Biofloc Technology System Research Articles

The super-intensive culture of Penaeus vannamei in low salinity water: A comparative study among recirculating aquaculture system, biofloc, and synbiotic systems

The culture of Penaeus vannamei in inland regions using low salinity water is a reality in several regions of the world. The dissemination of culture techniques that allow high stocking density and reduced water use can be used to optimize the production process, but they require comparative studies to better understand the functioning of these systems in those salinity conditions. Therefore, this study aimed to analyze the effects of different culture systems, which were recirculating aquaculture system (RAS), biofloc technology (BFT), and synbiotic system (Synbiotic) on the water quality, plankton composition, and growth of P. vannamei in low salinity (2 g L−1) and high stocking density (500 shrimp m−3) for 30 days. The shrimp were stocked at a mean weight of 1.27 ± 0.06 g. In the BFT, dextrose was used as the organic carbon source and administered at a carbon: nitrogen ratio of 15:1. In the Synbiotic, rice bran processed by probiotic microorganisms was used as an organic fertilization strategy. In the RAS treatment, all nitrogen species remained stable throughout the trial, without spikes, and with ammonia and nitrate concentrations lower than in BFT and Synbiotic. The BFT treatment had more events when total ammonia nitrogen exceeded 1 mg L−1, requiring water changes. The Synbiotic treatment had better control of nitrogenous compounds, and a more accentuated accumulation of nitrate compared to BFT, suggesting more effective nitrification. The BFT treatment had more microalgae than Synbiotic and RAS. However, the abundance of zooplankton was higher than that of phytoplankton in BFT and Synbiotic, indicating a dominance by heterotrophic organisms. The Synbiotic treatment had a higher abundance of ciliates and amoeba than the other treatments. Furthermore, the Synbiotic treatment provided higher survival, yield, and lower FCR than BFT and RAS. Our findings indicate that the Synbiotic system can be considered as an alternative for the P. vannamei super-intensive culture in low salinity water, as it presented better control of nitrogenous compounds compared to BFT, higher abundance of ciliates and amoeba, and provided better production rates to the culture.

Influence of Biofloc Technology and Continuous Flow Systems on Aquatic Microbiota and Water Quality in Japanese Eel Aquaculture

Biofloc technology (BFT) systems heavily rely on microbiota to mitigate ammonia toxicity and manage essential nutrient cycling. Understanding the diversity and functional role of microbiota within BFT-applied aquaculture systems is crucial for ensuring sustainable operations. Though some studies exist on BFT microbiota, research on microbial differences in Japanese eel aquaculture is still limited, hindering the wider application of BFT systems. In this study, we analyzed the characteristics of water quality factors and microbiota in Japanese eel (Anguilla japonica) breeding water, applying the BFT system. Using a metabarcoding approach, the diversity and community structure of aquatic microbiota were compared between BFT and continuous flow (CF) systems. The pH was significantly higher in CF water, while total ammonia nitrogen (TAN) and nitrite (NO2−-N) was higher in BFT water. Alpha diversity was significantly higher in BFT compared to CF systems, and it was correlated significantly with pH and TAN. In both BFT and CF water, the phyla Proteobacteria and Bacteroidota were found to be the most abundant. In the BFT water, a diverse array of bacterial taxa, including BFT-specific clades, were consistently present, while the microbiota in CF water was more variable and contained fewer specific taxa. In addition, bacterial functions related to nitrate reduction, sulfur compound oxidation, and chitinolysis were significantly more abundant in BFT than in CF systems. These findings highlight differences in water quality and microbiota between aquaculture systems, which can inform future research on the use of BFT for sustainable fish farming.

