential commercial yield at the two densities. There was no significant effect of planting density on performance or crop yields and planted beds consistently outperformed the control beds removing 62.0±34.6mmolNm−2d−1 (34–73% of influent TDIN) compared to 23.0±26.8mmolNm−2d−1 (−1% to 41% of influent TDIN) by control beds. Results for DIP were less clear, significant removal occurred only once, with reduction of 18.3±5.0mmolPm−2d−1 by planted beds and 18.1±2.6mmolPm−2d−1 by the unplanted controls. The results demonstrate the effectiveness of halophyte-planted CW in treatment of marine aquaculture wastewater.

Culture of yellowtail kingfish (Seriola lalandi) in a marine recirculating aquaculture system (RAS) with artificial seawater

The development of new species is a high priority for the diversification of the Chilean aquaculture sector. The yellowtail kingfish (Seriola lalandi) is a promising candidate for commercial production in recirculating aquaculture systems (RAS). This paper presents data on the culture of yellowtail kingfish in a marine RAS working for 488 days using artificial sea water. Growth performance, feed conversion, feeding rate, condition factor and mortality were determined for fish having an average initial weight (±S.D.) of 0.7±0.2g up to a final average weight of 2006±339.0g. The RAS configuration (drum filter, protein skimmer with ozone, biological nitrification and denitrification, carbon dioxide removal and oxygenation) showed performance stability under the conditions assayed (low water renewal rate). Total ammonia nitrogen and nitrite-nitrogen concentration averaged 0.74±0.42mg/L and 0.21±0.24mg/L respectively. After installation, the denitrification reactor kept nitrate-nitrogen concentrations below 40mg/L. Nitrate-nitrogen was totally reduced at oxidation reduction potential values between −150 and −250mV. Water temperature averaged 22.6±1.4°C and oxygen was maintained close to saturation levels. Carbon dioxide concentration was in average 8.3±2.47mg/L and pH 7.5±0.1. Water renewal rate was 0.45% of the total system volume per day. The system proved the capability to maintain optimal water quality and secured animal welfare.

Integrated Membrane Bioreactor for Water Quality Control in Marine Recirculating Aquaculture Systems

The aquaculture live feed organisms Acartia tonsa (a calanoid copepod, experiment 1) and Brachionus “Cayman” (a rotifer, experiment 2) were cultivated in marine recirculating aquaculture systems (RAS), respectively. The pilot plant was built as a combination of conventional RAS (cRAS) and as a modified RAS which implemented an ultrafiltration membrane bioreactor (MBR) for the removal of fine suspended solids and colloidal particles as part of the treatment system (mRAS). The two treatment schemes were connected to the same biofilter (a moving bed bioreactor). In the first experiment, the membrane was operated with no extraction of concentrate, and hydraulic retention time (HRT) of 6 hours (i.e., water exchange in the cultivation tanks of 4 times per day). In the second experiment, the membrane was operated with daily extraction of concentrate, and HRT of 12 hours. Results show that the MBR option is more efficient in removing particles from the recycle stream than conventional RAS. However, the impact this has on the number of particles in the live feed cultivation tanks is not readily apparent based on particle analysis. The amount of suspended solids added during feeding exceeds the amount removed in the recycle system. This requires a higher recirculation rate and different membrane operating conditions.

Waste treatment in recirculating aquaculture systems

Recirculating aquaculture systems (RAS) are operated as outdoor or indoor systems. Due to the intensive mode of fish production in many of these systems, waste treatment within the recirculating loop as well as in the effluents of these systems is of primary concern. In outdoor RAS, such treatment is often achieved within the recirculating loop. In these systems, extractive organisms, such as phototrophic organisms and detritivores, are cultured in relatively large treatment compartments whereby a considerable part of the waste produced by the primary organisms is converted in biomass. In indoor systems, capture of solid waste and conversion of ammonia to nitrate by nitrification are usually the main treatment steps within the recirculating loop. Waste reduction (as opposed to capture and conversion) is accomplished in some freshwater and marine indoor RAS by incorporation of denitrification and sludge digestion. In many RAS, whether operated as indoor or outdoor systems, effluent is treated before final discharge. Such effluent treatment may comprise devices for sludge thickening, sludge digestion as well as those for inorganic phosphate and nitrogen removal. Whereas waste disposed from freshwater RAS may be treated in regional waste treatment facilities or may be used for agricultural purposes in the form of fertilizer or compost, treatment options for waste disposed from marine RAS are more limited. In the present review, estimations of waste production as well as methods for waste reduction in the recirculating loop and effluents of freshwater and marine RAS are presented. Emphasis is placed on those processes leading to waste reduction rather than those used for waste capture and conversion.

