Sustainability in Ponds Management: Recent Developments, Challenges and Prospects

Abstract

Sustainable aquaculture growth necessitates innovative strategies to meet the global protein demand while minimizing environmental impacts. This narrative review synthesizes the current understanding and emerging approaches for optimizing nutrient cycling and trophic transfer efficiency in pond-based aquaculture systems. We highlight two primary strategies: ‘demand-oriented feeding’, which adaptively balances feed inputs with natural food availability, and the ‘nutritious pond concept’, which enhances pond ecology through carbon/nitrogen ratio management and waste-driven nutrient recycling. A critical examination of the scalability and environmental trade-offs associated with these strategies is also presented. Despite the challenges presented by these strategies, their combination could create a more dynamic, ecosystem-based approach to aquaculture that is more resource-efficient and environmentally friendly, contributing to the development of ponds as sustainable, productive ecosystems that enhance efficiency, reduce waste, and support economic viability. Finally, we explored polyculture as an ecological strategy, highlighting its synergistic mechanisms for maximizing food web efficiency and its potential to enhance the two primary strategies.

1. Introduction

Sustaining aquaculture growth requires the integration of innovative technologies, substantial investments, and enhanced scientific knowledge. This is crucial for ensuring animal health, welfare, profitability, and compliance with increasingly stringent environmental and food safety regulations [1]. Indeed, the rising global demand for sustainable and resilient protein sources has catalyzed significant transformations in the aquaculture industry, gradually shifting the sector away from traditional extensive pond systems towards more technologically advanced and intensive production methods, such as recirculating aquaculture systems. These innovations reflect a broader industry trend towards closed-loop and resource-efficient operations and are primarily driven by the need to increase productivity while simultaneously addressing long-term environmental concerns, such as water scarcity, biosecurity threats, eutrophication, and land use conflicts, especially in peri-urban regions [2,3,4].

While these technological advancements address many challenges, they often overshadow the fundamental drivers of aquaculture productivity, which are the efficient capture, transfer, and utilization of energy and nutrients within production systems. In modern intensive systems, feed is the principal source of energy and nutrients, with formulated diets accounting for the majority of input costs in global aquaculture [5,6]. However, there is increasing recognition of the value and potential of no-fed/low-fed systems, especially in the cultivation of grazing species, which leverage the pond’s natural productivity, including autotrophic and heterotrophic microbial communities, as endogenous nutrient sources [7].

Pond-based aquaculture systems represent most of the global aquaculture production and offer a unique opportunity for ecological intensification. Species with strong capacities to utilize natural food resources, including plankton and suspended particles—such as shrimp, Nile tilapia, grass carp, and silver carp—rank among the top five aquaculture species globally, with a combined production exceeding 40 million tons [2]. These species are particularly well suited to no-fed/low-fed systems, which have historically been practiced across Europe and Asia in large earthen ponds. In these systems, pond productivity is often stimulated through organic manuring or the addition of carbohydrate-rich materials to boost microbial and algal activities [8]. Renewed interest in such systems stems from their inherently low environmental footprint, minimal external input requirements, and alignment with circular bioeconomy principles. However, they remain under-optimized, particularly in resource-constrained settings, where oxygenation, nutrient dynamics, and microbial management are inadequately controlled. Consequently, nutrient conversion efficiency is often suboptimal, and the systems can rapidly become ecologically imbalanced [6,9]. Frequently, excess phosphorus and nitrogen can lead to eutrophication and harmful algal blooms, which deplete oxygen levels and harm aquatic health. This imbalance stems from the nutrient-rich fish waste and feed, which, while high in nitrogen and phosphorus, are low in carbon, limiting the ability of microorganisms to process waste effectively [10]. This has spurred several innovations, such as Integrated Multi-Trophic Aquaculture (IMTA) and aquaponics integrate fish farming with other species like shellfish or plants to absorb excess nutrients and improve water quality [11]. Green water technology harnesses algae to enhance water quality and provide a natural food source for fish [12,13,14,15]. Partitioned pond systems and in-pond raceways improve water flow and oxygen distribution, mitigating nutrient hotspots [16]. Biofloc technology (BFT) has emerged as a notable innovation aimed at enhancing in situ microbial productivity through carbon supplementation and intensive aeration [17,18,19]. Although BFT has been successful in improving water quality and reducing feed costs, its applicability in traditional low-input pond systems is limited by the high-energy demands associated with continuous aeration. Moreover, emerging evidence suggests that microbial biomass in BFT systems, primarily composed of bacteria, may offer less nutritional value to grazer feeders than algae-based food sources, which better support the growth of primary consumers [20]. More broadly, these limitations reflect a systemic inefficiency in how pond-based aquaculture captures and utilizes internally generated nutrients.

A total of 60–80% of the input nutrients in aquaculture ponds end up in the sediment [5]. Bosma and Verdegem [21] indicated that aquaculture ponds produce far more primary biomass from planktonic and microbial sources than that which is converted into harvestable fish. Indeed, Barbosa et al. [5] found that only up to 20% of carbon, 45% of nitrogen, and 60% of phosphorus are assimilated by the fish, suggesting that the natural biological productivity of these systems remains largely underexploited. This significant loss of input nutrients and underutilization of primary biomass highlights a critical inefficiency in current aquaculture practices, which limits the sustainability of aquaculture.

