Aquaculture Systems Research Articles

Phosphate ester-linked carbonized polymer nanosheets to limit microbiological contamination in aquaculture water

In this study, we developed a simple, low-temperature method to synthesize carbonized polymer nanosheets (CPNSs) using sodium alginate, a biopolymer derived from algae, and diammonium hydrogen phosphate. These nanosheets are produced through a solid-state pyrolysis at 180 °C, involving dehydration, cross-linking through phosphate ester bonds, and subsequent carbonization, forming 2D structured CPNSs. These synthesized CPNSs exhibit excellent bacterial adsorption capabilities, particularly against V. parahaemolyticus and S. aureus. When applied to ordinary filter paper, the CPNS-modified paper efficiently filters bacteria from aquaculture water, removing over 98% of V. parahaemolyticus within two hours and maintaining effectiveness after 24 h. In contrast, control filter paper showed significantly reduced efficiency over the same period. Our filtration tests demonstrated enhanced survival rates for shrimp in aquaculture systems, highlighting the potential of CPNSs-modified filter paper as a suitable treatment to reduce the microbiological contamination levels in recirculating aquaculture systems in the event of a disease outbreak.

Application Of Microbubble Technology To Increase Oxygen Content In The Aquaculture Of Tambaqui (Colossoma Macropomum)

The oxygen consumed is used to oxidize food substances to produce energy. Therefore, the metabolic rate is usually indicated by the rate of oxygen consumption per time unit. In most intensive aquaculture systems, oxygen content is widely used due to the high stocking density and maximum feeding rates. This study aimed to evaluate the growth performance of freshwater pomfret (Colossoma macropomum) treated with increased oxygen in two different systems. The study was conducted in a laboratory scale by applying T-test data analysis. The difference of treatment level applied in the comparison of aeration and microbubble consists of two treatments and three replications. The researcher used commercial floating pellets PF0 with 25% protein content, the feeding rate was 5% of the biomass. The feed was given daily during the culture for two times a day. Data of the study were analyzed using T-test on the Statistical Product and Service Solutions (SPSS) software Version 17.0. Results of the study showed that aeration system using microbubble resulted in dissolved oxygen (DO) of 6.5 ± 0.17, 100% pomfret fish survival rate (SR), Survival Growth Rate (SGR) of 1.83 ± 0.24, Feed Conversion Ratio (FCR) of 1.37 ± 0.17, Protein Efficiency Ratio (PER) of 2.79 ± 0.37, Feed Utilization Efficiency (FUE) of 0.67 ± 0.09, Absolute Weight Growth of 52.02 ± 1.60; it was better than using aeration. This study has developed a model of freshwater pomfret fish aquaculture to provide growth value.

Effects of settleable versus unsettled biofloc removal strategy on aquaculture system performance and microbial community

The management of biofloc quality and quantity is critical in biofloc-based aquaculture systems. This research explores the effects of the selective removal of settleable and unsettled bioflocs on biofloc quality, fish growth, nitrogen transformation and bacterial community dynamics in these systems. Nile tilapia (Oreochromis niloticus) was reared at a density of 2.7 kg/m3 in nine 250-L conical breeding tanks over a 47-day period. Systems where unsettled bioflocs were removed outperformed others, achieving a 26 % higher weight gain in tilapia and maintaining more stable and lower levels of total ammonia (0.45 mg-N/L) and nitrite (0.35 mg-N/L). Additionally, these systems maintained a healthier bacterial environment, evidenced by a 27 % increase in beneficial bacterial populations and a 30 % reduction in harmful bacteria. Conversely, tanks removing settleable bioflocs showed a 19 % higher microbial diversity but experienced fluctuations in nitrogen levels. Notably, the intestinal bacterial community in tilapia from the unsettled biofloc group closely mirrored (87 % similarity) that of their corresponding bioflocs, with significant pathogenic symptoms observed (p < 0.05). These findings suggest the importance of implementing precise biofloc management strategies, highlighting that the selective removal of unsettled bioflocs enhances fish growth and improves overall system health. Future research should explore the mechanistic relationships between settleable and unsettled bioflocs to refine management strategies that bolster sustainability and economic benefits.

