Recirculating Aquaculture System System Research Articles

Optimisation of plasma-activated water: Plasma DBD technology and application in recirculating aquaculture system for Nile tilapia larval culture

Plasma-activated water (PAW) is a useful tool for producing pathogen-free seed fish. This study aimed to apply dielectric barrier discharge (DBD) plasma to reduce the microbial population in the water of a recirculating aquaculture system (RAS) for Nile tilapia larval culture. Initially, a PAW system prototype was developed and found to effectively reduce bacterial populations in both stagnant and circulating water. Additionally, a slight increase in water temperature was observed in the circulating water. Subsequently, the optimisation of PAW conditions in the circulating water was performed. The PAW system, with a copper anode distance of 2 cm and a 1 cm distance between the copper tip and the water surface, combined with a non-spaced cathode pad, exhibited the highest bactericidal effect. Using the optimised PAW conditions from Experiment I, Nile tilapia larval culture was established in the RAS, supplemented with a bacterial suspension (Bacillus subtilis, Streptococcus agalactiae and Aeromonas hydrophila) to assess the bactericidal effects. Three treatments were applied: 1) control (no PAW or antibiotics), 2) PAW, and 3) antibiotic treatment for Nile tilapia larvae cultured in the RAS system for 672 h. The results demonstrated that both PAW and antibiotic treatments significantly reduced the bacterial populations in the water in relation to the control (P < 0.05). Moreover, a substantial reduction in bacterial population was observed in the whole body of the fingerlings in both the PAW and antibiotic groups in relation to the control fingerlings (P < 0.05). In Experiment II, Nile tilapia larval culture in the RAS was conducted under three different conditions: 1) control (no PAW or antibiotic), 2) PAW, and 3) antibiotic treatment, to evaluate the antimicrobial effects of PAW on waterborne bacterial populations for 672 h. Similar to Experiment I, both antibiotic and plasma treatments significantly reduced the bacterial populations in the water and whole-body fingerlings in relation to the control (P < 0.05). Notably, the growth performance and whole-body composition (moisture, crude protein, crude fat, and ash) of the fingerling fish appeared comparable among the experimental groups (P > 0.05), suggesting that PAW had no detrimental effects on long-term fish culture. Therefore, PAW can be employed to effectively reduce bacterial populations in water, thus minimising bacteria-related issues in fish without adverse impacts on fish growth.

Fish Growth Performance in RAS Pond Using Hydrocyclone Mechanical Filter

The high feeding and the metabolic output of the fish in intensive aquaculture can cause various problem, such as poor water quality and slowing down the fish growth performance. Recirculating Aquaculture System (RAS) is a solution to maintain water quality. Unfortunately, the conventional mechanical filter in RAS such as japmat is inefficient. One strategy that can be applied is to use a hydrocyclone. This research aims to observe the fish growth performance in RAS pond using hydrocyclone mechanical filter and its comparison with the use of japmat. Research method was performed by comparing hydrocyclone and japmat in the pond with the RAS system. The research design is completely randomized design (CRD), with three replications in each treatment. The research was carried out through five stages, namely hydrocyclone set-up, RAS ponds set-up, water quality analysis, fish growth measurement, and statistical analysis. Based on the Independent Samples Test, the use of hydrocyclone mechanical filters has a significant effect (P&lt;0.05) on the measured water quality parameters (DO, Temperature, pH, TDS, NH3) except for NO2. Hydrocyclone significantly affect Average Daily Growth and Specific Daily Growth parameters. Whilst, the Survival Rate and Feed Conversion Ratio parameters, it did not give significant effect

Physico-Chemical Dynamics of Vanname Shrimp (Litopenaeus vannamei) Cultivation Pond Water Quality with A Recirculation System