Kinetics of nitrogen compounds in a commercial marine Recirculating Aquaculture System

This work reports the degradation of nitrogen compounds in a commercial marine Recirculating Aquaculture System (RAS) aimed at the culture of sea bream (Sparus aurata) and sea bass (Dicentrarchus labrax). The annual production of fingerlings is around 18 million and the process includes a drum filter and a biological treatment in order to enhance the water quality.Ammonia measurements at the inlet of the biological system showed that the concentration of this compound followed a diurnal pattern closely related to the feeding of the fingerlings; thus every day after feeding around 8am, the concentration of ammonia started increasing, it reached a maximum about 8h after feeding and then continued decreasing until the following morning.With regard to nitrite concentration, no significant differences were observed between the values measured at the inlet and the outlet of the biological system during the day, with an average concentration of this compound ranging between 0.08 and 3.66mg NO2−Nl−1.A drawback of ammonia removal by means of nitrification is the subsequent increase of nitrate as the final product of ammonia oxidation in the culture system. The nitrate concentration in the biofilters inlet was found to fluctuate between 22.33 and 55.44mg NO3−Nl−1 during the characterization period. Partial water exchange was needed during the day in order to minimize the water losses during fish handling and to keep the concentration of nitrate below the maximum allowable level of 46mg NO3−Nl−1 due to production requirements in the hatchery under study.The ammonia degradation within the biological system, obtained by the ammonia measurements and comparison of the values at the inlet and outlet of the trickling filters has been fitted satisfactorily to ½-order/0-order kinetic expressions in good agreement with the results found in literature for laboratory and pilot plant studies. Rate constants k(1/2-order)=0.49g1/2m−1/2day−1 and k(0-order)=0.64gm−2day−1, have been obtained in this study for commercial trickling biofilters.Thus, this work reports for the first time the kinetics of ammonia oxidation in trickling biofilters installed in a commercial recirculating aquaculture marine water system. These results will provide useful information for the design of an appropriately sized biofilter in order to optimize the water quality and reduce the need to exchange water in this activity.

The effects of moderate ozonation or high intensity UV-irradiation on the microbial environment in RAS for marine larvae

Marine fish larvae are sensitive to infections by opportunistic bacteria. Procedures like disinfection and pulse feeding may destabilise the microbial community and promote r-selection and proliferation of opportunists in intensive rearing tanks. Recirculation aquaculture systems (RAS) have been hypothesised to stabilise and mature the microbial community, creating a more beneficial environment for the larvae during the live feed period. Two marine RAS with Atlantic cod larvae (Gadus morhua L.) with either moderate ozonation (RAS O3) or high intensity UV-irradiation (RAS UV) were compared with a flow-through system (FTS). The two RAS developed a different and more stable composition of the microbial community than the FTS. The RAS O3 had a more mature and stable microbial community than the RAS UV. The density and the activity of bacteria were higher in the rearing tanks than in the in-flowing water in the RAS UV system, whereas for the RAS O3 system densities and activity of bacteria were similar, indicating low disinfection efficiency with moderate ozonation. Atlantic cod larvae reared in the RAS O3 showed the best survival and growth, whereas the RAS UV larvae performed equally well or better than their siblings in the FTS. This was in spite of the fact that the physicochemical water quality of the two RAS was inferior to that of the FTS. The agar-based method used to quantify opportunists may be too general to capture important differences in the microbial community of the rearing water. For the future, molecular methods could be used to identify which functional groups or species of bacteria are contributing to the observed RAS effect. Our results support the hypothesis of RAS as a microbial control strategy during first feeding of larvae. However, a RAS for marine larvae should probably not include strong disinfection because it leads to a reduction in bacterial numbers, which is likely to result in a destabilization of the microbial community.