Dying for a canape: the welfare implications associated with both traditional and “ethical” production of caviar from sturgeon

The farming of sturgeon to produce caviar is increasing globally, even though little is known about the welfare implications of aquaculture for these unique, long-living, and large animals. The use of non-lethal methods for egg harvesting is increasing, as these methods are thought to offer a more ethical alternative to traditional methods where the female is killed. However, these “non-lethal” methods raise significant welfare concerns including routine handling, surgical procedures, and painful procedures, and could potentially perpetuate suffering. Consequently, there is an urgent need for significant exploration and research into this field. This review presents and discusses some of the welfare concerns associated with producing caviar from sturgeon, including the traditional and non-lethal methods of egg harvesting and the concerns associated with rearing them in aquaculture systems. It concludes in stating that the welfare issues involved with non-lethal caviar production are too sizeable to warrant its description as an “ethical or humane” alternative to traditional caviar production.

Unveiling the pathogenic and multidrug-resistant profiles of Vibrio alfacsensis: A potential identified threat in turbot (Scophthalmus maximus) aquaculture

Vibrio alfacsensis is traditionally seen as an environmental symbiont within its genus, with no detailedly documented pathogenicity in marine aquaculture to date. This study delves into the largely unexplored pathogenic potential and emerging antibiotic resistance of V. alfacsensis. The VA-1 strain, isolated from recirculating aquaculture system (RAS) effluent of cultured turbot (Scophthalmus maximus), underwent comprehensive analysis including biochemical identification, antibiotic susceptibility testing and reinfection trials. The results confirmed VA-1's pathogenicity and significant multiple antibiotic resistance. VA-1 could induce systemic infection in turbot, with symptoms like kidney enlargement, exhibiting virulence comparable to known Vibrio pathogens, with an LD50 around 2.36 × 106 CFU/fish. VA-1's remarkable resistance phenotype (14/22) suggested potential for genetic exchange and resistance factor acquisition in aquaculture environments. Phylogenetic analysis based on 16S rDNA sequences and whole-genome sequencing has firmly placed VA-1 within the V. alfacsensis clade, while genome-wide analysis highlights its similarity and diversity in relation to strains from across the globe. VA-1 contained numerous replicons, indicating the possibility for the spread of resistance and virulence genes. This study suggests V. alfacsensis may acquire and transfer pathogenic and resistant traits through horizontal gene transfer, a likelihood intensified by changing environmental and aquaculture conditions, highlighting the need for vigilant pathogen monitoring and new non-antibiotic treatments.

Effects of Formulated Pellet Feed or Live Fish Food on the Intestinal and Aquaculture Water Microbial Communities in Goldfish, Carassius auratus

This study investigates the impact of different diets on fish growth and bacterial community structure present in the intestine of goldfish (Carassius auratus) and their aquaculture water under recirculating water conditions. We assumed that different types of diet would form different intestinal microbiota that may affect host growth. Using Illumina MiSeq high-throughput sequencing, we analyzed bacterial communities in goldfish fed with formulated pellet feed, Tubifex worms (Limnodrilus hoffmeisteri), and an alternating diet of both. Over a 14-day feeding trial, no significant differences in juvenile goldfish growth were observed between groups. After 7 days, diet changes significantly influenced the abundance and diversity of intestinal bacteria, with the alternating diet notably enhancing bacterial diversity in both the intestines and water. However, these differences in bacterial diversity decreased by day 14. The results indicate that diet type affects microbial community diversity in the intestines and water of goldfish, and that goldfish intestines maintain a stable core bacterial community structure. This highlights the potential for optimizing diet types to enhance microbial health and stability in aquaculture systems and, in addition, provides an important scientific basis for alternative diets in goldfish aquaculture in the industry.

