Fish Welfare in Aquaponic Systems: Its Relation to Water Quality with an Emphasis on Feed and Faeces—A Review

Effects of ammonia nitrogen stress on the physiological, biochemical, and metabolic levels of the gill tissue of juvenile four-finger threadfin (Eleutheronema tetradactylum)

In this study, the impact of ammonia nitrogen stress on juvenile four-finger threadfin in pond culture was examined. The 96-hour median lethal concentration (LC50-96h) and safe concentration of ammonia nitrogen were assessed in juveniles with a body weight of 7.4 ± 0.6 g using ecotoxicological methods. The study design included a stress group exposed to LC50-96h levels of ammonia nitrogen and a control group without ammonia nitrogen exposure. To examine the physiological, biochemical, and metabolic effects of ammonia nitrogen on gill tissue, gill tissue samples were collected after 12, 24, 48, and 96 h of stress, with a resumption of treatment after 48 h. Compared to the control group, ammonia nitrogen adversely affected juvenile four-finger threadfin, with LC50-96h and safe concentration values of 20.70 mg/L and 2.07 mg/L, respectively. Exposure to ammonia nitrogen resulted in substantial gill damage, including fusion of lamellae, epithelial cell loss, and proliferation of chlorine-secreting cells. This tissue damage persisted even after a 48-h recovery period. Ammonia nitrogen stress triggered an increase in antioxidant enzyme activity (superoxide dismutase, catalase, and glutathione peroxidase) and malondialdehyde levels in gills, indicating oxidative stress from 12 h onwards. Although enzyme activity decreased over time, oxidative stress persisted even after recovery, suggesting an ongoing need for antioxidant defense. Metabolomics analysis showed significant alterations in 423 metabolites under ammonia nitrogen stress. Key metabolites such as L-arginine, taurine, 20-hydroxyarachidonic acid, 11,12-dihydroxy-5Z, 8Z, and 14Z eicosotrienic acid followed an increasing trend; uridine, adenosine, L-glutathione, and thymidine 5'-triphosphate followed a decreasing trend. These changes reflect metabolic adaptations to stress. In enriched metabolic pathways, the main differential pathways are membrane transport, lipid metabolism, and amino acid metabolism. After 48 h, significant differences were observed in 396 metabolites compared to the control group. Notably, L-arginine, choline, and L-histidine increased, while linoleic acid, adenosine, and glutathione decreased. Amino acid and lipid metabolism pathways were key affected pathways. Under ammonia nitrogen stress, juvenile four-finger threadfin increased the synthesis of unsaturated and saturated fatty acids to cope with low temperatures and bolster immune function by consuming spermidine. This adaptation helps to clear peroxides generated during fatty acid synthesis, thereby protecting cells from oxidative damage. This study provides insights for pond aquaculture and breeding of ammonia nitrogen-tolerant fish strains.

Starvation and re-feeding of Gilthead seabream (Sparus aurata) and European seabass (Dicentrarchus labrax) co-cultured with glasswort (Salicornia europaea) in a polyculture aquaponic system

The aim of this study was to evaluate the effect of starvation and refeeding on the growth and food intake of gilthead seabream (Sparus aurata) and seabass (Dicentrarchus labrax) and on the growth and nitrogen uptake of glasswort (Salicornia europaea) in a polyculture aquaponic system under 12 ppt salinity for 75 days. Nine small-scale autonomous aquaponic systems were used, each containing 10 gilthead seabreams (average weight of 6.33 ± 0.73 g and average length of 5.73 ± 0.72 cm) and 10 seabasses (5.82 ± 0.77 g and 6.35 ± 0.45 cm), as well as five glasswort plants. Three fish feeding treatments were performed, a control (A), in which fish were fed daily until satiation, and two fasting treatments for 4 (B) and 7 days (C). Fish growth performance was significantly lower (p < 0.05) in the C treatment for both species compared to treatments A and B. Food consumption (FC) and feed conversion ratio (FCR) were significantly higher (p < 0.05) in treatment C. Glasswort growth performance was significantly higher in treatment C (p < 0.05). The results showed that the 4-day food-deprived fish were similar to the control fish by achieving partial compensatory growth. The more extended fasting period (7 days) resulted in significantly lower growth performance. The lipid and nitrogen retention levels in both species were significantly lower in food-deprived fish than in the control fish both before and during compensatory growth. The results suggest that a feeding schedule involving starvation-refeeding cycles is a promising feed management option for these species in polyculture aquaponic systems. The effect of food deprivation was also significantly beneficial (p < 0.05) for the growth performance of glasswort compared to the control treatment.

The effect of swimming activity and feed restriction of rainbow trout (Oncorhynchus mykiss) on water quality and fish-plant growth performance in aquaponics

In this study, we investigated the effects of swimming activity and feed restriction on juvenile rainbow trout (Oncorhynchus mykiss) in decoupled aquaponic systems. Our focus was on assessing their impact on water quality parameters within the aquaponic setup and evaluating the growth performance of the fish, including final weight (FW), condition factor (K), coefficient of variation (c.v.) in weight, specific growth rate (SGR), total feed intake (g/fish), feed conversion rate (FCR), hepatosomatic index (HSI), and viscerosomatic index (VSI), as well as the growth of lettuce (Lactuca sativa L. var. elmaria). The study involved 108 juvenile rainbow trout with an average initial weight of 26.54 ± 0.36 g and 60 ten-day-old lettuce seedlings, over a period of 42 days. We designed four treatment groups, each with three fish tanks: static ad libitum (SA), where fish were in static water conditions and fed to satiation; static restriction (SR), with fish in static water and a 25% feed restriction; current ad libitum (CA), where fish experienced forced swimming at 1 BL s-1; and current restriction (CR), with swimming exercise at 1 BL s-1 and a 25% feed restriction. Using a flow rate of 1 BL s-1 in the tanks for rainbow trout yielded several benefits. Notably, the fish in the CA group exhibited increased feed intake (60 ± 1.78 g fish-1) and enhanced fish growth with an FW of 91.72 ± 0.91 g, compared to the SA group (55.88 ± 0.88 g fish-1 for feed intake and 89.26 ± 0.81 g for FW). In contrast, the CR group showed a reduced feed intake (39.02 ± 2.78 g fish-1) and a lower FW (67.85 ± 1.49 g) compared to the CA group. In addition, the CA group demonstrated positive contributions to fish development with a reduced HSI (1.26 ± 0.02) in comparison to the SA group (1.56 ± 0.14). Inadequate nutrient provisioning in the SR and CR groups negatively impacted fish growth and system efficiency. Our findings suggest that optimizing water flow and feed benefits fish and plants and enhances system sustainability.