To address this, we propose a synergistic framework wherein the real-time responsiveness of demand-oriented feeding and the ecological stimulation of the nutritious pond concept converge to form a self-regulating ecosystem. When further optimized through polyculture, this integrated model maximizes nutrient use efficiency and economic viability by minimizing reliance on external inputs and systematically eliminating the ecological ‘dead ends’ that characterize traditional pond management. This study adopts a narrative review approach to describe the strategies and critically assess their theoretical foundations, practical applications, and challenges, thereby identifying key priorities for future research and development aimed at advancing circular bioeconomy principles in aquaculture. In this review, we employed an exploratory search strategy across Google Scholar, Scopus, ScienceDirect, and PubMed, utilizing a combination of core technical terms (e.g., ‘aquaculture’, ‘nutrient cycling’, ‘natural productivity’) and broader systemic frameworks including climate-smart solutions and the circular economy. Rather than adhering to rigid systematic inclusion quotas, the literature collected was curated based on conceptual relevance and its capacity to elucidate the intersections of pond ecology and management efficiency. The selection prioritized peer-reviewed articles that offered substantive insights into nutrient use efficiency, while excluding undated or non-verifiable sources. The resulting evidence was synthesized through a thematic and interpretive lens, structured specifically around the mechanisms and scalability of both strategies.

2. Understanding Pond Ecosystems

2.1. Ponds as Stables and Pastures

Sustainable aquaculture is increasingly acknowledged as a key solution for meeting the rising global food demand while minimizing environmental degradation. At its core, sustainability in aquaculture involves maintaining ecological balance, ensuring economic viability, and promoting social responsibility [22]. To meet the needs of the growing global population, aquaculture must expand its production capacity without proportionally increasing its ecological footprint [3].

A critical strategy for achieving this balance lies in optimizing the ecological functionality of aquaculture systems, particularly pond-based systems, which remain the most traditional and widely utilized form of fish cultivation worldwide [20,22]. These systems represent more than just holding units for aquatic organisms; they are dynamic ecosystems in which biological production, nutrient cycling, and energy flow are tightly intertwined. Conceptually, ponds can be interpreted using analogies from terrestrial livestock systems. They function as both stables, providing a controlled environment with containment and protection where fish are managed similarly to livestock in a confined space, and pastures, offering natural forage through autochthonous primary production where fish are able to interact more freely with the ecosystem, relying on natural resources for sustenance and survival. This dual role not only supports higher productivity but also enhances ecological resilience through habitat heterogeneity and nutrient recycling.

However, this dual role also implies a responsibility for managing the outputs of productive pastures, particularly the accumulation of organic matter and nutrients. Without adequate intervention, the accumulation of organic matter and nutrients can impair water quality and reduce system efficiency. Indeed, the transformation of nutrients into biomass follows a non-linear and often unpredictable path, frequently resulting in ecological inefficiencies or “dead ends.” Strategies such as regular water exchange and bioremediation are essential for maintaining an ecological balance. For instance, farmers often utilize static production systems with infrequent pond drainage. Although this approach effectively manages waste treatment within the production system and reduces nutrient discharge into the surrounding ecosystems [23,24], it often leads to higher feed conversion ratios. In their study, Ajiboye et al. [25] demonstrated that frequent water exchange significantly improves FCR, with daily water exchange achieving an FCR of 0.40, compared to 0.52 in treatments with less frequent exchanges. Similarly, Gabber et al. [26] observed lower FCR values (2.8 vs. 3.5) in tiger shrimp cultured in earthen ponds with a 20% water exchange rate compared to a 10% exchange rate.

Recognizing and managing ponds as integrated ecological systems is essential for advancing the sustainability of aquaculture. By leveraging natural biological processes, producers can reduce their dependence on external inputs, such as commercial feeds and synthetic fertilizers, enhance carbon sequestration, and ensure the long-term productivity of their systems. These practices, akin to IMTA, where waste or by-products from one species serve as inputs for others [27], and to aquaponics which promotes closed-loop nutrient cycling and water reuse [28], closely align with circular economy principles, contributing to the transformation of aquaculture into a more resource-efficient and environmentally responsible industry.

2.2. Nutrient Cycling in Ponds

Nutrient cycling is one of the most significant ecological functions in pond-based aquaculture. Ponds act as biogeochemical reactors where nutrients introduced through feeds, fertilizers, or organic waste such as manure and plant residues are transformed through a combination of biological and physicochemical processes [29]. Nutrients not used by the fish contribute to the production of natural food organisms (algae, periphyton, zooplankton, and detritus) which in turn complement the fish diet [21]. In a well-fed tropical pond and under optimal circumstances, this primary productivity can be about 4 g C/m²/day which is equivalent to 8 g organic matter/m²/day. This is well illustrated when fish are confined in cages, resulting in less growth than when they roam freely in ponds [30]. Free-swimming fish have access to more natural food than confined fish and, therefore, grow better. Additionally, fish can selectively target nutrients based on their feeding requirements and the abundance of natural foods. In an experiment with GIFT tilapia reared in active suspension ponds under no water exchange, Khalil et al. [31] observed that groups fed a lysine-deficient diet were able to compensate their dietary lysine deficiency through plankton selectivity.