Influence of various carbon and nitrogen ratios in a jaggery-based biofloc rearing system on the Asian stinging catfish Heteropneustes fossilis

Biofloc technology (BFT) is becoming popular in aquaculture. As the human population has rapidly increased, so has the demand for protein, driving the expansion of aquaculture. The increased use of aqua medicines in aquaculture has led to resistant microbes. BFT offers a promising, eco-friendly solution by promoting beneficial microbes to improve fish health and reduce chemical use, supporting the industry's long-term sustainability. BFT recycles waste without water exchange by maintaining an optimal carbon-nitrogen (C:N) ratio and adding an external carbon source, which promotes the growth of heterotrophic bacteria and other essential microbes that absorb ammonia from feed and waste, forming beneficial microbial aggregates. This study evaluated the effects of various C:N ratios in a jaggery-based BFT system on water quality, growth, feed efficiency, and the well-being of Heteropneustes fossilis. A completely randomized design with triplicates (2.33 kg/m³ in 1500 L tanks) was used to compare a control group without biofloc to three BFT treatments with C:N ratios of 8:1 (CN8), 12:1 (CN12), and 16:1 (CN16) over 180 days. Daily feeding was conducted at 5–2 % of the fish's body weight (initial weight of 5.0±0.5 g). Higher C:N ratios were linked to reduced dissolved oxygen, ammonia, and nitrite levels, alongside increased total suspended solids, floc volume, and heterotrophic bacteria counts, while the CN12 had the highest levels of beneficial microbes (Firmicutes and Actinobacteria), leading to superior fish growth, survival, and biomass compared to CN8 and CN16. The CN12 also showed better stress response, hematology, immunity, and antioxidant properties. Histologically, fish in CN12 and CN8 had healthier liver and intestines compared to CN16 and control. The results suggest that a C:N ratio of 12:1 was optimal for biofloc systems used in cultivating H. fossilis, enhancing both microbial growth and water quality.

Application of Biofloc-Down flow hanging sponge system to remove nitrogen components in recirculating zero water exchange aquaculture system

This study presents a novel approach to sustainable aquaculture by integrating biofloc technology (BFT) with a compact down-flow hanging sponge (DHS) reactor. The integrated BFT-DHS system effectively removed nitrogen compounds while maintaining ammonia–nitrogen (NH4+-N) concentrations below 1 mg-N L-1 without water exchange. Application of this system in a tank bred with juvenile Oreochromis niloticus showed a high NH4+-N removal rate of up to 97 % and nitrite (NO2– −N) concentrations were maintained at 0.1 ± 0.1 mg-N L-1. Microbial analysis revealed Gordonia as the predominant genus in the biofloc contributing to heterotrophic nitrification, while the Peptostreptococcaceae family dominated the DHS reactor. Heterotrophic nitrification seemed to be the primary process for enhanced nitrogen removal. Pathogenic bacteria, Vibrio sp. was absent throughout the study. This study highlights the potential integration of BFT and DHS system for sustainable aquaculture practice with effective nitrogen removal.

Appling machine learning for estimating total suspended solids in BFT aquaculture system

Biofloc Technology (BFT) systems are used to improve water quality and the production of aquatic organisms, and they influence dissolved oxygen, alkalinity, and pH, directly affecting the efficiency and success of this production system. Measuring total suspended solids (TSS) in water demands substantial investments and involves a time-consuming process to obtain results. This delay in obtaining results poses a significant challenge to the operations of these farms. In this study, we applied Artificial Neural Networks (ANN) and Support Vector Machine (SVM) methods based on artificial intelligence and water quality parameters (easy to measure, low cost, and quick response) to identify the most accurate method for measuring TSS. The best TSS estimate was achieved with SVM using nitrite and turbidity as predictive variables, which tended to overestimate the real value by 19 %, presenting a potential for application in estimating TSS in the BFT aquaculture system.

Integrated biofloc technology in red tilapia aquaculture: Salinity-dependent effects on water quality, parental stock physiology, reproduction, and immune responses

