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A recirculating aquaculture system (RAS) represents a forward-looking form of aquaculture. A RAS consists of fish tanks and water treatment processes in a closed loop to sustain the environmental conditions for fish production. However, the rapid industrialization of the technology is fraught with transfer problems. This review justifies a RAS process chain based on fish biology. The underlying concept has been evaluated by the author in experimental and commercial RAS projects. The core idea is that the fish must be considered as a technical subcomponent in a RAS, determining the technology. Fish, when considered as small biological machines, are still a black box in many ways. However, their basic biology and physiology provide all the knowledge to implement them in a technical setting. The information required to understand this concept is presented and discussed based on current scientific knowledge. The conclusion is that the technology is available but needs to be rigorously implemented. If this were carried out, fish production in RASs would be ecologically sustainable, which is already claimed for RASs but is not always the reality in commercial applications. [ABSTRACT FROM AUTHOR]

In recirculating aquaculture systems (RAS), off‐flavours accumulated in fish muscle tissue can be problematic in terms of consumer acceptance and the reputation of farmed fish products. Off‐flavours often give fish earthy, muddy, or other undesirable flavours. Typically, off‐flavours are removed during a depuration period in which fish are fasted and held in clean water. Unfortunately, this causes additional costs and delayed sales, while fish lose weight and show a decrease in lipid content. First, we studied fish growth in a partial RAS (PRAS) where the conditions are very similar to those in depuration with a water exchange rate of 4000 L kg−1 feed, compared to RAS with a 650‐L water kg−1 feed. Rainbow trout (Oncorhynchus mykiss) was reared in both systems. Our aim was to combine the benefits of a higher water exchange rate: the lack of need for biofilters and a lower accumulation of off‐flavours while obtaining stable rearing conditions. Additionally, we studied the effects of moderate feeding and H2O2 addition during depuration. The fish grew faster in a PRAS than in a RAS when fed ad libitum. Thirteen off‐flavour compounds were found in the fish flesh and 11 in the circulating water. The H2O2 addition led to decreased levels of off‐flavours in the tank water and in fish muscle. The results showed no significant differences in off‐flavours between the fed and not‐fed systems, showing that moderate feeding did not prevent a good depuration result. However, the lipid content and the overall fish weight were higher in the fed systems, which suggests more effective depuration. Increased depuration efficiency can be an important tool when considering ways to improve the profitability of production. [ABSTRACT FROM AUTHOR]

Haliotis tuberculata coccinea is a candidate of growing interest to diversify aquaculture in the Canary Islands, principally based on fish production, to improve aquaculture development opportunities. The economic viability of commercial abalone farming depends largely on the rearing system employed and the feeding sources employed during the grow-out culture period. We studied the effects of two land-based culture systems on the growth performance of abalone and the nutritional quality of their tissues, in a crossed design. Recirculated (RAS) and open flow (FLOW) culture systems were compared. Fresh macro algae (FMA) (Gracilaria cornea and Ulva rigida) were compared to manufactured compound feed (CF) and a mixture of both (MIX). Survival rates were high (97–100%) regardless the treatments tested. MIX and FMA diets produced the best results for Shell Growth Rate, Specific growth rates for shell growth (SGRsl) and weight (SGRw) as well as Food Conversion Ratio (FCR). The highest value for feed intake was recorded for the MIX diet. A positive relationship has been observed between the amounts of protein and lipids in diets and the disposition of these in the viscera of animals fed such diets. The rearing system used had no significant effect on growth and nutritional parameters. [ABSTRACT FROM AUTHOR]

Global increase in aquaculture production has created a need to reduce its environmental impacts. Nutrients could be recycled especially at land-based recirculating aquaculture systems (RAS) by cultivating green microalgae in aquaculture effluent. However, microalgae are difficult to harvest. As a multi-trophic solution, mussels could be used in harvesting microalgae. We tested three European freshwater mussels (duck mussel Anodonta anatina, swan mussel A. cygnea, and swollen river mussel Unio tumidus) for filtering two common green microalgae (Monoraphidium griffithii and Selenastrum sp.) grown in RAS effluent. Mussels decreased microalgal concentrations in the tanks 42–83% over three consecutive trials. Algal concentrations at the end of each trial were lowest for both microalgae in tanks containing Anodonta mussels. Clearance rates were higher for Anodonta mussels than for U. tumidus. Mussels biodeposited more microalgae to tank bottoms when M. griffithii was filtered. Ammonium concentration decreased or did not change in tanks with M. griffithii, but increased in tanks containing Selenastrum sp. These results suggest that of the tested species Anodonta mussels and M. griffithii show best potential for RAS effluent bioremediation application. We conclude that a co-culture of microalgae and unionid mussels could be used for recycling nutrients in aquaculture. [ABSTRACT FROM AUTHOR]

ABSTRACT In recirculating aquaculture systems (RAS), off‐flavours accumulated in fish muscle tissue can be problematic in terms of consumer acceptance and the reputation of farmed fish products. Off‐flavours often give fish earthy, muddy, or other undesirable flavours. Typically, off‐flavours are removed during a depuration period in which fish are fasted and held in clean water. Unfortunately, this causes additional costs and delayed sales, while fish lose weight and show a decrease in lipid content. First, we studied fish growth in a partial RAS (PRAS) where the conditions are very similar to those in depuration with a water exchange rate of 4000 L kg−1 feed, compared to RAS with a 650‐L water kg−1 feed. Rainbow trout (Oncorhynchus mykiss) was reared in both systems. Our aim was to combine the benefits of a higher water exchange rate: the lack of need for biofilters and a lower accumulation of off‐flavours while obtaining stable rearing conditions. Additionally, we studied the effects of moderate feeding and H2O2 addition during depuration. The fish grew faster in a PRAS than in a RAS when fed ad libitum. Thirteen off‐flavour compounds were found in the fish flesh and 11 in the circulating water. The H2O2 addition led to decreased levels of off‐flavours in the tank water and in fish muscle. The results showed no significant differences in off‐flavours between the fed and not‐fed systems, showing that moderate feeding did not prevent a good depuration result. However, the lipid content and the overall fish weight were higher in the fed systems, which suggests more effective depuration. Increased depuration efficiency can be an important tool when considering ways to improve the profitability of production.

Stress in farmed fish is associated with poor feeding, slow growth, disease, and mortality. Therefore, it is essential to closely monitor stress levels in fish to optimize farming practices, which could then enhance productivity and welfare in aquaculture operations. Cortisol, a circulating stress hormone, is a reliable biomarker for evaluating fish stress. As blood sampling is highly invasive, alternative cortisol sampling methods such as fin, mucus, and the surrounding water that contains released cortisol, have been proposed as less invasive or non-invasive sampling methods. However, a comprehensive understanding of their temporal dynamics and associations with plasma cortisol levels is still lacking. In this study, we subjected Lates calcarifer, Asian sea bass within a farm-scale (3000 L tank, 9000 L system) and high-flow rate (8000 L/h) Recirculating Aquaculture System (RAS) to an acute handling stress challenge involving chasing and air exposure, and quantified cortisol dynamics within different biological samples, including blood, fin, and mucus, and in tank water from multiple sampling points. We showed that handling stress induced an expected increase in plasma and mucosal cortisol, peaking at 1 h and 24–48 h, respectively, and that plasma and mucosal cortisol were moderately correlated, especially during the stress period. Fin cortisol did not show consistent dynamics. Water cortisol similarly rose, but peaked within 40 min from the start of the stressor, in a pattern that was dependent on the site of sampling within the RAS system, likely due to RAS circulation dynamics. Our study is the first to examine the impact of stress on cortisol accumulation and release in Asian Sea bass in a farm-scale RAS, thus complementing existing research on the efficacy of fin, mucus, and water cortisol as stress indicators that could help optimize aquaculture productivity and welfare.