Nitrogen and phosphorus, two essential nutrients for aquatic productivity, are cycled through microbial pathways, including nitrification, denitrification, and mineralization. Fish contribute to this loop through excretion, which increases the availability of nutrients for primary producers such as phytoplankton. This supports higher trophic levels, including zooplankton and fish [32].

The pond food web is a complex network linking autotrophs (e.g., phytoplankton and aquatic macrophytes), heterotrophs (e.g., zooplankton, detritivores, and fish), and decomposers (e.g., bacteria and fungi). Microbial communities, particularly heterotrophic bacteria, play a crucial role in decomposing organic matter and mineralizing nutrients. This microbial activity not only sustains the food web but also enhances resource use efficiency by recycling waste into usable biomass [33].

In fertilized or semi-intensive systems, where input levels are moderate, the retention and reuse of nutrients within the pond help mitigate environmental pollution. Compared with high-input intensive systems, these approaches reduce nutrient losses and make better use of the available resources. When properly managed, pond systems contribute to both ecological stability and productivity, embodying the principles of sustainable and circular aquaculture [34].

2.3. Ponds as Sources and Sinks of Carbon

In addition to the nutrients described above, every living thing needs organic carbon to survive, and the carbon cycle in ponds is tightly interwoven with the structure of the food web.

Primary production via photosynthesis captures atmospheric carbon dioxide (CO₂) and converts it to organic carbon. This fixed carbon is then transferred through trophic levels, from phytoplankton to zooplankton, and ultimately to fish and other higher-level consumers [35]. As CO₂ is consumed, carbon molecules become part of the phytoplankton structure, allowing it to function effectively. Concurrently, detrital pathways, which involve the breakdown of dead organic matter and feces, recycle carbon and nutrients, supporting microbial loops and benthic food chains [36]. Therefore, if phytoplankton are not eaten by another organism (passing on the carbon up the food chain), they will sink into the pond when they die. Like other detrital organic matter, phytoplankton are decomposed by bacteria, consuming oxygen and converting organic carbon into dissolved inorganic carbon released as CO₂, which is recycled within the pond through microbial respiration and photosynthetic uptake, while a smaller fraction settles and is ultimately deposited in bottom sediments.

Ponds act as both carbon sources and sinks [37].

Ponds may sequester carbon in sediments during periods of high primary productivity and organic matter accumulation. Integrated aquaculture systems (e.g., aquaponics or rice–fish farming) often enhance carbon capture by promoting plant uptake and reducing reliance on external feeds [38]. In this sense, ponds behave like micro-wetlands or carbon sinks, contributing to greenhouse gas mitigation strategies [18].

However, microbial respiration and decomposition can also release CO₂ and methane (CH₄), particularly under anaerobic conditions [39].

2.4. Other Factors Affecting Energy Flow in Ponds

In pond ecosystems, energy transfer occurs through complex food webs and physical processes such as heat exchange. Ponds rely on solar radiation as their primary energy source, which drives photosynthesis in phytoplankton, algae, and macrophytes. Light availability is controlled by diurnal and seasonal cycles as well as geographic factors and is further reduced by shading or turbidity from suspended solids, algae, or organic matter [40]. High turbidity induces “autoshading” where dense suspended particles or phytoplankton attenuate and scatter light, thereby restricting photosynthesis in deeper water layers and shifting the system toward enhanced decomposition and increased oxygen demand [41,42,43].

Temperature regulates the metabolic rate, growth, and oxygen consumption of aquatic organisms. Stratification, with warm surface waters over cooler bottom layers, restricts mixing and can create hypoxic zones [40,43,44]. Dissolved oxygen (DO) fluctuates daily: photosynthesis increases DO during the day, whereas nighttime respiration decreases DO, sometimes to critical levels, under poor aeration [40,44]. Pond morphology also influences these processes. Depth, surface area, and volume affect the heating, stratification, water retention, and DO dynamics. Wind-driven mixing can disrupt stratification, redistribute nutrients, and balance oxygen levels. Shallow ponds heat and cool rapidly but risk oxygen depletion at night, whereas deeper ponds often stratify, creating low-oxygen zones.

3. Optimizing In Situ Pond Productivity: Emerging Strategies and Perspectives

Food webs are fundamental for sustaining in situ productivity in ponds, as they regulate energy flow and mediate nutrient recycling across trophic levels. Nonetheless, energy transfer along trophic chains is intrinsically inefficient, with typically less than 15% of the energy at one trophic level being transferred to the next [45,46]. Consequently, shorter food chains, such as phytoplankton → zooplankton → fish, tend to support higher productivity compared to more complex chains that incorporate additional microbial or detrital intermediates [47].

An important advantage of food web-based feeding is that it aligns with the natural feeding behavior and immunological adaptations of many commonly farmed species. However, despite these ecological benefits, many aquaculture systems remain underutilized, relying predominantly on externally supplied feed inputs rather than optimizing natural trophic pathways to enhance their productivity and sustainability.

