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The biofloc technology (BFT) offers benefits in improving feed utilization and reducing the feed conversion ratio compared to the recirculating aquaculture system (RAS). In this study, high-throughput 16S rRNA gene sequencing was employed to investigate and compare the bacterial communities in these aquaculture systems and the gut microbiota of grass carp reared in them. We observed a significant distinction between the microbial communities of the aquaculture systems and the intestinal microbiota of grass carp. The genera cetobacterium and bacillus were more abundant in the BFT system, accounting for only 0.05% and 0.25% in the RAS. Our study also demonstrated that BFT could influence the intestinal microorganisms of grass carp (Ctenopharyngodon Idella) by reducing the relative abundance of burkholderia-caballeronia-paraburkholderia and increasing that of cetobacterium. Based on bugBase community predictions, the potential pathogenicity in BFT and grass carp intestine was lower than in RAS. Regarding gene expression in the grass carp intestine, immunosuppressive genes showed higher expression, while pro-inflammatory genes exhibited lower expression in grass carp reared in BFT. Furthermore, the final average length and weight of grass carp in the BFT system were significantly higher than those in the RAS. This study provides valuable insights into gut microbiome ecology in relation to two grass carp aquaculture systems, which could be effectively applied in grass carp management to promote health and improve water quality. [ABSTRACT FROM AUTHOR]

Recirculating aquaculture system (RAS) technology is seen worldwide as a solution for sustainable fish production. However, there are still deficiencies in the process technology imperiling consistent operation and thus economic results. Drawbacks are linked to essential processes of the water treatment systems such as denitrification. Nitrogenous waste needs to be removed from RAS process water to maintain an adequate production environment for fish and to mitigate the environmental impact of discharged process water. At present, denitrification lacks reliable process control, especially regarding the organic carbon feed to heterotrophic denitrification processes. An investigation into heterotrophic denitrification in an experimental RAS resulted in the discovery of a virtual sensor based on measurements of the oxidation reduction potential (ORP). The virtual sensor responds to an insufficient carbon feed to denitrification. It is based on the oxidation of nitrite in an ozone-enhanced foam flotation installed downstream of the denitrification. The sensor essentially delivers a binary signal denoting either a complete or an incomplete denitrification process. The virtual sensor can be used for reliably controlling heterotrophic denitrification. It requires an upgraded process chain employing ozone-enhanced foam flotation (protein skimmer) downstream of the denitrification. However, the virtual sensor does not require any additional instrumentation. [ABSTRACT FROM AUTHOR]

Simple Summary: Recirculating aquaculture systems (RASs) have gradually become a highly recommended aquaculture mode due to their environmental friendliness. However, due to their high factory and equipment investments and high electricity consumption, they usually require the farming objects to have high economic value in order to cover their high running costs. Seahorses have high economic value and may be suitable for RASs. Currently, there are almost no reports on the large-scale farming of seahorses using RASs. To provide a new farming object for RASs, in the present study, the lined seahorse (Hippocampus erectus) was employed to determine a suitable stocking density in RASs. As is well known, optimizing the stocking density of farmed objects is a prerequisite for their commercial aquaculture. The present study determined suitable stocking densities for lined seahorse juveniles at different growth stages, which will contribute to the development of recirculating aquaculture for the lined seahorse. Seahorses are increasingly regarded as a promising farming object suitable for recirculating aquaculture systems (RASs) due to their high economic value. However, reports on the large-scale farming of seahorses in RASs are rare, and some key parameters, such as stocking densities, are still unclear. In the present study, we employed the lined seahorse (Hippocampus erectus), for which large-scale farming has been achieved, to determine the suitable stocking density for three different-sized juveniles in RASs. The three different-sized juveniles had body heights of 4.0, 7.0, and 9.0 cm, and their test density gradients were 1.0, 0.8, 0.6, and 0.4 inds/L; 0.6, 0.5, 0.4, and 0.3 inds/L; and 0.4, 0.3, 0.2, and 0.1 inds/L, respectively. The juveniles were cultivated for one month, and then their survival, growth, and plasma cortisol and brain serotonin contents (two stress-related indicators) were analyzed. The results show that, regardless of the size of the juveniles, a high density can inhibit growth and trigger stress responses. In addition, for small- (4.0 cm) and medium-sized (7.0 cm) juveniles, a high density can also exacerbate size heterogeneity and cause death. Taking into account the welfare and yield of farmed seahorses, the present study suggests that the suitable stocking densities for 4.0, 7.0, and 9.0 cm juveniles in RASs are 0.6, 0.4, and 0.2 inds/L, respectively. [ABSTRACT FROM AUTHOR]

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The land-based recirculating aquaculture system (RAS) has been widely applied to fish farming as a new eco-friendly culture model. This system consists of circular culture tanks on land integrated with water treatment and recycling systems. This study investigated the growth performance of juvenile gibel carp (Carassius gibelio) cultured at high stocking density (HSD, 0.3 kg/m3) and low stocking density (LSD, 0.15 kg/m3) conditions in RAS, and evaluated the comprehensive economic profit of RAS. The body weight, body length, weight gain rate, and condition factor of gibel carp in the LSD group were significantly higher than those in the HSD group (p < 0.05). The feed conversion ratio increased significantly in the HSD group (p < 0.05). A histological analysis revealed a significantly higher density of white muscle fibers in the LSD group (p < 0.05). Relative mRNA expression levels showed that ubiquitin–proteasome system (UPS)-related genes, ub, psma2, and mafbx, were significantly expressed in the HSD group, while the s6k1 expression was elevated in the LSD group (p < 0.05). The mRNA expression levels of keap1 and hsp70 in the dorsal muscle were significantly higher in the HSD group (p < 0.05). Throughout the rearing period, the water temperature remained consistent between the two density groups. The pH value gradually decreased and the dissolved oxygen levels in the HSD group were generally lower than in the LSD group. The nitrite nitrogen (NO2−-N) content was higher in the HSD group. Compared to the LSD group, the return on investment was significantly lower in the HSD group. In conclusion, the water quality and growth rates of juvenile gibel carp were better in the LSD group. An appropriate stocking density improved the growth performance and aquaculture economic efficiency. [ABSTRACT FROM AUTHOR]

In aquaculture, real-time and rapid detection of dead fish is important for early risk warning and improving aquaculture efficiency. However, the complex actual environment and uncontrollable fish movement have brought great challenges to the detection of dead fish. Therefore, this paper proposes a high-precision and lightweight dead fish-detection transformer (DF-DETR) based on machine vision and original RT-DETR (real-time detection transformer). The specific implementation is as follows: Firstly, the backbone of the original RT-DETR was replaced by the RepNCSPELAN module which extracts multi-scale features. This not only improves the model’s ability to detect targets of different sizes but also reduces the amount of model parameters. Secondly, the AIFI in the RT-DETR was improved to CascadedGroupAttention (CGA). By changing the original feature fusion method, different levels of features are grouped and attention mechanism is added, so as to capture more target features. Finally, the CCFM_CSP module was constructed to fuse important features using parallel dilated convolution with different expansion rates, which improves the detection accuracy. The experimental results show that the mAP@.5 of the proposed dead fish detection model DF-DETR can reach 96.6%, and the parameter amount is reduced by 27% compared with the original RT-DETR. In summary, the proposed DF-DETR model realizes real-time and high-precision dead fish detection, which can provide effective technical support for the development of intelligent inspection robots. [ABSTRACT FROM AUTHOR]

In recirculating aquaculture system, precise estimation of perch size from images is essential for developing intelligent management system. However, variations in fish postures and visual field lead to different fish sizes in RGB images, posing challenges for accurate fish detection and localization. To address the above issues, this paper proposes a nondestructive target detection and size measurement method for perch, based on depth information and RGB-D images. The details are as follows: firstly, the capture ability of perch key point features is augmented by a bi-level routing attention (BRA) mechanism. Secondly, the enhanced CSPDarknet53 to 2-Stage FPN(C2f) module and new detection layer are introduced into the model’s backbone and neck, further improving the learning ability of perch features and the recognition accuracy of small-size targets. Finally, based on the detected key point coordinates, the perch size is calculated by combining the three-dimensional transformation from depth camera and measurement model. The experimental results show that the mAP@.5:.95 for key point detection reaches 86.4%, which is 3.6% higher than the baseline model, and the average relative error of perch size measurement is ± 5%. The proposed model provides an important basis for developing scientific feeding strategies and harvest plans. [ABSTRACT FROM AUTHOR]

