A review on feed strategy for culture of finfish and shellfish in biofloc technology, recirculating aquaculture system, and recirculating biofloc system

Abstract

Despite growing developments in aquaculture technologies, there is still a lack of clear understanding of the aspects of feeding strategies, nutrient dynamics, and resource-use efficiency between Biofloc Technology (BFT) and Recirculating Aquaculture Systems (RAS). This gap in knowledge limits the utilization of these systems for its full capacity for meeting the rising global demand for fish protein. This review aims to critically analyze and integrate existing knowledge on BFT and RAS, focusing on their roles in nutrient utilization, feeding strategies, water quality management, and overall fish growth performance. The adoption of advanced technologies, such as Biofloc Technology (BFT) and Recirculating Aquaculture System (RAS), in the fisheries sector can significantly improve fish production, thereby compensating for the protein needs of the growing population. The major role of RAS in waste removal and that of BFT in improving nutrient retention would help to accomplish the need for accurate utilization of land and water resources. The feeding strategy in the biofloc system differs from that of semi-intensive culture, where maintaining a proper C/N ratio is necessary. Even though the contribution of biofloc in the daily feeding ratio depends upon cultured fish species, with reported values of 30% for shrimp, 50% for tilapia, and 25% for common carp, it still indicates a favorable effect on growth and survivability. This is primarily due to the superior nutritional profile of biofloc. Biofloc systems are constrained by challenges in maintaining optimal C/N balance and managing excess solids. Meanwhile, in the RAS system, the feeding strategy focuses mainly on achieving energy satiation and maintaining a precise feeding frequency, resulting in reduced feed waste in the tank through the mechanical, chemical, and biological filtration systems. However, RAS involves high capital and operational costs. Therefore, integration of BFT and RAS into a Recirculating Biofloc System (RBS) can offer a synergistic approach that combines efficient waste utilization with advanced filtration, improving system stability, productivity, and can mitigate the risks associated with these two culture systems.

1 Introduction

Aquaculture has steadily flourished over recent decades, playing an increasingly major role in meeting the annual growth in fish production. The major finfish and shellfish species that have been commercially important in global aquaculture include carp, tilapia, catfish, salmon, trout, white leg shrimp, oysters, and clams (FAO, 2024). Fish production has peaked with the culture of these fish species, particularly through semi-intensive and intensive culture methods (Khan et al., 2021). For the development of aquaculture in line with the goals of the blue revolution, it is necessary to adopt intensive fish culture methods and innovative techniques. In the future, this will help enhance fish production and meet the growing food and protein demands of the expanding human population. In view of the increasing demand for fish production in terms of efficiency, sustainability, and high-tech control, various techniques have evolved, including the recirculating aquaculture system, biofloc system, In-pond raceway system, and precision aquaculture using AI (Lal et al., 2024). The RAS and biofloc system can address the primary constraint of fish culture: the scarcity of land and water. The introduction of new, innovative fish culture information to farmers has long been a significant challenge in terms of adoption worldwide (Obiero et al., 2019). Farmers who have entirely depended on the semi-intensive fish culture method initially often show reluctance to adopt this method due to the high investment and associated culture risk. To solve these kinds of problems, one needs to deliver the importance and technique behind the success of these methods using specific models (Obiero et al., 2019). As it’s a common practice in fish culture methods, 60% of the investment in the culture method is allocated to feed (Ragasa et al., 2022). These intensive fish culture methods enable the reduction of feed requirements while promoting better growth and health of fish during the culture period. This review focuses on feed management practices in BFT, RAS, and their integrated form, the Recirculating Biofloc System (RBS), with emphasis on finfish and shellfish culture.

2 Biofloc system: concept and functional aspects

Biofloc technology (BFT) is widely adopted due to its environmental and economic benefits. The adoption of BFT can be seen as a boon for arid and semi-arid areas, where water scarcity demands innovative and resource-efficient purification methods. BFT reduces water exchange and improves water quality by facilitating the assimilation of toxic nitrogenous wastes into protein-dense microbial biomass that acts as a supplementary in situ feed; it effectively lowers the dependency on external feed inputs (Hargreaves, 2013; Khanjani et al., 2023). Khanjani and Sharifinia (2020) reported that BFT absorbs inorganic nitrogen from aquaculture wastewater, improving water quality while producing microbial protein for the animals. This process is an effective way to harness the microbial community to recycle waste. In practice, BFT allows much higher stocking densities with reduced feed costs and enhanced biosecurity (due to minimal effluent discharge) (Khanjani and Sharifinia, 2020; Khanjani et al., 2022). BFT is a potential alternative for sustainable aquaculture and can contribute considerably to meet FAO’s Sustainable Development Goal related to food security (El-Sayed, 2021). Based on the method of waste treatment, BFT can be classified as in-situ or ex-situ. In-situ BFT is the most common method, where bioflocs are formed alongside the cultured animal in the culture environment. In the ex-situ method, effluents are sent to a bioreactor, where bioflocs are generated, then collected and used as feed (Martínez-Córdova et al., 2017; Walker et al., 2020).

Biofloc Technology (BFT) involves the addition of carbon-rich, protein-poor substrates (e.g., molasses, rice bran, tapioca flour) into aquaculture systems to stimulate the proliferation of heterotrophic microbial communities. These microbes assimilate inorganic nitrogenous wastes into microbial biomass, thereby improving water quality and generating in-situ protein source. Maintaining an optimal carbon-to-nitrogen (C/N) ratio, typically above 10:1, is crucial for promoting microbial growth and effective nutrient assimilation (Khanjani and Sharifinia, 2020;Khanjani et al., 2024). Under conventional feeding regimes, only approximately 20-30% of dietary nitrogen is retained in fish biomass, while the remaining 70-80% is excreted into the culture environment, predominantly as ammonia (NH₃⁺) (Hargreaves, 2013). In BFT systems, this excess nitrogen, originating from excreted ammonia, fecal organic matter, and uneaten feed is recycled through microbial assimilation processes. Thus, regulation of the C/N ratio represents a fundamental operational principle of BFT, directly governing nitrogen dynamics and overall system efficiency (Figure 1). This surplus nitrogen, if unaddressed, can lead to the buildup of toxic inorganic nitrogen compounds, including ammonium (NH₄⁺) and nitrite (NO₂^-), which pose significant risks to aquatic health and water quality. To mitigate such toxicity, the Total Ammonium Nitrogen (TAN) concentration in the pond water is routinely monitored. By maintaining a C/N ratio of at least 15:1 through the addition of carbohydrate sources, heterotrophic microbial populations are stimulated to assimilate excess nitrogen, thereby preventing the accumulation of harmful nitrogenous compounds. This microbial conversion not only stabilizes water quality but also contributes to the formation of beneficial biofloc (Figure 2), particularly through the activity of ammonia-assimilating organisms such as bacteria and algae (Joshna et al., 2024).