Innovative inbuilt moving bed biofilm reactor for nitrogen removal applied in household aquarium

An innovative inbuilt moving bed biofilm reactor (MBBR) was created to protect fish from nitrogen in a household aquarium. During the 90 experimental days, the ammonia nitrogen (NH4+-N) concentration in the aquarium with the inbuilt MBBR was always below 0.5 mg/L, which would not threaten the fish. Concurrently, nitrite and nitrate nitrogen concentrations were always below 0.05 mg/L and 4.5 mg/L, respectively. However, the blank contrast aquarium accumulated 1.985 mg/L NH4+-N on the 16th day, which caused the fish to die. The suspended biofilms could achieve the specific NH4+-N removal rate of 45.43 g/m3/d. Biofilms presented sparsely with filamentous structures and showed certain degrees of roughness. The bacterial communities of the suspended biofilms and the sediment were statistically different (p < 0.05), reflected in denitrifying and nitrifying bacteria. In particular, the relative abundance of Nitrospira reached 1.4%, while the genus was barely found in sediments. The suspended biofilms showed potentials for nitrification function with the predicted sequence numbers of ammonia monooxygenase [1.14.99.39] and hydroxylamine dehydrogenase [EC:1.7.2.6] of 220 and 221, while the values of the sediment were only 5 and 1. This study created an efficient NH4+-N removal inbuilt MBBR for household aquariums and explored its mechanism to afford a basis for its utilization.

Inoculum and pH effects on ammonium removal and microbial community dynamics in aquaponics systems

Understanding the ecology of microorganisms is essential for optimizing aquaponics systems. Effects of pH and inoculum on ammonium removal and dynamics of microbial community composition from all compartments of lab-scale aquaponics systems were examined. Initial ammonium accumulation in systems with comammox-enriched inocula were 47% and 69% that of systems enriched with ammonia-oxidizing bacteria (AOB), with higher rates of ammonium removal and transient nitrite accumulation measured in the latter systems. By the end of operation, Nitrosomonas and Nitrosospira AOB were dominant nitrifiers in systems at pH 7.6-7.8, whereas comammox (Nitrospira) nitrifiers and plant growth-promoting microbes were abundant in systems operating at pH 5.8-6.0. Lower pH systems supported more robust plant growth with no significant effects on fish health. This study demonstrated functional redundancy of aquaponics microbiota, with selectivity of nitrifying taxa as a function of pH. The results suggest that inoculum and pH are important considerations for aquaponics system initiation and optimization.

Transcriptomic profiling reveals the immune response mechanism of the Thamnaconus modestus induced by the poly (I:C) and LPS

Aquatic animals immune response to pathogenic is a hotspot and related to high-quality development of aquaculture industry and the conservation of fisheries resources. Thamnaconus modestus is an important commercial and economical species which is suffering from various pathogens but by now lack relevant research about revealing the immune response mechanism to the pathogens invasion. In the study, the polyriboinosinic polyribocytidylic acid [poly (I:C)] and Lipopolysaccharides (LPS), respective mimics of viral and bacterial infections, were used to demonstrate the immune response of the species via transcriptome analysis. The results showed that T. modestus had sensitive responses to the viral analog infection at 6 h and 48 h, and at 6 h, the first five major functional genes were NFKBIA, IL1B, JUN, IGH, FOS, and at 48 h, the genes were NFKBIA, IL1B, JUN, IGH, FOS. The genes IL1B, IRF3, PTGS2, THBS1 could helping the fish to fight against the bacterial infection in both the times. Similarly for the bacterial infection, the species had a sensitive response at 6 h, and the first five major functional genes were NFKBIA, JUN, FOS, L1B, GRIN2C. Our study provided an insight about the immune response mechanism of this species and demonstrated that if need for treatment of the virus and bacteria by the biotechnology, the artificial interferential time would be suggested before 6 h since the pathological features occur and the genes NFKBIA, JUN, IL1B, FOS, TRAF2, IL8, SOCS3, PTGS2 should be payed more attention.

Septicemic Outbreak in A Rainbow Trout Intensive Aquaculture System: Clinical Finds, Etiological Agents, and Predisposing Factors

On the 23rd of September 2022, a small intensive aquaculture unit populated with rainbow trout (Oncorhynchus mykiss) reported increased mortality in adults and juvenile fish. The unit comprised 12 enclosed concrete basins with a capacity of ten cubic meters of water, populated with 150 kg of fish each. Fish were subjected to a clinical examination on the site, after which whole fish were harvested for a bacteriological and histopathological examination. Water quality parameters were examined using classic biochemical methods and Fourier Transform Infrared Spectroscopy in order to find out whether the environment in which the fish live is also a predisposing factor that could facilitate different pathogens and induce a state of disease in the fish. Real-time PCR was performed on strains of Aeromonas spp. sampled from the fish to accurately identify the pathogen species. The goal was to accurately identify the problems and predisposing factors that lead to disease outbreaks.

Aquaponics production system: A review of historical perspective, opportunities, and challenges of its adoption

The aquaponics production system integrates hydroponics and recirculatory aquaculture system for the simultaneous production of plants and fish. At a time, such as the postpandemic era, the aquaponics system represents an efficient green farming and eco-friendly alternative to sustainable agricultural production. In this review, the history and development of the production systems were traced vis-a-vis its pros and cons. Although there has been much dispute about the origin of the system, the numerous records of developmental attempts in history have all led to the current complexity of the systems and their efficiency. Water conservation, improved performance, food security, less pollution, and low energy consumption are some of the advantages identified in the use of aquaponics systems for food production. Challenges to the domestication of the system, however, include moderately high start-up capital, the need for stable electricity to operate the system, nutrient availability, as well as treatment of diseases in the system. Although the aquaponics production system could be a panacea for food security in Africa, modalities for the domestication of this technology are largely not in place, hence the need for some government interventions in this regard.

