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Two components of the greenwater system, the tilapia water and Chlorella, were investigated separately for their effect on the population of luminous bacteria. For the investigation of tilapia water, Tilapia hornorum was stocked at different biomasses 0, 1 and 3 kg/10 m3. Vibrio harveyi was introduced to the tanks at a final concentration of 103 cfu/ml. Luminous bacteria could not be detected in tanks stocked at 3 kg/10 m3 from day 4 to day 6, and on day 6 in tanks stocked at 1 kg/10 m3. The bacteria could still be recovered in tanks without tilapia on day 6. Investigation of the effect of chlorella alone on V. harveyi was undertaken using sterile flasks containing 500-ml autoclaved seawater provided with aeration. In treated flasks Chlorella was added, whereas no Chlorella was added to control flasks. No luminous bacteria were recovered on day 2 and day 3 in flasks with Chlorella, while those without the microalgae still harboured luminous bacteria at day 3.

This study determined the holding capacity of semi-intensive and intensive milkfish ponds and water quality in relation to fish biomass and feed input. Six units of 1000 m2 brackishwater ponds were used, three ponds for intensive system (20,000 fish ha−1) and three for semi-intensive system (8000 fish ha−1). Average production was significantly higher in intensive pond (3652 kg ha−1) than in semi-intensive pond (1352 kg ha−1) after a desired marketable size of fish was reached. Highest concentrations in effluents (mg l−1) of rearing water measured every 2 weeks were 0.369 and 0.289 for chlorophyll a (chl a), 0.485 and 0.512 for PO4–P, 0.279 and 0.811 for TAN, 0.094 and 0.082 for NO2–N, and 14.040 and 8.649 for NO3–N, 216 and 142 for total suspended solids (TSS), 15.0 and 21.7 for biological oxygen demand (BOD), in intensive and semi-intensive ponds, respectively. Lowest morning dissolved oxygen (DO) in intensive pond was 2.2 mg l−1, and did not decrease further because of aeration. In unaerated, semi-intensive pond, morning DO ranged from 1.3 to 5.0 mg l−1 but occasionally went below 1.0 mg l−1 resulting to fish mortalities at biomass of 835, 1206, and 1489 kg ha−1. Levels of NO3–N and dissolved inorganic N are linear functions of fish biomass or feed input in all systems (P<0.05). The buildup of nutrients is more pronounced at biomass of 1610 kg ha−1 and above while nutrient transformation (conversion of PO4–P or TAN to phytoplankton or vice versa) is apparent at biomass below 1419 kg ha−1. The holding capacity of unaerated, semi-intensive pond is below 1348 kg ha−1 or 54 kg feed ha−1 day−1 based on DO concentration of less than 1.0 mg l−1. However, the holding capacity can be lower than 835 kg ha−1 or 3

Nine recirculating aquaculture systems utilizing three biofilter types were placed on line and stocked with yellow perch, Percaflavescens, fingerlings. Biofilter type differed among systems, and included upflow pulsed bed bead filter, packed tower trickling filter, and rotating biological contactor. Following filter acclimation, a comparative analysis of biofilter performance was conducted, involving measurement of temperature, pH, dissolved oxygen, total ammonia-nitrogen, nitritenitrogen, nitrate-nitrogen, alkalinity, total hardness, carbonaceous biochemical oxygen demand, dissolved organic carbon, and total suspended solids. Filter bed emergence promoted effective carbon dioxide stripping, pH maintenance, and consistent nitrification performance in trickling filters and rotating biological contactors. Higher total ammonia nitrogen mass removal rates were observed in trickling and rotating biological contactor filters than in bead filters. Low total ammonia nitrogen mass removal rates and nitrification efficiencies for all filters resulted from relatively high carbonaceous biological oxygen demand loadings. Analysis of areas under mass removal curves showed that RBC filters were surface area limited. Foam formation in trickling filters effectively removed total suspended solids from the culture water. Filter type did not have a significant effect on median organic water quality parameter values in the production tanks. Although differences in nitrification performance and certain water quality parameters were observed between filter types, the data set did not indicate that one filter type should be considered generally most effective at treating wastewater produced in a recirculating aquaculture system.