Environmental assessment of industrial aquaponics in arid zones using an integrated dynamic model

Land desertification, water scarcity, and food security challenges in arid zones are intensifying, driving the need for sustainable agricultural solutions like aquaponics. This study investigated innovative water and energy-saving strategies using an integrated dynamic model for an on-demand industrial aquaponics system in Israel. The model evaluated the performance of a recirculating aquaculture system (RAS), hydroponics system (HPS), and desalination unit (DU) by adjusting physical and operational parameters to optimize water and nutrient use efficiency, energy consumption, and yield. Optimizing the system design resulted in an aquaponics system with approximately 420 m3 RAS, 6.85 ha HPS and 40 m3/d DU, achieving phosphorus use efficiency of 96 %, a water use efficiency of 97 %, freshwater input of 1.5 L/day/m2, and energy consumption of 0.56 kWh/day/m2. To mitigate the challenges of extreme arid climates, evaporative cooling combined with outdoor shading and mechanical cooling was found to be a feasible option to control temperature and humidity in the greenhouse. Dehumidification technologies further improved system performance by recovering 22 % freshwater from seawater and increasing nitrogen use efficiency by 18 %. Achieving daily energy self-sufficiency required 4500 m2 photovoltaic panels and 5000 m2 solar heating system. While the system model was initially devised with a specific focus on conditions in Israel, it has been designed with scalability, allowing it to be adapted and applied extensively across diverse peri-urban regions and arid zones globally.

IoT based Smart Aquaculture Monitoring System for Fish Tank Management

Aquaculture, the farming of aquatic organisms, plays a critical role in meeting the increasing global demand for seafood. Effective monitoring and management of aquaculture systems are essential for ensuring optimal conditions and maximizing productivity. This research presents a comprehensive aquaculture-based fish tank monitoring system designed to enhance operational efficiency and fish welfare. At the heart of the system is the Arduino Uno microcontroller, serving as the central processing unit to coordinate various functions. Key components include pH sensor for continuous monitoring of acidity levels, turbidity sensor for detecting suspended particles, and water level sensor for maintaining optical water levels within the tank. In the event of abnormal pH levels or high turbidity, the system triggers automated alerts, sending notifications to the designated owner through SMS and transmitting data to an IoT website for remote monitoring. To ensure consistent environmental conditions, two pump motors are utilized: one for automatic water replenishment in case of water level fluctuations and another for removing water in case of particle accumulation. Furthermore, the system integrates a servo motor mechanism for precise dispensing of fish feed at predetermined intervals, promoting healthy growth and nutrition. Control over pump motors and feeding schedules is facilitated through a user-friendly website interface, providing operators with seamless management capabilities.

Innovative approaches for enhanced nutrient (N and P) removal and biosecurity in marine recirculating aquaculture systems using biofloc and ultrafiltration combined systems

Marine recirculating aquaculture systems (marine RAS) are increasingly utilized for their high productivity and minimal environmental impact. However, effective nutrient management and biosecurity measures remain crucial for sustainable operation of marine RAS. This study successfully established a simultaneous nitrification and denitrification (SND) process using a biofloc technology (BFT)–ultrafiltration (UF) combined approach. A stable autotrophic marine nitrification system was rapidly initiated within 23 days using a ceramic ring (CR)–granular activated carbon (GAC)–UF process (CGUF), followed by the substitution of polyhydroxyalkanoates (PHA) for GAC filter to achieve rapid start-up of SND in 24 h (CG/PUF). Soluble reactive phosphate (SRP) was removed in-situ via biofloc adsorption. The co-existence of ammonia-oxidizing archaea (Candidatus_Nitrosopumilus) and denitrifying bacteria (Stenotrophomonas, Ruegeria and Ilumatobacter) synergistic promoted the SND start-up in CG/PUF process. Stenotrophomonas emerged as the keystone species which closely linked to amoA/B/C, hao and nosZ genes (p < 0.05). The CG/PUF process effectively enhanced the biosecurity of marine RAS, with 100 % elimination of potential pathogens (Vibrio and Tenacibaculum). UF membrane could maintain fluxes at 15 L∙ m−2∙ h−1 (LMH) for 180 days, with a 2-day intermittent hydraulic flushing keeping transmembrane pressure below 50 kPa. These findings provide insights for broader application of BFT–UF combined process in marine RAS.