A recirculating aquaculture system (RAS) represents a forward-looking form of aquaculture. A RAS consists of fish tanks and water treatment processes in a closed loop to sustain the environmental conditions for fish production. However, the rapid industrialization of the technology is fraught with transfer problems. This review justifies a RAS process chain based on fish biology. The underlying concept has been evaluated by the author in experimental and commercial RAS projects. The core idea is that the fish must be considered as a technical subcomponent in a RAS, determining the technology. Fish, when considered as small biological machines, are still a black box in many ways. However, their basic biology and physiology provide all the knowledge to implement them in a technical setting. The information required to understand this concept is presented and discussed based on current scientific knowledge. The conclusion is that the technology is available but needs to be rigorously implemented. If this were carried out, fish production in RASs would be ecologically sustainable, which is already claimed for RASs but is not always the reality in commercial applications.

Abstract Malachite Green (MG) dye of the triphenylmethane group is a toxic compound used in the aquaculture industry as an antifungal agent, however, it can accumulate in fish and pose toxicity. The present work aims to remove MG in Microbial Fuel Cell (MFC) as a sustainable and eco-friendly solution. Out of six samples, the highest malachite green degradation was obtained by a sample obtained from Robiki tannery site in agar plates in 24 h at 37 °C. Robiki sample was used to inoculate the anodic chamber in Microbial Fuel cell, the resulting average electricity production was 195.76 mV for two weeks. The decolorization average was almost 88%. The predominant bacteria responsible for MG decolorization and electricity production were identified using 16S rRNA as Shewanella chilikensis strain MG22 (Accession no. OP795826) and formed a heavy biofilm on the anode. At the end of the decolorization process, MG was added again for re-use of water. The results showed efficiency for re-use 3 times. To ensure the sterility of treated water for re-use, both UV and filter sterilization were used, the latter proved more efficient. The obtained results are promising, MFC can be used as recirculating aquaculture system (RAS). The same aquaculture water can be treated multiple times which provides a sustainable solution for water conservation. Graphical Abstract

The genus Ulva is globally distributed and has been thoroughly studied because of its functional biochemical composition, rapid growth rates and opportunistic features, and interest in Ulva cultivation is growing worldwide. In Europe, mostly near- and on-shore flow-through cultivation systems are used and land-based recirculating aquaculture systems (RAS) using fresh water or artificial seawater have not been developed for Ulva. While RAS provides quality control and can be located inland, maintenance costs are high. Using selected strains adapted to low-salinity could reduce seawater production costs and improve the economic feasibility. Therefore, our study assessed how salinity can be used as a tool for strain selection and optimization of functional traits. Growth rates and antioxidant activity of three species (four strains) of tubular and foliose Ulva from the NE-Atlantic and Mediterranean (foliose: Ulva lacinulata – two geographical strains, tubular: Ulva linza and Ulva flexuosa) were followed for three weeks at salinities ranging from 10 to 30 PSU. The tubular strains achieved optimal growth at a lower salinity than U. lacinulata. However, growth rates of both foliose strains were higher than of tubular strains, even at sub-optimal salinity. Therefore, U. lacinulata is a good candidate for RAS with artificial seawater, and the cost of salt can be reduced by up to 33.3% (20 PSU) without significantly reducing the growth rate of U. lacinulata. Higher antioxidant activity was achieved by reducing the salinity to 10 PSU for 10 days, suggesting that the functional traits of cultivated Ulva lacinulata can be optimized prior to harvest. [ABSTRACT FROM AUTHOR]

Malachite Green (MG) dye of the triphenylmethane group is a toxic compound used in the aquaculture industry as an antifungal agent, however, it can accumulate in fish and pose toxicity. The present work aims to remove MG in Microbial Fuel Cell (MFC) as a sustainable and eco-friendly solution. Out of six samples, the highest malachite green degradation was obtained by a sample obtained from Robiki tannery site in agar plates in 24 h at 37 °C. Robiki sample was used to inoculate the anodic chamber in Microbial Fuel cell, the resulting average electricity production was 195.76 mV for two weeks. The decolorization average was almost 88%. The predominant bacteria responsible for MG decolorization and electricity production were identified using 16S rRNA as Shewanella chilikensis strain MG22 (Accession no. OP795826) and formed a heavy biofilm on the anode. At the end of the decolorization process, MG was added again for re-use of water. The results showed efficiency for re-use 3 times. To ensure the sterility of treated water for re-use, both UV and filter sterilization were used, the latter proved more efficient. The obtained results are promising, MFC can be used as recirculating aquaculture system (RAS). The same aquaculture water can be treated multiple times which provides a sustainable solution for water conservation. [ABSTRACT FROM AUTHOR]

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 (NO2−-N), and nitrate (NO3−-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 NO2−-N after 4 h of treatment. However, it resulted in the significant accumulation of NO3−-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. [ABSTRACT FROM AUTHOR]

Highlights: The anammox process is a promising technique to treat nitrogen-rich marine RAS WW. The anammox strain Ca. Scalindua was successfully acclimated to high salinity marine RAS wastewater. Despite a slight decrease in population over the time, Ca. Scalindua remained the major species within the granules and was able to maintain a high nitrogen removal rate while exposed to RAS WW in the absence of TE supplementation. Recirculating aquaculture systems (RAS) are promising candidates for the sustainable development of the aquaculture industry. A current limitation of RAS is the production and potential accumulation of nitrogenous wastes, ammonium (NH4+), nitrite (NO2−) and nitrate (NO3−), which could affect fish health and welfare. In a previous experiment, we have demonstrated that the marine anammox bacteria Candidatus Scalindua was a promising candidate to treat the wastewater (WW) of marine, cold-water RAS. However, the activity of the bacteria was negatively impacted after a direct exposure to RAS WW. In the current study, we have further investigated the potential of Ca. Scalindua to treat marine RAS WW in a three-phase experiment. In the first phase (control, 83 days), Ca. Scalindua was fed a synthetic feed, enriched in NH4+, NO2− and trace element (TE) mix. Removal rates of 98.9% and 99.6% for NH4+ and NO2−, respectively, were achieved. In the second phase (116 days), we gradually increased the exposure of Ca. Scalindua to nitrogen-enriched RAS WW over a period of about 80 days. In the last phase (79 days), we investigated the needs of TE supplementation for the Ca. Scalindua after they were fully acclimated to 100% RAS WW. Our results show that the gradual exposure of Ca. Scalindua resulted in a successful acclimation to 100% RAS WW, with maintained high removal rates of both NH4+ and NO2− throughout the experiment. Despite a slight decrease in relative abundance (from 21.4% to 16.7%), Ca. Scalindua remained the dominant species in the granules throughout the whole experiment. We conclude that Ca. Scalindua can be successfully used to treat marine RAS WW, without the addition of TE, once given enough time to acclimate to its new substrate. Future studies need to determine the specific needs for optimal RAS WW treatment by Ca. Scalindua at pilot scale. [ABSTRACT FROM AUTHOR]