The farming of Marsupenaeus japonicas in recirculating aquaculture system (RAS) is relatively recent; consequently, knowledge of their dietary protein requirements is still insufficient. Due to the specific ecological conditions of RAS, these systems may affect the nutritional requirements of shrimp. Therefore, this study aimed at assessing the optimal protein requirement of M. japonicas in RAS. Six experimental diets were devised to contain 35%, 40%, 45%, 50%, 55%, and 60% crude protein (P35, P40, P45, P50, P55, and P60, respectively) and were fed in triplicate groups of 20 shrimp (initial body weight 1.86 ± 0.01 g) at a feeding rate of 3.0% body weight per day for 56 days. At the end of the feeding period, the optimal protein requirement was estimated at 46.13% for weight gain rate, and specific growth rate with all groups exhibited high survival rates. The P45 diet increased the digestive enzyme activities, antioxidant indices, and improved intestinal morphology, while the P50 diet showed the highest intestinal microbiome diversity. The experimental results showed that diets containing higher protein seemed to have compromised the antioxidant status of shrimp and did not necessarily result in better growth. Hence, results from this study suggested that the optimal protein requirement of M. japonicas fed in RAS was determined to be 46.13%, but protein levels up to 50% can be beneficial to the intestinal microbiome diversity. [ABSTRACT FROM AUTHOR]

The nanofiltration (NF) membrane technology implemented in the recirculating aquaculture system (RAS) suffers from fouling issues, which cause a decrease in the flux value and performance of the NF membrane. Fouling can be reduced by incorporating pre-treatment units such as the multimedia filter unit (MMF) and activated carbon filter (CF). Therefore, this research aims to minimize fouling and maintain optimal membrane flux and performance by integrating pre-treatment units such as MMF and CF, as well as conducting detailed flux modeling. The models simulate transport phenomena within the NF membrane system, emphasizing the impact of concentration polarization and fouling on flux and overall performance across various pre-treatment configurations under non-steady state conditions. Configuration of MMF-CF-NF demonstrated the highest overall efficiency in reducing ammonia concentration by 97.5%, nitrite by 100%, and 100% by TSS. Furthermore, the values of the solvent transport coefficient (Aw), the solute transport coefficient (Bs), and the contaminant accumulation volume (X) varied for each configuration due to different treatments, leading to varying membrane workloads. Validation and statistical analysis of the permeate concentration model demonstrated that the developed model has a strong capability to accurately describe and predict the filtration process using the NF membrane, with solute transport coefficient contributing most significantly to influencing the concentration permeate NF. [ABSTRACT FROM AUTHOR]

In this study, the status and efficiency of the wastewater treatment system of a semi-recirculated aquaculture system (RAS) in Firoozkooh County were investigated. Information regarding aquaculture systems in the region was obtained with the guidance of the experts at the Agriculture Organization in Firoozkooh County. During visits to the recommended aquaculture systems, Namrud Aquaculture was selected. To evaluate the effect of water pollutants on fish, National Standards 8726 and 7961 were employed to determine water quality parameters and to guide sampling and sample protection. Water quality parameters were assessed at four stations to determine the extent of pollution. The results indicated that ammonia (NH3), nitrite (NO2), and nitrate (NO3) were the main issues in this aquaculture system. Rainbow trout (Oncorhynchus mykiss) exposed to ammonia levels exceeding the limits set by National Standard 8726 displayed behavioral changes, including altered swimming speed, total distance traveled, average direction change, and increased average distance from a central point. The second aeration tower was found to be ineffective in releasing dissolved gases due to its inappropriate design, including the spacing between floors and lack of proper atmospheric connection. It is recommended to redesign the second aeration tower, elevate the second entrance pond, and adjust the return flow to the grit chamber to reduce suspended particles and improve the water quality parameters of the effluent. [ABSTRACT FROM AUTHOR]

Factory recirculating aquaculture system (RAS) is facing in a stage of continuous research and technological innovation. Intelligent aquaculture is an important direction for the future development of aquaculture. However, the RAS nowdays still has poor self-learning and optimal decision-making capabilities, which leads to high aquaculture cost and low running efficiency. In this paper, a precise aeration strategy based on deep learning is designed for improving the healthy growth of breeding objects. Firstly, the situation perception driven by computer vision is used to detect the hypoxia behavior. Then combined with the biological energy model, it is constructed to calculate the breeding objects oxygen consumption. Finally, the optimal adaptive aeration strategy is generated according to hypoxia behavior judgement and biological energy model. Experimental results show that the energy consumption of proposed precise aeration strategy decreased by 26.3% compared with the manual control and 12.8% compared with the threshold control. Meanwhile, stable water quality conditions accelerated breeding objects growth, and the breeding cycle with the average weight of 400 g was shortened from 5 to 6 months to 3–4 months.

Water quality is crucial for Apostichopus japonicas farming and may affect its growth and physiological functions. The accumulation of residual bait and feces usually leads to turbidity and high concentration of solid particles in aquaculture water, resulting in nutrient accumulation and frequent disease outbreaks. This poses a huge threat to the A. japonicas farming industry. Therefore, this study aims to explore the effects of different feed binders on water quality, growth and intestinal microbiota of A. japonicus in recirculating aquaculture system (RAS). Five groups were set up, including no binder group and four groups with added 5% sweet potato starch, xanthan gum, guar gum and carrageenan respectively. A. japonicus weighing 20. 0±5. 0 g were used for researching. Each group had three replicates and the experiment last for 42 days. Kruskal-Wallis rank sum test was used to analyze the difference of intestinal microbiota between groups. Redundancy analysis (RDA) and Canonical correlation analysis (CCA) were used to investigate the relationship between water quality and intestinal microbiota of A. japonicus. The results showed that adding binders improved water quality well, with the guar gum group would give a better result. The concentrations of ammonia nitrogen (NH+4-N), nitrate nitrogen (NO-3-N) and total nitrogen (TN) in guar gum group were the lowest at the end of the experiment, and fluctuated less during the experiment. The specific growth rate(RSGR) and feed conversion rate of A. japonicus in sweet potato starch and guar gum groups were significantly higher than that in other groups (P<0. 05) and the skin exfoliation rate (RSER) were increased in both groups. The dominant intestinal microflora of cultivation were Proteobacteria. Vibrionaceae and Rhodobacteraceae were the dominant family. And there was significantly different in intestinal microbiota among the groups. The sweet potato starch group had the highest intestinal microflora richness and diversity, while the lowest in the xanthan gum group. The results of significance difference test between groups showed that the feed with added sweet potato starch increased the abundance of beneficial bacteria of A. japonicus, such as Flavobacteriaceae. There was significant correlation between water quality and intestinal microbiota of A. japonicus(P< 0. 05). At the phylum level, NH+4-N, NO-2-N, NO-3-N were negatively correlated with Firmicutes, Actinobacteriota and Bacteroidota. But positively correlated with Verrucomicrobia and Proteobacteria. At the family level, NH+4-N, NO-2-N, NO-3 -N were positively correlated with Vibrionaceae and Shewanellaceae, while negatively correlated with Flavobacteriaceae and Enterobacteriaceae. Considering the water quality, growth and intestinal microflora of A. japonicus, sweet potato starch and guar gum as feed binder were more conducive to healthy culture of A. japonicus and maintenance the water treatment in RAS. [ABSTRACT FROM AUTHOR]

In order to further study the feasibility of recirculating aquaculture system in the production process of marine fish fry. Using the principle of material balance, combined with the construction technology of recirculating aquaculture water treatment facilities and equipment. The water treatment process was optimized and the key parameters such as volume and circulation of moving bed bioreactor were designed. A set of recirculating aquaculture hatchery system was constructed. Two water treatment loops were designed, and efficient water treatment technologies and equipment such as dual drain system in hatchery tank, radial flow separator and moving bed bioreactor were integrated. The experiment of hybrid grouper (Epinephelus lanceolatus♂ × E. fuscoguttatus♀) hatching was carried out by using this system, focusing on three water quality parameters of dissolved oxygen concentration (DO), pH and total ammonia nitrogen (TAN), as well as three growth parameters of total length, body weight and emergency rate. Results: The growth of larvae and juveniles was well, with an average length of (75. 1±0. 55) mm, an average body weight of (9. 2±0. 42) g, and a hatching emergence rate of 16. 28%. The water quality test results showed that the temperature was 26. 8 -27. 7℃, dissolved oxygen concentration was 6. 6 - 7. 2 mg/L, the average pH was 8. 31, and the average concentration of total ammonia nitrogen was (0. 183 ± 0. 191) mg/L, indicating good water quality. The economic analysis results show that the single crop profit is 18 600 yuan, and the annual profit is 55 800 yuan (calculated based on three crops per year), which has good economic benefits. Conclusion: This research can provide technical support for the application and popularization of recirculating aquaculture system. [ABSTRACT FROM AUTHOR]