Influence of different stocking densities of pearlspot (Etroplus suratensis) on plankton diversity indices of biofilm-based rearing system

Aim: Biofilm-based aquaculture systems, proven cost-effective, reduce the need for expensive supplementary feed. The biofilm acts as a natural planktonic food source for reared organisms. Previous research highlighted the influence of fish stocking density and biomass on plankton diversity in different aquaculture settings, underscoring the significance of these factors in biofilm-based systems. Hence, the present study attempted to understand how varying stocking densities of pearlspot (Etroplus suratensis) influence plankton diversity indices in the biofilm-based aquaculture system. Methodology: The present experiment was designed in 5 Practical Salinity Unit (PSU) brackishwater with soil-bottomed FRP circular (500 L) tanks for 60 days. The sugarcane bagasse was used as a substrate forbiofilm production after fertilization with cow dung, urea, and lime. Fries of pearlspot (4.67 ± 0.04 mm 1.71 ± 0.03 g-1) were stocked at four different stocking densities in triplicates viz T1 (50 nos); T2 (100 nos), T3 (150 nos) and T4 (200 nos) fish fry m-3 in the biofilm-based rearing system. Plankton samples were collected from water and biofilm deposited on the substrate and analyzed for diversity indices. The Shannon Diversity Index, Simpson Diversity Index, Simpson Dominance Index, and Margalef Richness Index were used to compute the plankton diversity indices in different treatments using standard equations. Results: In the current investigation, lower stocking densities with lower fish biomass were associated with significantly higher (P≤0.05) Shannon Diversity Index, Simpson Diversity Index, and Margalef Richness Index in water. In contrast, the Simpson Dominance Index in water showed a significantly lower (P≤0.05) value for treatments with lower fish biomass than for treatments with higher biomass. Interpretation: The values obtained for various diversity indices indicated that a biofilm-rearing system with lower E. suratensis biomass produced more planktonic abundance, evenness, and species richness. Key words: Biofilm, Pearlspot, Plankton diversity, Stocking density

Utilization of rice husk ash as a potential catalyst for diatom growth and adsorbent for heavy metals in aquaculture systems

Many aquaculture environments suffer from significant silicon deficiencies and severe heavy metal contamination, posing substantial risks to both production and safety in aquaculture. This study aimed to assess the release of silicate from rice husk ash (RHA) and its impact on phytoplankton abundance and community composition, which are key factors affecting shellfish growth and survival. Additionally, the capacity of RHA to adsorb mercury (Hg2+) was examined using different modification methods. The results demonstrated that the concentration of dissolved silicate in seawater increased with higher RHA doses, reaching a maximum of 189.77 ± 45.61 μmol L−1 in the high RHA treatment (HR) with 1.0 g L−1 of RHA. Notably, the HR treatment group exhibited a significant increase in chlorophyll-a concentration for nano-phytoplankton (2–20 μm), with an up to eightfold rise in abundance compared to the control group. Moreover, the HR treatment resulted in a maximum diatom abundance of 4217 ± 741.98 cells L−1, benefiting diatom species such as Coscinodiscus sp., Nitzschia sp., and Cyclotella sp. These findings underscore the potential of RHA as a catalyst for diatom growth, which in turn supports the growth of shellfish. Furthermore, no concentrations of mercury (Hg), lead (Pb), cadmium (Cd), arsenic (As), copper (Cu), zinc (Zn), and chromium (Cr) were detected in any of the silicate enrichment treatments, confirming the safety of the RHA. The treatment of RHA with NaOH achieved an impressive removal efficiency of Hg2+, reaching up to 97.41 ± 0.33 %. This study highlights the promising application of agricultural waste RHA as a catalyst for diatom growth and an adsorbent for heavy metals in water systems relevant to aquaculture practices.