Relevance of Nitrospira for nitrite oxidation in a marine recirculation aquaculture system and physiological features of a Nitrospira marina‐like isolate

In biofilters of recirculation aquaculture systems (RAS), nitrification by lithoautotrophic microorganisms is essential to prevent the cultivated organisms from intoxication with ammonium and nitrite. In moving-bed biofilters nitrifying microorganisms are immobilized together with heterotrophic bacteria in dense biofilms on carrier elements like plastic beads. Analyses of fatty acid profiles of these biofilms from a marine biofilter revealed a high abundance of Nitrospira-related lipid markers (8-12% of total fatty acids). Further results of a labeling experiment with (13) C-bicarbonate in mineral salts medium with 3 mM nitrite confirmed that Nitrospira is the major autotrophic nitrite oxidizer in the biofilter system. According to 16S rRNA gene sequence analyses the nitrite-oxidizing community in the biofilter consisted of at least two different representatives of Nitrospira, one of which could be successfully isolated. The marine isolate 'Ecomares 2.1' belongs to cluster IVa and showed 98.8% 16S rRNA gene sequence similarity to Nitrospira marina, whereas the enrichment 'M1 marine' is only distantly related (94.0% 16S rRNA gene sequence similarity to N. marina). In laboratory experiments, the isolate exhibited remarkable tolerances against high substrate and product concentrations (30 mM nitrite and 80 mM nitrate) as well as ammonium (50 mM). During the isolation process a strong tendency of this strain to develop biofilms became apparent. Thus, Ecomares 2.1 seems to be well adapted to the attached lifestyle in biofilters and the nitrogenous load prevailing in the effluent waters of RAS. Both members of Nitrospira could be detected by PCR-based methods in environmental samples of marine and brackish RAS biofilters and are therefore considered to be characteristic for these engineered ecosystems.

Potential and limitations of ozone for the removal of ammonia, nitrite, and yellow substances in marine recirculating aquaculture systems

The high levels of water-reuse in intensive recirculating aquaculture systems (RAS) require an effective water treatment in order to maintain good water quality. In order to reveal the potential and limitations of ozonation for water quality improvement in marine RAS, we tested ozone's ability to remove nitrite, ammonia, yellow substances and total bacterial biomass in seawater, considering aspects such as efficiency, pH-dependency as well as the formation of toxic ozone-produced oxidants (OPO). Our results demonstrate that ozone can be efficiently utilized to simultaneously remove nitrite and yellow substances from process water in RAS without risking the formation of toxic OPO concentrations. Contemporaneously, an effective reduction of bacterial biomass was achieved by ozonation in combination with foam fractionation. In contrast, ammonia is not oxidized by ozone so long as nitrite and yellow substances are present in the water, as the dominant reaction of the ozone-based ammonia-oxidation in seawater requires the previous formation of OPO as intermediates. The oxidation of ammonia in seawater by ozone is basically a bromide-catalyzed reaction with nitrogen gas as end product, enabling an almost complete removal of ammonia-nitrogen from the aquaculture system. Results further show that pH has no effect on the ozone-based ammonia oxidation in seawater. Unlike in freshwater, an effective removal of ammonia even at pH-values as low as 6.5 has been shown to be feasible in seawater. However, as the predominant reaction pathway involves an initial accumulation of OPO to toxic amounts, we consider the ozone-based removal of ammonia in marine RAS as risky for animal health and economically unviable.

The toxicity of ozone-produced oxidants to the Pacific white shrimp Litopenaeus vannamei

In marine recirculating aquaculture systems ozone, as a strong oxidant, is often used to improve water quality by reducing the pathogen load and removing inorganic and organic wastes. However, mainly when disinfection of recirculating water is desired, high ozone dosage is required, which may lead to toxicity problems for the cultured species. Acute toxicity of ozone-produced oxidants (OPO) to juvenile Pacific white shrimp, Litopenaeus vannamei, was assessed by determining the medium lethal concentration (LC 50). Shrimp were exposed to a series of OPO concentrations for 96 h. Toxicity was analysed using standard probit regression. The 24, 48, 72 and 96 h LC 50 values were 0.84, 0.61, 0.54 and 0.50 mg/l chlorine equivalent, respectively . A safe level for residual oxidant concentration was calculated and further verified by chronic exposure experiments. While long-term exposure of juvenile white shrimp to an OPO concentration of 0.06 mg/l revealed no observable effect, long-term exposures to 0.10 and 0.15 mg/l induced incidence of soft shell syndrome which led to mortalities due to cannibalism. Thus, an OPO concentration of 0.06 mg/l is suggested to be the maximum safe exposure level for rearing juvenile L. vannamei. Furthermore, we proved this safe level to be sufficient to control and reduce bacterial biomass in the recirculating process water.