In 2021 Indonesia was experiencing an increase in shrimp exports. Litopenaeus vannamei shrimp is one of the shrimp with a good increase in exports and a type of shrimp with high resistance to environmental disturbances. Indonesia has land potential of about 2,964,331.24 hectares which can be used to increase shrimp production. The cultivation technique that can maximize this potential is a superintensive technique that uses closed aquaculture system. Recirculating Aquaculture system (RAS) is a closed aquaculture system that is suitable for shrimp farming because the water treatment is separated so that there is no significant change in environmental conditions. In this study, the RAS system was equipped with the use of an ultrafiltration membrane as a tool for the inflow water treatment. This study observe the physico-chemical water dynamics that occur during one cultivation cycle. It was observed that the DO of the pond decreased as the shrimp grew, the salinity increased during the cultivation process if there was no water replacement, the brightness decreased every day until it reached a specified point. Temperatures tended to be low due to weather factors, ammonia levels tended to decrease but nitrite and nitrate levels tended to increase due to the slower transformation rate of nitrite and nitrate. The operating system for this process was carried out by adding CaO and sugar. The addition of CaO ranges from 100-600 g/day. The effective addition of sugar if there was a spike in ammonia levels was 1.25 kg/day.

Nitrogen excretion by the lobsters Panulirus ornatus and Thenus australiensis and uptake by the brown algae Sargassum siliquosum: Implications for integrated recirculated aquaculture systems

Farming extractive species such as macroalgae that take up nitrogen (N), with fed species (e.g., lobsters, finfish, prawns) is termed integrated multi-trophic aquaculture (IMTA). In recirculating aquaculture systems (RAS), high concentrations of nitrogenous waste can become toxic to the fed species and macroalgae offers a method of mitigating N waste. To utilise macroalgae as a biofilter for N waste, an understanding of their N ecophysiology of both the fed and extractive species is needed. In this study we first determine the ammonium and urea excretion rates for emerging aquaculture candidates the tropical rock lobsters, Panulirus ornatus (TRL) and slipper lobster, Thenus australiensis (SL). Using multiple flask uptake experiments, we then determined the N ecophysiology of the tropical brown macroalga, Sargassum siliquosum, to assess its potential use as a biofilter in a lobster RAS. Routine (basal) N excretion was predominantly ammonium with only a minor contribution of urea (8 and 13% for TRL and SL respectively). For both lobster species, ammonium and urea excretion substantially increased post-prandial, peaking at levels 3.6 times greater than basal amounts for TRL and 3.2 times greater for SL, and remained elevated for between 32 and 38 h. Uptake of both ammonium and nitrate by S. siliquosum showed saturating kinetics, where the kinetic parameter Vmax is the maximum rate of uptake, Ks is the half-saturation constant and the Vmax:Ks-ratio is a proxy for the algae's affinity of uptake for that respective nutrient: for ammonium Vmax = 110.9 μmoles g−1 dry weight (DW) h−1 and Ks = 37.9 μM and for nitrate Vmax = 152.7 μmoles g−1 DW h−1 and Ks = 58.52 μM. Urea uptake was highly variable with both positive and negative (i.e. urea release from tissue) rates recorded; when positive values were considered, Vmax = 55.5 μmoles g−1 DW h−1 and Ks = 17.65 μM. We used uptake and excretion rates from our study to derive a unit mass stocking ratio of algae to lobster (algae: animal) to offset N pollution in RAS. The ratios of TRL to algae to offset NH4+ and urea post-prandial were 5.15E-04 and 3.09E-04 respectively and for SL, 4.46E-04 and 6.31E-04 respectively. The findings serve as a reference for future studies on integrating Sargassum species into RAS and IMTA systems.

Effect of Probiotics in Recirculating Aquaculture System (RAS) on the Concentration of Ammonia, Nitrite, and Nitrate in the Aquaculture of Catfish (Clarias sp.)

The purpose of this research is to determine the effect of probiotic administration on ammonia, nitrite, and nitrate levels in catfish cultivation (Clarias sp.) with the RAS system. The research was conducted in February – March at the Anatomy Laboratory and chemical laboratory of the Faculty of Fisheries and Marine Airlangga University. This study was conducted experimentally using the RAL method consisting of 5 treatments four replays, namely control treatment (P0), probiotic dose 0.5 mL/L (P1), probiotic dose 1 mL/L (P2), probiotic dose 1.5 mL/L (P3), and probiotic dose 2 mL/L (P4). Data analysis is processed using ANOVA and DMRT. The result of this study was the administration of probiotics with the bacterium Nitrosomonas sp. And Nitrobacter sp. with different doses has an effect (p<0.05) on the concentration of ammonia, nitrite, and nitrates.