Growth performance, feed utilization, hematological parameters, and histological features of Nile tilapia (Oreochromis niloticus) fed diets with supplementary herbal extracts under prolonged water exchange

Nile tilapia is known for its relative tolerance to some biotic and abiotic stressors. However, long-period water exchange may impair the health status and, thereby, the growth performance and feed utilization. In this regard, using herbal extracts may help to relieve the adverse impacts of low water quality on the productivity of this fish species. A 100-day feeding trial was designed to examine the effects of dietary supplements of Aloe vera leaves (AVE), and chamomile flowers, Matricaria chamomilla (CFE) extracts on water quality, growth performance, and well-being of Nile tilapia. Fish (3.95±0.05 g, n=1200) were distributed into five groups (15 fiberglass tanks, 2 m3) under a water exchange rate of 20% every two days for standard control (T0) without herbal supplements. In groups (T1, T2, T3, and T4), a long period water exchange period of 50% every month, wherein T1 (stressed control), T2, T3, and T4 groups were fed a diet supplemented with 0% herbal extract, 1% AVE, 1% CFE and 0.5% AVE +0.5% CFE, respectively. Results showed that feeding on a T2 diet exhibited a clear improvement under a long period of water exchange stress, and it is almost similar to their counterparts under normal conditions (T0) in terms of specific growth rate, survival rate, feed intake, feed conversion ratio, and protein efficiency ratio. Moreover, the lowest levels of aspartate aminotransferase were obtained with T2 and T0. In addition, the highest white blood cell count and hemoglobin values were recorded with group T0, followed by T2, and T4, while no significant difference between T3 and T1. Fish under stressed conditions without herbal extracts (T1) showed the lowest performance and survival rate compared to T0 and T2 groups. In conclusion, feeding diet supplied with 1% A. vera extract to stressed fish restored their performance and well-being to the level of their counterparts under normal conditions.

An Analytical Framework on Utilizing Various Integrated Multi-Trophic Scenarios for Basil Production

Here, we aim to improve the overall sustainability of aquaponic basil (Ocimum basilicum L.)-sturgeon (Acipenser baerii) integrated recirculating systems. We implement new AI methods for operational management together with innovative solutions for plant growth bed, consisting of Rapana venosa shells (R), considered wastes in the food processing industry. To this end, the ARIMA-supervised learning method was used to develop solutions for forecasting the growth of both fish and plant biomass, while multi-linear regression (MLR), generalized additive models (GAM), and XGBoost were used for developing black-box virtual sensors for water quality. The efficiency of the new R substrate was evaluated and compared to the consecrated light expended clay aggregate-LECA aquaponics substrate (H). Considering two different technological scenarios (A-high feed input, B-low feed input, respectively), nutrient reduction rates, plant biomass growth performance and additionally plant quality are analysed. The resulting prediction models reveal a good accuracy, with the best metrics for predicting N-NO₃ concentration in technological water. Furthermore, PCA analysis reveals a high correlation between water dissolved oxygen and pH. The use of innovative R growth substrate assured better basil growth performance. Indeed, this was in terms of both average fresh weight per basil plant, with 22.59% more at AR compared to AH, 16.45% more at BR compared to BH, respectively, as well as for average leaf area (LA) with 8.36% more at AR compared to AH, 9.49% more at BR compared to BH. However, the use of R substrate revealed a lower N-NH₄ and N-NO₃ reduction rate in technological water, compared to H-based variants (19.58% at AR and 18.95% at BR, compared to 20.75% at AH and 26.53% at BH for N-NH₄; 2.02% at AR and 4.1% at BR, compared to 3.16% at AH and 5.24% at BH for N-NO₃). The concentration of Ca, K, Mg and NO₃ in the basil leaf area registered the following relationship between the experimental variants: AR > AH > BR > BH. In the root area however, the NO₃ were higher in H variants with low feed input. The total phenolic and flavonoid contents in basil roots and aerial parts and the antioxidant activity of the methanolic extracts of experimental variants revealed that the highest total phenolic and flavonoid contents were found in the BH variant (0.348% and 0.169%, respectively in the roots, 0.512% and 0.019%, respectively in the aerial parts), while the methanolic extract obtained from the roots of the same variant showed the most potent antioxidant activity (89.15%). The results revealed that an analytical framework based on supervised learning can be successfully employed in various technological scenarios to optimize operational management in an aquaponic basil (Ocimum basilicum L.)-sturgeon (Acipenser baerii) integrated recirculating systems. Also, the R substrate represents a suitable alternative for replacing conventional aquaponic grow beds. This is because it offers better plant growth performance and plant quality, together with a comparable nitrogen compound reduction rate. Future studies should investigate the long-term efficiency of innovative R aquaponic growth bed. Thus, focusing on the application of the developed prediction and forecasting models developed here, on a wider range of technological scenarios.

Plasma for aquaponics

Global environmental, social, and economic challenges call for innovative solutions to food production. Current food production systems require advances beyond traditional paradigms, acknowledging the complexity arising from sustainability and a present lack of awareness about technologies that may help limit, for example, loss of nutrients from soil. Aquaponics, a closed-loop system that combines aquaculture with hydroponics, is a step towards the more efficient management of scarce water, land, and nutrient resources. However, its large-scale use is currently limited by several significant challenges of maintaining desirable water chemistry and pH, managing infections in fish and plants, and increasing productivity efficiently, economically, and sustainably. This paper investigates the opportunities presented by plasma technologies in meeting these challenges, potentially opening new pathways for sustainability in food production.

Fuzzy Logic-Based Adaptive Aquaculture Water Monitoring System Based on Instantaneous Limnological Parameters

Water quality is crucial for maintaining a sustainable living environment in aquaculture. Limnological parameters affects the fish physiology, growth rate, and feed efficiency and may lead to high mortality rate under extreme conditions. The development of an adaptive aquaculture monitoring system for water quality using fuzzy logic will address this problem. Using Mamdani-type fuzzy inferences system (FIS) model, the input limnological parameters such as pH, temperature, total dissolved solids, and dissolved oxygen levels were transformed to four output states: excellent, good, poor, and toxic, for the prediction of water quality. For the simulation and evaluation of the developed FIS, MATLAB Simulink was used. Results of this study can be integrated with a feedback system for appropriate treatments including filtering, aeration, and water flushing to maintain safe environment for Nile tilapia.

A systematic review and meta-analysis of the relationship between farm management, water quality and pathogen outbreaks in tilapia culture

A systematic review and meta-analysis of on farm management and water quality as risk factors triggering pathogen outbreaks in tilapia culture is presented. A total of 121 papers from 28 countries, 37 devoted to management and 84 to water quality associated with the presence of pathogens in tilapia culture were analysed. Most of research has been made on ponds, focusing on bacteria and metazoans. Meta-analysis reveals the proportion of research showing statistical inferences between management (34%), water quality (38% for bacteria and 16.2% for metazoans) and pathogen outbreaks. The most cited parameters related to pathogens outbreaks were temperature (>30°C), dissolved oxygen (<5.0 mg/L), pH (<8.0) and ammonia (1.0 >mg/L) 65, 38, 32 and 34 papers, respectively. However, statistical inference was <20%. Meta-analysis reveals tendencies between high temperatures (30-35°C), low dissolved oxygen (<5 mg/L) and high NH₃ (1-5 mg/L) with pathogen outbreaks. Despite the knowledge about the relationship between management and water quality as factors for pathogen effects, most information is descriptive and empirical. Future research on tilapia culture outbreaks should be focused on the effects of multiple stressors affecting tilapia pathogen outbreaks, thereby generating strategies to prevent diseases and financial losses.