A four-week trial was conducted to compare the effects of a conventional flow-through system diet (FTS) and an experimental RAS diet (ERAS) on fish performance, water quality and general system implication in a replicated recirculation aquaculture system (RAS). Six identical RAS, each with a total system water volume of 1500 L and cylindrical rearing tanks of 1000 L were stocked with Atlantic salmon (Salmo salar) post-smolts with an average weight of 199.7 ± 28 g, to an average stocking density of 30 kg/m3 and reaching approximately 49 kg/m3 at the trial end. The ERAS diet were composed to inhabit typical RAS feed characteristics compared with the FTS diet, such as a higher fecal stability and reduced protein levels (−12%), but at the same time increased fat content (+8%) to secure similar gross energy levels (22–23 MJ kg−1) between the two diets. Water quality parameters were measured individually. The total accumulation of minerals and metals was analyzed in water from different parts of the system at the start and end of the trial period for both diets. No differences in growth, condition factor, feed conversion rate (FCR), or survival of fish fed the two dietary adaptations were observed. The system using the ERAS diet showed significantly higher pH (+1.2%) and alkalinity (+17%) and lower total ammonia nitrogen (TAN) (−18%) and NO2− (−46%) compared with the FTS diet. The count of drum filter activations was also significantly lower (−13%) with the ERAS diet. Compared with the FTS diet, the ERAS diet had a lower probability (−4%) of generating particles smaller than 50 μm, and that the RAS was also more effective in removing particles from the drum filter, prompting a lower daily activation of the filter of 22.1 ± 3.0 counts compared with 25.5 ± 3.5 for the FTS diet. Mineral analysis showed a significantly lower accumulation of total phosphorus (TP) (−90%) and dissolved phosphorus (DP) (−92%) in the RAS units using the ERAS diet compared with those using the FTS diet. Compared with a traditional flow-through diet, these results highlight the benefits of using an RAS-adapted diet that matches the energy requirement of flow-through diets regarding water quality, system performance, satisfactory growth, and condition. [ABSTRACT FROM AUTHOR]

Large-mouth bass originally lived in rivers and lakes and now is often raised in recirculating aquaculture systems (RAS). However, the shortcoming of RAS is that there is very limited space for swimming fish in a high-density culture environment, thus leading to a lack of exercise. To investigate the effects of exercise training on growth performance, digestive enzymes, stress, and antioxidant capacity of large-mouth bass in a RAS, three training water flow velocities with three replicates were used in the present study: low water velocity: 0.5 body length per second (bl/s) (LV); medium water velocity: 1 bl/s (MV); and high water velocity: 1.5 bl/s (HV). 270 large-mouth bass (average initial body weight 47.51 ± 1.44 g, initial body length 12.71 ± 0.06 cm) were randomly divided into nine tanks (30 fish per tank). After 27 days experiment, the results showed that the growth performance of large-mouth bass, including feed intake, weight gain rate, and specific growth rate, in the HV group was significantly higher compared to the other groups. On the physiological level, the lipase and amylase activities were significantly increased in the HV group compared to the other groups. For the stress response parameters, the cortisol, glucose and lactate concentrations in the HV group were significantly increased, which may indicate higher stress in the HV group. Regarding the antioxidant enzyme activities, the activities of catalase (CAT) and glutathione peroxidase (GSH-PX) in the LV group were significantly higher than those in the HV group, which indicated that fish suffered higher oxidative stress in the LV group. Regarding the immune-related parameters, LZM and ACP activities had no significant differences among the groups, while AKP activities in the MV and HV groups were significantly higher than that in the LV group. Overall, the results demonstrated that exercise training had significant effects on the growth, digestion, stress, and immune response of large-mouth bass. It is suggested that exercise training with 1.5 bl/s can enhance fish growth, however, it also presents a potential risk of inducing stress in fish. Therefore, in rearing largemouth bass in RAS, the setting of water flow velocity should not only focus on the growth of large-mouth bass but also consider its welfare. [ABSTRACT FROM AUTHOR]

Recirculating aquaculture systems (RASs) offer significant advantages in aquaculture by markedly decreasing water usage and increasing culture density. A vital component within a RAS is the filler material, which serves as a surface for microbial colonization. Effective microbial treatment is crucial for the efficient operation of a RAS as it assists in purifying the wastewater generated within the system. Nevertheless, traditional fillers often show low efficiency in biofilm formation. The commercial silicon carbide used in this study is a foam ceramic filter with a density of about 0.4–0.55 g/cm3, a number of holes of about 10, and a through porosity of 80.9%, with a diameter of about 5 cm. This research investigates the utilization of a titanium dioxide–silicon carbide (TiO2-SiC) composite filler to improve the purification efficiency of ammonia nitrogen and chemical oxygen demand (COD) in aquaculture wastewater. The study involved the application of titanium dioxide films onto the surface of silicon carbide to produce the composite filler. This method takes advantage of the dipole interaction between titanium dioxide and microorganisms, which enhances biofilm culturing efficiency on the silicon carbide surface. The performance of three different fillers was assessed for their ability to purify aquaculture wastewater. Results showed that the TiO2-SiC composite filler was 1.67 times more effective in removing COD and 1.07 times more effective in removing ammonia nitrogen compared to using silicon carbide alone. These results demonstrate that the incorporation of a titanium dioxide coating substantially boosts the microbial colonization efficiency of silicon carbide, thereby enhancing the overall wastewater purification efficiency in RAS. [ABSTRACT FROM AUTHOR]

Introduction: Aquaponics is an integrated food production system that links recirculating aquaculture with hydroponics, leading to higher water use efficiency than conventional food production systems while also saving on fertilizers. In the present study, baby lettuce and baby rocket plants cultivated hydroponically in a deep water culture system using wastewater from rainbow trout were evaluated as part of a vertical decoupled aquaponic system. Materials and methods: More specifically, three different nutrient solutions were supplied: a) using fish wastewater only (designated as Fish); b) fish wastewater enriched with synthetic fertilizers (Mix); and c) a typical nutrient solution (Hoagland) as the control. Both lettuce and rocket plants were monitored in these nutrient solutions and in two different substrates, peat and perlite, as an organic and an inert substrate, respectively. The purpose of this study was to assess a vertical decoupled aquaponic system with regard to the resource use efficiency, such as water, land, and energy, while evaluating plant cultivation in the different treatments in terms of yield, growth, nitrate concentration on the leaf tissue, and foliar analysis. The photosynthetic rate and leaf color indices were also considered in the plant evaluation. Results: The Mix-Peat treatment was the most efficient growing combination in terms of land and water use efficiency, with approximately 7% better land use efficiency while using 38% less water and 10% less fertilizer than Hoagland-Peat. Moreover, lettuce plants had the highest yield in the Mix-Peat treatment, at 2,497 gm-2, which was approximately 6% higher than that of Hoagland-Peat while not being inferior in the quality measures. On the other hand, the yield of rocket was significantly higher in the Hoagland-Peat treatment, being 18% higher than that of Mix-Peat and 30% higher than that of Fish-Peat. Overall, the study confirmed that aquaponic systems could lead to higher water use efficiency and savings in fertilizers without undermining the yield and quality of lettuce, while the vertical arrangement developed within the scope of this study can increase the land useefficiency of the system. [ABSTRACT FROM AUTHOR]

Objective: We sought to evaluate several methods of operation of a foam fractionator for fine‐solids removal (organic matter < 55 μm) in a commercial‐scale, low‐salinity (11–13‰) recirculating aquaculture system (RAS) for marine finfish production. Methods: The total suspended solids (TSS) concentrations of the RAS microscreen drum filter inflow and outflow and the foam fractionator outflow were obtained under various foam fractionator operating conditions. The outflow TSS concentration of the drum filter also served as the inflow TSS concentration for the foam fractionator. Sample collection for TSS determination was divided into two categories: particles greater than 55 μm and particles less than 55 μm. The difference between inflow and outflow TSS concentrations was used to determine the removal percentage for each particle class of each unit. Additionally, the volume of foammate produced under operating conditions by the fractionator and the amount of solids contained within the foammate were quantified. Flow through the foam fractionator was also obtained to determine the amount of solids removed per volume of influent water treated. Result: The influent TSS concentration for the seven different operating conditions evaluated ranged from 4.8 to 6.3 mg/L, with the percentage of particles less than 55 μm ranging from 69.75% to as high as 86.1%. The drum filter removed over 90% of the particles larger than 55 μm and removed 8–26% of the particles smaller than 55 μm. No difference was observed in the overall removal efficiency of the drum filter, which ranged from 19% to 44%. There was no significant difference in the foam fractionator overall removal efficiency, which ranged from 6.5% to 38.5%. Operating the foam fractionator at a high water head height (HHH) with the submersible aspirating impeller provided the greatest removal percentage of particles less than 55 μm (26.9%). However, at the HHH, only half the amount of solids was removed compared to using a Venturi injector with ozone, but energy use was roughly 26% greater. Conclusion: The foam fractionator was operated at the HHH, about 0.31 m higher than the low water head height, for production operation. Additionally, Venturi injection of ozone provided the greatest removal of solids for the volume of influent water treated over a 12‐h operational period. The submersible aspirating impeller showed potential for low‐cost use with reasonable solids removal and warrants further evaluation. Impact statementAccumulation of fine solids and the removal thereof constitute an issue for commercial recirculating aquaculture system (RAS) production of marine finfish. This study evaluates the performance of a foam fractionator under various operational conditions with a Venturi injector and submersible aspirating impeller. Information from this work adds to base data for commercial‐scale units to support development of RAS marine finfish production in the United States. [ABSTRACT FROM AUTHOR]