Figure 1

Figure 2

The resulting biofloc comprises a complex consortium of microorganisms, including heterotrophic/chemoautotrophic bacteria, yeast, zooplankton, phytoplankton, and microalgae, as well as micro- and macroinvertebrates, extracellular polymeric substances (EPS), and conglomerates of particulate organic matter. These bioflocs serve as a valuable in situ supplementary feed within pond systems and can also be harvested, processed, and utilized as a feed ingredient known as ‘biofloc meal’ (Ekasari et al., 2019; Abakari et al., 2022; Khanjani et al., 2023). Biofloc can supply the culturing organism with a wide range of nutrients, including protein, lipid, vitamins, and minerals. The presence of heterotrophic bacteria such as Lactobacillus sp. and Bacillus sp. Biofloc could act as a potential probiotic-like effect for fish. Microbial derivatives contained in the biofloc, such as lipopolysaccharides, peptidoglycans, β-1,3-glucan, and poly-β-hydroxybutyrate (PHB), trigger the host’s immune system, providing immunostimulatory effects and improving the animal’s health status. In addition, biofloc also contains bioactive compounds, including carotenoids, phytoestrogens, bromophenols, vitamins, minerals, and amino sugars. Because of the aforementioned reasons, natural (wet) biofloc mass or dry biofloc meal can be considered as a potential tool to reduce the dietary protein content, a promising alternative protein source (APS) to fish meal, and a practical additive (Khanjani et al., 2023; Sanchez-Muros et al., 2020; Rombenso et al., 2021).

2.1 Role of biofloc technology in immune enhancement, nutrient recycling, and protein-sparing effect

2.1.1 Immunostimulatory effect of biofloc

The health status of fish reared in biofloc is superior to that of other practices, as reflected in a 100% survival rate of fish (Azim and Little, 2008). Many aquaculture practices, unlike RAS, lack standard filtering practices, exposing fish to biological hazards and environmental toxicants that lead to morbidity and mortality during the culture period. Despite this negativity, the biofloc system has achieved a 100% survival rate (Luo et al., 2014; Najdegerami et al., 2016). This high survivability is mainly due to improved immune capacity in fish. Improved immunity in fish is primarily due to two different functional mechanisms of the ingested biofloc microbial community: Poly-beta-hydroxybutyrate (PHB) accumulation and Quorum-sensing mechanism disruption (Crab et al., 2012). Defoirdt et al. (2018) explained that PHB is a bacterial storage compound; chemically, it is a polymer of short-chain fatty acids, mainly 3-hydroxybutyrate, and it has been reported to protect various aquatic animals from bacterial disease. 3-hydroxybutyrate is the dominant short-chain fatty acid, and it decreases the activity of hemolysis, lipase, phospholipase, protease, and swimming motility in bacteria. Research revealed that poly-β-hydroxybutyrate improved the survival of various aquaculture species, including finfish, crustaceans, and mollusks (Figure 3) (Sui et al., 2014; Laranja et al., 2014; Thai et al., 2014; Van Hung et al., 2015; Situmorang et al., 2016; Ludevese-Pascual et al., 2017).

Figure 3

Pathogens communicate with members of the population through quorum sensing (Austin, 2016). This is a gene-regulating mechanism in which bacteria monitor one another’s presence by the production, release, and detection of a small signaling molecule (Camilli and Bassler, 2006). Austin (2016) demonstrated (Figure 4) that the higher the detection of a signaling molecule, the higher the presence of pathogens, thus exhibiting virulence. Three types of quorum-sensing systems are presently based on the signaling molecule: Acylated homoserine lactones (AHLs), Peptides of auto-inducer 1(AI-1), and Auto-inducer 2(AI-2).

Figure 4

Disruption of quorum sensing through several techniques has proved to be an efficient new anti-infective strategy. The methods may involve inhibition of signal molecule biosynthesis, application of quorum-sensing antagonists (including naturally occurring as well as synthetic halogenated furanones, antagonistic quorum-sensing molecules, and undefined exudate of higher plants and algae), chemical inactivation of quorum-sensing signals by oxidized halogen antimicrobial, signal molecule biodegradation by bacterial lactones, and by bacterial and eukaryotic acylases. This involves the application of a quorum-sensing agonist to trigger the host response, as illustrated in Figure 5 (Defoirdt et al., 2004).

Figure 5

The microbial community of a biofloc is still not completely understood, so the various microbes present in the biofloc are involved in disrupting the quorum-sensing mechanism. For example, the inhibition of AHL-mediated quorum sensing, analogues of S-adenosylmethionine (such as S-adenosyl cysteine) are required to inhibit the activity of the Pseudomonas aeruginosa LuxI homolog RhlI by up to 97% (Defoirdt et al., 2004). Hypothetically, these analogues of S-adenosylmethionine may be present in the biofloc microbial community.

In the aquaculture industry, where feed input accounts for the majority of operational costs, it is crucial to find ways to reduce feed costs. Fish meal is one of the most essential and costly ingredients in most aqua feeds. It is considered the ‘gold standard’ of the ingredients because of its high palatability, balanced amino acid (AA) profile, and high content of long-chain polyunsaturated fatty acids (LC-PUFA) (Glencross et al., 2007; Turchini et al., 2019; Glencross et al., 2020). However, the dependency on pelagic fish to produce fish meal and fish oil has a drastic impact on marine resources and the food chain in the seas (Naylor et al., 2021). It’s essential to find alternative protein sources to spare fish meal, thereby reducing both the stress on marine resources and the cost of feeding in aquaculture (Kok et al., 2020; Naylor et al., 2021). Due to the presence of fairly well-nourished nutrients, bioactive compounds, and potential probiotics, biofloc meal (BFM) can serve as a potential alternative to conventional fish meal usage.

2.1.2 Nutritional profile of biofloc

The biochemical composition of biofloc is not always the same; factors such as the species cultured, type of carbon source used, carbon to nitrogen ratio, light and aeration intensity, water quality parameters such as temperature, dissolved oxygen, and salinity have been found to affect the nutrients available in the biofloc (De Schryver et al., 2008; Widanarni et al., 2012; Ekasari et al., 2014; Martínez-Córdova et al., 2015; Dauda, 2020). From the available literature, we found a wide variation in the total protein (1.18 to 53.65%), lipid (0.33 to 24.33%), and ash (3 to 61.70%) levels of the biofloc (Khanjani et al., 2023) (Tables 1, 2, 3, 4). The nutritional composition of biofloc has been considered to sufficiently meet the requirements of some aquaculture species, including shrimp (Ekasari et al., 2014; Kuhn et al., 2010), crucian carp (Wang et al., 2015), tiger shrimp (Anand et al., 2014), rohu (Kheti et al., 2017), and sea cucumber (Chen et al., 2018). BFM-based diets exhibit more or less similar feed conversion efficiency, weight gain, and survival rate, even though BFM inclusion in aquafeed at higher levels can impact the palatability and digestibility (Kuhn et al., 2010; Promthale et al., 2019).