Phylogenetic characterization of the heterotrophic bacterial communities inhabiting a marine recirculating aquaculture system

The aim of the present work was to characterize the heterotrophic bacterial community of a marine recirculating aquaculture system (RAS). An experimental RAS was sampled for the rearing water (RW) and inside the biofilter. Samples were analysed for bacterial abundances, community structure and composition by using a combination of culture-dependent and -independent techniques. The most represented species detected among biofilter clones was Pseudomonas stutzeri, while Ruegeria spp. and Roseobacter spp. were more abundant among isolates. In comparison, the genera Roseobacter and Ruegeria were well represented in both the biofilter and the RW samples. A variety of possible bacterial pathogens (e.g. Vibrio spp., Erwinia spp. and Coxiella spp.) were also identified in this study. Results revealed that the bacterial community in the RW was quite different to that associated with the biofilter. Moreover, data obtained suggest that the whole bacterial community can be involved in maintaining an effective and a stable rearing environment (shelter effect). Improving the reliability and the sustainability of RAS depends on the correct management of the bacterial populations inside it. This study furnishes more accurate information on the bacterial populations and better clarifies the existing relationships between the bacterial flora in the RW and that associated with the biofilter.

Removal of ammonium-N from marine recirculating aquaculture systems by immobilized nitrifiers

Removal of ammonium-N from marine recirculating aquaculture systems by immobilized nitrifiers

Environmentally sustainable land-based marine aquaculture

Reduced fishery harvests and increased consumer demand for seafood have precipitated an increase in intensive fish farming, predominantly in coastal and open ocean net-pens. However, as currently practiced, aquaculture is widely viewed as detrimental to the environment and typical operations are vulnerable to environmental influences, including pollution and endemic diseases. Here we report the development of a land-based, marine recirculating aquaculture system that is fully contained, with virtually no environmental impact as a result of highly efficient biological waste treatment and water recycling. Over 99% of the water volume was recycled daily by integrating aerobic nitrification to eliminate toxic ammonia and, for the first time, simultaneous, anaerobic denitrification and anaerobic ammonium oxidation, to convert ammonia and nitrate to nitrogen gas. Hydrogen sulfide generated by the separated endogenous organic solids was used as an electron source for nitrate reduction via autotrophic denitrification and the remaining organic solids were converted to methane and carbon dioxide. System viability was validated by growing gilthead seabream ( Sparus aurata) from 61 g to 412 g for a total of 1.7 tons in a record 131 days with 99% fish survival. Ammonia nitrite and nitrate did not exceed an average daily concentration of 0.8 mg/l, 0.2 mg/l and 150 mg/l, respectively. Food conversion values were 16% lower than recorded levels for net-pen aquaculture and saltwater usage of less than 16 l/every kg of fish produced. The system is site-independent, biosecure, devoid of environmental contaminants and is not restricted to a single species.

Stimulating Denitrification in a Marine Recirculating Aquaculture System Biofilter Using Granular Starch as a Carbon Source

Stimulating Denitrification in a Marine Recirculating Aquaculture System Biofilter Using Granular Starch as a Carbon Source

Aerobic and Anoxic Growth and Nitrate Removal Capacity of a Marine Denitrifying Bacterium Isolated from a Recirculation Aquaculture System

Bacterial biofilters used in marine recirculation aquaculture systems need improvements to enhance nitrogen removal efficiency. Relatively little is known about biofilter autochthonous population structure and function. The present study was aimed at isolating and characterizing an autochthonous denitrifying bacterium from a marine biofilter installed at a recirculation aquaculture system. Colonization of four different media in a marine fish farm was followed by isolation of various denitrifying strains and molecular classification of the most promising one, strain T2, as a novel member of the Pseudomonas fluorescens cluster. This strain exhibits high metabolic versatility regarding N and C source utilization and environmental conditions for growth. It removed nitrate through aerobic assimilatory metabolism at a specific rate of 116.2 mg NO(3)-N g dw(-1) h(-1). Dissimilatory NO(3)-N removal was observed under oxic conditions at a limited rate, where transient NO(2)-N formed represented 22% (0.17 mg L(-1)) of the maximum transient NO(2)-N observed under anoxic conditions. Dissimilatory NO(3)-N removal under anoxic conditions occurred at a specific rate of 53.5 mg NO(3)-N g dw(-1) h(-1). The isolated denitrifying strain was able to colonize different materials, such as granular activated carbon (GAC), Filtralite and Bioflow plastic rings, which allow the development of a prototype bioreactor for strain characterization under dynamic conditions and mimicking fish-farm operating conditions.