Monopterus albus is one of China's renowned and superior aquaculture species, with its seedlings mainly sourced from wild capture. One of the bottlenecks in M. albus aquaculture is the high mortality rate and low feeding initiation rate from stocking wild fry to the initiation of feeding. In production, trash fish is commonly used to wean M. albus juveniles onto feeding. In this study, we introduced three other natural feeds, earthworms (EW), yellow mealworms (YMW), and fly maggots (FM), with frozen trash fish (TF) serving as the control group, to evaluate the effects of these four natural feeds on the survival rate, feeding initiation, antioxidant enzymes activity, and body composition of M. albus juveniles under recirculating water aquaculture conditions. The experiment comprised four treatments, each with three replicates. Each replicate consisted of stocking 150 M. albus juveniles weighing 10.02 ± 0.89 g in size, raised for 5 weeks. The survival rate of the YMW group was 73.33%-85.33%, which was significantly higher than that of the other three bait groups (p < 0.05). The four bait groups showed no significant differences in final body weight and specific growth rate (SGR) (p > 0.05). The EW group showed the highest final body weight, with an average SGR of 2.73, whereas the YMW group had an average SGR of 1.87. The average daily feeding amount was significantly higher in EW and YMW groups than in the other two groups (p < 0.05). The percentage of feeding amount to fish weight in the EW group reached 7.3% in the fifth week. After 5 weeks of cultivation, NO2--N content was significantly higher in the waters of the TF and EW groups than in the waters of the FM and YMW groups (p < 0.05), there was no significant difference in TAN content among the treatment groups (p > 0.05). Liver malondialdehyde content was significantly higher in the TF group than in the other bait groups (p < 0.05). GSH-Px activity was significantly higher in the EW group than in the FM group and YMW group. No significant differences in SOD and CAT activity and T-AOC were observed among the bait groups (p > 0.05). The increase in crude protein content was significantly higher in the TF group than in the FM group, but the increase in crude ash content was significantly lower in the TFgroup. In conclusion, Tenebrio molitor could potentially serve as one of the alternative feeds during the initial stages of M. albus juveniles stocking. [ABSTRACT FROM AUTHOR]

Groupers, as a popular economic fish species, are now more frequently cultured in land-based facilities, however, traditional pond-farming methods are plagued by frequent disease outbreaks, unstable economic benefits, and environmental pollution. To explore a new farming mode for a grouper, an 80-day cultivation experiment was conducted using both a simulated pond system (SPS) and a recirculating aquaculture system (RAS). The research aims to evaluate the growth performance, health (pathogenic bacteria, intestinal microbiota), off-flavor compounds (geosmin, 2-methylisoborneol), and nutritional component (amino acids, fatty acid composition and content) of a hybrid grouper (Pinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂) under different aquaculture systems. The results showed that the hybrid grouper in a RAS exhibited better growth performance; the concentration of Vibrio in the fish tissue in the RAS was significantly lower than that in the SPS. Moreover, the content of fresh amino acids in the RAS was significantly higher, and the levels of saturated fatty acids (SFAs) and w-6 polyunsaturated fatty acids (w-6PUFAs) were significantly higher in the RAS. This finding indicates the superior flavor and nutritional value of the grouper. These results prove that the RAS is suitable for the widespread cultivation of grouper. [ABSTRACT FROM AUTHOR]

Periods of fasting occur for a multitude of reasons in Atlantic salmon aquaculture. Feed withdrawal is widely used prior to transport, parasite treatments, preslaughter and for depuration purposes in recirculating aquaculture systems. Voluntary fasting is a coping response when fish have poor health or are exposed to poor farm environments. Owing to increased attention to animal welfare in aquaculture, concerns have been raised regarding ethical issues when farmed fish are subjected to fasting. However, thorough science‐based recommendations for fasting and feed‐withdrawal regimes have been lacking. The purpose of this review is to provide a synthesis of the various causes for fasting in Atlantic salmon aquaculture and evaluate their associated welfare implications so that guidelines for appropriate practices can be formulated. To interpret impacts, we describe biological responses and tolerance limits to fasting in Atlantic salmon and consider adaptations in the wild. Fry and parr are highly sensitive to feed withdrawal. However, post‐smolts and adults are well‐adapted to endure prolonged fasting without experiencing compromised functionality or health. Here, short periods of feed withdrawal prior to operations should therefore not constitute significant welfare concerns. Serious concerns are instead associated with voluntary fasting that may continue for weeks. We emphasize that environmental extremes that exceed appetite impairing thresholds must be avoided. Additionally, farmed fish should not be subjected to practices that lead to chronic stress that induce cessation of appetite. Diseases or parasites that impair appetite should also be mitigated. Fasting is here a symptom rather than a cause for poor welfare. [ABSTRACT FROM AUTHOR]

This study analyzed the rearing indicators of Siberian sturgeon (Acipenser baerii) juveniles reared in tanks of different shapes and at various stocking densities. Rearing was conducted in autonomous hatching and rearing modules. Fish of an average body weight of 47.3±1.0 g were divided into four experimental groups: CL, RL, CH, and RH, which differed in stocking density (20 specimens and 50 specimens) and tank shape (C – circular, R – rectangular). The experiment ran for 28 days. Two-factor analysis indicated that lower stocking density significantly affected the final body weight of juvenile Siberian sturgeon, while tank shape had no effect on growth. The results of the current study on rearing Siberian sturgeon juveniles indicated that tanks of different shapes can be applied, but faster growth was obtained at a lower stocking density.

To gain a comprehensive understanding of the evolution, current status, trends, and hot topics in recirculating aquaculture, this study conducted data analysis and literature mining on recirculating aquaculture using the core collection database of Web of Science, China Weipp, and China National Knowledge Network from 1992 to 2023. The results were visually analyzed using Cite Space software. The findings indicated that: 1) research on recirculating aquaculture has gradually become a focal point for various countries, institutions, and universities with numerous re- search outcomes; 2) developed countries in Europe and the United States started studying recirculating aquaculture between 1998 and 2001, demonstrating an early start with the highest number of publications; 3) China VIP has published the most papers with close collaboration among authors and institutions. The research hotspots primarily focus on fishery equipment and equipment automation. These findings provide valuable data support for constructing "high - quality, low energy consuming, intelligent" industrial recirculating aquaculture systems. [ABSTRACT FROM AUTHOR]

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Water quality and the management of nitrogenous compounds are of key importance within aquaculture. In this paper, automated and portable analysers for in situ analysis of nitrite and nitrate in water were deployed in freshwater and saline recirculating aquaculture systems (RAS). The analysers were based upon ion chromatography (IC) and employed a NaCl eluent with an anion exchange guard column for low backpressure anion separation, in combination with selective 235 nm ultra-violet light-emitting diode (UV-LED) based absorbance detection. The analysers were monitored and delivered real-time concentration data using a cellular internet of things (IoT) module and cloud-based dashboard. Overall performance and chromatographic repeatability were tested across various temperature profiles and 500 sequential runs within the laboratory. Deployments in freshwater and saline RAS, with concentrations ranging between 0.1–3.6 mg L−1 nitrite and 0.6–392 mg L−1 nitrate, were successful and the analytical performance was comparable to that of accredited lab-based instrumentation. [ABSTRACT FROM AUTHOR]

Catfish was cultivating by the Sujafish Farm, Cikole District, Sukabumi City, in early 2023. Urban cultivation land is increasingly narrow, feed costs are increasingly expensive, and limited water availability hinders freshwater fish cultivation development in Sukabumi City. One solution to get around this is developing Recirculating Aquaculture System (RAS) technology. RAS is a cultivation technology where water can be reused after being filtered mechanically and biologically. The maintenance container uses six round ponds with a diameter of 2 m and is filled with water to e height of 0,8 m. The volume of water in each tub is 2.152 L of water. The seeds measured 8-10 cm with a density of 318 individuals/m 2 . The observation parameters were temperature, Ph, DO, ammonia, nitrite, nitrate, and fish growth. The RAS application has been proven to maintain water quality, temperature, Ph, DO, and ammonia. RAS systems growth and survival value are higher than circulation, so that RAS technology can be an alternative environmental friendly cultivation technology solution in urban areas. [ABSTRACT FROM AUTHOR]

Hydrogen sulphide (H2S) is considered an immunotoxicant, and its presence in the water can influence the mucosal barrier functions of fish. However, there is a significant knowledge gap on how fish mucosa responds to low environmental H2S levels. The present study investigated the consequences of prolonged exposure to sub-lethal levels of H2S on the mucosal defences of Atlantic salmon (Salmo salar). Fish were continuously exposed to two levels of H2S (low: 0.05 µM; and high: 0.12 µM) for 12 days. Unexposed fish served as control. Molecular and histological profiling focused on the changes in the skin, gills and olfactory rosette. In addition, metabolomics and proteomics were performed on the skin and gill mucus. The gene expression profile indicated that the gills and olfactory rosette were more sensitive to H2S than the skin. The olfactory rosette showed a dose-dependent response, but not the gills. Genes related to stress responses were triggered at mucosal sites by H2S. Moreover, H2S elicited strong inflammatory responses, particularly in the gills. All mucosal organs demonstrated the key molecular repertoire for sulphide detoxification, but their temporal and spatial expression was not substantially affected by sub-lethal H2S levels. Mucosal barrier integrity was not considerably affected by H2S. Mucus metabolomes of the skin and gills were unaffected, but a matrix-dependent response was identified. Comparing the high-concentration group's skin and gills mucus metabolomes identified altered amino acid biosynthesis and metabolism pathways. The skin and gill mucus exhibited distinct proteomic profiles. Enrichment analysis revealed that proteins related to immunity and metabolism were affected in both mucus matrices. The present study expands our knowledge of the defence mechanisms against H2S at mucosal sites in Atlantic salmon. The findings offer insights into the health and welfare consequences of sub-lethal H2S, which can be incorporated into the risk assessment protocols in salmon land-based farms.