The study examines the impact of integrated biofloc technology (BFT), different salinity levels, and their combined effects over 90 days on various physiological parameters. The investigation includes growth performance and feed utilization, water quality, the chemical composition of biofloc and fish, digestive enzymes, reproductive performance, stress and biochemical indicators, and antioxidant-immune responses in red tilapia (Oreochromis spp.) broodstock. The fish were initially weighed (males: n = 270; 104 ± 0.96 g; females: n = 270; 93.2 ± 0.66 g) and subsequently divided into 12 treatment groups (6 for males and 6 for females) spread across 36 separate tanks (3 tanks per treatment; 45 fish per treatment; 15 fish/tank). The treatments involved three salinity levels (18, 28, and 36 ppt) in both clear water (CW) and BFT systems. The outcomes demonstrated that fish in the 36 ppt salinity with BFT treatment demonstrated significant improvements (P < 0.05) in growth parameters (final body weight, weight gain, and specific growth rate, feed intake, and feed conversion ratio). The condition factor in BFT groups increased in all salinity situations. The survival rates of broodstock were consistently high in all experimental conditions The study found that BFT and salinity significantly impacted (P < 0.05) whole body contents (moisture, protein, lipid, and ash) in both males and females. Water quality parameters showed variations between BFT and CW, with notable impacts (P < 0.05) on dissolved oxygen and pH. The BFT and salinity influenced digestive enzyme activities (protease, amylase, and lipase) and reproductive performance (males) and the 36 ppt salinity with BFT recorded the highest values. The hemato-biochemical and antioxidant-immune responses were also impacted by BFT and salinity exposure. The study highlights the potential benefits of incorporating BFT into red tilapia aquaculture systems, particularly in optimizing growth, health, and reproductive performance under various salinity conditions, which can enhance sustainable intensification, disease control, and environmental stewardship.

Feeding rates affect growth, metabolism and oxidative status of Nile tilapia rearing in a biofloc system.

The biofloc system is a biotechnology available for fish farming. Feeding rate is an important factor as it influences production costs and fish performance. The aim og this study was to evaluate the effects of feeding rates (2, 4, 6 and 8%) on growth, body composition, biochemical parameters and thiobarbituric acid-reactive-substances in tilapia. An experiment was conducted for 4 weeks, using 144 tilapias juvenile (initial weight = 12.06 ± 0.16g), in triplicate for feeding rate tested. Fish fed three times a day, with comercial extrude diet (36%CP). After the end of the experiment, measurements were carried out and samples were collected for analysis. The feeding rate of 6% increased fish growth parameters, not differing between 4 and 8%. Since apparent feed conversion increased proportionally to increase in feed supply. Body protein of fish was higher at 8% feeding rate and the dry matter raised according to the rate. The feeding rates affected the body lipids in fish. Fish that fed 6% and 8% showed more lipid in the whole body. The biochemical parameters presented a lower amount of protein, amino acids, and hepatic glucose when employing a feed rate of 6%. Higher levels of ammonia were observed in the muscle of fish reared at 4% of feeding rate. There was no difference in amino acids and ammonia regarding the gills. Fish reared at lower feeding rates (2% and 4%) showed better oxidative parameters, which may be due to the consumption of the biofloc phenolic compounds. We recommend the use of a 4% feeding rate for juvenile tilapia in a Biofloc Technology system.

Environmental performance of Penaeus vannamei shrimp production in intensive and super-intensive biofloc systems

Shrimp farms worldwide have been responsible for a series of social and environmental issues that affect their surrounding regions. Modern aquaculture seeks to achieve sustainable growth that offers a balance between environmental, economic, and social perspectives, and new aquaculture technologies have been developed and improved in recent decades. One such innovation is the biofloc technology (BFT) system, which is considered an alternative to conventional aquaculture because it allows for aquatic organism production with minimal water exchange, high stocking densities, and the possibility of high levels of productivity. Life Cycle Assessment (LCA) is one of the most common methodologies used to compare the environmental performance of different systems, considering resource consumption and the emission of pollutants during the productive life cycle. The present study uses LCA to compare the environmental performance of Penaeus vannamei shrimp production in two BFT systems, an intensive system in a pond and a super-intensive system in a greenhouse. The Functional Unit used was 1.0 ton of shrimp (animals with an average final weight of 12 g). The boundaries of the system were defined as from the cradle to the farm gate. Input data related to the use of natural resources, energy consumption, and environmental emissions were obtained over eight cycles of intensive and super-intensive production. The following results were obtained for intensive and super-intensive systems, respectively: global warming (GWP100a) 5691.12 and 5512.42 kg CO2 eq; acidification 59.57 and 59.05 kg SO2-eq; eutrophication 25.96 and 25.80 kg PO4 eq; ozone layer depletion (OLP) 0.000319 and 0.000311 kg CFC-11 eq; human toxicity 1165.98 and 1233.33 kg 1.4-DB-eq; aquatic ecotoxicity 1344.13 and 1925.96 kg 1.4-DB eq; marine ecotoxicity 1881,643.65 and 2070,517.23 kg 1.4-DB eq; terrestrial ecotoxicity 24.26 and 33.54 kg 1.4-DB eq; photochemical oxidation 2.10 and 2.03 kg C2H4 eq; abiotic depletion 0.006487 and 0.008359 kg Sb eq; abiotic depletion of fossil fuels 35,612.80 and 34,504.39 MJ. Among the eleven evaluated impact categories, the intensive system showed better results in five categories, while the super-intensive system showed better performance in six categories. Feed (reference diet) was the most significant factor in the environmental performance of the evaluated systems. Based on these results, we conclude that feed and electricity had the most environmental impact in both systems. In general, when comparing the use of production factors and productivity between the systems, it becomes more evident that the SS is more efficient than the SI.