Ekasari et al. (2014) noted that based on the essential amino acids index, biofloc originating from a shrimp culture unit could be considered as a good protein source for shrimp. In comparison, Kuhn et al. (2016) reported that biofloc meal generated from confectionery food effluent water could be used to replace soybean meal and fishmeal in shrimp diet up to 20% and 30%, respectively. Tilapia and shrimp in BFT grow better than in traditional systems, with studies showing 50–80% biomass increases in larval shrimp and similar productivity boosts in tilapia (Raza et al., 2024; Khanjani et al., 2022). Moreover, dietary inclusion of biofloc meal has been reported to confer some positive effects on the health status of the target species (Chen et al., 2018), thus increasing the potential use of biofloc meal as a feed raw material. This biofloc meal has a positive effect on fish growth performance, feed utilization, and health status of the fish (Ekasari et al., 2019).

The data in Tables 2-4 indicate that the nutritional composition of biofloc varies across cases. These are influenced by species, carbon source (like molasses), and the C: N ratio used in the system. Biofloc is also rich in saturated (SFA) and monounsaturated fatty acids (MUFA), with variable levels of essential fatty acids such as EPA and DHA. Systems using molasses as a carbon source and with higher C: N ratios showed better PUFA content. The biofloc also contains a balanced essential amino acid profile; hence, biofloc can act as a supplementary protein source and can reduce feed cost. Biofloc is also rich in macro- and micro-minerals such as calcium, phosphorus, magnesium, and iron, which are essential for fish growth, bone development, and metabolic functions.

2.1.3 Protein-sparing role of biofloc

Identifying cost-effective, high-value alternative protein sources to replace fish meal (FM) in aquafeeds remains a key objective for nutritionists aiming to support the sustainable development of the aquaculture industry. In biofloc systems, as the in-situ microbial biomass contains significant amounts of protein, it is possible to reduce dietary protein inclusion, thereby reducing feed costs (Khanjani et al., 2023). Azim and Little (2008) found, in their experiment on juvenile Nile tilapia reared in BFT, that dietary protein content could be reduced by up to 11% without affecting growth. They maintained precise water control with a 35% CP feed and two biofloc treatments using 35% and 24% CP feed. They recorded 45% higher net fish production in BFT tanks than in precise water control. This suggests that the microbial protein available in the water column enhances the feed conversion ratio. There was no significant difference in growth performance between BFT tanks fed 35% and 24% CP. Hence, this study suggests a considerable reduction in the CP levels of the feed without affecting the production.

Adineh et al. (2025) experimented with dietary protein levels and feeding ratios in common carp. Based on the growth performance, digestive enzyme activities, antioxidant status and immunological responses, it was concluded to reduce dietary protein from 35% to 25% and daily feeding rate from 3% to 2% BW simultaneously in the biofloc system for common carp. Similarly, Sgnaulin et al. (2018) suggested that dietary protein can be reduced from 27% to 22% CP without affecting growth performance in Pacu fish. Adineh et al. (2023) also reported that microbial proteins in bioflocs can compensate for a 10% protein decrease in Caspian roach fry diets. Hence, in practical culture systems, such as biofloc-based systems, it’s important to consider natural production when designing feed. Using high-protein feeds may be inefficient (Zhao et al., 2021).

2.2 Feeding strategy for finfish and shellfish in biofloc technology

2.2.1 Shellfish feeding strategy in biofloc

Shrimps and prawns are the most suitable candidate species for BFT, due to their omnivorous feeding behavior, high tolerance to dissolved solids, biological distribution, and commercial importance. Publications related to shrimp biofloc technology contribute more than 40% to aquaculture (El-Sayed, 2021). Suitable shellfish species for BFT include Litopenaeus vannamei, Penaeus monodon, Fenneropenaeus paulensis, Fenneropenaeus brasiliensis, Fenneropenaeus setiferus, and Macrobrachium rosenbergii (Emerenciano et al., 2013). Several feeding strategies for shrimp production using biofloc technology (BFT) have been tested and found to be effective. The strategies emphasize reducing environmental impact, improving feed efficiency, and lowering costs, while maintaining or enhancing shrimp health and growth performance.

2.2.1.1 Shrimp feeding rate optimization in biofloc systems

Biofloc used in shrimp aquaculture provides natural food, thereby minimizing the dependency on commercial feed. However, the extent to which biofloc can alter the feeding rate is not fully understood. Weldon et al. (2021) conducted a study to optimize the feeding rate for shrimp in a biofloc system. They tested feeding rates from 30% to 150% of the amount offered four times per day. In 30%, 60%, and 90% feeding rate treatments, approximately 17% of the total shrimp biomass gain is contributed by biofloc consumption, which implies that the shrimp in the biofloc unit need notably less artificial feed under optimized conditions, as they derive significant nutrients from the biofloc community. The same study also concludes that feeding just below 101% of the standard feeding rate maximized feed conversion efficiency, growth and survival rates. Beyond this point, FCR increased, and growth gains diminished, signaling inefficiencies due to overfeeding. Emerenciano et al. (2012) suggested a reduction of feeding rate from 8% to 2.5% in grow-out culture under BFT using feed containing 45% CP. Furthermore, Kusmiatun et al. (2024) investigated the impact of reducing feeding rates on the growth performance of Litopenaeus vannamei. A 25% reduction in feeding rate showed improved feed utilization, with a lower feed conversion ratio and higher protein retention in shrimp reared under a biofloc system.

Bajracharya et al. (2025) studied the effect of varying dietary protein and feeding rates on the performance of white leg shrimp in a biofloc system. Feeding lower protein diets at higher rations (25% and 30% CP at 140% and 116.7% of the standard ration, respectively) did not lead to significant growth improvements. Still, it resulted in a higher FCR, indicating potential overfeeding. This finding demonstrated that shrimp raised in the biofloc system performed better in terms of growth and feed utilization as protein intake increased. The shrimp fed with a 40% CP diet at 100% standard ration had the better growth performance with lower FCR.