Aquaponics as a Promising Strategy to Mitigate Impacts of Climate Change on Rainbow Trout Culture

Simple Summary

Climate change and overexploitation of natural resources drive the need for innovative food production within a sustainability corridor. Aquaponics, combining the technology of recirculation aquaculture systems (RAS) and hydroponics in a closed-loop network, could contribute to addressing these problems. Aquaponic systems have lower freshwater demands than agriculture, greater land use efficiency, and decreased environmental impact combined with higher fish productivity. Rainbow trout is one of the major freshwater fish cultured worldwide, which, however, has not yet been commercially developed in aquaponics. Nevertheless, research conducted so far indicates that the trout species represents a good candidate for aquaponics.

Abstract

The impact of climate change on both terrestrial and aquatic ecosystems tends to become more progressively pronounced and devastating over the years. The sector of aquaculture is severely affected by natural abiotic factors, on account of climate change, that lead to various undesirable phenomena, including aquatic species mortalities and decreased productivity owing to oxidative and thermal stress of the reared organisms. Novel innovative technologies, such as aquaponics that are based on the co-cultivation of freshwater fish with plants in a sustainable manner under the context of controlled abiotic factors, represent a promising tool for mitigating the effect of climate change on reared fish. The rainbow trout (Oncorhynchus mykiss) constitutes one of the major freshwater-reared fish species, contributing to the national economies of numerous countries, and more specifically, to regional development, supporting mountainous areas of low productivity. However, it is highly vulnerable to climate change effects, mainly due to the concrete raceways, in which it is reared, that are constructed on the flow-through of rivers and are, therefore, dependent on water’s physical properties. The current review study evaluates the suitability, progress, and challenges of developing innovative and sustainable aquaponic systems to rear rainbow trout in combination with the cultivation of plants. Although not commercially developed to a great extent yet, research has shown that the rainbow trout is a valuable experimental model for aquaponics that may be also commercially exploited in the future. In particular, abiotic factors required in rainbow trout farming along, with the high protein proportion required in the ratios due to the strict carnivorous feeding behavior, result in high nitrate production that can be utilized by plants as a source of nitrogen in an aquaponic system. Intensive farming of rainbow trout in aquaponic systems can be controlled using digital monitoring of the system parameters, mitigating the obstacles originating from extreme temperature fluctuations.

Multi-Gene Genetic Programming of IoT Water Quality Index Monitoring from Fuzzified Model for Oreochromis niloticus Recirculating Aquaculture System

Real-time water quality index (WQI) monitoring – a simplified single variable indication of water quality (WQ) – is vital in attaining a sustainable future in precision aquaculture. Although several monitoring systems for water quality parameters (WQP) use IoT, there is no existing WQI IoT monitoring for Oreochromis niloticus because the current WQI models are too complex to be deployed for low-level computing platforms such as the IoT modules and dashboards. Thus, the development of the IoT-based WQI fuzzy inference system (FIS) was simplified by the multi-gene genetic programming (MGGP) to search for non-linear equations given the simulated WQP fuzzy sets. Results have shown that the implemented novel system can accurately predict the WQI IoT monitoring with an average of R2 and RMSE of 0.9112 and 0.6441, respectively. Implementing WQI in the IoT monitoring dashboard using the MGGP has significantly addressed the present challenges in deploying other complex AI-based models for WQI, such as the FIS and neural networks in low-computing capable platforms.

Role of dietary Spirulina platensis and betaine supplementation on growth, hematological, serum biochemical parameters, antioxidant status, immune responses, and disease resistance in Nile tilapia

Spirulina platensis is, a freshwater microalga, broadly used worldwide. It not only stimulates the immune systems of aquatic organisms but also provides a protein-rich diet and commonly used in the manufacture of aquafeeds. This study was planned to evaluate the growth performance, hepato-renal, and immune response biomarkers of Spirulina and Betaine on Nile tilapia (Oreochromis niloticus) and their protective effect against infection with Aeromonas hydrophila. O. niloticus juveniles (20.22 ± 0.86 g) were divided into four groups (n = 10 per replicate). For 8 weeks, the first and second groups (T_S&T_B) were fed with 0.5% and 0.3% concentrations of Spirulina and Betaine supplemented diets, respectively; the third group (T_SB) was fed with a Spirulina and Betaine mixed diet; the fourth group was fed with a basal diet (without supplementation, T₀), which served as control. Dietary inclusion of Spirulina and Betaine significantly improved (P ˂ 0.05) the weight gain, final weight, and food conversion ratio, especially in the T_S group. The activities of hepatic malonaldehyde were unchanged in T_S & T_SB groups and the muscular significantly decreased (P ˂ 0.05) in the same groups, while both increased in the T_B group; meanwhile, levels of glutathione reductase were significantly upregulated in all treated groups. Serum interleukins, TNF- alpha, and IL-10 levels were also significantly reduced in all treatment groups. A significant protective power against pathogenic Aeromonas infection was evidenced in all treated groups. Findings in this study highlight the reputation of Spirulina and Betaine as immunostimulants and protective agents against A. hydrophila infection in O. niloticus.

Is Aquaponics Beneficial in Terms of Fish and Plant Growth and Water Quality in Comparison to Separate Recirculating Aquaculture and Hydroponic Systems?

Aquaponics is a technique where a recirculating aquaculture system (RAS) and hydroponics are integrated to grow plants and fish in a closed system. We investigated if the growth of rainbow trout (Oncorhynchus mykiss) and baby spinach (Spinacia oleracea) would be affected in a coupled aquaponic system compared to the growth of the fish in RAS or plants in a hydroponic system, all systems as three replicates. We also investigated the possible effects of plants on the onset of nitrification in biofilters and on the concentration of off-flavor-causing agents geosmin (GSM) and 2-methylisoborneol (MIB) in rainbow trout flesh and spinach. For the fish grown in aquaponics, the weight gain and specific growth rates were higher, and the feed conversion ratio was lower than those grown in RAS. In spinach, there were no significant differences in growth between aquaponic and hydroponic treatments. The concentration of GSM was significantly higher in the roots and MIB in the shoots of spinach grown in aquaponics than in hydroponics. In fish, the concentrations of MIB did not differ, but the concentrations of GSM were lower in aquaponics than in RAS. The onset of nitrification was faster in the aquaponic system than in RAS. In conclusion, spinach grew equally well in aquaponics and hydroponic systems. However, the aquaponic system was better than RAS in terms of onset of nitrification, fish growth, and lower concentrations of GSM in fish flesh.