Investigation on aeration efficiency and energy efficiency optimization in recirculating aquaculture coupling CFD with Euler-Euler and species transport model

Aeration plays a crucial role in maintaining the overall health and sustainability of the recirculating aquaculture system. Conventional aeration operates continuous and consumes 35.06 % of equipment energy consumption. How to optimize aeration while ensuring normal fish growth remains a great challenge. To address these challenges, this research paper established a coupled model of computational fluid dynamics and species transport model (CFD-STM). Aeration tests were carried out in a 33.3 m3 culture tank using a 0.31 m diameter aerator to find out the impacts of operating variables (aeration flow rate, bubble diameter, inlet velocity, and aerator position) on oxygen transfer using a microporous aeration system. A CFD-STM model was coupled to obtain the optimum values of aeration parameters. Results revealed that the Standard Aeration Efficiency (SAE) reductions by 32.1 % for 50 % larger aeration flow rate and 86.4 % for 50 % larger bubble diameter, as well as SAE achieved 5.67 kg/kWh with an aerator position scale factor equal to 0.48. In addition, the energy consumption of the Roots blower was compared for a single aeration and dissolved oxygen saturation. Results indicated that smaller bubbles microbubbles can effectively improve oxygen transfer coefficient. The energy consumption was reduced by 15.7 % for 50 % larger aeration flow rate and 38.6 % for 50 % lower bubble diameter. Based on the results, this study demonstrated that CFD is a useful tool to optimize the aeration system design and operation in order to enhance aeration efficiency. It provides a theoretical foundation the future optimization of energy conservation through intermittent aeration practices.

Early warning system for nocardiosis in largemouth bass (Micropterus salmoides) based on multimodal information fusion

The high-density culture of the recirculating aquaculture system (RAS) makes bacterial and parasitic diseases in fish likely to spread within these systems. Therefore, preventing and controlling the occurrence of fish diseases in RAS is crucial for the future development of aquaculture. However, the current circulating water system lacks early warning measures to prevent and control diseases, resulting in poor accuracy in early warning and detection of diseases. To tackle this challenge, this study introduces an early warning system for largemouth bass (Micropterus salmoides) disease, which is based on You Only Look Once vision 8 (YOLOv8), ByteTrack, Long-Short-Term-Memory(LSTM), and Fuzzy Inference System (FIS). The system utilizes the water quality, surface characteristics, and behavioral traits of diseased fish to predict and prevent disease outbreaks. The system achieved an accuracy of 79.33% for identifying infected body surface features, 80.65% for identifying diseased water quality, and 81.08% for predicting diseased behavior. The experimental results indicate that the early warning system is highly reliable and effective, achieving integrated disease identification accuracy as high as 94.08%. This study enhances the accuracy of early disease warning in fish disease conditions, achieving early warning of nocardiosis in largemouth bass. The study provides crucial technical support for the sustainable and high-quality development of the aquaculture industry.