Effects of stocking density on water quality, survival, blood parameters and growth performance of juvenile matrinxã (Brycon amazonicus) in the biofloc system

Biofloc technology (BFT) may be a promising alternative for production of juvenile matrinxã (Brycon amazonicus) as it allows greater fish productivity compared to ponds and is considered an economic and environmentally sustainable system. This study evaluated the effects of different stocking densities on water quality, survival, blood parameters and growth performance of juvenile matrinxã in the biofloc system. Juveniles of 5.89 ± 0.11 g were randomly distributed in five stocking densities (50, 140, 230, 320 and 410 fish ∙ m−3), in triplicate, in a BFT system. Extruded commercial feed (36% crude protein) was offered until apparent satiety four times per day for 61 days. In general, the increase in stocking density resulted in a reduction in dissolved oxygen, pH and alkalinity. Although nitrogenous compounds, total suspended solids, settleable solids and turbidity were greater in higher stocking densities, the water quality parameters were within the recommended range for matrinxã in all treatments. The stocking density had a quadratic effect on the variables specific growth rate, daily weight gain and mean final body weight. For the final stocking density and feed conversion ratio, the effect of stocking density was positive and linear. Survival rates were over 90% at stocking densities >230 fish ∙ m−3. We found a lower concentration of erythrocytes in juvenile matrinxã at the lowest stocking density (50 fish ∙ m−3) and the lymphocyte concentration was higher in the fish kept at 140 fish ∙ m−3 compared to those kept at 410 fish ∙ m−3; however, there was no difference among the other treatments. In conclusion, juvenile matrinxã can be efficiently produced using BFT at stocking densities of 291–293 fish ∙ m−3 or 13.50–13.60 kg ∙ m−3. Although the increase in stocking density is favorable for increasing the biomass and survival of matrinxã, an intensive management of solids and nitrate, as well as alkalinity corrections, are necessary to ensure proper functioning of the production and to avoid mortality of fish due inadequate water quality.

A Review: Microbes and Their Effect on Growth Performance of Litopenaeus vannamei (White Leg Shrimps) during Culture in Biofloc Technology System.

In the modern era of Aquaculture, biofloc technology (BFT) systems have attained crucial attention. This technology is used to reduce water renewal with the removal of nitrogen and to provide additional feed. In BFT, microorganisms play a crucial role due to their complex metabolic properties. Pathogens can be controlled through multiple mechanisms using probiotics, which can promote host development and enhance the quality of the culture environment. During culturing in a biofloc technology system, the supplementation of microalgae and its accompanying bacteria plays a beneficial role in reducing nitrogenous compounds. This enhances water quality and creates favorable environmental conditions for specific bacterial groups, while simultaneously reducing the dependency on carbon sources with higher content. The fluctuations in the bacterial communities of the intestine are closely associated with the severity of diseases related to shrimp and are used to evaluate the health status of shrimp. Overall, we will review the microbes associated with shrimp culture in BFT and their effects on shrimp growth. We will also examine the microbial impacts on the growth performance of L. vannamei in BFT, as well as the close relationship between probiotics and the intestinal microbes of L. vannamei.

A biofloc system avoids the adverse effects of diets with suboptimal protein levels on zootechnical performance, intestinal histomorphometry, and protein metabolism of Nile tilapia juvenile fed Spirulina biomass (Arthrospira platensis) as an alternative protein source.