IntroductionAquaponics is an integrated food production system that links recirculating aquaculture with hydroponics, leading to higher water use efficiency than conventional food production systems while also saving on fertilizers. In the present study, baby lettuce and baby rocket plants cultivated hydroponically in a deep water culture system using wastewater from rainbow trout were evaluated as part of a vertical decoupled aquaponic system.Materials and methodsMore specifically, three different nutrient solutions were supplied: a) using fish wastewater only (designated as Fish); b) fish wastewater enriched with synthetic fertilizers (Mix); and c) a typical nutrient solution (Hoagland) as the control. Both lettuce and rocket plants were monitored in these nutrient solutions and in two different substrates, peat and perlite, as an organic and an inert substrate, respectively. The purpose of this study was to assess a vertical decoupled aquaponic system with regard to the resource use efficiency, such as water, land, and energy, while evaluating plant cultivation in the different treatments in terms of yield, growth, nitrate concentration on the leaf tissue, and foliar analysis. The photosynthetic rate and leaf color indices were also considered in the plant evaluation.ResultsThe Mix–Peat treatment was the most efficient growing combination in terms of land and water use efficiency, with approximately 7% better land use efficiency while using 38% less water and 10% less fertilizer than Hoagland–Peat. Moreover, lettuce plants had the highest yield in the Mix–Peat treatment, at 2,497 g m−2, which was approximately 6% higher than that of Hoagland–Peat while not being inferior in the quality measures. On the other hand, the yield of rocket was significantly higher in the Hoagland–Peat treatment, being 18% higher than that of Mix–Peat and 30% higher than that of Fish–Peat. Overall, the study confirmed that aquaponic systems could lead to higher water use efficiency and savings in fertilizers without undermining the yield and quality of lettuce, while the vertical arrangement developed within the scope of this study can increase the land useefficiency of the system.

With the development of the aquaculture industry for high efficiency, energy saving, and environmentally friendly methods, recirculating aquaculture has attracted increasing attention from researchers and practitioners. A recirculating aquaculture system (RAS) consists primarily of an aquaculture module and a water purification module. In the aquaculture module, nitrogen in the feed could be released into the water phase through various routes (i.e., the feedstuff residue and aquaculture animal excretion), whose species can be transformed by microbes. Free ammonia and nitrite have acute toxic effects on aquaculture animals, rendering the efficient removal of ammonia and nitrite essential for the RAS. Compared with physical and chemical methods, biological treatment methods based on microbial nitrification can convert ammonia and nitrite into less toxic nitrate with the advantages of good treatment performance, low operation cost, and little secondary contamination, and have been widely utilized in the purification of multiple wastewaters (e.g., municipal wastewater, industrial wastewater, agricultural wastewater, and ammonia-contaminated groundwater). For the treatment of recirculating water with low and fluctuating nitrogen loads, a biofilm process based on the attached growth of microbes is more suitable than an activated sludge process based on the suspended growth of microbes. To date, a variety of biofilm processes have been developed, among which the fixed-bed biofilm reactor (FBBR) and moving-bed biofilm reactor (MBBR) have been widely investigated for the control of ammonia and nitrite in aquaculture wastewater. However, the relevant studies were mostly conducted in laboratory- and pilot-scale RASs. Thus, there is still a lack of comparative investigations of FBBR and MBBR, which are simultaneously operated in a full-scale RAS.Therefore, a parallel FBBR and MBBR were joined to a full-scale RAS for Macculochella peeli. The FBBR and MBBR were simultaneously and continuously operated for 35 d to investigate variations in their water quality and microbial community structures. The results indicate that the FBBR and MBBR had similar variations in ammonia, nitrite, nitrate, and pH in the effluents. Over the entire operational period, the dissolved inorganic nitrogen (DIN) concentrations gradually increased; the ammonia and nitrite concentrations and their proportions in DIN first increased and then decreased stepwise; and the nitrate concentrations increased gradually, while the variation in the nitrate proportions in DIN was opposite to that of ammonia and nitrite. Both the FBBR and MBBR could transform ammonia and nitrite to nitrate, which resulted in nitrate accumulation and a pH decrease in aquaculture water. During the operation period, the nitrification capacity gradually matured, and ammonia oxidation could occur prior to nitrite oxidation. At 35 d, the concentrations of ammonia, nitrite and nitrate were 0.32 (0.29), 0.27 (0.22) and 29.75 (29.76) mg/L with their proportions in DIN of 1.05% (0.96%), 0.90% (0.72%) and 98.05% (98.32%) in FBBR (MBBR) effluent; pH declined from7.62 (7.59) to 7.25 (7.22) in FBBR (MBBR) effluent.The number of operational taxonomic units (OTU) obtained from the FBBR and MBBR samples were 2, 088 and 1, 852, respectively, and 1, 174 OTUs were shared between FBBR and MBBR. The α indices (Chao1, ACE, Shannon, and Simpson) from the biofilm reactors indicated that FBBR possessed higher richness and diversity of the microbial community than MBBR, which could be attributed to the difference in the internal environment between FBBR and MBBR. In total, 16 phyla, 28 classes, and 149 genera were identified in the FBBR samples, which were slightly fewer than those from the MBBR samples (i.e., 19 phyla, 31 classes, and 155 genera). However, the relative abundance of microbes demonstrated that FBBR and MBBR had similar predominant microbes: Proteobacteria (69.42% in FBBR and 86.92% in MBBR) at the phylum level, γ-Proteobacteria (40.71% in FBBR and 64.36% in MBBR) and α-Proteobacteria (26.58% in FBBR and 21.74% in MBBR) at the class level, and Acinetobacter (27.50% in FBBR and 53.29% in MBBR) at the genus level. Nitrosomonas and Nitrospira constituted the nitrifiers in both FBBR and MBBR, but the relative abundance of nitrifiers was higher in FBBR. Furthermore, the relative abundance of Nitrospira was far higher than that of Nitrosomonas, indicating that complete ammonia oxidation bacteria might exist in FBBR and MBBR. In addition, Vibrio was not found in FBBR and MBBR, but Bdellovibrio was observed. The results of this study can provide technical support for the selection of biological purification technology for RAS, and thus improve the green development of the aquaculture industry.Future studies will focus on: Investigating the effects of water quality conditions and operational parameters on the water treatment performance of FBBR and MBBR; Determining the species of complete ammonia oxidation bacteria and their relative abundances on the filler surface in FBBR and MBBR; Effectively eliminating nitrate in the aquaculture water by introducing microbial denitrification process after FBBR and MBBR to control the total nitrogen in RAS; Establishing a flexible and feasible strategy for controlling the pH in recirculating water by exploring the solid-phase buffers that could serve as the slow-release sources of alkalinity in the biofilm reactor.

Seahorses are increasingly regarded as a promising farming object suitable for recirculating aquaculture systems (RASs) due to their high economic value. However, reports on the large-scale farming of seahorses in RASs are rare, and some key parameters, such as stocking densities, are still unclear. In the present study, we employed the lined seahorse (Hippocampus erectus), for which large-scale farming has been achieved, to determine the suitable stocking density for three different-sized juveniles in RASs. The three different-sized juveniles had body heights of 4.0, 7.0, and 9.0 cm, and their test density gradients were 1.0, 0.8, 0.6, and 0.4 inds/L; 0.6, 0.5, 0.4, and 0.3 inds/L; and 0.4, 0.3, 0.2, and 0.1 inds/L, respectively. The juveniles were cultivated for one month, and then their survival, growth, and plasma cortisol and brain serotonin contents (two stress-related indicators) were analyzed. The results show that, regardless of the size of the juveniles, a high density can inhibit growth and trigger stress responses. In addition, for small- (4.0 cm) and medium-sized (7.0 cm) juveniles, a high density can also exacerbate size heterogeneity and cause death. Taking into account the welfare and yield of farmed seahorses, the present study suggests that the suitable stocking densities for 4.0, 7.0, and 9.0 cm juveniles in RASs are 0.6, 0.4, and 0.2 inds/L, respectively.