A recirculating aquaculture system (RAS) aims to achieve fish production with negligible discharge into the environment. RASs have been applied for fish production in several countries, but nitrate removal is often a limiting factor for production increases. In this study, a pilot-scale RAS (10 tons of fish/year) was connected to a water treatment field which consisted of a denitrifying woodchip bioreactor (9 m × 14 m) filled with birch woodchips (Betula pendula), a constructed wetland (7.5 m × 6 m), and sand infiltration (16 m × 31 m) to achieve high water quality with low-maintenance treatment units. In the constructed wetland, a perennial common reed (Phragmites australis) was used in a well-drained soil for nutrient re-use. Concentrations of different elements, diluted anions, and selected hydrocarbons were monitored and quantified. Some Mn leaching occurred during the sand infiltration stage. However, Mn concentrations decreased towards the end of the experiment. Concentrations of total-Fe increased up to 2.75 mg L−1 and Mn up to 5 mg L−1 in the sand infiltration stage of the water treatment field, probably due to anoxic conditions and leaching of fine particles. This type of process design offers effective but low-maintenance treatment of circulating water. HIGHLIGHTS Passive water treatment was sufficient for treating recirculating water.; Elevated concentrations of Mn and Fe were found after sand filtration.; The concentrations of anions were low in the water treatment field.; Glucose and fructose of woodchip-origin were found at low levels in water.;

Coupled aquaponics is the integration of recirculating aquaculture systems (RAS) with hydroponic cropping systems (HCS) into a single system with shared water treatment units. Potential benefits of integration include water conservation, reduced reliance on finite mineral fertilizers, and intensive year-round location-independent production of lean proteins and fresh vegetables. However, coupled aquaponic practitioners have found minimal commercial success to date. This has been mostly due to the use of system designs which are not based on contemporary water treatment principles, especially those for commercial aquaculture. Instead, conventional coupled aquaponic system design has been based on a linear framework assuming fish wastes are readily utilized as plant fertilizers, with minimal emphasis on waste treatment or individual component hydraulic retention times. The result has been economic failures due to misbalancing the cost of inputs, the value of the outputs, and the time required to reach a marketable harvest size for both crops: fish and plants. This manuscript provides theoretical calculations based on existing standards in commercial RAS and HCS for sizing plant, fish, and biofiltration units focused on nitrogenous waste production from fish. Successful integration of HCS and RAS is defined as achieving industry standard production timelines for lettuce (seed to harvest time of 35 days) and Nile tilapia (fry to a 624 g average harvest weight in 35 weeks). Equations and examples to calculate lettuce yield, daily lettuce nitrogen requirement, fish feed rates to achieve specific nitrogen production rates, and fish tank and biofilter volumes are provided.

Two Emergy Assessments (EMA) were conducted to evaluate the ecological performances of novel eco-intensification innovations for the treatment and valorisation of sludge and fish mortalities from finfish aquaculture, including upstream directly and indirectly used resources such as energy, materials, and labour. One innovation consists in a novel process to filter and dry particles from the reject water out of a Recirculating Aquaculture System (RAS), with dried nutrients and biomass being reused as organic fertiliser or as an energy source. The other process concerns the disposal of fish mortalities, which are mixed with by-product from the brewery industry and dried. The resulting product can be used in the pet food industry or as an energy source. Both innovative solutions were tested on a RAS for smolt production in Norway. A set of standard Unit Emergy Values and emergy indicators was selected and calculated, including specific emergy (sej/kg), environmental loading ratio, and emergy sustainability index, among others. The results are compared with Life-Cycle Assessment values derived from the same innovations and with other emergy values obtained for other aquaculture processes. All in all, the novel solutions imply higher impacts related to water and technological inputs, yielding savings in the other indicators, thus confirming overall positive performances, yet requiring either some trade-off to be addressed and assessed more widely, or more efforts to possibly abate the factors that are responsible for increased impacts.

Our research was performed on juvenile sterlets (Acipenser ruthenus), aged between 346-431 days, maintained in five round pools (Ø=3 m, V=6 m3, h-100 cm) and fed with a commercial extruded pellet (3 mm granulation, 48% CP, and 10% EE). Body weight and total body length on 30 individuals from each tank were determined every two weeks. Weighing and somatic measurements achieved at the end of experimental period (standard length-l, body weight-G, maximum body high–H, maximum body perimeter (Pmax), head length–lh,, caudal peduncle length-lp) allowed us to calculate the following body indices: profile index, thickness index, Fulton index, Kiselev index, meat index. Statistical analysis was performed by using the SPSS IBM 22 and Minitab 16 software. Data were reported as Mean±Sx at a significant level of p

In recirculating aquaculture systems (RAS), off-flavors that accumulate in fish muscle tissue can be problematic in terms of consumer acceptance and the reputation of farmed fish products. Although off-flavors are not toxic at low concentrations, they often give fish muscle earthy, muddy, or other unwanted flavors. Traditionally, muddy off-flavors caused by geosmin (GSM) and 2-methylisoborneol (MIB) have been detected, but a variety of other compounds and flavors have also been identified. In this study, a method based on solid phase micro extraction (SPME) coupled with gas chromatography and mass spectroscopy was developed to identify and quantify 14 off-flavor–inducing compounds in RAS–farmed fish. The selected off-flavors were quantified in circulating water and in fish from a pilot-scale RAS rearing rainbow trout (Oncorhynchus mykiss). The method showed high accuracy and precision with limits of detection and quantification at a low ng L−1 level. In this study, 13 compounds were found in the fish muscle which decreased in concentrations during the 15-day depuration period. This study showed that off-flavors in fish can also be induced by other compounds besides GSM and MIB. This emphasizes the need for sufficient off-flavor control in the RAS, but also the importance of an accurate and reliable analytical quantitation method. [ABSTRACT FROM AUTHOR]

Diseases are one of the most critical limiting factors in aquaculture. Recirculating aquaculture systems (RAS) are one of the most functionally viable sustainable aquaculture production systems adopted world over. In the event of any eventuality caused by bacterial pathogens, antibiotics or other antibacterial agents cannot be applied due to the vulnerability of biological filters which form an integral part of the RAS. Because of this, newer drugs are required for the effective control of diseases in RAS which would not interfere with the activity of nitrifying bacteria used in the biological filters. The antagonistic activity of pyocyanin, a bioactive compound produced by Pseudomonas aeruginosa, against vibrios is well established. The purpose of this study was to prove the effectiveness of pyocyanin as an aquaculture drug for application in RAS by employing a pilot-scale shrimp culture under RAS. It was noted that at the concentration of 5 mg L−1, pyocyanin could significantly bring down the population of Vibrio spp. in RAS without affecting noticeably the other natural heterotrophic bacteria. Also, pyocyanin at this concentration did not inhibit the activity of nitrifying bacterial consortia used in the SBSBR (stringed bed suspended bioreactor) of RAS. The reared shrimp (Penaeus monodon) showed 100% survival after the application of pyocyanin, besides exhibiting normal health signs. Pyocyanin was non-toxic to the shrimp hybrid cell line (PmLyO-Sf9) at the concentration required for its application in disease management (IC50 = 419.26 mg L−1). The present study has demonstrated that pyocyanin is effective as an environment-friendly and safe aquaculture drug for the application in RAS-based shrimp culture to control Vibrio spp. without impeding nitrification established through the deployment of nitrifying bioreactors. [ABSTRACT FROM AUTHOR]

Fish is increasingly produced in recirculating aquaculture systems (RAS), which can offer some production and environmental benefits. Unfortunately, there is a tendency to develop off-flavors in RAS, mainly caused by geosmin (GSM) and 2-methyl isoborneol (MIB) accumulating in the fish flesh from the circulating water. These off-flavors are objectionable to consumers, reducing the profitability of production and causing an unwanted reputation for this fish production sector. In this study, combinations of oxidative chemicals: ozone (O3), hydrogen peroxide (H2O2), and peracetic acid (PAA) were applied in a commercial, full-scale (1.3 M kg a−1) RAS rearing rainbow trout (Oncorhynchus mykiss). Inlet water from a nearby lake, circulating water, and depuration water were treated to increase their quality and enhance the depuration procedure. The results showed a decrease of 77% (MIB) and 93% (GSM) in the concentrations of off-flavors in circulating water after the treatments with oxidative chemicals. [ABSTRACT FROM AUTHOR]