2.2.1.2 Use of biofloc meal in diets

In-situ biofloc can be directly consumed by animals, and excessive production can be harvested and processed to produce biofloc meal. Dried biofloc contains protein levels that have shown promise as a partial substitute for fishmeal (Khanjani et al., 2023). A study was conducted to determine the optimal biofloc inclusion in L. vannamei diets. 0% to 40% of inclusion levels were tested by feeding them 10% of their body weight four times a day. A 30% inclusion of biofloc meal in shrimp feed is optimal for growth, immune performance, and digestive enzyme activity. Higher or lower levels than this resulted in suboptimal outcomes (Nethaji et al., 2022). Ekasari et al. (2019) also reported, from their experiment on L. vannamei, that a 30% inclusion of biofloc meal in the diets improved survival, specific growth rates, and feed efficiency compared to the control, which was fed a FM-rich diet. According to Khanjani et al. (2022), wet biofloc can substitute up to 50% of commercial feed without affecting the ability of banana shrimp postlarvae to grow, survive, or produce high-quality carcasses. Biofloc meal contains beneficial bioactive compounds, including carotenoids, chlorophyll, and vitamins, enhancing immunity and resistance to infections in L. vannamei (Khanjani et al., 2023). Biofloc meal is a promising feed ingredient for low-salinity aquaculture systems due to its mineral content, which is especially advantageous in these environments. Its inclusion in diets in oligohaline environments enhances nitrate resistance without affecting L. vannamei development, leading to ion enrichment in the culture water (Rosas et al., 2025).

When BFT is used alone, after production reaches approximately ten metric tons per pond, the sludge must be removed. Whereas the Recirculating Biofloc System (RBS), which integrates BFT with water recirculation, is an effective solution, with no such risk, and significantly enhances survivability and overall production.

2.2.2 Finfish feeding strategy

Finfish, such as tilapia, hybrid bass, and common carp, are suitable for BFT due to their feeding behavior high tolerance to solid concentration (except hybrid bass), and commercial importance (Hargreaves, 2013). The overall maintenance principle is the same as that of the shellfish but differs in the maintenance range of TSS and settlement solids. In many of the research studies, it was reported that the fingerling size of fish is suitable for BFT (García-Ríos et al., 2019).

2.2.2.1 Fish feeding rate optimization in biofloc systems

Fish performance and production costs are influenced by feeding rate, making it a crucial aspect in aquaculture. Najdegerami et al. (2016), from their experiment on common carp of average weight 58.6 ± 0.2g, in grow-out culture using feed of 35% CP, found that feeding only 75% of the daily ration, along with in-situ biofloc consumption, resulted in better growth with low FCR, high SGR, and zero mortality rate compared to other feeding rations. The stocking density of the experiment was set at 25.4 kg/m³. A similar kind of result was obtained in tilapia, when tilapia of 32g initial weight were cultivated in biofloc with a C: N ratio of 6:1. It was proven that a feeding rate of 75% in relation to apparent satiety is good for better utilization of protein, and this did not alter the protein content of the floc. Feeding up to 100% satiation in a biofloc setup may not be profitable as it results in a higher feed conversion ratio and a reduction in water quality. Twice daily feeding at a 75% feeding rate with 36% crude protein is recommended for tilapia in BFT (da Silva et al., 2020).

According to Villes et al. (2024), the feeding rate influenced the oxidative parameters in the biofloc system. Tilapia reared at lower feeding rates (4%) consumed more biofloc and phenolic compounds, leading to decreased levels of lipoperoxidation caused by reactive species (RS). Hence, 4% feeding rate was recommended for improving the health of aquatic organisms by reducing oxidative stress in biofloc. Aliabad et al. (2022) reported that water quality, growth indices, and immune status were improved in tilapia cultured in biofloc compared to a clear water system. They further stated that it is possible to reduce the feeding ration by 15 per cent without affecting the growth performance of the fish.

2.2.2.2 Use of biofloc meal in diets

Dietary incorporation of biofloc meal (BM) has demonstrated considerable potential to partially replace fish meal (FM) in finfish diets without compromising performance. For instance, up to 30–50% replacement of FM with BM can be achieved without adverse effects on growth (Khanjani et al., 2023). Similarly, Durigon et al. (2024) evaluated graded inclusion levels of BM (0, 4, 8, 12, and 16%) in tilapia diets and reported that 4% inclusion yielded better growth performance, along with improved hematological and oxidative stress parameters.

In another study, Padhan and Athithan (2024) reported that 20% inclusion of BM in the diet of Rohu fingerlings improves growth, feed consumption, body composition, and digestibility. Wei et al. (2024), in their experiment on Cyprinus carpio (common carp), found that a 40% replacement of FM by BFM had a positive impact on growth, immunity, and protein metabolism. They also reported that the exact replacement thresholds were species- and system-dependent. Furthermore, Khanjani et al. (2024) observed that wet biofloc could substitute up to 25% of commercial feed in Nile tilapia diets without negatively affecting growth, survival, body composition, digestive and hepatic enzyme activities, or mucosal immunity. Supporting these findings, Romano et al. (2025) reported a significant improvement in the growth performance of red drum when 25% of FM was replaced with BM supplemented with an amino acid mixture. Overall, the inclusion of BM in aquafeeds has not only proven to improve sustainable production but also contributes to reducing feed costs. The effect of BM-based diets on cultured finfish and shellfish is summarized in Tables 5 and 6.

The reviewed papers consistently report BFT’s potential to improve sustainability (e.g., lower FCR, higher yield, better water reuse); they also note obstacles such as energy use, monitoring needs, and environmental variability. Another primary concern is the risk of diseases, as newly established biofloc systems may harbor pathogens, requiring vigilant biosecurity and microbial management. A recurring issue with BFT is the high energy demand and management costs, as it requires intensive aeration and mixing to keep flocs suspended and oxygenated, which increases costs and maintenance needs. Water quality in BFT can be challenging to control; even minor changes in carbon-to-nitrogen ratios or environmental conditions can significantly impact ammonia, nitrite, pH, and suspended solids. Thus, BFT needs sharp supervision to be successful (Raza et al., 2024; Khanjani et al., 2024).

2.3 Limitations and practical challenges in biofloc system implementation

Despite the many advantages of the Biofloc System, its practical implementation presents several challenges. The produced biofloc tends to settle easily in calm water, as the optimal positioning of aerators in the system is still not well established; inadequate aeration reduces turbulence, leading to floc accumulation and enlargement, which may cause gill blockage in fish (Shivkumar et al., 2022). Maintaining proper turbulence is therefore critical, as insufficient mixing results in floc settling, whereas excessive agitation can induce stress in cultured fish (Avnimelech, 1999; Hargreaves, 2013). Continuous nitrification throughout the culture period leads to nitrate accumulation, which may adversely affect fish health under low water-exchange conditions (Crab et al., 2012; Emerenciano et al., 2011). Furthermore, increasing organic load during the culture period can cause abrupt ecological shifts; high algal density reduces light penetration, thereby limiting photosynthesis and increasing biochemical oxygen demand (BOD) (Hargreaves, 2013). The lack of standardized guidelines for optimal aerator placement further contributes to inconsistencies in system performance (Tucker and Hargreaves, 2008). Additionally, extended light exposure may promote excessive algal growth, disrupting microbial balance and overall system stability (Emerenciano et al., 2011).