Among halophyte plants, Salicornia species (also known as glasswort or sea asparagus) are increasingly grown in open fields and greenhouses for edible or non-edible purposes. Their salinity tolerance makes it possible to irrigate Salicornia plants with saline waters and even seawater, which cannot be used by other crop species. In this work, S. europaea (L.) was cultivated in pots under the typical climatic conditions of the fall season in the Mediterranean region and irrigated with non-saline standard nutrient solution (SNS) or saline wastewater discharged from a greenhouse semi-closed hydroponic (substrate) culture of tomato or a saltwater recirculating aquaculture system (RAS) with Gilthead sea bream (Spaurus aurata L., which was used as such or after dilution (50:50) with SNS. Plant growth was not significantly affected by the composition of irrigation water, while higher antioxidant capacity (measured using the DPPH assay) and concentration of photosynthetic pigments, phenols, flavonoids, and ascorbic acid were found in the shoots of SNS plants than in those of plants irrigated with wastewater. The level of lipid peroxidation and H2O2 production significantly increased in the SNS plants, which also showed higher activity of superoxide dismutase and lower activity of catalase. These results suggest that S. europaea can be cultivated using wastewater with moderate to high salinity discharged from greenhouse hydroponic crops or RASs, and that salt is not strictly required for the growth of this species. Using non-saline nutrient solution can result in moderate oxidative stress that improves the shoot quality of S. europaea. [ABSTRACT FROM AUTHOR]

To investigate the effect of different C / N on the accumulation of off flavor in biofloc reactor,different initial DOC / DIN(Dissolved organic carbon,DOC:Dissolved inorganic nitrogen,DIN) gradients were set up for group A (no glucose added,C / N of 6),group B (C / N of 10) and group C (C / N of 20) by adding glucose to the bioflocs released from shrimp farming and a 7-day experiment was conducted. Water quality monitoring was carried out everyday. The concentrations of Geosmin (GSM) and 2-Methylisoborneol (2-MIB) in the BFT water were detected at the beginning and end of the experiment and the flocs were taken for nutrient index detection. The results showed that the accumulation of Geosmin (GSM) and 2-Methylisoborneol (2-MIB) was 22. 41 ng / L and -0. 19 ng / L at C / N of 10,which were significantly lower than those in the C / N of 6 group (76. 4 ng / L and 4. 43 ng / L) and C / N of 20 group (50. 98 ng / L and 3. 52 ng / L),respectively; the total ammonia nitrogen and nitrite nitrogen concentrations were lower than 0. 10 mg / L and 0. 15 mg / L,respectively, in all groups during the experiment; the crude protein content of bioflocs was highest at 31. 64 %±0. 22 % at C / N of 10. It was shown that the addition of glucose can effectively reduce the accumulation of GSM and 2-MIB production,and the most effective of reducing the accumulation of GSM and 2-MIB production was achieved when the C / N in the biofloc reactor was 10,as well as having water quality improvement effect. [ABSTRACT FROM AUTHOR]

During the process of circulating aquaculture, high concentrations of nitrate will accumulate. A simultaneous denitrification and fermentation process is described to remove nitrate from a recirculating aquaculture system using endogenous carbon on a biofilm. 15N isotope technology was used to assess the nitrate removal, mainly through heterotrophic denitrification. The nitrate removal rate could be as high as 98.97%, with a final concentration of nitrate below 1 mg/L. The denitrification process obeys a Michaelis–Menten-type enzyme kinetic model, with a half saturation constant of 99.91 mg/L and a maximum nitrate removal rate of 0.39 mg L−1 h−1 at 28 °C. The functional genes narG and narH for nitrate removal were obtained from Nitrospirae spp. at proportions of 39.13% and 26.16%, respectively. The acetate, propionate and iso-valerate produced by anaerobic fermentation provided the principal electron donors for denitrification. [ABSTRACT FROM AUTHOR]

In recirculating aquaculture systems, nitrification is usually accelerated by inoculating nitrifier or mature biocarriers. In this study, the performance of the establishment of nitrification in the MBBR according to three different strategies: conventional method (Control group A), inoculation with biofloc recovered from a tilapia biofloc culture system (Group B), and addition with extra nitrite (Group C) in the Moving bed biofilm reactor (MBBR) was compared. Among them, the biofloc-inoculated group considerably accelerated the nitrification process in the MBBR (38 d), which is roughly 18 d faster than the control group (A) (56 d) and 21 d faster than group C (59 d). Less ammonia (8 mg/L NH4+-N, 10 mg/L in other groups) and external nitrite (2 mg/L NO2−-N) in the influent caused effluent ammonia to drop more slowly (5 d slower than the control group, 8 d slower than the B group), which is detrimental to the nitrification process' development. Notably, the influent's hydraulic retention time (HRT) was reduced from 12 h to 6 h following the successful establishment of nitrification. During the adaptation to reduced HRT, the MBBR inoculated with biofloc experienced short-term changes in the water quality index of the effluent water, whereas the other groups did not. The biofilm seeded with biofloc had the highest mean gray value ratio (1.42) of live/dead cell fluorescence, which grew better and could cover the entire groove under multiple microscope observations. However, the other groups did not demonstrate a similar trend. In summary, the research found that seeding biofloc use as nitrification bioaugmentation into the MBBR of the recirculating aquaculture system (RAS) to greatly speed up the nitrification process.

The land-based recirculating aquaculture system (RAS) has been widely applied to fish farming as a new eco-friendly culture model. This system consists of circular culture tanks on land integrated with water treatment and recycling systems. This study investigated the growth performance of juvenile gibel carp (Carassius gibelio) cultured at high stocking density (HSD, 0.3 kg/m3) and low stocking density (LSD, 0.15 kg/m3) conditions in RAS, and evaluated the comprehensive economic profit of RAS. The body weight, body length, weight gain rate, and condition factor of gibel carp in the LSD group were significantly higher than those in the HSD group (p < 0.05). The feed conversion ratio increased significantly in the HSD group (p < 0.05). A histological analysis revealed a significantly higher density of white muscle fibers in the LSD group (p < 0.05). Relative mRNA expression levels showed that ubiquitin–proteasome system (UPS)-related genes, ub, psma2, and mafbx, were significantly expressed in the HSD group, while the s6k1 expression was elevated in the LSD group (p < 0.05). The mRNA expression levels of keap1 and hsp70 in the dorsal muscle were significantly higher in the HSD group (p < 0.05). Throughout the rearing period, the water temperature remained consistent between the two density groups. The pH value gradually decreased and the dissolved oxygen levels in the HSD group were generally lower than in the LSD group. The nitrite nitrogen (NO2−-N) content was higher in the HSD group. Compared to the LSD group, the return on investment was significantly lower in the HSD group. In conclusion, the water quality and growth rates of juvenile gibel carp were better in the LSD group. An appropriate stocking density improved the growth performance and aquaculture economic efficiency.

A four-week trial was conducted to compare the effects of a conventional flow-through system diet (FTS) and an experimental RAS diet (ERAS) on fish performance, water quality and general system implication in a replicated recirculation aquaculture system (RAS). Six identical RAS, each with a total system water volume of 1500 L and cylindrical rearing tanks of 1000 L were stocked with Atlantic salmon (Salmo salar) post-smolts with an average weight of 199.7 ± 28 g, to an average stocking density of 30 kg/m3 and reaching approximately 49 kg/m3 at the trial end. The ERAS diet were composed to inhabit typical RAS feed characteristics compared with the FTS diet, such as a higher fecal stability and reduced protein levels (−12%), but at the same time increased fat content (+8%) to secure similar gross energy levels (22–23 MJ kg−1) between the two diets. Water quality parameters were measured individually. The total accumulation of minerals and metals was analyzed in water from different parts of the system at the start and end of the trial period for both diets. No differences in growth, condition factor, feed conversion rate (FCR), or survival of fish fed the two dietary adaptations were observed. The system using the ERAS diet showed significantly higher pH (+1.2%) and alkalinity (+17%) and lower total ammonia nitrogen (TAN) (−18%) and NO2− (−46%) compared with the FTS diet. The count of drum filter activations was also significantly lower (−13%) with the ERAS diet. Compared with the FTS diet, the ERAS diet had a lower probability (−4%) of generating particles smaller than 50 μm, and that the RAS was also more effective in removing particles from the drum filter, prompting a lower daily activation of the filter of 22.1 ± 3.0 counts compared with 25.5 ± 3.5 for the FTS diet. Mineral analysis showed a significantly lower accumulation of total phosphorus (TP) (−90%) and dissolved phosphorus (DP) (−92%) in the RAS units using the ERAS diet compared with those using the FTS diet. Compared with a traditional flow-through diet, these results highlight the benefits of using an RAS-adapted diet that matches the energy requirement of flow-through diets regarding water quality, system performance, satisfactory growth, and condition.