Fish Welfare in Urban Aquaponics: Effects of Fertilizer for Lettuce (Lactuca sativa L.) on Some Physiological Stress Indicators in Nile Tilapia (Oreochromis niloticus L.)

The combination of hydroponics and aquaculture, or aquaponics, normally requires adding fertilizer to recirculated water to ensure optimal plant growth, but the effect of that fertilizer on fish welfare has not been studied in detail, especially for small urban and coupled aquaponic systems. In this study, a commercial fertilizer was placed in two small aquaponic systems (less than 250 liters each) to test its effect on the stress levels of Nile tilapia (Oreochromis niloticus) compared to controls without any fertilizer. Fish production parameters were not significantly different between treatments, nor were physiological indicators of fish stress (plasma cortisol, glucose, and triglycerides). On the other hand, lettuce growth (leaf and root weight and length) was up to three times higher in the treatment that received fertilizer.

Effect of different fish feeds on water quality and growth of crucian carp (Carassius carassius) in the presence and absence of prometryn

Few data are available regarding comprehensive or quantitative assessment of fish feed considering both the environmental and feeding impacts. Aiming to fill the gap, an experimental study to investigate the effects of three fish feeds on concentrations of nutrients and crucian carp (Carassius carassius) growth was conducted in laboratory aquariums in the presence and absence of prometryn. Results showed that weight gain rates of crucian carp treated with Tong Wei (TW) feed were 106.3% and 2.0% higher than that of Zhong Shan (ZS) and Zhong Liang (ZL) feeds, a possible explanation was that the quality of protein in TW feed was highest as evidenced by the protein efficiency ratios. Meanwhile, TW feed posed relatively lighter effects on water qualities (between ZL and ZS). Prometryn significantly inhibited the growth of crucian carp and thus affected concentrations of nutrients in water indirectly. The relationships between weight gain rates of fish and concentrations of nutrients in water (R² = 0.929-0.990) were developed. In sum, this study suggested that it is realizable to obtain better fish growth performance with lesser degrading effects on water qualities by producing and selecting appropriate feed regardless of prometryn existence, and the developed equations could be used as a basis for future studies.

Smart Indoor Farms: Leveraging Technological Advancements to Power a Sustainable Agricultural Revolution

Conventional farming necessitates a large number of resources and infrastructure such as land, irrigation, manpower to manage farms, etc. Modern initiatives are required to automate conventional farms. Smart indoor farms offer the potential to remedy the shortfalls of conventional farms by providing a controlled, intelligent, and smart environment. This paper presents a three-dimensional perspective consisting of soilless farming, energy harvesting, and smart technologies, which could be considered as the three important characteristics of smart indoor farms. A six-layer smart indoor farms architecture has also been proposed, which explains how data are collected using various sensors and devices and then transmitted onto the cloud infrastructure for further analysis and control through various layers. Artificial lighting, smart nutrition management, and artificial climate control, to name a few, are some of the important requirements for smart indoor farms while considering control and service management factors. The major bottleneck in installing such systems is both the economical and the technical constraints. However, with the evolution of technology (and when they become widely available in the near future), a more favourable farming scenario may emerge. Furthermore, smart indoor farms could be viewed as a potential answer for meeting the demands of a sustainable agricultural revolution as we move closer to Agriculture 4.0. Finally, in order to adapt smart indoor farms and their study scope, our work has presented various research areas to potential researchers.

Development of an aquaponics microbial inoculum for efficient nitrification at acidic pH

Maintaining an optimal pH that simultaneously supports plants, fish, and nitrifying microorganisms is a challenge in recirculating aquaponics systems as nitrification is optimal at a slightly alkaline pH and plant growth is optimal at a slightly acidic pH. Freshwater fish tolerate pH > 5.5. Our aim was to adapt a microbial inoculum for a recirculating aquaponics system from an operational pH of 7.6 to 5.6, compare nitrification activity and production of N₂O, and describe changes in the adapted versus unadapted microbial communities. Four adaptation strategies were tested; our results indicated that a gradual reduction from pH 7.6 to 5.6, along with a gradual reduction followed by a gradual return of available ammonium, was the best strategy resulting in retention of 81% nitrification activity at pH 5.6 compared to pH 7.6. 16S rRNA gene amplicon sequencing and qPCR enumeration of nitrification-related genes showed that the composition of pH 5.6 adapted microbial communities from all four adaptation strategies was similar to one another and distinct from those operating at pH 7.6, with enrichment of comammox clade B bacteria over ammonia-oxidizing bacteria and thaumarchaeota. N₂O production of the pH 5.6 adapted microbial communities was below detection in all adaptation experiments, likely due to the increased proportion of comammox bacteria. Aquaponics biofilters enriched with comammox bacteria and adapted to function at pH 5.6 can be a desirable inoculum for freshwater recirculating aquaponics systems to retain nitrification activity and improve crop yields.Key points• Microbial communities adapted from pH 7.6 to pH 5.6 retained 81% nitrification activity.• Microbial communities adapted from pH 7.6 to pH 5.6 were enriched in comammox bacteria.• Comammox-enriched microbial communities did not produce N₂ O.

Comparison of two commercial recirculated aquacultural systems and their microbial potential in plant disease suppression

BACKGROUND

Aquaponics are food production systems advocated for food security and health. Their sustainability from a nutritional and plant health perspective is, however, a significant challenge. Recirculated aquaculture systems (RAS) form a major part of aquaponic systems, but knowledge about their microbial potential to benefit plant growth and plant health is limited. The current study tested if the diversity and function of microbial communities in two commercial RAS were specific to the fish species used (Tilapia or Clarias) and sampling site (fish tanks and wastewaters), and whether they confer benefits to plants and have in vitro antagonistic potential towards plant pathogens.

RESULTS

Microbial diversity and composition was found to be dependent on fish species and sample site. The Tilapia RAS hosted higher bacterial diversity than the Clarias RAS; but the later hosted higher fungal diversity. Both Tilapia and Clarias RAS hosted bacterial and fungal communities that promoted plant growth, inhibited plant pathogens and encouraged biodegradation. The production of extracellular enzymes, related to nutrient availability and pathogen control, by bacterial strains isolated from the Tilapia and Clarias systems, makes them a promising tool in aquaponics and in their system design.

CONCLUSIONS

This study explored the microbial diversity and potential of the commercial RAS with either Tilapia or Clarias as a tool to benefit the aquaponic system with respect to plant growth promotion and control of plant diseases.