3 Recirculatory aquaculture system: concept and functional aspects

Currently, the majority (63%) of global aquaculture production occurs in freshwater systems, which are facing escalating pressure from intensified land and water use, pollution, and climate change. This has consequent effects on freshwater biodiversity and ecosystem services, including aquaculture itself. Hence, there is a significant opportunity to boost aquaculture production of both freshwater and seawater species through the use of recirculating aquaculture systems (RAS) (Brown et al., 2025). Recirculating Aquaculture Systems (RAS) are intensive, typically indoor tank-based systems that achieve higher water reuse rates through mechanical, chemical, and biological filtration, as well as additional treatment processes. RAS technology can be beneficial where ideal sites are scarce or of limited availability, or where quality is lacking (such as in the case of land or water). It is also applicable in situations where enhanced management of effluent streams and biosecurity measures (such as pathogen exclusion and/or germplasm retention) are required to comply with environmental norms and regulations. These systems also offer market benefits, such as enhanced capacity to align seasonal supply with demand, situate production near consumer and processing hubs, and bolster traceability and consumer confidence.

3.1 Recirculatory aquaculture system components

RAS is an interdisciplinary engineering approach that combines biology, mechanical engineering, hydrochemistry, hydromechanics, electrical engineering, and aquaculture science. It recycles and purifies water used in aquaculture through a sequence of treatment processes. In conventional aquaculture, the major limitation is the improper disposal management of fish excretory waste, which is challenging to separate from the culture area. Accumulating waste inside the production unit creates an unfavorable environment that hinders fish growth. Meanwhile, the release of wastewater into natural water bodies will cause eutrophication in the aquatic ecosystems. Thus, RAS is an emerging technique known globally for its ability to help maintain water quality (TSS, TS, Ammonia, Nitrate) and uniform water temperature. RAS is equipped with mechanical filtration, biological filtration, foam fractionation, UV disinfection, ozone filtration, degassing units, and an oxygen dissolver, as shown in Figure 6.

Figure 6

During the culture period, in the culture system, many unwanted materials accumulate, such as uneaten feed, fecal matter, slime, and fish scales. Increasing load of these matters may choke the fish gills and develop bacteria to digest the detritus, leading to depletion of water oxygen and an increase in biological oxygen demand in culture systems. There are two varied filtration methods, such as mechanical and physical methods. In mechanical methods, the suspended organic and inorganic wastes are allowed to settle by means of gravity, and solids collect from the lower part of the culture system. The physical methods involve partitioning of waste and water, which is accompanied by forcing water to pass through the screen or media, for example, drum filter, screen filter, Sand filter (Ranjan et al., 2022).

All the organic matter is not possible to remove out using mechanical filters; some smaller particles are dissolved together with phosphate and nitrogen. Phosphate is an inert substance, so no toxic effect, but the nitrogen in its ammonia form is toxic to fish. The biofilters function to convert this toxic form of nitrogen to a non-toxic form. There are different types of biofilters used for this process, like trickling filter, Fluidized bed reactor, rotating biological contractor, and submerged filters, etc (Ranjan et al., 2022).

The degassing unit and aeration system have a vital role in the RAS system. As the carbon dioxide produced in the system due to fish respiration and/or by the bacterial activity and nitrogen gas produced due to the process of nitrification, these gases are harmful for fish growth and well-being, so before water reaches the fish tank after passing through the series of filtration units, it’s necessary to remove the gases using a degassing unit (Ranjan et al., 2022).

It is necessary to understand that bacteria can grow easily on organic matter, so after a series of filtrations, it’s necessary to destroy the microorganisms. For that, the UV disinfection works better by passing a light wavelength to destroy the DNA of biological organisms. As UV disinfection only comes in contact with water, there is no harm to fish. To effectively control microbial contaminants, water must be exposed to appropriate levels of treatment energy. A dose in the range of 2000–10,000 µWs/cm² is generally sufficient to inactivate about 90% of bacteria and viruses. In contrast, fungi require higher exposure levels, typically between 10,000 and 100,000 µWs/cm², while small parasitic organisms demand even greater doses, ranging from 50,000 to 200,000 µWs/cm² for effective reduction (Ranjan et al., 2022).

3.2 Feeding strategy for finfish and shellfish reared in RAS

In intensive aquaculture, feeding accounts for about 60% of overall production expenses. The goals of optimal feed management include avoiding overfeeding, reducing waste, and improving the efficiency of fish production (Pěnka et al., 2023). Feed management primarily influences fish survival, growth, welfare, feed utilization, and production cost. These aspects include daily feed intake, feeding rate and time, and feeding technique. To optimize the performance of cultured animals, reduce expenses, and increase efficiency, precise feeding should be used in RAS in accordance with the feeding habits of various species. Improving the FCR will have a significant positive impact on production efficiency, as fish will gain more weight per kilogram of feed used, and the load on mechanical and biological filters in the RAS will be reduced. Feeding frequency not only affects food conversion rates and fish performance, but also aquaculture water quality. Feeding frequency causes fluctuations in water quality, thus directly affecting the efficiency of the biofilter. Improper feeding can lead to the accumulation of waste and increase the levels of ammonia and nitrite in the water (Guo et al., 2025).

Several factors, including biological suitability for intensive culture, market demand, growth rate, disease resistance, water quality tolerance, availability of seed, feed requirements, operational costs, and adherence to regulatory and sustainability standards, influence the selection of species in RAS. Nowadays, RAS is widely adopted globally, with at least 46 fish species, 11 crustacean species, seven mollusk species, and seven echinoderm species successfully reared in these systems (Viet et al., 2025). Most commercially important species, such as tilapia, rainbow trout, Arctic charr, barramundi, pangasius, and hybrid striped bass, are among the top choices for RAS due to their adaptability, growth performance, and market value. The fry and fingerling stage is the most preferred because “the lower the fish size, the faster the growth rate.” Species such as Atlantic salmon, tilapia, trout, carp, eel, grouper, sturgeon, arctic char, sea bass, freshwater catfish, perch, turbot, cobia, cod, and shrimp are all suitable for RAS systems, as shown in Figure 7, described by Bregnballe (2015).

Figure 7

3.2.1 Finfish feeding strategy

The RAS system is fabricated and equipped with various filters as a preliminary step, followed by maintaining a uniform water flow with the required dissolved oxygen levels. The fish (fry/fingerling) are stocked, based on the tank size, fish species, and size. Feeding in RAS is managed in accordance with the species-specific feeding behavior of fish under culture. Feed is dispersed into the water column, allowing fish sufficient time to consume it; any uneaten feed remaining after 30 minutes is removed, and feeding rates are adjusted accordingly. In general, a feeding frequency of 3–4 times per day is considered optimal practice in RAS. The major challenge of RAS is the removal of the accumulated waste (uneaten feed and feces) within the system. An RAS-adapted diet can also significantly reduce the environmental impact of the aquaculture sector by lowering N and P emissions, thereby bringing overall emission levels closer to those of the Norwegian industry as a whole. Dietary adaptation to the production system and technology is clearly one of the most critical factors in lowering local pollution and ensuring the aquaculture industry’s long-term, sustainable growth. In addition to strengthening fecal stability and increasing particle size, diet modification increases the binding of N and P to the feces, making it easier to remove them from the system (Flo et al., 2024).