This study aimed to evaluate the effect of the biofloc technology (BFT) system and the replacement of fish meal with Spirulina biomass on productive performance, intestinal histomorphometry, plasma biochemistry, and oxidative stress of Nile tilapia juveniles (Oreochromis niloticus) fed suboptimal levels of protein. Two factors were evaluated: production systems (clear water × BFT) and replacement of fish meal with Spirulina (0, 33, 66 e 100%). The design was in a 2 × 4 randomized factorial scheme with four replications, and the fish were evaluated for 48days. Four isoproteic (28% crude protein) diets were formulated with gross energy values close to 4300kcalkg-1. Nile tilapia juveniles (0.23 ± 0.01g) were distributed in 16 circular tanks (70 L) at seven fish/tank. The diets were formulated with protein levels approximately 20% below that required for the species and life stage. No interaction was observed between the factors evaluated (production systems × Spirulina inclusion). Rearing the fish in the BFT system avoided the adverse effects of diets with suboptimal protein levels on performance, intestinal histomorphometry, and protein metabolism. Lower values lower lipid peroxidation and higher antioxidant capacity were observed in fish reared in the BFT system, showing evidence of improvements in antioxidant responses and lower levels of physiological oxidative stress. Spirulina completely replaced fish meal in the diets of Nile tilapia juveniles without adverse effects on intestinal morphometry, protein metabolism, and antioxidant response. Replacing 66% of fish meal with Spirulina improved the productive performance, regardless of the rearing system.

Use of Bacillus subtilis multiplicate in the water used for biofloc formation: Growth, hemato-biochemistry, intestinal bacteria colonies, and bacterial resistance evaluations of Nile tilapia

Probiotics in the biofloc technology (BFT) system improve fish growth and immune response and promote a favorable intestinal microbiota balance. This study aimed to investigate the growth, hemato-biochemical parameters, bacterial resistance, and the number of intestinal bacteria colonies of Nile tilapia (6.23 g) reared in the BFT system with graded levels of Bacillus subtilis multiplicate (BSM) in the water. The multiplication of these microorganisms was performed in a biofactory. Fish were distributed into four different groups with graded BSM concentrations in the water of 0.00, 0.25, 0.50, and 0.75% (or 0; 750; 1500; and 2250 mL; called BSM0 (control), BSM25, BSM50, and BSM75, respectively). The experimental procedure had 45 days for growth performance evaluations and seven additional days of bacterial challenge with Aeromonas hydrophila. The experimental design was randomized into four treatments in triplicate (n = 20 fish per tank; initial stocking density of 0.50 kg m−3). Survival was 100% before and after the bacterial challenge. Increasing BSM in the BFT system had a positive linear effect on nitrite, nitrate, settled solids, hemoglobin, and hematimetric indices. BSM50 showed the highest specific growth rate, weight gain, intestinal total bacteria, and B. subtilis counts and the lowest feed conversion rate. In BSM50 and BSM75, liver glycogen levels and aspartate aminotransferase (AST) activity were higher and lower, respectively, than in the other treatments. Plasma total cholesterol, total proteins, albumin, and skin mucus total proteins and albumin were highest in BSM25. After the bacterial challenge, the number of lesions was lower in BSM75 than in the control group. In conclusion, we recommended BSM50 because it increased the growth performance and bacterial colonization in the intestine. It also decreased liver AST activity in Nile tilapia reared in the BFT system without compromising water quality and hematological and plasmatic parameters.

Cumulative mortalities in white leg shrimp, Litopenaeus vannamei Boone 1931, cultured in biofloc system in Egypt reflected new record of Fusarium verticillioides infection