In the following sections, we outline two principal strategies developed to better harness food web dynamics for aquaculture. Both approaches are grounded in the dual objectives of reducing overall feed inputs and minimizing reliance on costly dietary components, thereby improving ecological efficiency and economic viability.

3.1. Demand-Oriented Feeding: Can This Carp Model Be Adaptable to Other Species [48]?

3.1.1. Daphnia as a Proxy for Natural Productivity

According to Gatlin [49], fish feeding practices must account for the climatic conditions of the pond, the type and quantity of natural food available, and the nutritional and physiological requirements of the cultured species. When natural food is insufficient, it should be supplemented appropriately with the ultimate objectives of feeding being to optimize the utilization of natural food resources, increase fish yield, and minimize nutrient loading in the pond environment. As highlighted by Azim and Little [50], three critical factors govern the effectiveness of natural food-based aquaculture: the quantity and regeneration capacity of natural foods under grazing pressure, the nutritional quality of natural food, and the capacity of fish to harvest, digest, and assimilate these resources. However, pond ecosystems are characterized by complex nutrient and energy flows, where the pathway from input nutrients to fish biomass is often non-linear.

Figure 1 illustrates two (2) different nutrient/energy flow pathways, where differing dynamics can create unintended outcomes, including primary production that is either edible or inedible to secondary producers, potentially leading to a dead end.

• When fish population density and feeding rates are balanced, a stable population of large-bodied zooplankton and phytoplankton will emerge, fostering their reproductive success.
• At high fish stocking densities, intense grazing on large/edible zooplankton shifts zooplankton communities towards smaller taxa, reducing their ability to control phytoplankton and promoting the formation of algal blooms [47].
• Similarly, when fish density is too low to exert pressure on zooplankton, the persistence of large-bodied zooplankton (e.g., Daphnia spp.) can increase water clarity, which in turn promotes plant growth, leading to turbid conditions and recurrent algal blooms [51].

Biomass and energy transfer are regularly inhibited at the phytoplankton–zooplankton link [52]. Phytoplankton, the base of aquatic food webs, drive natural productivity in pond aquaculture and can be both beneficial and problematic depending on management. Desirable groups such as diatoms and green algae (e.g., Chlorella, Chaetoceros, Isochrysis, Tetraselmis) enhance water quality by assimilating inorganic nutrients, providing shading, supporting zooplankton growth, and supplying essential compounds like omega-3 fatty acids and antioxidants to shrimp and fish larvae. While phytoplankton uptake temporarily removes ammonia from the water column, this nitrogen is stored only in cellular protein; upon senescence, heterotrophic bacteria mineralize it back into ammonia [53]. Excessive phytoplankton biomass can thus lead to oxygen depletion, strong diurnal pH fluctuations, and accumulation of toxic metabolites or harmful blooms, highlighting the need for balanced phytoplankton management. In addition to phytoplankton and bacteria, grazers—particularly large-bodied zooplankton—and other microbial community members (e.g., fungi and actinobacteria) interact as consumers or nutrient sources. Zooplankton body size influences predator–prey dynamics and trophic cascades [54], and large-bodied Daphnia species are particularly key in transferring nutrients and energy from phytoplankton to fish, making fish production dependent on their density [55]. Beyond Daphnia, copepods, krill, rotifers, and gelatinous zooplankton dominate global zooplankton biomass [56], mediate energy flow from microscopic primary producers to higher trophic levels, and play key roles in carbon cycling. Therefore, zooplankton body size and biomass can serve as valuable indicators of pond water quality and fish nutritional status.

The demand-oriented feeding strategy aims to provide pond managers with a practical, science-based tool for balancing fish feeding with the availability of natural food, particularly zooplankton. It relies on quantifying natural food availability using the settling volume method as a practical proxy and adjusting supplemental feeding to stabilize natural food stocks, thereby avoiding overexploitation and underutilization of zooplankton populations. This strategy focuses on modulating the feeding pressure on Daphnia by providing a flexible diet, variable in both quality and quantity, aligned with the observed natural food dynamics.

3.1.2. Linking Natural Food Assessment to Feeding Actions

This is based on the study by Scholtt et al. [48], where reference values for natural food in ponds were derived from long-term monthly Daphnia data in natural ponds which reflect fish feeding pressure and pond productivity. Significant deviations from these values indicate imbalances between fish density, natural food, and supplemental feeding, leading to ecological and economic risks. It is assumed that increasing supplemental feed lowers feeding pressure and supports Daphnia growth, whereas reducing or stopping feed intensifies pressure and diminishes the population.