Comparative evaluation of nutritional quality and flavor characteristics for Micropterus salmoides muscle in different aquaculture systems

To investigate the nutritional quality and flavor characteristics of Micropterus salmoides muscle cultivated in the pond (P), in-pond raceway (IPRS), and industrial aquaponics (ARAS) systems, we comprehensively analyzed texture properties, nutrient compositions, and volatile compounds. Our results revealed firmer flesh in P-cultured fish due to greater hardness and mastication. ARAS fish exhibited lower crude fat but higher crude protein and muscle glycogen. Notably, recirculating aquaculture significantly elevated total amino acids, minerals, and ΣPUFA/ΣSFA ratio, enhancing nutritional value. Pyrazine,2-methoxy-3-(2-methylpropyl)-, and β-Ionone were identified as key flavor compounds. Volatile metabolites in all systems were dominated by woody, herbal, and sweet aroma profiles, with ARAS achieving the highest odor activity value, suggesting improved overall flavor. This study underscores the pivotal role of recirculating aquaculture in enhancing Micropterus salmoides quality, positioning it as a new quality productive force.

A multi-pronged approach to assessing antimicrobial resistance risks in coastal waters and aquaculture systems

Antimicrobial resistance (AMR) is a global challenge that has impacted aquaculture and surrounding marine environments. In this study, a year-long monitoring program was implemented to evaluate AMR in two different aquaculture settings (i.e., open cage farming, recirculating aquaculture system (RAS)) and surrounding marine environment within a tropical coastal region. The objectives of this study are to (i) investigate the prevalence and co-occurrence of antibiotic-resistant bacteria (ARB), antibiotic resistance genes (ARGs), antibiotics (AB) and various associated chemical compounds at these study sites; (ii) explore the contributing factors to development and propagation of AMR in the coastal environment; and (iii) assess the AMR risks from different perspectives based on the three AMR determinants (i.e., ARB, ARGs and AB). Key findings revealed a distinct pattern of AMR across the different aquaculture settings, notably a higher prevalence of antibiotic-resistant Vibrio at RAS outfalls, suggesting a potential accumulation of microorganisms within the treatment system. Despite the relative uniform distribution of ARGs across marine sites, specific genes such as qepA, blaCTX−M and bacA, were found to be abundant in fish samples, especially from the RAS. Variations in chemical contaminant prevalence across sites highlighted possible anthropogenic impacts. Moreover, environmental and seasonal variations were found to significantly influence the distribution of ARGs and chemical compounds in the coastal waters. Hierarchical cluster analysis that was based on ARGs, chemical compounds and environmental data, categorized the sites into three distinct clusters which reflected strong association with location, seasonality and aquaculture activities. The observed weak correlations between ARGs and chemical compounds imply that low environmental concentrations may be insufficient for resistance selection. A comprehensive risk assessment using methodologies such as the multiple antibiotic resistance (MAR) index, comparative AMR risk index (CAMRI) and Risk quotient (RQ) underscored the complexity of AMR risks. This research significantly contributes to the understanding of AMR dynamics in natural aquatic systems and provides valuable insights for managing and mitigating AMR risks in coastal environments.

Response of CH4 and N2O emissions to the feeding rates in a pond rice-fish co-culture system.

Feeding rate is an important factor influencing the carbon and nitrogen input and greenhouse gas emission from aquaculture systems. However, the quantitative relationship between feeding rates and GHG emissions is still poorly understood. In this study, we conducted a laboratory-scale experiment to examine the impact of feeding rate (0%, 2%, 4%, 6%, and 8%) on the CH4 and N2O emissions from a pond rice-fish co-culture system. The results showed that the total amount of CH4 emission did not significantly differ when the feeding rate was no more than 6%, but increased more than four times when the feeding rate reach to 8%. The amount of N2O emission showed a linearly increasing trend with the feeding rate. The emission factors of CH4 and N2O was significantly higher for 8% feeding rate than other feeding rates. The variation of CH4 emission was primarily attributed to the ratio of mcrA/pmoA in the sediment and the contents of biological oxygen demand (COD) and dissolved oxygen (DO) in the water; and the variation of N2O was primarily affected by the available nitrogen in the water and sediment and the content of DO in the water. The overall emission of CH4 and N2O showed an exponential relationship with feeding rate. The total yields of fish and rice did not continuously increase when the feeding rate exceeded 4%. The lowest emission intensity per unit yield was reached at the feeding rate of 2.99%. These results can provide a reference for the determination of low-carbon feeding strategy for pond rice-fish co-culture system.