Process for nutrient recycling from intensive aquaculture through microalgae-bacteria consortium

This work studies a biological process based on a microalgae-bacteria consortium for recycling nutrients in a recirculating aquaculture system (RAS) implanted in an intensive marine aquaculture farm. Additionally, some techniques were used for microalgae biomass harvesting and tested the effectiveness of filtration by a column with multi-layer sand to reduce the solids concentrations in the effluent.The consortium was grown in photobioreactors in batch and semi-continuous operation modes using the solids concentrated stream generated in the RAS system. The semi-continuous operation showed a high percentage of TDN and TDP removal, achieving final concentrations of 1.09 ± 0.02 mg·L−1 and 0.01 ± 0.01 mg·L−1, respectively, while DOC was reduced to 3.87 ± 0.06 mg·L−1. The values of productivity 44 ± 9 mg TSS·L−1 indicated that the studied stream is a suitable culture medium for the growth of the microalgae-bacteria consortium.A combination of harvesting techniques was studied, coagulation-flocculation-settling and coagulation-flocculation-flotation. The first step was to optimise the dose of FeCl3 through the coagulation-flocculation test to pre-concentrate the biomass generated, achieving an optimal dose of 0.106 mg Fe·mg TSS−1. Then, two separation processes were applied to the stream and compared: settling and flotation. The maximum removal efficiency (90.2 ± 0.3 %) was obtained in the settling process, so the coagulation-flocculation-settling was select as the best combination of harvesting techniques.Finally, sand filtration was studied as an effluent refining process to improve solids reduction of the water obtained in the harvesting step resulting in an effluent with 17.18 ± 1.49 mg TSS·L−1.The proposed sequence process is capable of recycling nutrients from an intensive marine aquaculture farm by using these resources via transformation into microalgae biomass and generating quality effluent.

L-Tryptophan Mitigates Cannibalism and Improves Growth of Asian seabass, Lates calcarifer Reared in a RAS System

Severe cannibalism can result in a significant loss of productivity during the nursery phase of Asian seabass, Lates calcarifer. The present study aimed to determine the effect of dietary tryptophan on growth, feed utilization, cannibalism, survival, and muscle proximate composition of Asian seabass juveniles (initial size, 2.77 ± 0.04 cm in length and 0.29 ± 0.01 g in weight) in a recirculating aquaculture system (RAS) at different stocking densities. The tryptophan levels were set at 0.41% (control diet, standard dosage for normal growth and survival of Asian seabass), 1.00% (Diet 1), and 1.50% (Diet 2), while the stocking densities were set at 0.5 ind./L and 1.5 ind./L. The results indicated that dietary supplementation with L-tryptophan (TRP) and fish stocking density had a significant effect on fish growth parameters, feed utilization, cannibalism, survival, and muscle lipid content (p &lt; 0.05) over the 45-day trial. The maximum length, weight, WG, and SGR were 11.64 ± 0.35 cm, 22.93 ± 2.67 g, 22.64 ± 2.67 g, and 9.63 ± 0.27%, respectively, in the fish fed Diet 2, and 11.35 ± 0.22 cm, 24.38 ± 1.28 g, 24.09 ± 1.28 g, and 9.82 ± 0.11% at a 1.5 ind./L stocking density. The lower FCR (0.81 ± 0.04) and higher PER (2.98 ± 0.16) ensured better utilization of Diet 1 than the other diets. Moreover, significant interaction effects between diet and stocking density were observed in total yield, cannibalism, and survival of the Asian seabass. Significantly higher survival rates of 76.11 ± 3.90% in the Diet 1 group and 76.28 ± 2.88% in 0.5 ind./L stocking density were obtained, which is promising. The study concludes that dietary supplementation with 1.00% TRP was effective in reducing cannibalism and increasing the survival of the Asian seabass nursery reared in RAS at a lower stocking density (i.e., 0.5 ind./L), whereas 1.50% supplemental TRP at a higher stocking density (i.e., 1.5 ind./L) significantly increased the cannibalism and growth, which in turn reduced the survival rate.