The density of Daphnia (diameter > 1 mm) in ponds is used as a reliable measure of natural food availability for fish. Monitoring individuals >1 mm focuses on the size classes most important for population dynamics and energy flow. Larger juveniles and adults drive productivity, reproduction, and phytoplankton grazing, while smaller neonates (<1 mm) contribute little per individual. Predation patterns support this threshold, as fish and other predators preferentially feed on Daphnia >0.8–0.9 mm, leaving smaller individuals largely unaffected [57]. The following recommendations are made:

• 20–40 Ind./L (optimal range): Natural food resources are at sustainable levels. Supplemental feeding should maintain this equilibrium by providing a balanced diet of protein-rich natural foods and carbohydrate-based grains. This consists of reducing supplemental grain feeding when natural food is abundant and increasing it when natural food becomes scarce to balance fish nutrition and preserve pond resources.
• <20 Ind./L (deficit range): This indicates a lack of natural food sources. There is a risk of overexploitation and reproductive impairment in Daphnia. Feeding pressure must be reduced, and high-quality commercial feeds should be used to supplement missing protein sources. This results in indirect fertilization via nutrient release from uneaten feed and fish waste, stimulating algal growth and thereby supporting Daphnia recovery. However, caution is necessary to avoid excessive organic loading and oxygen depletion.
• >40 Ind./L (surplus range): This represents an underutilization of natural food resources, a risk of overpopulation, and possible oxygen depletion. In this scenario, supplemental feeding should be reduced or temporarily halted because natural food is not being adequately utilized.

3.1.3. Implication and Significance

Figure 2 illustrates two examples of extreme pond management variants.

Figure 2A highlights a demand-oriented feeding strategy in common carp culture that balances fish requirements with the availability of natural food, preventing both overgrazing and feed waste; this results in low supplemental grain input (393 kg/ha), higher production (334 kg/ha), and a better FCR of 1.2. In contrast, Figure 2B shows a rigid feeding regime that disregards natural food dynamics, causing severe overexploitation of Daphnia, limited recovery, and inefficient reliance on supplemental grains. Despite nearly double the grain input (707 kg/ha), the loss of protein-rich natural feed could not be offset, leading to low production (162 kg/ha) and a poor FCR of 4.4.

Feed consumption data and filet composition from feed trials in three experimental ponds (2009–2010, Northern Waldviertel, Lower Austria, Austria) showed feed savings of up to 722 kg/ha and optimal fat levels in cultured fish with the demand-oriented feeding method, demonstrating reduced feed use, lower costs, and maintained nutritional quality [48].

The implications and significance of this approach are extensive and far-reaching.

By using natural food dynamics as a direct indicator, pond management decisions can be information-based rather than relying on fixed schedules. This promotes sustainability by optimizing the use of zooplankton alongside supplementary feed, thereby creating a system that supports ecosystem-based pond management. It also improves efficiency through better feed conversion ratios and reduced feed costs. Simultaneously, it provides environmental benefits by preventing overfeeding, reducing nutrient loading, and enhancing overall water quality. Economically, this translates to cost savings and improved profitability for fish farmers. Altogether, this approach represents a shift from rigid, schedule-based feeding practices to adaptive and ecosystem-driven aquaculture management.

However, to expand this model beyond carp and across diverse environments, several challenges must be overcome.

• Species- and environment-specific thresholds: Because fish differ in feeding mode, prey size preference, and grazing intensity, while pond systems differ in productivity, temperature, nutrient availability, and predation pressure, zooplankton density benchmarks may need to be recalibrated for different species or pond systems, which poses practical difficulties, as they require extensive research and validation for each new species or pond system. In contrast to the carp model, benchmarks for species like Nile tilapia may be lower due to their opportunistic omnivory, while intensive shrimp systems may require benchmarks that balance natural food availability with the stringent water quality demands of high-density production. This process demands significant time and resources, and incorrect calibration or application can result in suboptimal management decisions and reduced production efficiencies.
• Standardized monitoring methods: A universally applicable, low-cost method for assessing natural productivity is needed. While the settling volume technique is a practical option, innovations such as AI-powered near-infrared (NIR) sensors could significantly enhance precision monitoring. By moving beyond simple settling measurements, AI-NIR systems can directly detect real-time biological indicators such as algal biomass, pigment concentration, and physiological status. When integrated with environmental data (e.g., temperature and oxygen), AI can distinguish true biological changes from physical noise, predict productivity trends, and provide early warnings of imbalances like algal blooms, enabling continuous, spatially detailed, and more accurate pond productivity assessment with reduced reliance on manual sampling.
• Reliance solely on Daphnia as a proxy for natural productivity may result in inaccurate estimations, as fish grazing is not restricted to zooplankton. For example, tilapia are known to graze effectively on phytoplankton [58,59] as well as bacterial communities [60].
• Knowledge transfer: Challenges in disseminating protocols for low-cost sampling equipment may limit adoption among small- and medium-scale farmers in developing countries. Barriers such as low literacy, weak extension services, cultural resistance, and insufficient training programs may further hinder effective implementation.

While the demand-oriented feeding strategy provides a good framework for adapting feed inputs to existing natural food levels, it primarily treats the pond’s productivity as an external variable to be monitored. However, a truly circular approach to aquaculture would require more than just passive adaptation; it necessitates the active stimulation of the pond’s internal nutrient cycles. This shift from monitoring natural food availability to intentionally cultivating it leads to the ‘nutritious pond concept.’ Rather than simply balancing supplemental feed with what is already present, this second strategy seeks to transform the pond into a self-sustaining food production unit by optimizing the microbial and planktonic web through targeted nutritional management.