A better understanding of recirculating aquaculture system (RAS) biosecurity is crucial for the sustainable and ethical production of Atlantic salmon smolt and post-smolt in these systems. This study described and evaluated the performance of a RAS facility for fish infection research with Atlantic salmon as the main animal model. Fish body weight, length, water quality, and system metrics from five independent experimental trials conducted between September 2020 and July 2021 were used to analyze the variation within and between treatments. Statistical power analysis was performed to determine the minimum number of fish required. The fish parameters variability showed that the inter-class correlation coefficient was on average low (0.1) and that the variation within tanks was larger than the variation between the tanks. The power analysis showed that 15 fish were required to be sampled per tank under these study conditions. Variation of water quality and system management metrics among the five experimental trials was higher compared to the variation within the five experimental trials. Moreover, the variation of the water quality parameters controlled by sensors was relatively low, whereas the parameters depending on biofilter maturation level and performance presented a very high variation. Water exchange rate-dependent quality parameters showed a similar variation value, i.e., nitrate and water turbidity. The established baseline for variability and performance presents an important reference for the design and realization of future experiments in RAS facilities. It is foreseen that the current research facility will develop new knowledge to improve the RAS biosecurity in the Atlantic salmon aquaculture industry.

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Pacific salmon (Oncorhynchus spp.) produced in United States conservation hatcheries are commonly reared in tanks and raceways supplied with single-pass water. As controlled studies comparing water reuse vs. traditional single-pass aquaculture systems are limited, we conducted a 20-week growth trial followed by a one-week saltwater challenge to compare growth, survival and saltwater tolerance of juvenile spring Chinook salmon (O. tshawytscha , 5.2 g initial weight) reared in single-pass rectangular tanks (hereafter rectangular tanks), single-pass circular tanks (hereafter circular tanks), or in circular tanks of recirculating aquaculture systems (RAS, 3% constant makeup water on a flow basis) or partial recirculating aquaculture systems (PRAS, 20% constant makeup water on a flow basis). Water volume provided to rearing tanks did not differ among systems, but water velocities in the circular tanks and in the RAS and PRAS fish culture tanks were higher than in the rectangular tanks. Dissolved oxygen levels declined throughout the study in all systems and were significantly lower in RAS than in the single-pass systems. By week 16, ammonia levels were significantly reduced while nitrite‑nitrogen (NO 2 -N) and nitrate‑nitrogen (NO 3 -N) levels were significantly elevated in RAS compared with single-pass systems. Salmon grown in rectangular tanks exhibited significantly lower weight gain and feed efficiency (FE; g gain/g feed) compared with fish reared in the other systems. Survival of salmon grown in the rectangular tanks (99.1%) also was significantly lower than that of fish reared in circular tanks (100%) or PRAS (100%), but was not different from that of fish reared in RAS (99.8%). Survival during the saltwater challenge was significantly reduced in salmon that were reared during the growth trial in rectangular tanks (70%) compared with that of fish that were reared in the other systems (92–96%). Results of this study suggest lower growth and survival of salmon reared in rectangular tanks may be related to reduced water velocity and that RAS and PRAS may be appropriate for rearing spring Chinook salmon for conservation purposes. • Rearing Chinook in a reuse system required 21-fold less well water than control tanks. • Growth of Chinook in reuse systems did not differ from that of fish in circular tanks. • Growth of Chinook in reuse systems was higher than that of fish in rectangular tanks. • Results suggest reuse systems may be appropriate for rearing Chinook salmon. [ABSTRACT FROM AUTHOR]

The quality of smolts is one of the key factors for successful salmon production. We compared growth performance, physiological traits, and environmental adaptation in Atlantic salmon (Salmo salar) after transfer into a sea cages farm site from recirculating aquaculture system (RAS) to a similar sized group of the same genetic linage and produced in the same husbandry facility but under flow through system (FTS) conditions. Fish vertical distribution within the sea cages and water environment were continuously recorded, while biometry data and biological samples were collected monthly. No significant difference in size and smolt development between the FTS and RAS-produced fish were observed at the end of the freshwater phase. However, after transfer into seawater, the RAS fish showed an array of physiological and molecular differences that were maintained and resulted in significantly increased mortality and lower growth over the full production cycle. The RAS smolts were characterized by lower body weight, length, K factor, HSI (indicator of energy reserve), NKA activity, plasma levels of lactate, triacylglycerol, sodium, calcium, and phosphorus than FTS fish in seawater. This implicated osmoregulatory and allostatic maladaptation for the RAS fish during the first months in seawater. Both FTS and RAS fish showed physiological and behavioral adjustments during the seawater production linked with predictable (e.g., seasonal, diurnal) and short-term unpredictable variation in water temperature and oxygen. However, the RAS fish were characterized by lower physiological response to stressful effects of unpredictable environmental variability. Based on our data, the freshwater history sets the basis for the performance success of the FTS and RAS smolts in seawater. FTS fish showed faster adaptation to the seawater environment, with higher osmoregulatory capacity, and higher physiological robustness to seasonal changes than RAS fish, which reflected in their difference in growth and harvest size. We emphasize the crucial role of the freshwater rearing conditions as the foundation for successful physiological adaptation to seawater, growth, and the success of salmon farming production. • Freshwater history affects fish ability to cope with seawater transfer. • RAS smolts show slower osmoregulatory adaptation in seawater than FTS smolts. • FTS and RAS smolts respond differently to seasonal changes in seawater. • RAS smolts show lower physiological response to seawater seasonal changes than FTS. • Seawater temperature is a major factor in modulating fish performance in sea cages. [ABSTRACT FROM AUTHOR]

The world is facing soil, air and water pollution problems which may arise the soil degraded, global warming, food shortage and droughts. For our future generations we have to develop sustainable environment technologies. Many studies have addressed some scientific aspects and have been limited focus on the commercial implementation based on urban food production industrial-scale production in rural areas small scale farming is developed in different countries for education and decoration inside buildings. We must encourage the sustainable small farming as indoor fish farming which is the farming of the new millennium aquaponic is a structure of closed-loop combine the elements of hydroponics and aquaculture which could contribute the addressing these problems. This system emphasis on improvement through management and integration of the living components and the bio filter system. From trickling bio filters and plant uptake of aquaculture wastewater results in improved water and nutrients use efficiency and conversation. The challenge to sustainability centers on balancing the aquaculture system environment for the optimum growth of these organism’s maximum production outputs and minimize effluent discharges to the environment emission and might develop the future application of aquaponic for food security.