Luo et al. (2014) reported that a feeding rate of 2% body weight (BW) yielded better results in tilapia than the standard feeding rate in intensive or semi-intensive culture. Sun et al. (2016) observed that the salmon fed with a commercial diet composed of 47% crude protein and 17% Crude lipid at a feeding rate of 1.6% of BW was considered ideal in the RAS system, with experimental evidence of better growth. Generally, four meals per day were considered suitable for salmon for better growth with increased SGR and less FCR, as collectively shown in Table 6. Throughout the experiment, water quality was maintained with TSS <500mg/l, DO is >6mg/l, the temperature was maintained at 24-26 °C (For salmon, 16 ± 0.3 °C), pH 7.0-7.5, Nitrate-N 70-100mg/l, Nitrite-N is <0.97mg/l, and Ammonia is 0.4-0.5mg/l for better growth of the fish.

Pink ear emperor (Lethrinus lentjan) broodstock was fed fresh, cleaned sardines, mackerel, and anchovies twice daily at a rate of 3–4% of their body weight. In addition to vitamin C and vitamin E tablets once a week, fresh squid was provided three times a week. Additionally, fish were given compounded semi-moist feed (protein −40%, fat −9.5%, fiber −2%, and moisture −31%) on an ad libitum basis which proved that Lethrinus larvae could be reared to seed size with reasonable level of survival rate in 40–50 days with feeding and water quality management practices in RAS (Anil et al., 2019). Male and female broodstock weighing more than 1.5 kg is the ideal size for successful captive breeding and hatchery production of high-quality larvae in the case of wild-caught silver pompano in RAS (Gop et al., 2024). In pikeperch intensive aquaculture, the automatic feeding method has generally proven beneficial, as the fish have become accustomed to utilizing the feeders. This was the first experiment to produce percid fish in RAS using automatic feeding systems (Pěnka et al., 2023). In comparison to animals fed continuously for 56 days, juveniles of Colossoma macropomum that were subjected to feed restriction for one day per week maintained their body reserves and hematological and biochemical variables (except for triglycerides at 56 days) unchanged and performed well. But, due to the enormous diversity, periodic weight classifications are advised for the production of this species in RAS, as the animals are primarily obtained at the conclusion of the experimental period (56 days) (Assis et al., 2020). A study was conducted to evaluate the different feeding methods such as self-feeder systems (free choice to eat); apparent satiation twice daily (09:00 h and 17:00 h); apparent satiation 3 times per day (09:00 h, 12:00 h and 17:00 h) and at fixed rates (2% BW per day) twice daily in Arapaima gigas and reported that the self-feeding method can be used without compromising growth and survival (Pedrosa et al., 2019). Some of the finfish reared under the RAS system are explained in Table 7.

As discussed earlier, globally, the commercially important fish species under culture in RAS are Tilapia, hybrid striped bass, Barramundi/Asian seabass, Rainbow trout, Sturgeon, and yellow perch. In India, the species of importance under RAS are Asian seabass, Tilapia, pearl spot/Karimeen, Pangasius, and trout. Besides these, other species, such as cobia, Indian pompano, and catfish, are also being explored in RAS for their commercial potential. Manual feeding, adjusting the feeding rate based on biomass/bodyweight, scheduling feeding frequencies, and providing complete formulated diets are some of the conventional strategies employed in the feed management of RAS. However, over the past few years, there has been significant advancement in the adoption and operation of RAS in terms of feed management, water quality management, and species selection.

Since 2020, advancements in RAS have been made by focusing on integrating cutting-edge technology, precision, and sustainability, which includes Artificial intelligence, machine learning, intelligent and automated feeding systems, and behavior-based and predictive feeding. AI methods, such as deep learning, genetic algorithms, and machine learning, have been utilized to develop models that predict growth trajectories, identify optimal environmental conditions, and optimize feeding strategies. By examining past growth data, these artificial intelligence models can learn and adjust to enhance ecological monitoring, feed management, and water quality control, ultimately improving growth performance and resource efficiency (Mandal and Ghosh, 2024).

3.2 Shellfish feeding strategy in RAS

In the world’s fisheries production, the contribution of shellfish plays a very significant role. Among shrimp, L. vannamei is currently considered an important species. Lin et al. (2003) conducted an 80-day experiment to investigate the functionality and efficiency of the RAS system in fish production, using a stocking density of 200 PL/m² (individual weight: 5-6mg). During the initial 4 weeks, the PL was fed a commercial powder feed and later switched to a pellet diet. The commercial feed is composed of 45% CP 2% fat. The feeding rate was fixed at 3-5% based on observed feeding behavior, and two feedings per day were maintained with whole light to improve feed utilization. Throughout the experimental period, the water quality parameters, including DO > 3 mg/L, SS 26 mg/L, nitrite-N 0.013 mg/L, nitrate-N 0.39 mg/L, and ammonia < 0.5 mg/L, were maintained. The amount of feed given to shrimp is dependent on their body weight. During days 1 to 30, the daily feeding amount should account for approximately 7–10% of their body weight, while during days 31 to 60, it should be reduced to 5–7%. In the later stage, the feeding amount should be further reduced to 3–5% of their body weight (Sun et al., 2023). An indicus pellet feed (CIBA, Indicus plus) containing 35% of crude protein (CP) was used to feed Penaeus indicus PL at 10 to 12% of body weight without any water exchange for a period of 60 days in different systems, notably the RAS, hybrid system with RAS and biofloc, and RAS with a biofloc-enriched rotifer system, and concluded that the growth and production of the Penaeus indicus were higher in the RAS with a biofloc-enriched rotifer system. Blue swimming crabs showed improved weight gain, SGR (%), PER, FER, and growth of carapace length when fed with a squid diet than the crabs fed with scad fish and acetes shrimp in the RAS system (Kohinoor et al., 2018). Kohinoor et al. (2019) observed that when the first crab instars were fed at 15% body weight with shrimp pellet feeds No. 5002 (C.P. Aquaculture Private Limited) twice a day, the blue swimming crabs showed better growth, which is expressed in terms of carapace width or length. As it’s an experiment focused on the maintenance of water quality of RAS, a low amount of ammonia and other harmful nitrogenous compounds in the water had a positive effect on the health, feeding efficiencies, and growth performance of the crab, which was mainly attributed to the combined treatment by the biological filter, as compared to the conventional culture systems. Usman et al. (2024) reported the possibility of mud crab fattening through the inclusion of different types of feeds such as beef liver, squid, clam meat, and tilapia fish in the RAS system without influencing the water quality parameters and growth. The development of larval production in RAS for bivalves proved efficient in yielding Perna larvae that are able to settle, and it represents a viable alternative for obtaining young forms more sustainably than in static models (Silveira et al., 2023). When casein and fishmeal were used as the main protein sources, the optimal dietary protein requirement for Marsupenaeus japonicus fed in RAS was 46.13%. Additionally, the findings indicated that raising protein levels by up to 50% could improve the diversity of the intestinal microbiome (Meng et al., 2025). If P. vannamei PL are cultivated in clear-water RAS without natural productivity, a high-protein aquafeed during the nursery phase is necessary because inert diets are the only source of nutrients in this kind of system of production. Additionally, they imply that the shrimp PL protein requirements in clear-water farming might not be met by feeds that perform well in semi-intensive or biofloc systems. When designing micro diets for the nursery phase of white leg shrimp PL grown in clear-water RAS, it is recommended to include at least 47% protein, as this is ideal for weight gain and survival. Furthermore, findings suggest that protein inclusion levels of up to 54% may also appear to enhance the general antioxidant status of PL white leg shrimp (Barreto et al., 2023). Therefore, it is necessary to improve the feeding management of the species under culture to enhance system production, particularly in RAS. A comparison of production under semi-intensive culture and RAS systems is shown in Table 8.