Comparative life cycle assessment of whiteleg shrimp (Penaeus vannamei) cultured in recirculating aquaculture systems (RAS), biofloc technology (BFT) and higher-place ponds (HPP) farming systems in China

Recirculating aquaculture systems (RAS), biofloc technology (BFT), and higher-place ponds (HPP) are considered as alternative technologies in addressing major environmental challenges linked to conventional Whiteleg shrimp farming systems. Global concern about energy consumption and carbon emission in aquaculture industries, especially in countries like China. The application of life cycle assessment (LCA) in shrimp aquaculture, especially in comparing different shrimp production systems, is being used. In our study, surveys on three RAS, three BFT and nine HPP farms have been conducted, and the data inputs were used to establish a cradle to farm-gate LCA by means of software SimaPro 9.3.0.2 and CML-IA methods to evaluate the environmental performance. The methods are well suited to this LCA, as it focuses mainly on energy consumption input, pollution output, and ecological damage. A ton of live weight shrimp production did generate 4424.2, 4657.2, and 4965.6 kg CO2 eq; 21.8, 25.9, 36.2 kg PO4 eq; 38.7, 40.6 and 43.5 kg SO2 eq in RAS, BFT and HPP systems, respectively. Regarding the characterization and normalization results, eleven categories (abiotic depletion, acidification, eutrophication, etc.) were considered. In most impact categories, the results showed that HPP had the highest environmental impact per unit production when compared to RAS and BFT. Acidification potential (AP) and eutrophication potential (EP) were the top two contributing factors to RAS, BFT and HPP. And AP and EP is closely related to the production of electricity. Electricity was identified as primary contributors in all farming processes. Results indicate that BFT and RAS could be used in combination to reduce environmental impacts. In order to improve the environmental performance of these farming systems, feed ingredients substitution; feeding management and effluent treatment are among the suggested measures. In order to enhanced aquaculture LCI databases and support aquaculture LCA research, the life cycle inventory for shrimp farming were established.

Recent advances in marine ornamental breeding and seed production at Vizhinjam Regional Centre of CMFRI India

The marine ornamental fish trading industry is an ever-expanding one, as indicated by its bolstering statistics, which amount to about US$ 300 million. Although the trade is booming, the natural habitats that foster these fishes, such as coral reefs, are steadily declining. One of the reasons for this is the overdependency of the industry on wild-caught fishes. To surpass this, the Central Marine Fisheries Research Institute (CMFRI) has developed hatchery technology for breeding marine ornamental fishes such as seahorses, clownfishes, damsels, and serranids. It began with the breeding of Hippocampus kuda. This progressed to breeding clownfishes such as Amphiprion chrysogaster, A. ocellaris, A. nigripes, A. peridarion, and A. ephippium and Premnas biaculeatus. Damsel fishes that were bred successfully include Chrysiptera cyanea, C. hemicyanea Neopomacentrus cyanomos, N. nemurus, and Dascyllus carneus. The recirculating aquaculture system (RAS) designed in the Vizhinjam Regional Centre of CMFRI is being used for broodstock development of serranids, tangs, squirrel fishes, and soldier fishes. A standard method was developed for captive breeding and hatchery rearing of anthias Pseudanthias marcia and P. squamipinnis in an advanced indigenous RAS system. The present article provides a bird’s eye view of the important research work done in India concerning marine ornamental fish breeding and reviews important breeding work carried out at Vizhinjam Regional Centre of CMFRI.