3.2. The Nutritious Pond Concept

The nutritious pond concept represents a paradigm shift in aquaculture nutrition, moving away from exclusive reliance on formulated feeds to a system that nourishes both cultured organisms and the pond’s microbial–planktonic food web. Developed and refined through collaborations between Wageningen University & Research (WUR) and partners such as WorldFish, this approach integrates ecological nutrient cycling with feed formulation strategies to enhance productivity, nutrient use efficiency, and environmental sustainability [61].

Figure 3 illustrates the differences between a ‘traditional pond’ and a ‘nutritious pond.’

Central to this concept is the recognition that, rather than passive production units, ponds are complete ecosystems in which algae and bacteria grow on nutrients and energy from waste streams and contribute to water purification and the supply of natural foods [63]. In turn, fish and shrimp consume formulated feeds and rely on natural foods (algae, protozoa, zooplankton, and periphyton) [64]. Optimizing the interaction between feed inputs and pond ecology, particularly through carbon/nitrogen management, feces-mediated nutrient recycling, and substrate quality (e.g., non-starch polysaccharides, NSPs), defines the success of the nutritious pond model.

3.2.1. C:N Ratio as Central Regulatory Lever

Conventional aquafeeds are typically protein- and nutrient-rich but carbon-poor, leaving pond microbes with insufficient energy to fully mineralize waste [65]. This imbalance leads to nutrient accumulation, reduced nutrient use efficiency, and increased greenhouse gas emissions. Elevating the C:N ratio in feed inputs promotes microbial activity, facilitating the sequestration of nitrogenous waste into microbial protein that supplements the pond’s natural food web [66,67,68]. Consistent evidence links higher C:N ratios to enhanced system productivity. In BFT systems, maintaining a C:N ration between 10 and 20 is essential for sustaining stable microbial community dynamics [69]. For instance, enriching freshwater shrimp ponds to a ratio of 15–20 has been shown to boost biomass across the food web, increasing phytoplankton by 15%, crustaceans by 6%, rotifers by 11%, and bacterial biomass by a substantial 70% [66]. When combined with periphyton-developing substrates, C:N ratio management can increase net yield by 70% [70]. Similar benefits are observed in tilapia farming; fish reared at C:N ratios of 12 exhibited biomass increases, nitrogen gains, and increased nitrogen retention compared to those reared at a ratio of 8, largely due to an increased reliance on natural foods sources [67,68]. While survival rates remained stable at 74% across all treatments, the economic advantages were pronounced: increasing the C:N ratio improved the gross margin by 95% and the benefit cost ratio by 22% [68].

However, not all carbon is equivalent.

Evidence shows that carbon composition, not just quantity, strongly influences microbial and natural food productivity [20]. Slowly degradable non-starch polysaccharides (NSPs) (e.g., cellulose and wheat bran) support sustained microbial activity, whereas rapidly fermentable carbohydrates (e.g., molasses and starch) lead to quick CO₂ release without long-term benefits [71]. This distinction underpins the importance of substrate selection in nutritious pond diet formulation.

3.2.2. Feces as a Crucial Nutrient Input

Unlike conventional systems, such as BFT, where carbon sources are directly added to water, nutritious pond systems rely on fish feces as the primary source of carbon in the pond ecosystem. Aquaculture research often emphasizes excretion as the primary nutrient recycling pathway; however, recent studies have highlighted the critical role of feces (egestion) in sustaining ecosystem functions.

Fish feces contain substantial amounts of energy and nutrients owing to incomplete absorption. Schiettekatte et al. [72] observed that elemental concentrations in food vs. feces differ only slightly, with fecal composition of carbon and phosphorus rarely lower than half of the stomach content, underscoring the importance of egested material. In addition, fecal nutrient release (especially N and P) often exceeds excretory recycling, making egestion the dominant pathway for nutrient return to the system. Animal-mediated nutrient recycling can satisfy a substantial share of phytoplankton nutrient demand, directly linking consumer biomass to primary production [73,74]. Within the nutritious pond concept, feces act as vectors for carbon substrates (especially NSP fibers), seeding the pond environment with slowly degradable carbon that fuels microbial and planktonic productivity. This dual role—as waste and as a resource—has been underappreciated in conventional feed–waste frameworks. This oversight is partly due to the fact that high dietary fiber reduces nutrient digestibility by shortening feed residence time in the fish gut, representing a trade-off between the system’s needs and those of the fish.

3.2.3. Substrate Type and the Role of NSP Fibers

Only 5% of the energy derived from digested NSP contributes to the energy gain of tilapia fish [75]. Unlike readily digestible carbohydrates, fiber passes largely undigested through the fish gut and enters ponds via feces [76,77]. This material serves as a gradual carbon source for microbial communities, with several ecological and economic benefits, such as slow decomposition (preventing sharp CO₂ spikes), extended microbial activity (supporting nutrient assimilation for longer periods), enhanced natural food production (compensating for the reduced direct feed quality), and improved resource use efficiency (by balancing protein use with ecological recycling) [20].