Measure-correlate-predict methods to improve the assessment of wind and wave energy availability at a semi-exposed coastal area

To reduce the carbon footprint of near-shore and land-based Recirculating Aquaculture Systems (RAS), there is interest to harness renewable energy from local sources. When estimating power availability from wind and waves, it is imperative to ensure that the metocean resource data accurately represents the energy flux at the specific site. Here, four measure-correlate-predict (MCP) models are investigated for wind speed, significant wave height and peak wave period. The MCP relationships are obtained from higher spatial resolution wind and wave data, from a weather research and forecasting model, met-mast measurements at Stord airport (wind), and spectral downscaled DNORA/SWAN model (wave), correlated to the NORA3 database over a common time interval. These relations are used to improve the predictions of metocean parameters from the NORA3 model at the RAS location for the period 2012–2021, and hence allow more accurate estimates of renewable power availability. The prediction accuracy of the MCP models improves in all four cases when an appropriate data sorting criterion and algorithm is implemented. Between 2012 and 2021, average wind power density and wave power density are lowest in July at 182 W/m2 and 0.6 kW/m, and highest in December at 538 W/m2 and 7.5 kW/m, respectively.

Various effects of feeding level on ammonia tolerance in Carassius auratus under different ammonia exposure stress and the underlying mechanisms

Elevated ammonia levels in aquaculture systems could reduce fish growth and survival rates and produce a range of physiological problems. Ammonia toxicity in aquatic environments was regulated by various factors. Feeding was usually reported to help in the detoxification of fish, thereby increasing their capacity to tolerate ammonia nitrogen. However, the impact of different feeding amounts on fish in relation to ammonia exposure stress remains to be determined. To determine how feeding levels affected fish's responses to different ammonia nitrogen concentrations, two acute toxicity experiments were conducted with Carassius auratus gibelio, the major strain of gibel carp in aquaculture systems in China. In Test I, fed Carassius auratus gibelio (3 % body weight) showed a higher survival rate under a specific ammonia exposure stress. 96-h LC50 of NH3-N to 3 %F gibel carp was 1.1 times greater than that for NF (no feeding). In Test II, all fed groups (2 %F and 4 %F) under low and high ammonia stress exhibited improved ammonia detoxification, evidenced by higher liver GSase, GDH, and glutamine concentrations compared with the NF treatment. Muscle glycogen levels in feeding treatments were higher than those in NF, indicating that fed fish have more energy for ammonia detoxification. While compared with low ammonia treatment (2.70 mg L−1 TAN; NH3 0.06 mg L−1), fish exposed to high ammonia levels (26.03 mg L−1 TAN; NH3 0.57 mg L−1) demonstrated a decrease in food consumption, severe histopathological alterations in their liver, gill, and kidney, and decreased GSase, GDH, and glutamine production in the liver and brain. The results partly supported our hypothesis and suggested that increasing feeding enhances gibel carp's tolerance to ammonia nitrogen. The highest detoxification metabolism was observed under low ammonia stress. While excessive ammonia exposure could inhibit feeding and damage the detoxification organs of fish, and thus reduce the detoxification metabolism of gibel carp.