Increasing The Stocking Density of Grouper Nurseries for Aquabusiness Efficiency in Recirculating Aquaculture System (RAS) with Bioremediation

Water quality improvement was carried out by means of recirculation and bioremediation systems in grouper nurseries with high stocking density, thereby increasing production performance. The goal of this study was to evaluate the effectiveness of aquabusiness by analyzing the rise in grouper nursery stocking density using RAS and bioremediation systems. The test parameters consist of production performance, blood glucose levels, physic-chemistry-biology of water quality, and business efficiency based on productivity and business analysis. Treatment of 1,000 fish/m3 increased survival, blood glucose levels, total bacteria, Vibrio spp., ammonia, nitrite, and all productivity parameters. But it lowers all growth parameters, pH, and dissolved oxygen values. The recirculation system with bioremediation at up to 1,000 fish/m3 of stocking boosted the profit by 2.64 times. and 14.97% more efficient than 500 fish/m3 which could not be matched by the high production performance.

The Analysis of Clinical sign, Mortality and Histopathology of Cantang Grouper Infected with VNN in Recirculating Aquaculture System

Hybrid grouper is a variety of grouper that has become increasingly popular in recent years. The development of grouper cultured in Indonesia utilizing the Recirculating Aquaculture System (RAS) is currently underway; nevertheless, fish cultured in the RAS system continue to struggle with infectious diseases, one of which is VNN (viral nervous necrosis) infection caused by piscine betanodavirus. The purpose of this study was to know the clinical sign, mortality, and histopathology of cantang grouper (Epinephelus fuscoguttatus x E. lanceolatus) infected with VNN in RAS. Fish samples were obtained from the hatchery using RAS. This research uses a mixed methods approach and the type of research used is exploratory research. The parameters observed were clinical signs, mortality, and histopathology. Water quality, including temperature, DO, salinity, and pH at the time of VNN infection, was used as secondary data. The results showed that clinical signs of sick fish were weakness, staying at the bottom of the rearing tank, decreased appetite, swimming with the stomach facing up and the body dark in color. Fish mortality occurred for ± 10 days with a peak of mortality reaching 26.86 ± 7.45% on day 9 from initial signs. Histopathology result, diseased fish showed vacuolization in the brain and retina of the eye.

Abundance and Diversity of Nitrifying Microorganisms in Marine Recirculating Aquaculture Systems

Recirculating aquaculture systems (RAS) are important for water quality management in aquaculture facilities, and can help resume water consumption. However, information about the community structure of the micro-ecosystem existing in biofilters, especially the participation of the known nitrifying groups (i.e., AOA, AOB, NOB, and comammox Nitrospira), remains to be fully clarified. In this research, we compared the community structures in three RAS systems operated at different temperatures in a marine aquarium, through both amoA-targeted qPCR assay and 16S rRNA-targeted next-generation sequencing. As result, AOA was the primary nitrifier in the biofilters and was typically abundant and diverse in high-temperature samples (ca. 25 °C). NOB’s relative abundance patterns were numerically similar to that of AOA, suggesting a cooperation relationship between AOA and NOB in the marine RAS system. AOB was at a comparable level with AOA in medium-temperature samples (ca. 19 °C), while their abundance sharply decreased in high-temperature samples. The number of observed OTUs of AOA in high-temperature samples was 1.9 and 1.5 times as much as that detected in low (ca. 10 °C) and medium temperature samples respectively, suggesting a much more diverse and predominant occurrence of AOA at high temperatures. Comammox Nitrospira was only detected at a low level in the biofilter samples, suggesting a negligible contribution to the nitrification process in such ammonia-limited, saline biofilms. Although comammox Nitrospira cannot be detected by 16S rRNA-based analysis, the high diversity and abundance of NOB that were detected in high-temperature samples indicated the prospective possibility of the occurrence of complete ammonia oxidation at high temperatures.

Observations on Red Mark Syndrome in juvenile rainbow trout farmed in RAS system.

Observations on Red Mark Syndrome in juvenile rainbow trout farmed in RAS system.