Freshwater-adapted sea bass Dicentrarchus labrax feeding frequency impact in a lettuce Lactuca sativa aquaponics system

The aim of this study is to investigate the effect of three daily fish feeding frequencies, two, four and eight times per day (FF2, FF4, and FF8, respectively) on growth performance of sea bass (Dicentrarchus labrax)and lettuce plants (Lactuca sativa) reared in aquaponics. 171 juvenile sea bass with an average body weight of 6.80 ± 0.095 g were used, together with 24 lettuce plants with an average initial height of 11.78 ± 0.074 cm over a 45-day trial period. FF2 fish group showed a significantly lower final weight, weight gain and specific growth rate than the FF4 and FF8 groups. Voluntary feed intake was similar for all the three feeding frequencies treatmens (p > 0.05). No plant mortality was observed during the 45-day study period. All three aquaponic systems resulted in a similar leaf fresh weight and fresh and dry aerial biomass. The results of the present study showed that the FF4 or FF8 feeding frequency contributes to the more efficient utilization of nutrients for better growth of sea bass adapted to fresh water while successfully supporting plant growth to a marketable biomass.

Beneficiary of nitrifying bacteria for enhancing lettuce (Lactuca sativa) and vetiver grass (Chrysopogon zizanioides L.) growths align with carp (Cyprinus carpio) cultivation in an aquaponic system

The aquaponic system is an alternative strategy to treat aquaculture waste and achieve food independence. Bacteria play vital roles in the aquaponic system as they can transform ammonia or ammonium into nitrite and then into nitrate, which is more favorable for bacteria, fish, and plants. The objective of this study was to determine the effect of nitrifying bacteria (Nitrosomonas europaea Winogradsky and Nitrobacter winogradskyi Winslow) on the aquaponic system in terms of water quality, nutrient availability, and productivity of carp (Cyprinus carpio), lettuce (Lactuca sativa var. crispa), and vetiver grass (Chrysopogon zizanioides L.). The experiment consisted of four treatments: aquaculture of carp as a control for fish (A), hydroponic of lettuce and vetiver grass without nutrient addition as a control for plants (B), aquaponic (carp, lettuce, vetiver grass) (C), and aquaponic with nitrifying bacteria addition (D). The results showed nitrifying bacteria addition had a significant effect on daily growth rate (DGR) and relative growth rate (RGR) of lettuce within a treatment; on the other hand, the nitrifying bacteria did not give a significant effect to RGR of vetiver grass. The growth rate, specific growth rate, and survival rate of the carp in aquaculture treatment (A) were lower than in both aquaponic treatments (C and D). Nitrifying bacteria addition in the aquaponics system had a significant effect of increasing the orthophosphate concentration. Water quality was also indicated to be better in the aquaponic system than in the aquaculture system. The integration of aquaculture and hydroponics with the addition of nitrifying bacteria enables the formation of microorganism communities, nitrate, and orthophosphate, which lead to the improvement of water quality, nutrient availability, and plant growth.

Effects of dietary asafoetida (Ferula sinkiangensis K. M. Shen) levels on feeding attraction activity, growth performance, healthiness, and digestive enzyme activity in juvenile Lateolabrax japonicus

The study was to investigate effects of asafoetida (Ferula sinkiangensis K. M. Shen) powder on feeding attraction activity (FAA), growth performance, healthiness, and digestive enzyme activity of juvenile Lateolabrax japonicus. Six concentration levels (0, 5, 10, 15, 20, and 25 g/kg diets) were formulated for luring and feeding experiment. Results showed that asafoetida could stimulate the appetite of L. japonicus at the dietary levels from 10 to 25 g/kg; reduce the feed conversion ratio (FCR) and feed intake (FI) at 10-20 g/kg; increase the weight gain (WG) and specific growth rate (SGR) at 5-10 g/kg; increase the hepatosomatic index (HSI), body crude lipid content, serum total protein (TP) content, and lysozyme activity at 10-15 g/kg; decrease the moisture at 10-15 g/kg; and increase the serum total superoxide dismutase (T-SOD) activity at 5-15 g/kg, when compared with the control group (p < 0.05). Digestive enzyme activities including amylase (AMS) and trypsin in the intestine were significantly affected by the asafoetida powder (p < 0.05). Regression analyses between the FAA, FCR, WG, SGR, HSI, LZM, T-SOD, AMS, trypsin, and the dietary asafoetida powder levels showed that the optimal additional amount was 16.95, 13.65, 8.36, 8.15, 15.45, 9.94, 8.75, 11.77, and 7.07 g/kg, respectively, indicating that the optimal amount of asafoetida powder was located in 7.07-16.95 g/kg diet. However, combined with the significant difference analyses obtained from the current study, we would suggest the additive suitable dosage was 10 g/kg.

Black Soldier Fly Full-Fat Larvae Meal as an Alternative to Fish Meal and Fish Oil in Siberian Sturgeon Nutrition: The Effects on Physical Properties of the Feed, Animal Growth Performance, and Feed Acceptance and Utilization

Simple Summary

Research for alternative protein sources that may replace fish meal and fish oil in fish diets is one of the ongoing tasks for aquaculture. Sturgeons role captive fish production increases due to the rapid decrease in its wild stocks during the 20th century. Insect meals are a novel group of feed materials rich in nutrients that are produced in an environmentally sustainable way. Therefore, the aim of the study was to assess the effects of black soldier fly larvae full-fat meal (BSFL) usage as fish meal and fish oil replacement in Siberian sturgeon diets. The experimentally obtained data showed the possibility of extruded feed production with up to 30% of BSFL and physical parameters suitable for fish feeding. Moreover, feed acceptance increase was observed in treatments containing than 10% and higher shares of BSFL. In the groups whose feed contained 5 to 30% of BSFL in the diet, the growth of experimental fish as well as their feed utilization parameters were improved; however, with no effects on feed digestibility. All presented data make BSFL a suitable nutrient source alternative to fish meal in Siberian sturgeon nutrition.

Abstract

This study provides data on the use of black soldier fly (Hermetia illucens) full-fat meal (BSFL) in Siberian sturgeon (Acipenser baerii) nutrition, examining pellet physical properties, growth performance, feed acceptance and utilization, apparent protein, and fat digestibility. The study consisted of: feed quality assessment; a growth performance; feed acceptance; digestibility trials. The effect of the use of BSFL as a replacement for fish meal (FM) and fish oil (FO) was investigated. The applied BSFL shares were 5%, 10%, 15%, 20%, 25%, and 30% of the diet, replacing up to 61.3% of FM and allowing us to reduce FO use by up to 95.4% in the case of 30% incorporation. The applied substitution affected feed quality, increasing the expansion rate, and decreasing feed density, sinking speed and water stability. However, body weight gain, specific growth rate, feed, and protein conversion ratios, were improved in groups fed BSFL. Moreover, feed acceptance was increased with treatments containing 10 to 30% BSFL. No effects on nutrients digestibility were observed. The results show that the use of BSFL as an FM and FO replacement may have positive effects on sturgeon growth performance, and BSFL can be developed as a promising alternative feed material.