Four bar graders were designed and built to separate a mixed-size population of market-size reciprocal cross hybrid striped bass Marone chrysops x M. saxatilis in rectangular culture tanks in an indoor, recirculating aquaculture system. Grader frames were constructed of 5.1 cm (2 inch) PVC pipe and fittings. PVC electrical conduit ( 1.27 cm, 0.5 inch) was used to form a series of parallel, equally spaced vertical bars within the frame. Bar slot spaces were 1.90, 2.54, 3.20, or 3.80 cm (0.75, 1.0, 1.25, 1.5 inches). A strip of flexible vinyl siding was attached to the outer edges of the bar grader to permit a tight fit between the grader and tank walls, and prevent fish from swimming around the grader. The graders were placed sequentially into one end of the tank, largest slot size first, and maneuvered to the opposite end. Each grader remained in the tank for 60 min. Fish too large to pass through a grader were netted and measured for weight, length and width. Regression analysis was performed for average weight retained at each bar spacing (Y = 7.13619 + 0.070716 X; r2 = .9987). By rearrangement, an equation was derived which allows a culturist to select a bar spacing that retains fish of a predetermined weight: Grader bar slot size (mm)= Fish weight (g) -177.9 / 31.7). Construction of each grader required approximately 2 h, and materials cost $20.

The use of ultraviolet (UV) disinfection devices has become increasingly popular in wastewater and aquaculture industries. Although the effectiveness of UV disinfection has been well documented for flowthrough operation regimes in wastewater treatment, research focusing on water recirculating systems is still limited. In this study, the performance of single-lamp UV devices were tested on a recirculating system for fecal coliform (FC) disinfection. Experimental results indicated that UV power input, recirculating flow rate and water UV transmittance were three important factors determining UV disinfection efficiency. An UV disinfection model for a recirculating system was developed based on theoretical analysis and experimental data. A key model parameter, namely the first-order inactivation rate constant (k), was determined to be 0.0062 m2 J-1 for FC disinfection. Simulation using the model provided useful information for design and operation of recirculating UV disinfection systems. The model prediction of disinfection process for other microorganisms is also capable of using reported values of the inactivation rate constant.

Three types of seed (eggs, sac-fry, and fry) production for Rocky Mountain White® hybrid tilapia, (O. niloticus x O. aureus), were compared under green water conditions over a six-month period in an environmentally-controlled greenhouse at the Virginia Tech Aquaculture Center. Rectangular tanks were stocked with broodstock (mean wt. 680 g), at a sex ratio of 3 females to 1 male. Nine tanks were stocked at one of three densities (1, 2, and 4 females/m2), and seed was collected from the females' mouths weekly. Three additional tanks were stocked at a density of 2 females/m2, and fry were collected from the edges of the tanks daily. Average number of viable fry produced by the clutch removal method at 1 female/m2 was significantly higher than the combined average production of densities at 2 and 4 females/m2 (p< 0.02). Even though there was no significant difference between viable fry production per meter sq. (p>0.05), the highest density consistently produced more fry/m2. No significant difference was observed in viable fry production between the clutch removal method and the natural mouth-brooding method (p>0.05). The mean monthly hatchery seed survival was 65.7 ± 2.3%, which varied largely depending on initial seed developmental stage. The effects of stocking density on growth and survival were evaluated by stocking 14-16 day old artificially incubated fry (25.5 ± 0.32 mg, 12.1 ± 0.04 mm), into 150-liter troughs at three densities (3, 6, and 12 fry/ liter) under green water conditions for 30 days. Significant differences were observed between mean weight, length, survival, and feed conversion ratios among the various fry stocking densities (p<0.05).The greatest growth was at a density of 3 fry/liter, while survival was not affected until a density of 12 fry/liter was reached. These results suggest that to maximize fry production and reduce labor, a density of 4 females/m2 or higher be used under the natural mouth-brooding seed collection method. They also suggest a

The International Journal of Recirculating Aquaculture presents research and applications expertise in the area of recirculation systems and technology. This journal is intended to be a forum for the open exchange of reliable information on the subjects of recirculating aquaculture. The industry of recirculating aquaculture requires expertise from many different fields such as animal husbandry, economics, water chemistry, waste managment, food safety, genetics, and systems engineering. The following papers focus on a variety of topics, with recirculation as the common element.