Recirculating aquaculture systems (RASs) offer significant advantages in aquaculture by markedly decreasing water usage and increasing culture density. A vital component within a RAS is the filler material, which serves as a surface for microbial colonization. Effective microbial treatment is crucial for the efficient operation of a RAS as it assists in purifying the wastewater generated within the system. Nevertheless, traditional fillers often show low efficiency in biofilm formation. The commercial silicon carbide used in this study is a foam ceramic filter with a density of about 0.4–0.55 g/cm3, a number of holes of about 10, and a through porosity of 80.9%, with a diameter of about 5 cm. This research investigates the utilization of a titanium dioxide–silicon carbide (TiO2-SiC) composite filler to improve the purification efficiency of ammonia nitrogen and chemical oxygen demand (COD) in aquaculture wastewater. The study involved the application of titanium dioxide films onto the surface of silicon carbide to produce the composite filler. This method takes advantage of the dipole interaction between titanium dioxide and microorganisms, which enhances biofilm culturing efficiency on the silicon carbide surface. The performance of three different fillers was assessed for their ability to purify aquaculture wastewater. Results showed that the TiO2-SiC composite filler was 1.67 times more effective in removing COD and 1.07 times more effective in removing ammonia nitrogen compared to using silicon carbide alone. These results demonstrate that the incorporation of a titanium dioxide coating substantially boosts the microbial colonization efficiency of silicon carbide, thereby enhancing the overall wastewater purification efficiency in RAS.

Aquaculture is a sustainable solution to respond to the increasing demand for animal protein and also, food security in the world, and today, in order to develop it, it is necessary to pay attention to the sustainable aquaculture approach (economically, socially and environmentally). The development of modern aquaculture systems has been greatly expanded in recent years and each of them pursues the goals of sustainable aquaculture in some way. In fact, modern aquaculture systems enable the achievement of sustainable aquaculture by maximizing the productivity of resources, reducing costs, appropriate production quantitatively and qualitatively, and a slight environmental effects. Among the systems introduced so far, recirculating aquaculture system, cages, aquaponics, biofloc and integrated multitrophic aquaculture systems are known as promising systems in aquatic production in the world that can be developed in Iran as well. In this review study, in addition to introducing and discussing the importance of these systems in sustainable aquaculture, the resulting opportunities and also, the challenges of developing these systems in the country are addressed

Atlantic salmon (Salmo salar) might encounter toxic hydrogen sulphide (H2S) gas during aquaculture production. Exposure to this gas can be acute or chronic, with heightened levels often linked to significant mortality rates. Despite its recognised toxicity, our understanding of the physiological implications of H2S on salmon remains limited. This report details the mucosal and systemic physiological consequences in post-smolt salmon reared in brackish water at 12 ppt after prolonged exposure to elevated H2S levels over 4 weeks. The fish were subjected to two concentrations of H2S: 1 µg/L (low group) and 5 µg/L (high group). An unexposed group at 0 µg/L served as the control. Both groups exposed to H2S exhibited incremental mortality, with cumulative mortality rates of 4.7 % and 16 % for the low and high groups, respectively. Production performance, including weight and condition factors, were reduced in the H2S-exposed groups, particularly in the high group. Mucosal response of the olfactory organ revealed higher tissue damage scores in the H2S-exposed groups, albeit only at week 4. The high group displayed pronounced features such as increased mucus cell density and oedema-like vacuoles. Transcriptome analysis of the olfactory organ unveiled that the effects of H2S were more prominent at week 4, with the high group experiencing a greater magnitude of change than the low group. Genes associated with the extracellular matrix were predominantly downregulated, while the upregulated genes primarily pertained to immune response. H2S-induced alterations in the metabolome were more substantial in plasma than skin mucus. Furthermore, the number of differentially affected circulating metabolites was higher in the low group compared to the high group. Five core pathways were significantly impacted by H2S regardless of concentration, including the phenylalanine, tyrosine, and tryptophan biosynthesis. The plasma levels of phenylalanine and tyrosine were reduced following exposure to H2S. While there was a discernible distinction in the skin mucus metabolomes among the three treatment groups, only one metabolite – 4-hydroxyproline – was significantly impacted by H2S. Furthermore, this metabolite was significantly reduced in the plasma and skin mucus of H2S-exposed fish. This study underscores that prolonged exposure to H2S, even at concentrations previously deemed sub-lethal, has discernible physiological implications that manifest across various organisational levels. Given these findings, prolonged exposure to H2S poses a welfare risk, and thus, its presence must be maintained at low levels (

Biofilm is central for biological water treatment processes in recirculating aquaculture systems (RAS). A lack of suitable methods for quantifying biofilm activity, however, makes it difficult to assess and compare the microbial status of biofilm. This type of information of the biofilm will be useful to assess the colonization status of nitrifying biocarriers or to evaluate the effect of disinfectants on the biofilm activity.Here we introduce a novel assay for rapid assessment of microbial activities in the biofilm attached on bioelements from a RAS biofilter. The assay consisted of an intermittent respirometer platform where biofilter elements were exposed to 10 mg/L hydrogen peroxide (H2O2) for 1 h, following concurrent measurements of oxygen release from the decomposition of H2O2 caused by biofilm-associated enzymes. A different number of colonized, mature bioelements from a moving bed biofilter in a freshwater RAS were tested with repeated H2O2 exposure, and compared against their autoclaved forms. A substantial increase in dissolved oxygen (DO) concentration (0.92–2.31 mg O2/L) occurred with mature bioelements during 1 h of H2O2 exposure, compared to small amounts of DO release (≤0.27 mg O2/L) with autoclaved bioelements. This substantiates that H2O2 decomposition by biofilm is mainly governed by microbial enzymatic activities. A monomolecular model fitted well with the observed oxygen release profiles of tested mature bioelements after H2O2 exposure (R2 > 0.98). The kinetic rate constant of net oxygen release (kor, h−1) was proportional (R2 for linear fit = 0.99) to the number of mature bioelements tested. Repeated exposure of H2O2 to the same bioelements did not change kor, which indicates that 10 mg/L H2O2 with an exposure time of 1 h does not suppress enzymatic activity in biofilm. Our study provides a new rapid method that allows simple quantification of microbial activity in biofilm samples from aquaculture systems, which could potentially be also applied to study biofilm from wastewater treatment plants and other industries.

This study investigated the dissolved oxygen (DO) variation pattern in a Litopenaeus vannamei recirculating aquaculture system (RAS) and established an oxygen-utilization rate (UROxygen) model, pure oxygen addition (QOxygen) model, and control model that linked a microscreen drum filter (MDF) with a U-tube oxygenator. The main objective was to promote the application of the U-tube oxygenator and achieve the efficient, accurate, and automated management of DO in an RAS. To avoid wasting oxygen and ensure production safety, it was recommended to maintain the effluent of the aquaculture pond at 6.9 ± 0.4 mg/L. The modeled relationship between the RAS flow (QRAS), QOxygen, and UROxygen was UROxygen = 0.9626 × (−105.3406 + 0.9911QRAS + 10.6202QOxygen − 0.05964QRASQOxygen − 1.2628 × 10−3QRAS2 − 0.1821QOxygen2 + 6.8888 × 10−5QRAS2QOxygen + 6.3993 × 10−4QRASQOxygen2). The modeled relationship between QRAS, daily feeding rate (MFeeding), and QOxygen was QOxygen = 1.09 × (−12.8633 − 0.02793QRAS + 0.9369 MFeeding − 8.9286 × 10−4MFeedingQRAS + 5.6122 × 10−5QRAS2 − 2.3281 × 10−3MFeeding2). The modeled relationship between the MDF backwashing period (TMDF) and QOxygen was QOxygen = −11.57ln(TMDF) + 78.319. This study provided a theoretical basis and novel methods for the management of DO in an RAS, thus promoting the healthy and stable development of an L. vannamei RAS. [ABSTRACT FROM AUTHOR]

The experiment was to study the effect of iron oxide-porous ceramic composite filler on purification of ammonia nitrogen and chemical oxygen demand (COD) in aquaculture wastewater and the physical and chemical properties of iron oxide film. The porous ceramic was used as a carrier to load iron oxide film on the surface of the ceramic. Depending on the dipolar interaction between iron oxide and microorganisms, the microorganisms could have a higher film hanging efficiency on the surface of the ceramic, and the purification efficiency of ammonia nitrogen and COD in aquaculture wastewater by the two fillers was detected. The results showed that the removal efficiency of COD and ammonia nitrogen in aquaculture wastewater by the porous ceramic composite packing loaded with iron oxide film was 1.27 times and 1.07 times higher than that of the single porous ceramic packing. The experiment indicates the iron oxide-porous ceramic composite filler have advantages over single porous ceramic fillers in the microbial biofilm formation in circulating aquaculture systems. [ABSTRACT FROM AUTHOR]