This study aimed to evaluate the performance of the red alga Gracilariopsis tenuifrons as a biofilter in a multi-trophic cultivation system with Litopenaeus vannamei, using recirculation by zero water exchange. The species were cultivated for 4 weeks, while measurements were taken of the chemical and physical characteristics of water, the development of the cultivated organisms (biomass and growth rate), and the carbon, nitrogen, and phosphorus content assimilated by the seaweeds. The water enrichment produced by shrimp farming favored the seaweed development, which increased on average by 2.6 % day-1 ± 0.24 (0.4 to 4.08 % day-1). The seaweed species was able to remove up to 35.1% of the ammonium ion and increased its tissue nitrogen by about 4.8 times by the end of the experiment (1.2–4.8%). The shrimp presented an increase in biomass (8.0 to 12.7 g), with an average growth rate of 1.7% day-1 ± 0.1 and a survival of 100% at the end of the experiment. Based on these results, the cultivation of L. vannamei in a recirculating water system using Gp. tenuifrons as a biofilter can be an advantageous alternative, helping to reduce water usage and remove the main metabolites produced by shrimp cultivation. [ABSTRACT FROM AUTHOR]

Purpose. The State of Israel, for a short period in 1948, despite the difficult political and climatic and geographical conditions, demonstrates a stable development of aquaculture. In this regard, the Israeli experience of cultivating tilapia as one of the main objects of world aquaculture is relevant for Ukraine, especially since these fish species were successfully imported into our country, but not widely used in fisheries. Findings. Tilapia has become the third most important fish in aquaculture after carp and salmon; worldwide production exceeded 1,500,000 metric tons in 2002 and increases annually. Because of their high protein content, large size, rapid growth (6 to 7 months to grow to harvest size), and palatability, a number of tilapiine cichlids—specifically, various species of Oreochromis, Sarotherodon, and Tilapia – are the focus of major aquaculture efforts. The work written by the organizer and participants of the of the training course “Intensive Pond Fish Culture”, which was held in Israel in December 2016, is a brief overview of the role of tilapias in the world's aquaculture and the technological schemes by which they are cultivated in this country. In particular, data on world exports and imports of fish in 2016; the gastronomic value of meat is considered; the systematic position of the tribe of tilapias is described; summarizes fish breeding and biological characteristics of the main species used in fisheries. Special attention is focused on the species successfully cultivated in Israel and the technologies that allow it to be achieved. Results of research into tilapia breeding in domestic industrial fish breeding are provided in the article. Ways of effi ciency increase in tilapia breedingare focused in the article. Practical value. This review can be used to popularize tilapias as aquaculture facilities and upgrade existing technologies for their cultivation in Ukraine, as well as in educational and scientific activities.

Integration of intensive aquaculture systems with greenhouse plant production has been shown to improve aquaculture water quality conditions and improve plant nutrient use efficiency. The majority of the focus of integrated systems has involved raft culture or true hydroponics. Little work has been done on soilless culture utilizing drip irrigation. This study investigates the feasibility of integrating biofloc Nile tilapia (Oreochromis niloticus) production with greenhouse cherry tomato production (Solanum lycopersicum var. cerasiforme). Nile tilapia (157 g/fish) were stocked at 40 fish/m³ and grown for 149 days. The cherry tomato cvs. "Favorita" and "Goldita" were grown with aquaculture effluent (AE) waste and compared to plants grown with conventional fertilizer (CF) in soilless culture. Plants were grown for 157 days. Few differences in yield occurred between treatments until fish harvest (117 DAT). Post fish harvest, there was an 18.4% difference in total yield between CF and AE at crop termination for "Favorita". Differences in yield between AE and CF were observed for "Goldita" at fish harvest (117 DAT) and crop termination (157 DAT). Results from this study suggest the potential for successful integration of cherry tomato grown in a substrate-based system with AE from a tilapia biofloc production system. [ABSTRACT FROM AUTHOR]

Geosmin (GSM) and 2-methylisoborneol (MIB)-induced off-flavors can cause serious problems in a recirculating aquaculture system (RAS), such as delayed harvest and increased production costs, but also damage producers' reputation. Traditionally, off-flavors have been removed by depuration before harvesting. Rainbow trout (Oncorhynchus mykiss) and European whitefish (Coregonus lavaretus) are commercially valuable species produced for consumers, both being suitable for rearing in RAS. In this study, European whitefish and rainbow trout were raised from juvenile up to 240 g (European whitefish) and 660 g (rainbow trout) to monitor the long-term accumulation of off-flavors. The concentrations in fillet of rainbow trout reached 3.6 ng·g-1 (MIB) and 5.6 ng·g-11 (GSM) with lipid content of 22.5%, while for European whitefish up to 3.2 ng·g-1 (MIB) and 3.9 ng·g-1 (GSM) were found with 14.8% in lipid content. Concentrations up to 58 ng·L-1 (MIB) and 49 ng·L-1 (GSM) were found in the circulating water. Based on the results, the accumulation of MIB proceeds at similar pace for both species. In the case of GSM, the accumulation started similarly for both species but proceeded more quickly for rainbow trout after 140 days of the experiment, with a statistically significant difference (p < 0.05). [ABSTRACT FROM AUTHOR]

In recirculating aquaculture system (RAS), ammonium excreted by the fish is typically transformed to less toxic nitrate by microbial activity in bioreactors. However, nitrate-nitrogen load can be harmful for the receiving water body when released from the RAS facility. A new type of water treatment system for a RAS was designed, including a passive woodchip denitrification followed by a sand filtration introduced into a side-loop of an experimental RAS, rearing rainbow trout (Oncorhynchus mykiss). In the process, woodchips acted as a carbon source for the denitrification, aiming at a simultaneous nitrogen removal and reduction of water consumption while sand filtration was used to remove organic matter and recondition the circulating water. A variety of chemical analyses and toxicological tests were performed to study the suitability of the process and to ensure the absence of harmful or toxic substances in the system. The results did not show increased toxicity, and no increased mortality was reported for the raised species. After the start-up of the system, the concentrations of fatty acids (e.g., hexadecanoic acid −1) and heavy metals (e.g., Cd < LOD-0.45 μg L−1, Pb < LOD-14 μg L−1) remained at very low levels and below those of known toxic effects. In the beginning of the experiment, good denitrification efficiency was achieved, but it declined after 1 month, showing the need for improved stability and dimensioning of the application. [ABSTRACT FROM AUTHOR]

We studied the effect of sand filtration with natural esker material on the removal of total organic carbon (TOC), total suspended solids (TSS), and turbidity from the effluent of an experimental recirculating aquaculture system (RAS) farm. Separate experiments were performed with the same esker sand: (1) a soil column experiment in 2017 where the effluent (mean TOC 8.14 mg L−1) was percolated vertically through a 50-cm-thick sand column with the infiltration 1 m day−1; (2) a sand filtration experiment with water-saturated conditions in 2018 where the effluent from the woodchip denitrification (mean TOC 26.84 mg L−1) was infiltrated through a sand layer with the retention time of 1.2 days. In experiment 2, infiltration of 25 L day−1 through a 31-cm sand layer and 40 L day−1 through a 50-cm sand layer were studied. Both experiments were performed in association with rainbow trout (Oncorhynchus mykiss) grow-out trials. In sand filtration with vertical water flow through a soil column, the removal of TSS was 40%, while of TOC 6%, partly due to the small thickness of the soil column and coarse sand material. In water-saturated conditions, mean removal of TOC (3 mg L−1 1.2 day−1), TSS (1.2 mg L−1 1.2 day−1), and turbidity (0.4 FTU 1.2 day−1) reached 11% (TOC), 18% (TSS), and 15% (turbidity), even with the retention time of only 1.2 days. The removal of TOC in water-saturated conditions correlated with the removal of TSS and turbidity. [ABSTRACT FROM AUTHOR]

This experiment analysed the operation of submerged and dripping biological filters with three types of filling: commercial fitting HXF12KLL (CF), two innovative polypropylene aggregates (PPA) and polyethylene screw caps for PET bottles (PSC). The experiment determined the time needed to reach full filter functionality at the maturation stage, the time needed to start successive stages of the nitrification process and the maximum concentration of each nitrogen compound in water in the recirculation systems. The filter operation characteristics after the maturation stage were also examined. These issues are crucial during the preparation and launch of new aquaculture facilities. A literature analysis indicated that the ability of biological filters to oxidise nitrogen compounds is affected by a number of factors. Studies conducted at various centres have covered selected aspects and factors affecting the effectiveness of biological filters. During this study, the model fish common carp (Cyprinus carpio) was used. The current experiment involved examination of biological filter maturation and operation during the carp fry rearing stage, which allowed the biofilter operation characteristics to be determined. At the third day of the experiment, the ammonium concentration reached approximately 3 mg NH4-N/dm³. It remained at this level for 10 days and later decreased below 0.25 mg NH4-N/dm³. The maximum nitrite concentration ranged from 11.7 mg/dm³ to 20.9 mg NO2-N/dm³ within 9 to 20 days and later decreased with time. Nitrate concentrations were seen to increase during the experiment. The all applied biofilter media showed possibility to be used in commercial aquaculture systems. [ABSTRACT FROM AUTHOR]