The Egyptian aquaculture sector is still struggling to establish L. vannamei culture. In an effort to stimulate shrimp production with minimal environmental impact and less water loss, biofloc technology (BFT) has been employed. Chronic mortality was recently observed in L. vannamei which was raised in the BFT system. Examining samples of moribund shrimp revealed sporadic melanization on the musculature and gills, suggesting the potential existence of black gill disease. The present work was carried out to isolate and identify potentially implicated fungus species based on mycological properties of interest. To isolate and serve as initial identification tools, wet mount preparations and colonial features, along with slide culture techniques, were used. PCR assays, gene sequencing, and phylogenetic analyses were used in the molecular identification process to clarify the confirmation of the fungal isolates that were acquired. The pathogenicity tests were designed to fulfil Koch’s postulates in addition to clarifying the infectivity of isolated fungus. Moreover, histopathological examination was employed to notice tissues’ alterations associated with experimentally infected shrimp. The results revealed the isolation of three fungal isolates, namely, BNS 1117, BNS 2117, and BNS 3117, that were confirmatively identified as Fusarium verticillioides, and their selected sequences were submitted to Genbank. Moreover, experimental infection using F. verticillioides selected isolate (BNS 31,117) at both high (5 × 105 CFU/mL, group A) and low (3 × 105 CFU/mL, group B) doses of its conidial suspensions experienced cumulative mortality of 72.2% and 21.1%, respectively. Besides, the selected isolate was re-isolated from the experimentally infected shrimp in a pure form, which satisfied Koch’s postulates. Histopathological alterations demonstrated several degrees of either degenerative, oedema, or proliferative changes in the hepatopancreas, musculatures, and gills, respectively. This study sets a new record for F. verticillioides to be included in Fusarium species linked to shrimp mortality.

Enhancing Indoor Culture of Weather Loach (Misgurnus anguillicaudatus) and Caipira Lettuce (Lactuca sativa) in a Decoupled FLOCponics System

Interest in aquaponics (AP) is increasing due to its ability to minimize sewage and maximize feed efficiency in fish farming. However, owing to limitations of intensive cultures and a lack of nutrients such as NO3 for growing crops, AP requires the use of artificial nutrients. Therefore, novel approaches are required to develop AP-intensive culturing methods. An AP system based on biofloc technology (BFT) called FLOCponics (FP) has been recommended. Here, the productivity of the weather loach (Misgurnus anguillicaudatus) in the FP system, BFT system, and flow-through systems (FTSs), as well as these systems’ effect on Caipira lettuce (Lactuca sativa) growth, was analyzed. To compare crop productivity, a hydroponic (HP) bed was installed. The growth rate of M. anguillicaudatus showed significant differences, at 51.1 ± 3.69% in the FP system, followed by 24.0 ± 4.16% in the BFT system and −14.3 ± 1.4% in the FTS. Its survival rates were better in the FP system (91.1 ± 2.64%) than in the BFT system (82.1 ± 10.98%) or the FTS (66.8 ± 2.75%) (p &lt; 0.05). Total ammonia nitrogen and NO2−-N concentrations were stabilized in every plot during the experimental period. However, the NO3−-N concentration continuously increased in the BFT system but decreased in the FP system and was maintained. The shoot weight of the Caipira lettuce was 163.6 ± 8.65 g in the FP system and 149.6 ± 9.05 g in the HP system. In conclusion, FP system can provide a large amount of nutrients and improve the growth performance of both fish and crops in the FP system.

Biofloc technology in aquaculture: Advantages and disadvantages from social and applicability perspectives – a review

Abstract The world aquaculture industry seeks sustainable production strategies to respond to the needs of the growing world population for valuable food. Biofloc technology (BFT) is accepted as a novel sustainable method that reduces the pollution load on receiving water resources with its zero-water-discharge approach, eliminates extra water treatment costs with its biological cycles, and supports the growth performance of reared animals and thereby reduces feed costs. However, each BFT system has its own set of difficulties and obstacles. This review focuses on the advantages and disadvantages of BFT systems in terms of economy, sociability and applicability. The BFT shows more effective results in the conversion of toxic nitrogenous compounds to nontoxic compounds compared with the technologies based on nitrification processes. In addition, the growth performance and health of the cultured animals are generally better in BFT systems than those in conventional rearing systems (continuous water flow). The risk of common diseases occurrence due to pathogenic microorganisms appears to be lower in BFT systems compared to conventional aquaculture. It is also noteworthy that the immune system, biochemical stress indicators and antioxidant activities of organisms held in BFT systems are positively affected. In BFT systems based on microbial activity, the high water temperature demanded by bacteria is a limiter for the system. Moreover, a higher aeration/energy requirement is the case in BFT to meet the oxygen demand of all organisms including fish, shrimp, heterotrophic bacteria, nematodes, rotifers and others inside. There is also another concern about the acceptability potential of the cultured organism in BFT systems for consumption. Finally, since the high temperature demand of the system will create high energy costs, it should be considered as another restriction that forces the application. Considering the advantages and disadvantages of BFT systems as sustainable aquaculture, this review provides a guide for future studies and full-scale implementations.