Nine recirculating aquaculture systems utilizing three biofilter types were placed on line and stocked with yellow perch, Percaflavescens, fingerlings. Biofilter type differed among systems, and included upflow pulsed bed bead filter, packed tower trickling filter, and rotating biological contactor. Following filter acclimation, a comparative analysis of biofilter performance was conducted, involving measurement of temperature, pH, dissolved oxygen, total ammonia-nitrogen, nitritenitrogen, nitrate-nitrogen, alkalinity, total hardness, carbonaceous biochemical oxygen demand, dissolved organic carbon, and total suspended solids. Filter bed emergence promoted effective carbon dioxide stripping, pH maintenance, and consistent nitrification performance in trickling filters and rotating biological contactors. Higher total ammonia nitrogen mass removal rates were observed in trickling and rotating biological contactor filters than in bead filters. Low total ammonia nitrogen mass removal rates and nitrification efficiencies for all filters resulted from relatively high carbonaceous biological oxygen demand loadings. Analysis of areas under mass removal curves showed that RBC filters were surface area limited. Foam formation in trickling filters effectively removed total suspended solids from the culture water. Filter type did not have a significant effect on median organic water quality parameter values in the production tanks. Although differences in nitrification performance and certain water quality parameters were observed between filter types, the data set did not indicate that one filter type should be considered generally most effective at treating wastewater produced in a recirculating aquaculture system.

Nine recirculating aquaculture systems utilizing three biofilter types were placed on line and stocked with yellow perch, Percaflavescens, fingerlings. Biofilter type differed among systems, and included upflow pulsed bed bead filter, packed tower trickling filter, and rotating biological contactor. Following filter acclimation, a comparative analysis of biofilter performance was conducted, involving measurement of temperature, pH, dissolved oxygen, total ammonia-nitrogen, nitritenitrogen, nitrate-nitrogen, alkalinity, total hardness, carbonaceous biochemical oxygen demand, dissolved organic carbon, and total suspended solids. Filter bed emergence promoted effective carbon dioxide stripping, pH maintenance, and consistent nitrification performance in trickling filters and rotating biological contactors. Higher total ammonia nitrogen mass removal rates were observed in trickling and rotating biological contactor filters than in bead filters. Low total ammonia nitrogen mass removal rates and nitrification efficiencies for all filters resulted from relatively high carbonaceous biological oxygen demand loadings. Analysis of areas under mass removal curves showed that RBC filters were surface area limited. Foam formation in trickling filters effectively removed total suspended solids from the culture water. Filter type did not have a significant effect on median organic water quality parameter values in the production tanks. Although differences in nitrification performance and certain water quality parameters were observed between filter types, the data set did not indicate that one filter type should be considered generally most effective at treating wastewater produced in a recirculating aquaculture system.

Striped bass female (M. saxatilis) x white bass male (M. mississippiensis), (SBxWB, n = 300) and striped bass female x yellow bass male (M. chrysops) (SBxYB, n = 300) fingerlings, initial mean weight 91 g and 62 g, respectively, were reared in recirculating aquaculture systems at densities of 118 fish/m3 for 120 days. Mean weight increased 309 g and 151 gin SBxWB and SBxYB, respectively. ,final mean weight and total length, and rate of weight and length increase were higher for SBxWB than SBxYB. Condition factor and survival were higher for SBxYB (1.04 and 99.3%, respectively) than for SBxWB (1.01 and 96.0%,respectively). Mean feed conversion ratio (FCR) was lower for SBxWB (1.4) than for SBxYB (1.6). Significant time x hybrid interactions indicated that growth rate of SBxYB improved, relative to SBxWB, as the study progressed. Positive linear trends for total ammonia, unionized ammonia, and nitrite indicate water quality deteriorated as the study progressed. Time x hybrid interactions for growth rate may have been due to differential responses of SBxYB and SBxWB to deterioration of water quality. Although SBxYB had slightly better survival than SBxWB and their growth rate improved relative to that of SBxWB, the slow overall growth of SBxYB limits its potential for recirculating system production.