Purpose. The State of Israel is one of the world leaders in the development of modern technologies, particularly in fisheries industry. E.g., 30 fish farms annually provide production of over 18,000 tons of fish, with an average yield of more than 8 tons per hectare. The fish equipment manufactured in this country is supplied to the Asia, Africa, Europe, South and North America countries, Australia. Israelis' specialists and companies design, build and implement engineering and technological support of fish-breeding enterprises in the EU, China, Nigeria, Georgia, Russia, Belarus, etc. The ongoing shortage of water in the country has spurred innovation in water conservation techniques, and a substantial agricultural modernization, drip irrigation. Israel is also at the technological forefront of desalination and water recycling. The Sorek desalination plant is the largest seawater reverse osmosis (SWRO) desalination facility in the world. As of 2015, more than 50 percent of water for Israeli households, agriculture and industry is artificially produced. The country hosts an annual Water Technology and Environmental Control Exhibition & Conference (WATEC) that attracts thousands of people from all over the world. In 2011, Israel's water technology industry was worth around $2 billion a year with annual exports of products and services of dozens of millions of dollars. Due to innovations in reverse osmosis technology, Israel is set to become a net exporter of water in the incoming years. At the same time, publications in Ukraine about the aquaculture branch of Israel concern mainly statistical information, or are devoted to individual ichthyopathological problems, genetic studies, etc. It does not allow analyzing a comprehensive development in this industry of Israel. Thus, the compilation and analysis of existing information is a relevant issue. This article expands the awareness of specialists on the specifics of fisheries industry, marine and freshwater fisheries in Israel, aquaculture technologies, and other fisheries related topics in Israel. Findings. The work written by the organizer and participants of the training course "Intensive Pond Fish Culture", which was held in Israel in December 2016, is a comprehensive survey of modern aquaculture in Israel. In particular, it describes the characteristics of freshwater and marine fish farming and fishing, the technologies used as well as the state fisheries management system. Practical value. This review would help to modernize management approaches in fisheries sector of Ukraine, educational and scientific activities, and develop the international cooperation with Israel.

A recirculating aquaculture system with farmed tilapia is the most popular combination in aquaponics, an integration of aquaculture and hydroponics. Despite nutrient‐rich fish‐rearing water being regarded as a valuable resource for aquaponics, the quality and value of inhabitant microorganisms are certainly understudied. Our present research illustrates the feasibility of the tilapia‐rearing water as a valuable source of beneficial microorganisms called plant growth promoting bacteria (PGPB). Microbial communities were examined with a combination of culture‐independent high‐throughput 16S rRNA gene sequencing and cultivation methods. Microbial communities determined using high‐throughput sequencing indicated the usefulness of Bacteroidetes and Alphaproteobacteria as beneficial microbial indicators to assess the health condition of recirculating aquaculture systems. Siderophore production, ammonia production and phosphate solubilization assays were used for screening and 41% of isolates were identified as plant growth promoting bacteria. These bacteria were classified as Actinobacteria (eight strains [32% in total], Dietzia, Gordonia, Microbacterium, Mycobacterium and Rhodococcus), Bacilli (six strains [24%], Bacillus and Paenibacillus), Flavobacteriia (one strain [4%], Myroides), Betaproteobacteria (two strains [8%], Acidovorax and Chromobacterium) and Gammaproteobacteria (eight strains [32%], Aeromonas, Plesiomonas and Pseudomonas). We found that the tilapia‐rearing water naturally contained various lineages of PGPB and could be esteemed as a worthy seed bank of PGPB. Because aquaponics is a difficult system to use pesticides and herbicides, the role of PGPB to prevent plant pathogens and maintain healthy root system may be more important than traditional agricultural settings. [ABSTRACT FROM AUTHOR]

Highlights • Bacterial activity and abundance increased immediately after acetate addition to RAS water in beakers. • Bacterial activity remained constant in the water phase after acetate spike in RAS with submerged biofilter. • Submerged biofilters have a high capacity to attenuate fluctuations of organic matter in RAS. Abstract This study evaluated the effect of an abrupt increase in easily biodegradable carbon (acetate) on bacterial activity and abundance in the water of recirculating aquaculture systems (RAS). The study included a batch experiment with RAS water only, and an experiment at system level where twelve pilot scale RAS were used. The batch experiment was made to test how acetate concentration would influence the microbial state in RAS water. Further, we wanted to observe if the selected microbial analysis tools would be able to detect these changes. The second experiment was carried out in twelve identical and independent RAS that had been operated under constant loading conditions (1.6 kg/m3 make-up water) for five months prior to the trial. The twelve RAS were divided into four treatment groups in triplicates: i) control with submerged biofilter (Ctrl + bf); ii) control without submerged biofilter (Ctrl-bf); iii) acetate addition in RAS with submerged biofilter (Ac + bf); and iv) acetate addition in RAS without submerged biofilter (Ac-bf). The biofilter media from the groups without submerged biofilter (Ac-bf and Ctrl-bf) was removed just 5 h prior to the start of the trial. The two acetate treatment groups (Ac + bf and Ac-bf) were spiked with 40 mg/L of acetate three consecutive times (0, 24 and 48 h). Consumption of acetate, bacterial abundance and bacterial activity were followed for 72 h after the first acetate spike for both experiments. Bacterial activity was quantified by BactiQuant® and hydrogen peroxide (HP) degradation assay. Bacterial abundance was assessed by quantifying micro-particles and free-living bacteria. In the batch experiment we observed a significant increase in bacterial activity proportional to the amount of acetate added, and a corresponding significant increase in microparticles (1–3 μm). In the pilot scale RAS experiment, the acetate addition in RAS with submerged biofilter did not cause an increase in bacterial activity, or in the number of microparticles in the water phase but a significant increase in bacterial activity and number of microparticles were observed in the RAS without submerged biofilter (Ac-bf). These changes were particularly pronounced shortly after each acetate spike. In RAS with submerged biofilters, the acetate was presumably consumed primarily by the bacterial community within the biofilm, and consequently, only minor changes were observed in densities of free-living bacteria in the water phase. The results of the study suggest that heterotrophic bacteria in the submerged biofilter have a high capacity to handle fluctuation of organic matter loading in RAS, thereby stabilizing the abundance and activity of bacteria in the water column. [ABSTRACT FROM AUTHOR]

• AOPs produce reactive, short-lived species degrading organic pollutants. • Coupling ozonation photocatalysis results in a greater synergistic effects. • Electronic tongues and noses can real-time monitoring off-flavours compounds. Recirculating aquaculture system (RAS) popularity is threatened by the accumulation of off-flavour compounds such as geosmin (GSM) and 2-methylisoborneol (MIB) in the rearing water. Due to their lipophilic nature and the high bio-accumulation rate, they can be detected at very low concentrations in fish flesh, thus reducing product quality and marketability. The removal of these compounds often requires fish to be purged using high amounts of fresh and/or highly treated water before harvesting. A promising alternative is controlling the off-flavours throughout the production cycle by means of advanced oxidation processes (AOPs). In this review, the current state of the art of AOPs application to GSM and MIB degradation is reviewed under the perspective of their applicability to RASs. In particular the advantages of promising coupled processes such as photocatalytic ozonation have been highlighted. Finally, we critically reviewed the existing detection methods of off-flavour compounds in the rearing water, emphasising those allowing rapid and cheap measurements, in order to enable RAS plant managers to make real-time informed decisions, when off-flavours concentration increases above a certain threshold. [Display omitted] [ABSTRACT FROM AUTHOR]