3.3 Limitations and practical challenges in RAS implementation

The primary constraint of Recirculating Aquaculture Systems (RAS) is the substantial initial capital investment, which often discourages farmers from adopting this technology. The establishment of RAS requires significant financial input for specialized equipment, infrastructure development, influent and effluent treatment units, system engineering, construction, and operational management. In addition, suboptimal system design, particularly improper selection and integration of mechanical and biological components, can compromise system efficiency. Malfunction or inadequate performance of the biofilter may result in the accumulation of toxic nitrogenous compounds such as ammonia and nitrite, posing serious risks to fish health (Balami, 2021). Therefore, continuous technical monitoring is essential to ensure system stability.

Furthermore, the limited availability of skilled personnel throughout the culture period presents a major operational challenge, especially for maintaining equipment and managing water quality (Badiola et al., 2012). Low water exchange RAS are also more susceptible to disease outbreaks compared to high water exchange systems, such as flow-through systems (Good et al., 2009). The reuse of water in RAS facilitates the persistence of pathogens within the system, particularly within biofilms, leading to repeated exposure of cultured organisms and the potential development of asymptomatic carriers (Balami, 2021).

4 Recirculating biofloc system: concept and functional aspects

The RBS is a hybrid aquaculture system that integrates Recirculating Aquaculture Systems (RAS) and Biofloc Technology (BFT) to optimize water use, nutrient recycling, and productivity. In RAS, water is filtered both mechanically and biologically, and then reused, whereas BFT utilizes a heterotrophic microbial community to assimilate nitrogenous waste (mainly ammonia) into microbial biomass. By combining these systems, RBS maintains superior water quality while simultaneously providing a natural feed source from microbial bioflocs. This dual mechanism supports intensive aquaculture with reduced environmental discharge (Figure 8). RBS covers the snags of the biofloc system, making it a potential system to overcome the disadvantages of the biofloc system (Shivkumar et al., 2022).

Figure 8

In RBS, water from fish or shrimp tanks is continuously recirculated through filters (mechanical, biological, UV, etc.). Simultaneously, carbon sources (e.g., molasses, starch) are added to manipulate the C: N ratio in favor of heterotrophic bacterial growth, which converts toxic nitrogenous wastes into microbial biomass (bioflocs). These flocs are suspended in water by constant aeration and water movement. In systems like these, zero or minimal water exchange is practiced, and the microbial community both cleans the water and acts as a nutritional supplement for the cultured species. A general comparison of RBS with RAS and biofloc systems is shown in Table 9.

4.1 The advent of RBS

The development of RBS stems from the challenges of conventional aquaculture, such as water pollution, disease outbreaks, high feed costs, and low biosecurity. Intensive systems generate excessive nitrogenous waste that, when discharged untreated, leads to environmental degradation. Furthermore, frequent water exchange introduces pathogens. RBS was developed to retain water quality, reduce dependence on water exchange, and enhance biosecurity. It also supports sustainable intensification, allowing more production per unit area without compromising environmental integrity.

One of the core strengths of RBS is its ability to maintain water quality over extended periods of time. The microbial flocs assimilate ammonia, nitrite, and nitrate, reducing the need for frequent water exchanges. This biological waste management approach is supported by biofilters that handle residual waste through a process known as nitrification. Research by Hargreaves (2013) indicates that biofloc systems maintain lower ammonia and nitrite levels, while recirculation ensures stable dissolved oxygen and pH levels, both of which are critical for the health of fish and shrimp. Bioflocs provide supplemental nutrition rich in proteins, lipids, and microbial enzymes, leading to improved digestion and feed conversion efficiency. The microbial protein acts as a functional feed, boosting immunity and digestion. A study by Xu and Pan (2013) showed that Litopenaeus vannamei cultured in RBS had FCR values improved from 1.5 to 1.2, alongside enhanced immunity markers. In tilapia, growth performance and protein efficiency ratios were significantly better under RBS compared to traditional systems.

RBS has demonstrated excellent results in species such as tilapia (Oreochromis niloticus), pacu (Piaractus brachypomus), catfish (Clarias spp.), and shrimp (L. vannamei). For instance, Martins et al. (2017) reported that Nile tilapia raised in RBS achieved 30% higher growth rates and improved survival, with final weights significantly higher than those of fish raised in static systems. In shrimp, Emerenciano et al. (2013) found that RBS resulted in improved survival, reduced pathogen load, and enhanced feed efficiency, even at higher stocking densities. RBS improves fish and shrimp immunity by exposing them to beneficial microbial communities. This constant, low-level microbial exposure acts like an immune training mechanism. Shrimp and fish cultured under RBS show higher activity of lysozyme, catalase, and superoxide dismutase, all key immune markers. According to Ferreira et al. (2016), RBS-raised tilapia exhibited fewer incidences of bacterial infections, and when challenged with Aeromonas hydrophila, mortality was 60% lower than in the control group.

While RBS demands higher initial capital for filtration, aeration, and monitoring systems, its long-term economic returns are superior due to reduced water usage, lower feed costs, and improved survival rates. Studies have shown that biofloc feed supplementation can reduce formulated feed costs by up to 20%. The use of local carbon sources, such as jaggery or cassava starch, also reduces input costs. Additionally, the near-zero discharge characteristic of RBS aligns with environmental compliance norms, adding to long-term sustainability.