Production characteristics of palmetto bass (Morone saxatilis female x Morone chrysops male) reared at three stocking densities (36 fish/m3, 72 fish/m3, and 144 fish/m3) in a pilot-scale RAS were evaluated. A final mean ±SE fish weight of 412.1 ± 7.8 g at the high density was significantly lower than that of fish at the medium density weighing 542.1 ± 11 .8 g (P < 0.05). Fish weight (676.1 ± 17 .0 g) at_ the lowest density was significantly higher than at the high and medium densities (P < 0.05). The average daily weight gain at the low density (2.8 g/d) was 22% and 47% higher than fish reared at the medium and high densities, respectively. Total biomass gains of 733.8, 483.3, and 297.9 kg were obtafued at the high, medium, and low densities. Feed conversion and survival rates were similar among densities averaging 1.4 and 97 .1 %, respectively. Higher mean daily and cumulative feed totals at the highest density contributed to significantly higher ammonia and nitrite concentrations and lower pH levels at haryest. All other measured water quality parameters were similar among densities and remained within known acceptable limits for fish growth. The results indicated that palmetto bass reared in closed systems reached market size in 224 days at the low and medium densities. However, the relative biomass production may not justify such strategies when compared to the yield obtained at the highest rearing density.

The International Journal of Recirculating Aquaculture presents research and applications expertise in the area of recirculation systems and technology. This journal is intended to be a forum for the open exchange of reliable information on the subjects of recirculating aquaculture. The industry of recirculating aquaculture requires expertise from many different fields such as animal husbandry, economics, water chemistry, waste managment, food safety, genetics, and systems engineering. The following papers focus on a variety of topics, with recirculation as the common element.

This collaborative SEAFDEC/ASEAN project aimed to develop sustainable shrimp culture technology packages to address the problems in shrimp culture (e.g. discharges from shrimp farms threatening mangrove and marine ecosystems, clearing of mangrove forests to make way for shrimp ponds, etc.). In this context, a closed recirculating shrimp farming system is discussed touching on: pond preparation, water preparation, stocking, feeding, management, DO level, problems, record keeping, and harvesting.

The process required and options for water treatment in recirculating systems have been clearly identified. The four most critical processes are: (1) solids removal, to take out fecal waste, uneaten feed, excess bacterial biomass, and other solids also reducing biochemical oxygen demand (BOD) in the process; (2) biological filtration or biofiltration, primarily nitrification to convert toxic ammonia and intermediate from nitrite to nitrate; (3) gas exchange, which includes aeration to ensure sufficient oxygen supply for fish and biofiltration, and degasification to stripe carbon dioxide; and what may be called (4) ion balance, primarily to maintain pH and alkalinity and prevent the buildup of nitrate, dissolved organic, and other substance. System with extended hydraulic retention times must generally have an alkalinity replenishment regime to compensate for the alkalinity-consuming nitrification process. Additional treatment processes include denitrification (nitrate removal, which helps to augment alkalinity), ozonation (to remove color, organics and BOD; also sterilizes), ultraviolet (UV) sterilization (for disease/pathogen control), and foam fractionation (to remove dissolved organics surfactants). Heaters and/or chillers may be provided for temperature control. It must be emphasized that while the processes and equipment are provided for specific purposes, a complex interrelationship exists in recirculating systems. Recirculating system components and sizing criteria vary widely, and are mainly provided to comply with specific production needs. A combined upflow and fluidized sand filter design that is applicable and easily adaptable to any system that may be recirculated is presented. Design and operational criteria are provided, as applied to a milkfish broodstock system. In general, for better management and control of water quality, to conserve water and energy and reduce wastewater, and to essentially provide for complete treatment of wastes and mitigate i

The potential use of recirculating systems with facilities for waste removal for prawn (Penaeus monodon) hatchery and broodstock maturation tanks was investigated. Recirculating systems evaluated for larval culture tanks were biological filtration and zigzag stream sedimentation. Systems using airlift and airstones as aeration devices with partial water change but with no provision for recirculation served as control. Results showed successful rearing of Penaeus monodon (nauplii-postlarvae) in systems with facilities for wastewater recirculation. Aeration systems became ineffective in maintaining acceptable water quality as shown by increases in 5-day biochemical oxygen demand (BOD5), ammonia (NH4-N) and nitrite (NO2-N) nitrogen, and decreases in dissolved oxygen (DO). For broodstock maturation, a recirculating system with a preconditioned biological filter was compared with a flow-through system. Biological filtration proved to be useful in meeting water quality requirements. Nitrification was satisfactory with ammonia levels lower than 1·0 mg liter−1. The pH values in the biofilter effluent were maintained at 7·8–8·3. BOD5 levels were below 10 mg liter−1 while DO tended to drop due to the nitrifying activity of the filter. Better reproductive performance of Penaeus monodon broodstock was obtained in the recirculating system than in the flow-through system.