Purpose. To review scientific sources on the morphological and ecophysiological peculiarities of the transition of early sturgeon fry (Acipenseridae) to artificial formulated feeds. To summarize the biotechnological fundamentals of the use of artificial formulated feeds in the conditions of recirculating aquaculture systems (RAS). Findings. The transition of early sturgeon fry to artificial formulated feeds is one of the most difficult stages of their rearing, even under controlled conditions of RAS. The review contains the description of the peculiarities of sturgeon embryogenesis, their behavior and morpho-physiological changes at this stage of their development. It contains main requirements for the rearing of sturgeon larvae in RAS. We showed that the ultimate refuse from natural (live or frozen) forage organisms is not advisable; the optimum is their combination with artificial feeds with gradual predominance of the latters. We provided the schemes of their feeding based on the combination of natural and artificial feeds. We reviewed the most common biologically active supplements, which contributed to better feed digestion during the periods of the transition to exogenous feeding. We highlighted the effect of feeding with brine shrimp nauplii enriched with polyunsaturated fatty acids on the growth and development of early sturgeon fry. Practical value. The array of the summarized information will be important for scientists who study the peculiarities of the transition of early sturgeon fry to artificial formulated feeds in RAS. The data on the biotechnologies of rational feeding of early sturgeon fry in RAS in this period are important in the conditions of continuous search for the most effective replacement of live forage organisms and reduction of fish fry mortality in postembryogenesis.

Integration of intensive aquaculture systems with greenhouse plant production has been shown to improve aquaculture water quality conditions and improve plant nutrient use efficiency. The majority of the focus of integrated systems has involved raft culture or true hydroponics. Little work has been done on soilless culture utilizing drip irrigation. This study investigates the feasibility of integrating biofloc Nile tilapia (Oreochromis niloticus) production with greenhouse cherry tomato production (Solanum lycopersicum var. cerasiforme). Nile tilapia (157 g/fish) were stocked at 40 fish/m3 and grown for 149 days. The cherry tomato cvs. “Favorita” and “Goldita” were grown with aquaculture effluent (AE) waste and compared to plants grown with conventional fertilizer (CF) in soilless culture. Plants were grown for 157 days. Few differences in yield occurred between treatments until fish harvest (117 DAT). Post fish harvest, there was an 18.4% difference in total yield between CF and AE at crop termination for “Favorita”. Differences in yield between AE and CF were observed for “Goldita” at fish harvest (117 DAT) and crop termination (157 DAT). Results from this study suggest the potential for successful integration of cherry tomato grown in a substrate-based system with AE from a tilapia biofloc production system.

Geosmin (GSM) and 2-methylisoborneol (MIB)-induced off-flavors can cause serious problems in a recirculating aquaculture system (RAS), such as delayed harvest and increased production costs, but also damage producers’ reputation. Traditionally, off-flavors have been removed by depuration before harvesting. Rainbow trout (Oncorhynchus mykiss) and European whitefish (Coregonus lavaretus) are commercially valuable species produced for consumers, both being suitable for rearing in RAS. In this study, European whitefish and rainbow trout were raised from juvenile up to 240 g (European whitefish) and 660 g (rainbow trout) to monitor the long-term accumulation of off-flavors. The concentrations in fillet of rainbow trout reached 3.6 ng·g−1 (MIB) and 5.6 ng∙g−11 (GSM) with lipid content of 22.5%, while for European whitefish up to 3.2 ng·g−1 (MIB) and 3.9 ng·g−1 (GSM) were found with 14.8% in lipid content. Concentrations up to 58 ng·L−1 (MIB) and 49 ng·L−1 (GSM) were found in the circulating water. Based on the results, the accumulation of MIB proceeds at similar pace for both species. In the case of GSM, the accumulation started similarly for both species but proceeded more quickly for rainbow trout after 140 days of the experiment, with a statistically significant difference (p < 0.05).

This experiment analysed the operation of submerged and dripping biological filters with three types of filling: commercial fitting HXF12KLL (CF), two innovative polypropylene aggregates (PPA) and polyethylene screw caps for PET bottles (PSC). The experiment determined the time needed to reach full filter functionality at the maturation stage, the time needed to start successive stages of the nitrification process and the maximum concentration of each nitrogen compound in water in the recirculation systems. The filter operation characteristics after the maturation stage were also examined. These issues are crucial during the preparation and launch of new aquaculture facilities. A literature analysis indicated that the ability of biological filters to oxidise nitrogen compounds is affected by a number of factors. Studies conducted at various centres have covered selected aspects and factors affecting the effectiveness of biological filters. During this study, the model fish common carp (Cyprinus carpio) was used. The current experiment involved examination of biological filter maturation and operation during the carp fry rearing stage, which allowed the biofilter operation characteristics to be determined. At the third day of the experiment, the ammonium concentration reached approximately 3 mg NH4-N/dm3. It remained at this level for 10 days and later decreased below 0.25 mg NH4-N/dm3. The maximum nitrite concentration ranged from 11.7 mg/dm3 to 20.9 mg NO2-N/dm3 within 9 to 20 days and later decreased with time. Nitrate concentrations were seen to increase during the experiment. The all applied biofilter media showed possibility to be used in commercial aquaculture systems.

A feeding trial was conducted to investigate the effects of different dietary lipid and protein levels on both the physiological metabolism and the anti-oxidation of Pelteobagrus fulvidraco larvae cultured in recirculating aquaculture system (RAS). In the present study, four test diets (P52L13, P52L9, P48L13, P48L9) were formulated by two different lipid levels (13%, 9%) and two different protein levels (52% and 48%) in a factorial manner (2 × 2) to provide four different dietary protein-lipid ratios (P:L) 3.95, 5.71, 3.56 and 5.46. Each treatment was assigned in triplicate. Two days after hatching, larvae were fed with Artemia sp. for 1 day, and then were co-fed the Artemia sp.plus the tested diets for 2 days, finally fed test diets for 18 days. The results were in keeping with that of growth performance, showed that the larvae fed on P52L13 and P48L9 diets had significantly higher activities of lipoprotein lipase (LPL), glutamic-pyruvic transaminase (GPT), superoxide dismutase (SOD) and catalase (CAT) than other two groups ( P < 0.05 ). The highest activities of lysozyme (LZM) and glutathione (GSH) were observed in group P52L13 and P48L9, respectively ( P  < 0.05). Concerning dietary lipid levels, the highest activities of LPL, GOT, SOD, CAT and LZM were observed for larvae fed diets containing 13% lipid ( P  < 0.05). Regarding to antioxidative factors, same trend was observed for larvae fed diets with 52% protein ( P  < 0.05). Our results clearly suggested that P52L13 and P48L9 diets could promote the metabolism of protein and lipid, and antioxidative ability of P. fulvidraco larvae in RAS, meanwhile, P52L13 diet is the superior. [ABSTRACT FROM AUTHOR]