Comparative trials by Ray and Lotz (2017) on shrimp showed that traditional pond systems had FCRs of 1.8–2.2, whereas biofloc-RAS hybrids achieved FCRs between 1.1–1.4, with final biomass up to 40% higher. Similarly, fish raised in RBS systems show improved feed utilization efficiency due to the availability of live microbial biomass, which also improves gut health and nutrient absorption through in-situ probiotic effect. These studies highlight that the synergy between biofloc and recirculating systems optimizes nutrient conversion and enhances profitability. In summary, the Recirculating Biofloc System is a technologically advanced and ecologically responsible solution to intensive aquaculture. By merging the best of BFT and RAS, RBS enhances water quality, feed utilization, animal health, and sustainability. Research shows consistent improvements in growth rate, FCR, disease resistance, and economic viability across species. As global aquaculture moves toward intensification under environmental constraints, RBS stands out as a future-proof system capable of delivering high productivity with low ecological impact.

4.2 How RBS is better than RAS and BFT

The Recirculating Biofloc System (RBS) surpasses standalone Recirculating Aquaculture Systems (RAS) and Biofloc Technology (BFT) in numerous aspects, particularly in terms of growth performance, survival rate, feed conversion ratio (FCR), and feed intake. RBS combines the controlled, high-biosecurity, low water-use benefits of RAS with the natural feed production, nutrient recycling, and microbial community advantages of BFT. This synergistic integration not only enhances production efficiency but also reduces environmental impacts and operating costs.

Studies comparing RBS to RAS and BFT independently have shown significantly improved growth and survival rates. For example, Martins et al. (2017) observed that Oreochromis niloticus (Nile tilapia) cultured in RBS grew 25–30% faster than those in traditional RAS or BFT systems alone. Similarly, Emerenciano et al. (2012) found higher survival (up to 92%) in Litopenaeus vannamei reared in RBS, compared to 82% in BFT-only systems. The improvement is attributed to better water stability from RAS and enhanced microbial nutrition from bioflocs, which reduces physiological stress and supports continuous growth.

FCR is a critical indicator of aquaculture efficiency. In BFT, the microbial protein from bioflocs serves as a supplemental feed, while in RAS, precision water control enhances digestion and minimizes metabolic stress. However, when combined in RBS, the benefits are compounded. Ray and Lotz (2017) reported an FCR reduction from 1.8 (RAS) and 1.5 (BFT) to 1.2 in RBS for shrimp. This was due to dual mechanisms: enhanced digestion via microbial enzymes in bioflocs and optimized environmental parameters maintained by RAS. Improved nutrient retention and less feed wastage were also observed.

The RBS environment promotes improved feed intake due to more stable water parameters and the stimulation of appetite and gut health by microbes. Xu and Pan (2013) found that shrimp in RBS had increased feed intake and better gut histomorphology, which translated to improved nutrient assimilation. In contrast, traditional RAS, despite offering clean water, lacks the bioactive microbial particles that naturally enhance digestion. Meanwhile, in BFT alone, accumulation of suspended solids may negatively affect oxygen levels, potentially reducing feed intake over time. RBS balances this by maintaining water clarity through filtration while retaining beneficial flocs.

RBS fosters a probiotic-like environment. The presence of beneficial microbes competes with pathogens and enhances host immunity. While BFT alone provides some of these benefits, it lacks the water quality control of RAS, which can lead to microbial imbalance in long culture cycles. In RBS, studies such as those by Ferreira et al. (2016) on tilapia have shown significantly higher lysozyme activity and immune gene expression compared to RAS or BFT alone. Moreover, disease outbreaks were less frequent and milder in RBS due to lower pathogen loads and enhanced mucosal immunity from both clean water and microbial exposure.

From a systems perspective, RBS outperforms both RAS and BFT in terms of resource utilization, waste reduction, and economic efficiency. RAS is expensive to operate due to its energy-intensive filtration and water treatment requirements, while BFT requires vigilant carbon-to-nitrogen balancing and can experience water quality degradation over time. RBS mitigates these downsides by combining nutrient recycling of BFT with closed-loop filtration of RAS, reducing water exchange by over 90% and improving feed utilization. According to Avnimelech (2007), this hybrid approach not only supports higher stocking densities but also produces better economic returns per unit area than either system alone. Species-wise demonstration of better production in RBS compared to RAS and Biofloc system is shown in Tables 10, 11, 12.

In conclusion, RBS may represent the next generation of intensive aquaculture systems, offering superior performance across all critical metrics: growth, survival, FCR, feed intake, immunity, and sustainability. Its combination of precise environmental control and microbial nutrition creates an optimized culture environment that neither RAS nor BFT can consistently provide alone. Since this system is still in its initial phase, it’s difficult to identify its practical challenges and limitations at present.

5 Future research goals

Scientist should focus on the development of species-specific feeding strategies for the BFT, RAS, and their integrated form, i.e., RBS. This will improve nutrient utilization and production efficiency (Figure 9).

Figure 9

In-depth knowledge is required to understand nutritional dynamics, particularly the contribution of biofloc’s microbial biomass to dietary requirements. This will assist in re-optimizing feed formulations and will reduce input costs. Further research needs to be done for the development of a smart system that can automatically maintain optimum carbon-to-nitrogen ratios in integrated systems. At the same time, molecular techniques may be applied for characterization of microbial communities and their specific function. To minimize waste in RAS and maximize biofloc utilization, it is important to develop system-specific diets. As these culture technology demands high energy and operational costs; hence, R&D (Research and Development) should also focus on optimization and integration of renewable energy sources. A long-term study on disease dynamics and fish immunity is also required to validate that the system is truly sustainable. Finally, for wider adoption at a commercial scale, techno-economic validation is also required to assess its economic feasibility and life cycle analysis.

6 Conclusion

Feed management strategies in intensive aquaculture systems are important for enhancing fish productivity in an economically and sustainable way. In BFT, feed management is closely related to how microbes function through the manipulation of the carbon-to-nitrogen ratio, facilitating the conversion of waste nutrients into biofloc biomass that serves as a supplementary natural feed. On the other hand, RAS is based on precise feeding strategies by taking filtration capacity and water quality control into account. The combination of these two technologies in RBS takes the strengths of both culture systems by recycling of waste through microbial assimilation, combined with an engineered filtration system. This results in improved FCR, growth, and health outcomes. However, optimization of these systems is still required through species- specific and system-specific feeding strategies that account for microbial contributions and filtration dynamics. Hence, future research should focus on nutritional quantification of biofloc, development of tailored functional feeds, and integration of precision feeding technologies. However, the success of RAS, BFT, and RBS depends on species-specific tailored feed management practices that suit the system’s features and production goals. Hence, more research and development is required in the aspects of smart C: N management, microbial characterization, system-specific diets development, energy-efficient culture system, and long-term health research.

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