Anaerobic ammonium-oxidizing (anammox) bacteria and associated activity in fixed-film biofilters of a marine recirculating aquaculture system.

Microbial communities in the biological filter and waste sludge compartments of a marine recirculating aquaculture system were examined to determine the presence and activity of anaerobic ammonium-oxidizing (anammox) bacteria. Community DNA was extracted from aerobic and anaerobic fixed-film biofilters and the anaerobic sludge waste collection tank and was analyzed by amplifying 16S rRNA genes by PCR using anammox-selective and universal GC-clamped primers. Separation of amplified PCR products by denaturing gradient gel electrophoresis and sequencing of the different phylotypes revealed a diverse biofilter microbial community. While Planctomycetales were found in all three communities, the anaerobic denitrifying biofilters contained one clone that exhibited high levels of sequence similarity to known anammox bacteria. Fluorescence in situ hybridization studies using an anammox-specific probe confirmed the presence of anammox Planctomycetales in the microbial biofilm from the denitrifying biofilters, and anammox activity was observed in these biofilters, as detected by the ability to simultaneously consume ammonia and nitrite. To our knowledge, this is the first identification of anammox-related sequences in a marine recirculating aquaculture filtration system, and our findings provide a foundation for incorporating this important pathway for complete nitrogen removal in such systems.

Economic Evaluation of a Small-Scale Recirculating System for Ongrowing of Captive Wild Black Sea Bass Centropristis striata in North Carolina

An economic analysis of a hypothetical small-scale marine recirculating aquaculture system (RAS) is conducted for ongrowing small, wild black sea bass Centropristis striata at the University of North Carolina Wilmington, Center for Marine Science (UNCW-CMS) aquaculture facility in Wrightsville Beach, North Carolina (NC). The analysis is based on production data from field trials and marketing data from the sale of tank-grown product. The growout facility consists of four 16.7-m3 (dia. x ht. = 5.58 × 1 m) fiberglass tanks supported by state-of-the-art RAS components, including particle traps and swirl separators, drum screen filter, trickling biological filter, UV sterilizer, heat pump, protein skimmer, and oxygen cone. Wild-caught, above minimum legal size black sea bass (24.2 cm TL, 350 g, 0.77 lb) were purchased from a commercial fisherman for $3.14/ kg ($1.4011b), stocked at a density of 21.1 kg/m3, and grown to a final weight of 1 kg (2.24 lb) in 200 d at 23 C resulting in 1.8 production cycles per year. Fish were fed a commercial pelleted diet ($0.94/kg; $0.42/Ib) with a feed conversion ratio of 1.5. Final harvest density was 60 kg/m3 (0.50 lb/gal), and total harvestable weight was 3,982 kg (8,919 Ibs) of fish per cycle, or 6,760 kg (15,022 lb) per year. The economic analysis assumes that the facility owner manages and operates the system on coastal property zoned commercial/industrial, where full strength seawater is available on demand from natural sources. Under the base case scenario, initial investment in construction and equipment is $84,506 (10-yr life), fish are grown to a harvestable weight of lkg/fish (2.24 lb/fish), product price (farm gate basis) is $10.10/kg ($4.50/lb), and breakeven price is $7.02/kg ($3.13/lb). Depreciation, fingerlings, interest paid, electricity, and feed, account for 19.6%,17.4%, 16.9%, 16.6%, and 12.3%, respectively, of total annual costs. Measures of financial performance for the base case, 10-yr scenario are: annual return to management, $18,819; net present value (5% discount rate), $145,313; internal rate of return on initial investment, 37%; and discounted payback period on initial investment, 3.2 yr. Sensitivity analysis showed that product price changes have the largest impact on annual returns, while changes in daily growth rate, initial weight, and survival have a strong impact on financial performance. Moderate effects are seen with changes in fingerling costs, feed costs, feed conversion ratio (FCR), final weight, and interest rates.

Efficacy of Hydrogen Peroxide in Marine Recirculating Aquaculture Systems Holding Summer Flounder, Paralichthys dentatus

The effect of continuous dosing of hydrogen peroxide to a marine recirculating aquaculture system holding summer flounder was examined. Hydrogen peroxide is a strong oxidizing agent that may affect many chemical and biological processes. Results indicate that continuous dosing of hydrogen peroxide at the level tested is not an effective method to improve water quality in marine systems.