Evaluating the suitability of nitrate-nitrogen levels for post-smolt Atlantic salmon Salmo salar production in RAS with assistance from heart rate bio-loggers

Previous onsite research determined that post-smolt Atlantic salmon Salmo salar growth, health, and welfare were unaffected by exposure to 99 mg/L nitrate-nitrogen (NO3-N) in freshwater recirculating aquaculture systems (RAS). A subsequent study was conducted to determine if higher concentrations negatively impact Atlantic salmon within a similar size range. Salmon production metrics were compared in triplicate RAS with NO3-N levels increasing from 100 to 250 mg/L (“high”) vs. 50–100 mg/L NO3-N (“low”). An average feed loading rate of 2.53 kg feed/m3 makeup water/day was maintained to facilitate natural NO3-N accumulation up to 75–100 mg/L, and sodium nitrate was continuously dosed to achieve higher concentrations. All-female diploid and all-female triploid Atlantic salmon were comingled in six replicated RAS, resulting in 227 fish/tank with an initial mean weight of 0.35 kg. Six diploid salmon with surgically implanted heart rate bio-loggers were included in each RAS. Continuously logged heart rates were matched with frequently measured NO3-N levels to determine the onset of a physiological response. At the end of the 6-month study, salmon exposed to the high and low NO3-N conditions weighed 1.84 ± 0.05 and 1.91 ± 0.02 kg, respectively (p > 0.05). Diploid and triploid salmon growth rates, feed conversion ratios, maturation prevalence, survival, fin condition, and cataract scores were unaffected (p > 0.05). However, salmon heart rates were generally higher in the high NO3-N treatment after concentrations exceeded 150 mg/L NO3-N. Higher plasma chloride, hematocrit, and hemoglobin levels (p < 0.05) consistent with an adaptive response to a stressor were also measured in salmon from the high NO3-N RAS during this period. These findings suggest that NO3-N concentrations < 150 mg/L do not affect post-smolt Atlantic salmon under similar operating conditions, including freshwater RAS without denitrification technologies and water hardness >300 mg/L as CaCO3. Additional research is required to determine if higher NO3-N concentrations are suitable for Atlantic salmon production over longer exposure periods and with naturally produced NO3-N levels imparted by reduced water exchange. Feed- and nitrogen-loading rates conducive to maintaining the tested NO3-N levels are reported.

The impact of shade net use on total nitrogen removal by duckweed (Lemna perpusilla) at different levels of catfish farming effluent

Duckweed (Lemna perpusilla) has been shown to reduce nutrient levels in aquaculture effluent, particularly total nitrogen, which can be caused by a variety of organic contaminants in water. Duckweed biomass is an important source of bioenergy and phytoremediation in aquaculture. This aspect makes it a viable solution for sustainable integrated aquaculture, although appropriate duckweed biomass development is critical to its success and long-term survival. Duckweed growth, as an autotroph, is controlled by two factors: nutrition and sunlight. The aquaculture production cycle changes nutrient content in medium culture based on feed, fish age, and density, while weather influences solar radiation. The study aims to investigate duckweed growth response and phytoremediation capacity by analyzing changes in catfish farming waste-water quality grouped by fish age (L1: 2 months, L2: 3 months, and L3: 4 months) and shade net treatment at 25 % sunlight blocking (N25), 50 % (N50), and no shade net (N0). The experiment was carried out in triplicate in a semi-outdoor growth system placed in a greenhouse. It comprised of three series of duckweed culture containers filled with catfish farming wastewater, each with a working volume of 50 L. A total of 48 duckweed culture containers were floated inside a series of Recirculating Aquaculture System (RAS) tanks. Biomass harvesting and water quality monitoring were done every three days for a period of 18 days. N25 had the highest biomass weight, productivity, and average TN elimination efficiency, with values of 225.21 ± 140.04 g, 50.05 ± 10.06 g/(m2.d), and 61.94 ± 8.01 %, respectively (P < 0.05). The N0 values were 190.80 ± 117.52 g, 42.40 ± 9.29 g/(m2.d), and 55.61 ± 6.85 % (P < 0.05). The lowest values observed in N50 were 72.27 ± 55.70 g, 16.06 ± 4.90 g/(m2.d), and 51.67 ± 4.10 % (P < 0.05). This study proved the optimal duckweed growth and TN removal effectiveness with N25 under varying light intensity, allowing for the long-term use of duckweed in waste management and integrated aquaculture.