As demands for efficient and echo-friendly production of marine products increase, smart aquaculture based on information and communication technology (ICT) has become a promising trend. The smart aquaculture is expected to control fundamental farm environment variables including water temperature and dissolved oxygen (DO) levels with less human intervention. A recirculating aquaculture system (RAS) is required for the smart aquaculture which utilizes a purification tank to reuse water drained from the water tank while blocking the external environment. Elaborate water treatment should be considered to properly operate RAS. However, analyzing the water treatment performance is a challenging issue because fish farm circumstance continuously changes and recursively affects water fluidity. To handle this issue, we introduce computational fluid dynamics (CFD) aided water treatment analysis including water fluidity and the solid particles removal efficiency. We adopt RAS parameters widely used in the real aquaculture field to better reflect the real situation. The simulation results provide several indicators for users to check performance metrics when planning to select appropriate RAS without actually using it which costs a lot to operate. [ABSTRACT FROM AUTHOR]

As a strong oxidant, ozone is often used as a bactericidal disinfectant for MBBR systems. In order to obtain the effect of ozone on the water quality of MBBR treatment and on the bactericidal rate of Vibrio parahaemolyticus, a 10 L reactor was used to determine the nitrification capacity of the system and the number of viable dead cells of the biofilm samples under a 10 L reactor at 60% filling rate to study the effects of different concentrations of ozone(0, 1, 2, 4, 6 mg / L) on the nitrification capacity of the system and the killing of Vibrio parahaemolyticus. The results showed that 2 mg / L ozone had no significant effect on cell mortality in biofilm sample (P = 0. 49). The removal rates of TAN were 55. 11% ±5. 32%, 57. 89% ± 9. 01%, 49. 2% ± 5. 99%, 33. 07%±2. 68%, 34. 22% ±8. 89%, and the 4 mg / L ozone dose group was significantly lower than that of 0, 1, 2 mg / L ozone dose group (P = 0. 042). At ozone doses above 2 mg / L, Vibrio parahaemolyticus was not detected on TCBS plates. This study showed that according to the mortality rate of biofilm cells, the treatment efficiency of ammonia nitrogen and the sterilization rate of Vibrio parahaemolyticus. The 2 mg / L ozone can effectively kill Vibrio parahaemolyticus and do not affect the nitration reaction efficiency of MBBR. [ABSTRACT FROM AUTHOR]

The industrialized recirculating aquaculture system （RAS） has emerged as a promising approach to achieving standardized culturing and intelligent management in aquaculture. This system conforms to the principles of resource conservation and environmentally friendly green development, making it a leading direction for the future of the industry. The aquaculture tank, being a vital infrastructure component of RAS, plays a crucial role in optimizing space utilization, water-injection energy efficiency, waste collection and discharge effectiveness, and ensuring uniform distribution of dissolved oxygen to support the healthy growth of aquatic organisms. This article provides a comprehensive review of both domestic and international research on the hydrodynamic characteristics of RAS. By summarizing the current research hotspots and trends in this field, it aims to analyze how various factors such as tank structure, water circulation driving devices, and waste discharge devices influence hydrodynamics within RAS. The research results presented in this article lay a solid foundation for the development of an "energy-saving, emission-reducing, ecological, and efficient" aquaculture system. [ABSTRACT FROM AUTHOR]

The virtual, digital counterpart of a physical object, referred as digital twin, derives from the Internet of Things (IoT), and involves real-time acquisition and processing of large data sets. A fully implemented system ultimately enables real-time and remote management, as well as the reproduction of real and forecasted scenarios. Under the emerging framework of Precision Fish Farming, which brings control-engineering principles to fish production, we set up digital twin prototypes for land-based finfish farms. The digital twin is aimed at supporting producers in optimizing feeding practices, oxygen supply and fish population management with respect to 1) fish growth performances; 2) fish welfare, and 3) environmental loads. It relies on integrated mathematical models which are fed with data from in-situ sensors and from external sources, and simulate several dynamic processes, allowing the estimation of key parameters describing the ambient environment and the fishes. A conceptual application targeted at rearing cycles of rainbow trout (Oncorhynchus mykiss) in an operational in-land aquafarm in Italy is presented. The digital twin takes into account the disparate levels of automation and control that are found within this farm, and considerations are made on preferential directions for future developments. In spite of its potential, and not only in the aquaculture sector, the development of digital twins is still at its early stage. Furthermore, Precision Fish Farming applications in land-based systems as well as targeted at rainbow trout are novel developments.

Recirculating aquaculture systems (RAS) pose unique challenges in microbial community management since they rely on a stable community with key target groups, both in the RAS environment and in the host (in this case, Solea senegalensis). Our goal was to determine how much of the sole microbiome is inherited from the egg stage, and how much is acquired during the remainder of the sole life cycle in an aquaculture production batch, especially regarding potentially probiotic and pathogenic groups. Our work comprises sole tissue samples from 2 days before hatching and up to 146 days after hatching (-2 to 146 DAH), encompassing the egg, larval, weaning, and pre-ongrowing stages. Total DNA was isolated from the different sole tissues, as well as from live feed introduced in the first stages, and 16S rRNA gene was sequenced (V6-V8 region) using the Illumina MiSeq platform. The output was analysed with the DADA2 pipeline, and taxonomic attribution with SILVAngs version 138.1. Using the Bray-Curtis dissimilarity index, both age and life cycle stage appeared to be drivers of bacterial community dissimilarity. To try to distinguish the inherited (present since the egg stage) from the acquired community (detected at later stages), different tissues were analysed at 49, 119 and 146 DAH (gill, intestine, fin and mucus). Only a few genera were inherited, but those that were inherited accompany the sole microbiome throughout the life cycle. Two genera of potentially probiotic bacteria (Bacillus and Enterococcus) were already present in the eggs, while others were acquired later, in particularly, forty days after live feed was introduced. The potentially pathogenic genera Tenacibaculum and Vibrio were inherited from the eggs, while Photobacterium and Mycobacterium seemed to be acquired at 49 and 119 DAH, respectively. Significant co-occurrence was found between Tenacibaculum and both Photobacterium and Vibrio. On the other hand, significantly negative correlations were detected between Vibrio and Streptococcus, Bacillus, Limosilactobacillus and Gardnerella. Our work reinforces the importance of life cycle studies, which can contribute to improve production husbandry strategies. However, we still need more information on this topic as repetition of patterns in different settings is essential to confirm our findings. [ABSTRACT FROM AUTHOR]

This study was designed to explore the impact of the photoperiod on the gonadal development and somatic growth of Atlantic salmon raised in recirculating aquaculture systems (RASs), with specific focus on the role that microRNA (miR)-155 plays as a regulator in the Atlantic salmon's photoperiodic reproduction. These salmon were reared for 5 months under six different photoperiod regimens, including two with changing photoperiods (LL–SL = 24L:0D–8L:16D and SL–LL = 8L:16D–24L:0D) and four with constant photoperiods (24L:0D, 18L:6D, 12L:12D, and 8L:16D). The longer photoperiod groups (LL–SL and 24L:0D) were ultimately associated with higher gonadosomatic index (GSI) values and an increased proportion of mature fish relative to other exposure groups, indicating that the photoperiod positively impacted the Atlantic salmon's gonadal development in RAS environments. Hypothalamic miR-155 expression in these Atlantic salmon was also found to be influenced by the photoperiod, showing a markedly decreased expression in salmon exposed to a long photoperiod and upregulation following rearing under a short photoperiod. Functionally, miR-155 was found to suppress the expression of gonadal axis-related genes, including FSH and GnRH, through its ability to target the brain-derived neurotrophic factor (BDNF) and to thereby regulate photoperiod reproduction. Overall, these results suggested that the photoperiod could regulate gonad development in Atlantic salmon with miRNA-155 being involved in this process by targeting the BDNF. [ABSTRACT FROM AUTHOR]

Recirculating aquaculture is one of the main development directions of aquaculture in the future. The excessive enrichment of CO2 in the system will affect the filtration efficiency of biofilter and the growth and development of aquaculture objects. Therefore,the efficient removal of CO2 is the key technology in the whole circulating aquaculture system. In the development process of China’s circulating aquaculture industry for more than 30 years,various CO2 removal technologies have become increasingly mature. This paper focuses on the application status of industrial recirculating aquaculture system at home and abroad,introduces the source, harm and basic principle of CO2 removal in recirculating aquaculture system,summarizes the characteristics and research progress of three CO2 removal processes of gas exchange method,chemical method and ecological method,summarizes and compares the advantages of various removal technologies. In view of the problems of single method,large space occupied by main facilities and high cost of CO2 removal,this paper puts forward some future development countermeasures,such as the combination of various removal processes,intensive operation of equipment system,optimization of removal process and intelligent equipment. The purpose of this study is to provide reference for the optimization of CO2 efficient removal technology and the development of special equipment for industrial recirculating aquaculture in the future. [ABSTRACT FROM AUTHOR]