Carbohydrate addition strategy affects nitrogen dynamics, budget and utilization, and its microbial mechanisms in biofloc-based Penaeus vannamei culture

Biofloc technology (BFT) is a microbial biotechnology that has shown great potential in water quality control and nutrient re-utilization towards sustainable aquaculture. Carbohydrate addition is the main operation means for the application of BFT; however, we are still unclear how it affects microbial-driven nitrogen (N) transformation and utilization in BFT systems. In this study, autotrophic- and heterotrophic-dominated BFT systems (AS vs. HS) in triplicates were operated by two molasses addition strategies for a 13-week production trial of P. vannamei. Throughout the trial, more amount of bioflocs (in terms of VSS) were produced in HS than in AS. Higher concentrations of NH4+-N, NO2−-N, NO3−-N, TIN and TN while lower concentrations of TON were monitored in AS compared to HS. N budget analysis showed that the harvested shrimp deposited >34.4% of input N; and higher N retention in the final culture water while lower N loss and N discharge from the systems were found in AS compared to HS. Higher efficiencies of gross and feed N utilization were achieved in HS (36.6% and 38.8%) than in AS (34.5% and 34.9%). Metagenomic analysis revealed that abundant and diverse N-cycling microbial communities and functional genes in bioflocs constituted a complete and complex N-cycling network, which was the driving force of N transformation and recycling in the culture water of systems. The lower abundances of nitrifying bacteria and associated genes led to the inhibition of nitrification under high molasses addition in HS, which accounted for the differences in N dynamics, budget and utilization efficiency between AS and HS. Together, a quantitative model of N migration and transformation driven by N-cycling microbial communities of bioflocs was depicted in closed BFT systems for shrimp aquaculture. This study firstly revealed the N-cycling microbiome and functional effects in BFT systems, which provides theoretical and technical foundations for efficient N management in intensive aquaculture.

Determination of acute toxicity and evaluation of the chronic effect of nitrate on compensatory growth of Litopenaeus vannamei reared in a biofloc technology system

Understanding the effect of acute and chronic nitrate stress on Litopenaeus vannamei grown in intensive biofloc technology systems is essential for production optimization. The present study evaluated L. vannamei exposed to nitrate extremes at a salinity of 25 g.L−1 measuring survival and possible recovery through compensatory growth. An initial clear-water lethal test, revealed an LC50–96 h for nitrate of 2789.11 mg.L−1. The nitrate safe level was determined as 278.91 mg.L−1by the Sprague Factor (0.1 of the LC50–96 h). Consequently, a chronic exposure experiment was carried out in a Biofloc Technology System. A 3 × 2 experimental design was applied, with two nitrate concentrations (278.91 mg.L−1 and 139.45 mg.L−1) and three “stress” exposure times (10, 20 and 30 days) followed by 48, 38 and 28 days “recovery” time, respectively. A control, in which the nitrate was maintained below 25% of the calculated safe level was maintained for 58 days. The experiment was divided into two phases: (1) stress and (2) recovery. Survival did not differ among treatments during the experimental period. Shrimp exposed to concentrations of 278.91 mg.L−1 and 139.45 mg.L−1of nitrate over 20 and 30 days exhibited reduced growth, while growth of shrimp exposed 10 days did not differ from the control. After the end of the recovery phase (day 58), no significant differences were found in shrimp weights among treatments. Results indicate L. vannamei presents higher resistance to nitrate, but prolonged exposures (>20 days) to concentrations above 139.45 mg.L−1may negatively affect growth rates. However, when lower nitrate values are re-established, the animals exhibit compensatory growth nullifying significant differences to cohort members maintained at optimal nitrate throughout.