Cold-Resistant Heterotrophic Ammonium and Nitrite-Removing Bacteria Improve Aquaculture Conditions of Rainbow Trout (Oncorhynchus mykiss)

The aim of this study was isolation and characterization of heterotrophic bacteria capable of ammonium and nitrite removal at 15 °C (optimal temperature for growing rainbow trout Oncorhynchus mykiss). Environmental isolates were grown in liquid media containing ammonium or nitrite, and best strains in terms of growth and ammonium or nitrite removal were identified via 16S rRNA sequencing. Dyadobacter sp. (no. 68) and Janthinobacterium sp. (no. 100) were selected for optimal adaptation to growth at 15 °C and best ammonium and nitrite removal (P < 0.05), respectively. A heterotrophic ammonium and nitrite removal (HAN) microbial complex, containing selected strains, was prepared and applied in a trout culture system. After 10 days, the effect of microbial HAN complex was investigated in terms of ammonium and nitrite removal, as well as stress and immune indices present in the plasma of cultivated trout. Compared to a standard cultivation setup, addition of the HAN complex had a clear beneficial effect on keeping the un-ionized ammonia and nitrite level below prescribed standards (P < 0.05). This resulted in reduction of stress and immune reactions of cultivated fish (P < 0.05), leading to an augmentation of final weight and survival. Application of the selected microbial complex resulted in a significant improvement of the aquaculture ecosystem.

Characterizing Nutrient Composition and Concentration in Tomato-, Basil-, and Lettuce-Based Aquaponic and Hydroponic Systems

Aquaponic nutrient studies often use various types of water containing high levels of mineral nutrients for water supply, making it difficult to accurately determine deficient nutrients limiting crop yield and quality across the systems. To avoid interference with background nutrients, we used reverse osmosis water in this study. The objectives were to identify critical nutrients that affect the yield and quality of cherry tomato-, basil-, and lettuce by characterizing nutrient composition and concentration in aquaponic systems in comparison to hydroponic systems. Daily release rate (mg L−1) of macronutrients derived from fish feed (41% protein, 1.1% phosphorus, 1% fish weight) was in decreasing order of SO4–S (16) > PO4–P (2.4) > NO3–N (1.0) > K (0.8) > Cl (0.5) > NH4–N (0.4) > Ca (0.2) > NO2–N (0.13) > Na (0.11) > Mg (0.02), in which daily inputs of Mg and Ca in aquaponics were found to be only 1–2% and 4–6%, respectively, of those in hydroponics. Subsequently, the average concentrations of all nutrients were significantly lower in aquaponics than in hydroponics during a 3-month production except for Cl, NH4–N, NO2–N, and Na. The concentration of Mg remained below 5 mg L−1 in all aquaponic systems, while the concentration of Ca rapidly decreased in tomato-based aquaponics, especially during fruiting. SPAD value (chlorophyll content) was associated with concentrations of leaf N, Mg, and/or Ca. Specifically, lower SPAD value was correlated with lower leaf Mg and Ca for tomato and lower leaf Mg for basil but neither Mg nor Ca for lettuce. The aquaponic solution contained nearly six-times higher Na than the hydroponic solution, resulting in three-times higher Na concentration in the edible portion of the crops. Compared to a lettuce-based aquaponic system, tomato- and basil-based systems retained more desirable water quality parameters (i.e., stable pH, lower temperature), had lower electrical conductivity (EC) via greater biomass production and, therefore, more efficient nutrient removal, and had lower feed conversion rate and higher fish biomass increment. Regardless of crop species, vegetative shoot biomass was significantly reduced in aquaponics than in hydroponics. However, the marketable yield of tomatoes was similar between aquaponics and hydroponics, while those of basil and lettuce were reduced in aquaponics by 56% and 67%, respectively, in comparison to hydroponics. Our results highlighted potential solutions to design proper nutrient management practices essential for the development of successful aquaponic production systems. Considering that ingested fish feed does not provide sufficient levels of Mg and/or Ca for crop production, it is suggested to supplement Mg before crop transplanting and Ca before fruiting of fruity crops to improve crop growth and quality in aquaponic systems, especially when high-quality water is used for water supply.

Effects of Hydraulic Loading Rate on Spatial and Temporal Water Quality Characteristics and Crop Growth and Yield in Aquaponic Systems

Aquaponics is a rapidly growing food-production system integrating aquaculture and hydroponic crop production through an energy-intensive water recirculation process. Crop performance and yield in aquaponics are affected by essential and toxic nutrient levels in the root zone, which can be regulated by water flow rate. This study was conducted to examine the effects of hydraulic loading rate (HLR) on water quality and crop growth and yield in recirculating aquaponic systems set at three different loading rates: high (3.3 m3/m2/day; HFR, which is 12 times lower than recommended loading rate), medium (2.2 m3/m2/day; MFR), and low (1.1 m3/m2/day; LFR). Crop species varying in growth rate were examined for their optimal HLR: fast-growing Chinese cabbage (Brassica rapa) and lettuce (Lactuca sativa); medium-growing mustard (Brassica juncea) and chia (Salvia hispanica); and slow-growing basil (Ocimum basilicum) and Swiss chard (Beta vulgaris). Compared to LFR, HFR decreased water and leaf temperatures and total ammonium nitrogen (TAN) but increased dissolved oxygen and pH in aquaponic solution up to one and two weeks after transplant, respectively. HFR increased NO3–N concentration by 50 and 80%, respectively, compared to MFR and LFR, while reducing the exposure duration of roots to ammonia (NH3–N) and its peak concentration through rapid dissipation of the toxic compound. Lower electrical conductivity (EC) in HFR during the last two weeks of production was associated with higher plant nutrient uptake and greater biomass production. The leaf greenness, photosynthetic rate (Pn), and total plant N were significantly higher at HFR than LFR. Fish growth rate, fresh weight, and feed-conversion efficiency were also increased by HFR. The growth of fast-growing crops including total fresh weight, shoot fresh weight, leaf area, and Pn was not different between HFR and MFR, while HLR had less significant effects on the growth and performance (i.e., shoot fresh weight and whole plant photosynthesis) of slow-growing crops. In conclusion, the flow rate is an important component in aquaponic crop production as it affects spatial and temporal water characteristics and subsequently determines the growth and yield of the crops. HLR at 3.3 m3/m2/day was sufficient across the crops allowing better chemical and physical properties of the aquaponic solution for maximum yield and quality. HLR should be maintained at least at 2.2 m3/m2/day for the production of fast-growing crops but can be lowered for slow-growing crops.