Large culture tanks of several hundred or thousand m 3 size are generally encouraged for economic advantages in Recirculating Aquaculture Systems (RAS). Out of numerous possibilities in designing the inlet and outlet configurations in octagonal culture tanks, the inlet pipes near the corner walls and the outlets at the tank’s center and/or on side wall are some of the widely-used configurations. The use of wall drain to achieve a controlled flow pattern in the tank, however, influences distinct flow features such as pressure, velocity, uniformity and turbulence in the tank, which are of theoretical interest as well as practical importance. A finite volume description of the flow in an octagonal culture tank at full-scale was therefore developed using Realizable turbulence model with second order accuracy in space and time. The tank was equipped with an inlet pipe near the corner wall and dual-drain outlet system of Cornell-type. The base case had a flow configuration of 45% of flow through central bottom drain, and the rest through the wall drain. Model verification was performed using grid convergence tests, and validation was conducted using Acoustic Doppler velocimetry (ADV) based velocity measurements. The effect of wall drain on the large-scale and small-scale turbulent structures was studied using the distribution of turbulent kinetic energy and vorticity respectively. The parametric study on the flow-split between the two outlets was analyzed using different flowfield indicators, such as flow velocity, uniformity, vorticity strength, maximum absolute vorticity and swirl number. Such an inclusive analysis not only explores the hydrodynamics in the commercial culture tanks with Cornell-type dual-drain but also recommends the farmers with the suitable flow-split between such outlet systems. [ABSTRACT FROM AUTHOR]

The development of intensive recirculating aquaculture systems (RAS) with low water exchange has accelerated in recent years as a result of environmental, economic and other concerns. In these systems, fish are commonly grown at high density, 50 to 150 kg/m 3 , using high-protein (30%–60%) feeds. Typically, the RAS consists of a solid treatment and a nitrification unit; in more advanced RAS, there is an additional denitrification step. Nitrous oxide (N 2 O), a byproduct during nitrification and denitrification processes, is a potent greenhouse gas that destroys the ozone layer. The aim of this study was to measure and assess N 2 O emissions from a near-zero discharge land-based saline RAS. N 2 O flux was monitored from the RAS's fish tank, and moving-bed nitrification and activated-sludge (with intrinsic C source) denitrification reactors. N 2 O emission potential was also analyzed in the laboratory. N 2 O flux from the denitrification reactors ranged between 6.5 and 48 mg/day, equivalent to 1.27 ± 1.01% of the removed nitrate-N. Direct analysis from the fish tank and nitrification reactors could not be performed due to high aeration, which diluted the N 2 O concentration to below detection limits. Thus, its potential emission was estimated in the laboratory: from the fishponds, it was negligible; from the nitrification reactor, it ranged between 0.4 and 2.8% of the total ammonia-N oxidized. The potential N 2 O emission from the denitrification reactor was 3.72 ± 2.75% of the reduced nitrate-N, within the range found in the direct measurement. Overall, N 2 O emission during N transformation in a RAS was evaluated to be 885 mg/kg feed or 1.36 g/kg fish production, accounting for 1.23% of total N application. Consequently, it is estimated that N 2 O emission from aquaculture currently accounts for 2.4% of the total agricultural N 2 O emission, but will decrease to 1.7% by 2030. [ABSTRACT FROM AUTHOR]

Intensive recirculating aquaculture systems (RAS) with its hyper-eutrophic water offer ideal conditions for bacterial growth, abundance and activity, potentially affecting fish and system performance. Feed composition and feed loading in particular will have significant impact on organic and inorganic nutrients available for microbial growth in RAS. How these nutrient inputs affect and regulate bacteria in RAS water is, however, unclear. To investigate this relationship and the associated water quality dynamics, the effects of altered feed loading on microbial water quality in RAS was studied. The study included six independent, identical pilot-scale RAS, each with a total volume of 1.7 m 3 (make-up water: 80 L/day) stocked with juvenile rainbow trout ( Oncorhynchus mykiss ). All systems had been operating with constant and identical feed loading of 3.13 kg feed/m 3 make-up water for a period of three months before the experiment was initiated. Three controlled levels of feed loading where established in duplicates: no feed (0 kg feed/m 3 ), unchanged feeding (3.13 kg feed/m 3 ), and doubled feeding (6.25 kg feed/m 3 ). The experimental period was seven weeks, where microbial and chemical water quality was monitored weekly. Bacterial activity was measured using Bactiquant ® , and microbial hydrogen peroxide degradation. Bacterial abundance was quantified by flow cytometry, and water quality parameters by standardized methods The study showed that water quality as well as bacterial activity and abundance were affected by the changes in feed loading. The microbial water quality parameters, however, did not respond to feed loading changes as quickly and straightforward as the physicochemical parameters such as nitrate, chemical oxygen demand and biological oxygen demand. It was presumed that the fixed bed biofilter suppressed microbial response in the water phase. Hydrogen peroxide degradation assay proved to have considerable potential for assessing overall bacterial load in RAS water although further adjustments and standardization procedures are required. [ABSTRACT FROM AUTHOR]

The main objective of this study was to test an innovative biomitigation approach, where polychaete-assisted ( Hediste diversicolor ) sand filters were combined with the production of Halimione portulacoides in aquaponics, to remediate an organic-rich effluent generated by a super intensive fish farm operating a land-based RAS (Recirculating aquaculture system). The set up included four different experimental combinations that were periodically monitored for 5 months. After this period, polychaete-assisted sand filters reduced in 70% the percentage of OM and the average densities increased from ≈ 400 ind. m − 2 to 7000 ind. m − 2 . H. portulacoides in aquaponics contributed to an average DIN (Dissolved inorganic Nitrogen) decrease of 65%, which increased to 67% when preceded by filter tanks stocked with polychaetes. From May until October (5 months) halophytes biomass increased from 1.4 kg m − 2 ± 0.7 (initial wet weight) to 18.6 kg m − 2 ± 4.0. Bearing in mind that the uptake of carbon is mostly via photosynthesis and not though the uptake of dissolved inorganic carbon, this represents an approximate incorporation of ≈ 1.3 kg m − 2 carbon (C), ≈ 15 g m − 2 nitrogen (N) and ≈ 8 g m − 2 phosphorus (P) in the aerial part (76% of total biomass), and an approximate incorporation of ≈ 0.5 kg m − 2 carbon (C), ≈ 3 g m − 2 nitrogen (N) and ≈ 2 g m − 2 phosphorus (P) in the roots (24% of total biomass). In the present study, the potential of the two extractive species for biomitigation of a super-intensive marine fish farm effluent could be clearly demonstrated, contributing in this way to potentiate the implementation of more sustainable practices. [ABSTRACT FROM AUTHOR]

Microbial water quality in recirculating aquaculture systems (RAS) is important for successful RAS operation but difficult to assess and control. There is a need to identify factors affecting changes in the bacterial dynamics – in terms of abundance and activity – to get the information needed to manage microbial stability in RAS. This study aimed to quantify bacterial activity in the water phase in six identical, pilot scale freshwater RAS stocked with rainbow trout ( Oncorhynchus mykiss ) during a three months period from start-up. Bacterial activity and dynamics were investigated by the use of a patented method, BactiQuant ® . The method relies on the hydrolysis of a fluorescent enzyme-substrate and is a rapid technique for quantifying bacterial enzyme activity in a water sample. The results showed a forty-fold increase in bacterial activity within the first 24 days from start-up. Average BactiQuant ® values (BQV) were below 1000 at Day 0 and stabilized around 40,000 BQV after four weeks from start. The study revealed considerable variation in initial BQV levels between identically operated and designed RAS; over time these differences diminished. Total ammonia nitrogen, nitrite and nitrate levels were very similar in all six RAS and were neither related to nor affected by BQV. Chemical oxygen demand (COD) and biological oxygen demand (BOD 5 ) were highly reproducible parameters between RAS with a stable equilibrium dynamic over time. This study showed that bacterial activity was not a straightforward predictable parameter in the water phase as e.g . nitrate-N would be in identical RAS, and showed unexpected sudden changes/fluctuations within specific RAS. However, a bacterial activity stabilization phase was observed as systems matured and reached equilibrium, suggesting a successive transition from fragile to robust microbial community compositions. [ABSTRACT FROM AUTHOR]