Comparative Analysis of the Culture of Pink Shrimp Farfantepenaeus brasiliensis and Pacific White Shrimp Litopenaeus vannamei in Biofloc System

Shrimp farming in the Biofloc Technology System (BFT) is already considered an alternative to the traditional culture. The bioflocs maintain the water quality and can be used as a food supplement for shrimp. The Pacific white shrimp Litopenaeus vannamei forms the basis for most of the production in BFT. However, its culture is limited by the low temperatures. Thus, the BFT culture potential of native species, such as the pink shrimp Farfantepenaeus brasiliensis, should be considered. The present study aimed to compare the cultures of F. brasiliensis and L. vannamei in the grow-out phase in the BFT system. The experiment comprised two treatments: (FB), grown out of F. brasiliensis, and (LV), grown out of L. vannamei. The study lasted 70 days and was conducted at the Marine Station of Aquaculture at the Federal University of Rio Grande, Rio Grande do Sul State, Brazil. The stocking density was 100 shrimp/m² for both species. The shrimp were fed twice a day with commercial food. The physicochemical parameters of the water were monitored throughout the experimental period. The results showed that all physicochemical parameters of the water remained within the tolerated limits for both species. However, during the growth phase in the BFT, it was observed that the L. vannamei shrimp showed a better zootechnical performance than F. brasiliensis. The results indicate that L. vannamei has a higher capacity to catch bioflocs as supplementary food, demonstrating a better response of that species to the BFT system in the grow-out phase compared to F. brasiliensis.

Fermentation of Plant-Based Feeds with Lactobacillus acidophilus Improves the Survival and Intestinal Health of Juvenile Nile Tilapia (Oreochromis niloticus) Reared in a Biofloc System.

This study evaluated the effect of fermentation with Lactobacillus acidophilus on the biochemical and nutritional compositions of a plant-based diet and its effects on the productive performance and intestinal health of juvenile Nile tilapia (Oreochromis niloticus) reared in a biofloc technology (BFT) system. The in vitro kinetics of feed fermentation were studied to determine the L. acidophilus growth and acidification curve through counting the colony-forming units (CFUs) mL-1 and measuring the pH. Physicochemical and bromatological analyses of the feed were also performed. Based on the microbial growth kinetics results, vegetable-based Nile tilapia feeds fermented for 6 (FPB6) and 18 (FPB18) h were evaluated for 60 days. Fermented diets were compared with a positive control diet containing fishmeal (CFM) and a negative control diet without animal protein (CPB). Fermentation with L. acidophilus increased lactic acid bacteria (LAB) count and the soluble protein concentration of the plant-based feed, as well as decreasing the pH (p < 0.05). FPB treatments improved fish survival compared with CPB (p < 0.05). Fermentation increased feed intake but worsened feed efficiency (p < 0.05). The use of fermented feeds increased the LAB count and reduced pathogenic bacteria both in the BFT system's water and in the animals' intestines (p < 0.05). Fermented plant-based feeds showed greater villi (FPB6; FPB18) and higher goblet cell (FPB6) counts relative to the non-fermented plant-based feed, which may indicate improved intestinal health. The results obtained in this study are promising and show the sustainable potential of using fermented plant-based feeds in fish feeding rather than animal protein and, in particular, fishmeal.

Water Quality, Nutritional, Hematological, and Growth Profiles of Ompok pabda Fish Fry Reared in Biofloc Technology and Traditional Culture System with Different Stocking Densities.

The present study evaluated water quality, immune responses, nutritional condition, and production of Ompok pabda fry (0.29-0.31 g) reared in a Biofloc technology (BFT) system (C:N = 20:1; molasses as organic carbon source), compared to the traditional culture system (TS; farmer's practice). The experiment had stocking densities for the treatments of 17 (TS1) and 22 (TS2), 17 (BFTS1), 22 (BFTS2), and 27 (BFTS3) fish/m2. The fishes were fed at 3-10% of their body weight, and reared in cemented tanks for 90 days. Regarding water quality, dissolved oxygen (DO), pH, and total ammonia nitrogen (TAN) levels varied significantly (p < 0.05) between the traditional and BFT tanks. The highest specific growth rate (SGR) was in the BFTS1-reared fishes (4.11 ± 0.17) but the lowest was in the TS2-fish (3.51 ± 0.05). The fish reared in BFT had higher levels of protein, lipids, polyunsaturated fatty acids, essential amino acids, hematocrit, and neutrophil than the fish reared in TS tanks. Moreover, 98.33% survival was recorded in the BFTS1 while 86.67% was in the TS2. The highest BCR was estimated for the BFTS2 (1.22). Taking into account FCR and BCR values, a stocking density of 22 fry/m2 is likely practicable for an O. pabda BFT system.