Effect of probiotics addition on total organic matter and survival rate of catfish (Clarias sp.) maintenance using recirculating aquaculture system (RAS)

Most catfish farmers do not make efforts to manage water quality. This causes high organic matter. Therefore, water management is carried out through the Recirculating Aquaculture System (RAS). Continuous use of water in the RAS system causes filter performance to decrease, so technological improvements are needed with the addition of probiotics. The research was conducted on 22 February – 23 March 2021 at the Chemistry and Analysis Laboratory, Faculty of Fisheries and Marine, Universitas Airlangga to determine the influence of probiotic additions on the RAS system total organic matter and the survival rate of catfish.The study was conducted experimentally using RAL by adding different doses of probiotics, namely P0 (Control), P1 (0.5 ml/L), P2 (1 ml/L), P3 (1.5 ml/L) and P4 (2 ml/L ) with four replays. Data analysis using ANOVA and DMRT showed that the addition of probiotics in the RAS system has an effect (p<0.05) on total organic matter and survival rate. Organic matter was highest at P2 (46.89 mg/L) and lowest at P2 (34.07 mg/L). Survival rates were highest at P2 (85%) and lowest at P0 (71.25%).

Investigations on the performance of snubnose pompano Trachinotus blochii (Lacepede,1801) in a lowcost recirculating aquaculture system

Farming of snubnose pompano Trachinotus blochii (Lacepede,1801) in a low cost recirculating aquaculture system (RAS) was attempted by stocking fingerlings (5.3±0.02 g) at 33 fish m-3 and fed on a commercial pellet feed (45% protein). After 210 days, a specific growth of 1.68% per day was observed with final average weight of 180.78±4.54 g and a production of 29.28 kg (4.88 kg m-3) with 81% survival. The fishes exhibited a condition factor of 1.61 with an allometric growth (b = 2.94). The data can be used as baseline for upscaling the farming of the species in commercial RAS systems. Keywords: FCR, Fish growth, Mariculture, Water quality

COMPARISON OF GROW-OUT METHODS OF SAND LOBSTER (Panulirus homarus) WITH RECIRCULATION AQUACULTURE SYSTEM (RAS) AND FLOW-THROUGH (FT): STUDY OF BIOLOGICAL ACTIVITIES

Aquaculture technology using Recirculating Aquaculture System (RAS) is basically a technology for fish farming by reusing water used in production. This technology is based on the use of mechanical and biological filters, and this method in principle can be used for all species cultivated in aquaculture such as fish, shrimp, shellfish and others. This study was carried out at Station for Investigation of Fish Health and Environment (LP2IL) Serang’s field test facility starting from June to November 2020 (110 days of sand lobster grow-out period). In this study, the RAS system used for grow-out of sand lobster uses a series of containers, compartments, tanks and equipment for water treatment with the following purification stages (1) sedimentation containers; (2) physical filtration; (3) biological filtration, (4) disinfection of water by UV irradiation, (5) removal of CO2, (6) clean water reservoirs and (7) tanks for grow-out of sand lobster. In this study, a series of tests were carried out on several biological activities parameters of sand lobster including growth weight and length, FCR, SR, molting and biomass, which were measured every two weeks during grow-out period. From the results of this study activity, it is found that the biological parameters of sand lobster grow-out with RAS is improving when compared to sand lobster grow-out in flow through water system (FT).

Aquaculture in Serbia

Serbian aquaculture is practiced in warmwater (carp) farms, coldwater (trout) farms, cage systems, recirculating aquaculture systems (RAS) and fish tanks. The total area under carp farms (ponds) registered by the Statistical Office of the Republic of Serbia (SORS) in the last fourteen years has varied between 6,192 and 8,940 ha, while under the area under trout farms was between 33,255 m2 and 81,411 m2. Total fish production over the last fourteen years varied between 5,070 tons, recorded in 2017 and 8,195 tons of market fish, recorded in 2010. Fish production is dominated by common carp and rainbow trout (about 90% of total production). In addition to these two species, several other species are cultured at carp farms, such as catfish, pikeperch, pike, silver carp, bighead carp, grass carp, Prussian carp and tench. In trout farms, additional cultured species are usually brook trout, huchen and grayling, while cultured fish species in RAS systems are sterlet and Russian sturgeon.