Feeding Nile tilapia a high-fiber, low-protein diet led to greater biomass gain, higher protein use efficiency, and significantly improved economic returns compared to a commercial low-fiber, high-protein diet, mainly because of the increased reliance on natural food sources [71]. According to the authors, low-fermentable NSPs (e.g., cellulose) supported better fish performance and food web stability compared to highly fermentable NSPs. While substituting protein with fiber reduced the dietary quality of fish or shrimp, a high-fiber diet improved the gross margin and increased the benefit–cost ratio by 22%, and the resulting nutritious pond diet increased Nile tilapia’s biomass gain, gross margins, and protein use efficiency (from 52% to 71%) compared to conventional high-protein diets [20]. In Pacific White shrimp BFT systems, including high NSP (wheat bran) in an elevated C:N environment has proven to be beneficial. Increasing C:N ratios from 12 to 20 using wheat bran as a substrate contributed to a 32% increase in shrimp biomass [78]. Additionally, a wheat bran-mediated substrate positively promoted prokaryotic community composition in BFT at the end of the culture period, with several genera, such as Muricauda, Pirellula, and Cyanobacteriaceae, being enriched in BFT tanks compared to corn-based substrates [79].

These results highlight the importance of fiber as a strategic feed component that integrates fish nutrition and the ecological functioning of ponds.

3.2.4. Implications and Significance

Despite these promising outcomes, several critical limitations remain.

• Experimental scope: To date, most findings have been derived from a limited number of nutritious pond studies, raising concerns about scalability across diverse species and production systems.
  Table 1 lists the existing studies.

  Table 1. Existing nutritious pond studies.

  Species	Setting	C:N	Substrate	Metrics	Source
  Pacific White Shrimp	Indoor Mesocosms	11.8–20.5	Wheat bran, Non-Starch Polysaccharides	Survival 78–87%, FCR 1.2–2.5	[78]
  		12–20		FCR 0.6–1.1	[79]
  		17–21		Survival 87–88%, FCR 0.89–1.24	[80]
  		12–20		Survival 87–88%, FCR 1.18–1.70	[81]
  Nile Tilapia	Pond	10	NA	Survival 81–96%, FCR 1.54–1.81	[82]
  		10.8–12.3		Survival 76–98%, FCR 1.13–2.45	[71]
  		8–11		Survival 71–74%, FCR 0.95–1.12	[68]
  		8.8–11.8		Survival 52–86%, FCR 0.8–1.3	[62]

  Table 1. Existing nutritious pond studies.

  Species	Setting	C:N	Substrate	Metrics	Source
  Pacific White Shrimp	Indoor Mesocosms	11.8–20.5	Wheat bran, Non-Starch Polysaccharides	Survival 78–87%, FCR 1.2–2.5	[78]
  		12–20		FCR 0.6–1.1	[79]
  		17–21		Survival 87–88%, FCR 0.89–1.24	[80]
  		12–20		Survival 87–88%, FCR 1.18–1.70	[81]
  Nile Tilapia	Pond	10	NA	Survival 81–96%, FCR 1.54–1.81	[82]
  		10.8–12.3		Survival 76–98%, FCR 1.13–2.45	[71]
  		8–11		Survival 71–74%, FCR 0.95–1.12	[68]
  		8.8–11.8		Survival 52–86%, FCR 0.8–1.3	[62]

• Survival variability: In some pond trials, fish fed a low P:E diet with an increased C:N ratio of 11.8 reported reduced survival (up to 40% loss), indicating possible trade-offs in pond ecology [67].
• Quantifying natural food contributions: Estimating the exact role of microbial–planktonic foods in fish growth remains methodologically challenging, and a clearer partitioning of feed versus natural inputs is required. In addition, natural food production is governed by site-specific pond ecological factors, including light penetration, temperature regimes, dissolved oxygen concentration, nutrient dynamics, and plankton community composition, in addition to seasonal variability and water source characteristics.
• Natural food production capacity: The capacity of ponds to produce sufficient natural food for farmed species may vary widely, limiting the generalizability of the concept. Reliance on natural food, although ecologically sound, presents a limitation concerning the precise nutritional requirements of cultured species, especially during critical life stages. Natural food sources may exhibit variability in their essential nutrient profiles (e.g., specific amino acids, fatty acids, and vitamins), which could lead to nutritional deficiencies if not carefully balanced with supplemental feed. This is particularly challenging for species with complex dietary needs or during periods of rapid growth, where the exact composition of natural food contributing to growth and health is difficult to quantify and to control.
• Variability in fiber decomposition rate: The type of dietary fiber influences digestion, fecal composition, and fecal production by fish [83]. Understanding the variability in fiber decomposition is therefore crucial for ensuring that microorganisms recycle nutrients efficiently while maintaining pond ecosystem stability, as the goal is to achieve a moderate, steady fiber decomposition rate that aligns with primary production and nutrient uptake.
• Balancing greenhouse gas emissions: Although NSP reduces immediate CO₂ release, the long-term carbon cycling dynamics in ponds require more rigorous quantification.