Fish Feed Quality Is a Key Factor in Impacting Aquaculture Water Environment: Evidence from Incubator Experiments

The effect of fish feed quality has gained increasing attention to alleviate the harmful environmental impacts induced by intensive aquaculture. In current research, we have conducted an incubator experiment to highlight the effect of fish feed quality on aquaculture water environment. Fish feed from three manufactures with two different dosages (0.1000 g, 0.2000 g) was added to the culture medium with and without Microcystis aeruginosa. Treatments with Microcystis aeruginosa were named as MHT, MHP and MZT; while the treatments without Microcystis aeruginosa named as HT, HP and ZT. Microcystis aeruginosa densities and nutrients concentrations were measured in the study. Results have shown that fish feed quality (manufactures) has a great effect on nutrients concentrations in the absence of Microcystis aeruginosa (P < 0.05). Meanwhile, fish feed can stimulate Microcystis aeruginosa growth that is also influenced by fish feed quality excluding lag phase (0~12 day) significantly in general (P < 0.05). The maximum Microcystis aeruginosa density (N_max) is 1221.5, 984.5, 581.0, 2265.9, 2056.8 and 1766.6 1 × 10⁴ cells mL⁻¹ for MHT 0.1 g, MHP 0.1 g, MZT 0.1 g, MHT 0.2 g, MHP 0.2 g and MZT 0.2 g, respectively. In treatments with algae, fish feed quality affect total phosphorus (TP) concentrations (except the difference between MHT and MHP) and total nitrogen (TN) concentrations significantly (P < 0.05). For most of consumed nutrients, the obvious differences among all treatments were observed excluding lag phase in general (P < 0.05), which suggest that the nutrient utilization is also dependent on fish feed quality. Keeping in mind the above facts it is concluded that fish feed quality is a key factor in impacting aquaculture water environment.

An Experimental Brackish Aquaponic System Using Juvenile Gilthead Sea Bream (Sparus aurata) and Rock Samphire (Crithmum maritimum)

Brackish aquaponics using Mediterranean fish and plants provides an alternative opportunity for a combined production of high-quality food products with high commercial and nutritional value. This is the first study that investigates the effect of two different salinities (8 and 20 ppt) on growth and survival of Sparus aurata and Crithmum maritimum along with the cellular stress pathways using the activation of heat shock proteins (HSPs) and mitogen-activated protein kinase (MAPK) protein family members and the water bacterial abundance. In total, 156 fish were used (average initial weight of 2.55 g, length of 5.57 cm) and 36 plants (average initial height of 8.23 cm) in floating racks above the 135 L fish tanks. Survival rate for both organisms was 100%. C. crithmum grew better at 8 ppt (t-test, p < 0.05). The growth rate of S. aurata was similar for both treatments (p > 0.05). HSPs and MAPK were differentially expressed, showing tissue-specific responses. The average bacterial abundance at the end of the experiment was higher (p < 0.05) in the 20 ppt (18.6 ± 0.91 cells × 105/mL) compared to the 8 ppt (6.8 ± 1.9 cells × 105/mL). The results suggest that the combined culture of euryhaline fish and halophytes provides good quality products in brackish aquaponics systems.

Understanding nutrient throughput of operational RAS farm effluents to support semi-commercial aquaponics: Easy upgrade possible beyond controversies

The present research attempted to address a key industry-level question amidst Recirculating Aquaculture System (RAS) waste throughput and aquaponics limitations controversies. Nutrient throughput of three operational RAS farms with progressive size proportions (16, 130, 1400 m³), aquaculture intensity (24, 62, 86 kg stock m^-3) were studied. Results suggest - daily total efflux and potency of nutrients in effluents should not be generalized, extreme variability exists. Consistencies of nutrients in wastewater (except N, Ca and Na) are higher than in sludge. Asynchrony between patterns of nutrient loading and effluent nutrient concentrations exist for secondary macronutrients and micronutrients (S, Mg, Fe, Cu, Zn, B, Mo). Macronutrient output generally increases with increasing farm size and culture intensity but same cannot be said for micronutrients. Deficiency in wastewater can be completely masked using raw or mineralized sludge, usually containing 3-17 times higher nutrient concentrations. RAS effluents (wastewater and sludge combined) contain adequate N, P, Mg, Ca, S, Fe, Zn, Cu, Ni to meet most aquaponic crop needs. K is generally deficient requiring a full-fledged fertilization. Micronutrients B, Mo are partly sufficient and can be easily ameliorated by increasing sludge release. The presumption surrounding 'definite' phyto-toxic Na levels in RAS effluents should be reconsidered - practical solutions available too. No threat of heavy metal accumulation or discharge was observed. Most of the 'well-known' operational influences failed to show any significant predictable power in deciding nutrient throughput from RAS systems. Calibration of nutrient output from operational RAS farms may be primarily focused around six predictors we identified. Despite inherent complexity of effluents, the conversion of RAS farms to semi-commercial aquaponics should not be deterred by nutrient insufficiency or nutrient safety arguments. Incentivizing RAS farm wastes through semi-commercial aquaponics should be encouraged - sufficient and safe nutrients are available.

Performance of Water Treatment Techniques on Cocopeat Media Filled Grow Bed Aquaponics System

Aquaponics system is an innovative idea which combined both aquaculture and hydroponics systems. In this study performance of four different types of water treatment technique was investigated in cocopeat media filled grow bed aquaponics system. The techniques that had been investigated were mechanical filter, biological filter, combination of both mechanical and biological filters and grow media (cocopeat) itself as filtration media. The effectiveness these techniques were assessed through (i) water quality and nutrients level of circulated water and (ii) growth rates of plant (Gynura procumbens) and Red Nile Tilapia fish (Oreochromis niloticus) The (i) water quality (pH, temperature, total suspended solid and dissolved oxygen) (ii) nutrient level (ammonia, nitrite, nitrate) and (iii) grow rates of plant and fish were weekly measured for this study. The results revealed that cocopeat media filled grow bed only was insufficient to act as water treatment unit in the aquaponics system studied. The aquaponics system required at least a biological or mechanical filter to produce acceptable yields of fish and plant. For the long term, the combination of axial flow and biofilter with superlative ratio was suggested in order to produce the best performance of parameters studied. This integrated technique was able to maintain the water quality within the tolerance limit of fish besides supplying enough amount nutrients (especially nitrate) for the plant growth and easier maintenance work in terms of cleaning and disposal of sludge.