Slaughter yield and chemical composition of Siberian sturgeon reared in a recirculating aquaculture system (RAS)

Sturgeon fish species are food fish of commercial significance in many countries. Sturgeon farming in Serbia is a relatively new branch of aquaculture, and sturgeon farming has been developing in the last several years. The objective of this study was to examine morpho-physiological and slaughter characteristics and proximate composition of one-year-old sturgeons produced in a recirculating aquaculture system (RAS). Sturgeons were cultured in a RAS system nearby Novi Sad and were fed with commercial feed. Moisture content in fillets ranged from 75.63 to 77.91%, protein content from 18.06 to 18.89% and lipid content from 2.37 to 4.38%. The slaughter performance results are in agreement with those reported by various authors for different strains of sturgeons. Sturgeon species have potential to become an attractive fish in our aquaculture in terms of overall proximate composition and slaughter performance.

A Temporally Dynamic Gut Microbiome in Atlantic Salmon During Freshwater Recirculating Aquaculture System (RAS) Production and Post-seawater Transfer

Atlantic salmon aquaculture is undergoing an expansion of land-based recirculating aquaculture systems (RAS), especially for freshwater (FW) stages of production. Juvenile salmon undergo parr-smolt transformation, also known as smoltification and become pre-adapted to tolerate seawater (SW). One aspect requiring study is the development of microbial communities during this time, especially in RAS systems. Here we analyzed temporal changes in microbiome associated with the intestine in Atlantic salmon during smolt production in a commercial RAS production facility and followed the same cohort of fish post-seawater transfer (SWT), using 16S rRNA gene sequencing. Microbial diversity and richness showed an increase over time across FW production, but declined sharply and significantly 1-week post-SWT before re-establishing itself with a completely different community structure after 4 weeks. Core microbial taxa could be assigned to three distinct categories; (1) omnipresent, (2) salinity specific, or (3) transient. By including diet and water samples in the analyses, we classified true core taxa associated with the host, those associated with the diet, and transient cores associated with microbial communities in tank water. The rising trend observed in microbial richness in the water may be a consequence of a temporal increase in organic load while dominance of Vibrionaceae may be attributed to the higher temperatures maintained during RAS production and above average natural water temperatures post-SWT. Functional analysis suggests modulation of metabolic pathways post-SWT, but downstream impacts on fish growth and health in a commercial setting remain to be elucidated. A deeper understanding of the interplay between microbial composition and functionality can play a role in optimizing fish performance in tightly regulated RAS production.

Hydrogen peroxide oxygenation and disinfection capacity in recirculating aquaculture systems

Hydrogen peroxide (H2O2) treatment is an alternative for disinfection in aquaculture, which may be advantageous as it dissociates and disinfects while increasing water oxygen concentration. Yet, accurate dosing remains undeveloped in Recirculating Aquaculture Systems (RAS). Dosage requirements can depend on organic burden, stocking density, feeding frequency, salinity, temperature and biofilter performance. The present case study investigated the dual effect of H2O2 application for oxygen enrichment and disinfection when continuously applied to a RAS rearing European seabass. H2O2 addition equivalent to 2.4 and 15.8 H2O2 mg L−1 were applied for 4 h per day in three 5-days experiments. H2O2 was injected at the inlet of protein skimmer and/or the rearing tanks in or without combination with traditional disinfection methods. Water microbial load and oxygen saturation were determined, along with stress markers glucose and cortisol in blood plasma of fish. Doses of 15.8 mg L−1 H2O2 steadily increased oxygen levels in holding tank water from ∼50 % to over 100 % saturation while reducing microbial load (from 604.4 CFU ml−1 in the rearing tanks before dosing to 159.8 CFU ml−1 after application), achieving suitable conditions for commercial fish densities in RAS. The doses used had negligible impact on biofilter performance and did not affect the fish in terms of stress. Overall results indicate H2O2 is effective for disinfection and oxygenation of RAS systems when applied at appropriate dosage and we recommend the protein skimmer as the safest position in order to protect the bacterial community of the biofilters and the reared fish.