The nutritious concept approach can enhance nutrient recycling, reduce dependence on high-protein feeds, and improve production outcomes. Future research should focus on standardized methodologies for measuring natural food contributions, broader multi-species trials, and the integration of greenhouse gas assessments to fully realize the potential of nutritious pond systems as a circular and climate-smart aquaculture solution. While experiments have been conducted in extensive and semi-intensive settings, further research is required to assess whether the model can be scaled to more intensive production systems.

3.3. Bridging the Strategies

Demand-oriented feeding and nutritious pond strategies can be functionally integrated to establish a more holistic, ecosystem-based framework for sustainable aquaculture. Both approaches converge on the objective of minimizing reliance on externally supplied feeds while enhancing in situ primary productivity, nutrient recycling efficiency, and overall pond stability.

The integrated framework for both management strategies is proposed in Figure 4, detailing their combined impact on pond ecosystem efficiency.

The demand-oriented feeding strategy regulates supplemental feed inputs in accordance with the availability of natural food resources through continuous monitoring of natural food. This adaptive feeding regulation prevents both overexploitation and underutilization of natural trophic resources, thereby optimizing nutrient use efficiency and sustaining a balanced pond food web. In parallel, the nutritious pond concept reinforces internal nutrient cycling by manipulating feed formulations to stimulate microbial and planktonic productivity. Adjustments to the dietary C:N ratio and the inclusion of slowly degradable carbon substrates, such as NSPs, enhance microbial assimilation pathways, promote the generation of natural foods, and facilitate efficient nutrient recycling in pond ecosystems. In addition, feeding costs can potentially be reduced by adjusting the feed formulation according to the specific nutrient deficiencies present in the pond.

When integrated, demand-oriented feeding functions as a real-time trophic feedback mechanism within the nutritious pond framework. Quantitative monitoring of zooplankton and other natural food components can guide dynamic adjustments in feed input, C:N management, and substrate selection, ensuring that microbial productivity is effectively translated into accessible natural nutrition for cultured organisms. Conversely, nutritious pond-mediated improvements in microbial and planktonic biomass production stabilize the natural food base upon which demand-oriented feeding decisions are predicated, reinforcing a self-regulating ecological equilibrium. For instance, consistent monitoring showing low zooplanktons could signal the need to increase dietary C:N ratios or NSP inputs to stimulate microbial food production, thereby supporting their recovery. This promotes an ecosystem state where feedback between nutrient cycling, microbial and planktonic growth, and organism feeding naturally stabilizes populations and resource availability, maintaining balance without constant external control. Collectively, the integration of these two strategies could offer a highly efficient and adaptable approach to aquaculture nutrition management, wherein formulated feeds serve as direct nutritional inputs and drive the productivity of endogenous food webs. This synergistic interaction could enhance feed conversion efficiency, reduce nutrient loss, and support economic viability and environmental sustainability in aquaculture production systems.

Accurate estimation of natural food dynamics remains a prerequisite for understanding nutrient cycles in aquaculture, as detailed extensively by Tarigan et al. [60]. However, developing farm-scale models is not a standardized task; complexity varies according to the research intent. Given that this complexity arises from the constitutive laws governing reactions, effective modeling necessitates the strategic integration of prior (bio)chemical knowledge and defined system targets.

The practical implementation of both demand-oriented feeding and the nutritious pond concept highlights a common bottleneck: the inherent complexity of managing single-species interactions within a dynamic ecosystem. To address these limitations and further maximize the efficiency of nutrient capture, we explore the possibilities of moving beyond monoculture systems. By integrating multiple species with complementary feeding niches, polyculture serves as the overarching ecological framework that can operationalize these primary strategies at a system-wide level, ensuring that no nutrient ‘dead ends’ remain unexploited.

4. Polyculture: An Ecological Strategy for Maximizing the Food Web in Aquaculture

Polyculture, although rooted in centuries-old aquaculture practices, represents one of the most scientifically validated strategies for enhancing food web efficiency and ecological stability in aquatic production systems. Unlike monoculture systems, polyculture exploits species complementarity in feeding niches, energy use, and nutrient cycling, leading to significant improvements in ecological sustainability and productivity.

4.1. Synergistic Mechanisms in Polyculture

At its core, polyculture enhances production through multiple ecological mechanisms, including substrate provision, optimization of carbon-to-nitrogen (C:N) ratios, and synergistic interactions between species [21,84]. Such synergies occur when fish with partially overlapping but non-antagonistic feeding niches convert otherwise unutilized resources into biomass, thereby increasing overall system productivity without elevating nutrient inputs [84,85]. This principle underlies the striking increase in production, where polyculture has been shown to perform better than monoculture systems [50,86].

Carp polyculture is one of the most established traditional practices, particularly in China. Contemporary studies have reaffirmed its ecological and production benefits. For instance, recent grass carp pond experiments have demonstrated that polyculture increases effective trophic levels, elevates energy conversion efficiency, and improves the overall stability of the ecosystem compared to monoculture [87]. The energy flow through the system was 13–15% higher (evaluated through the Ecopath routine in the Ecopath with Ecosim software 6.6.8), emphasizing the role of polyculture in enhancing trophic transfer efficiency and ecosystem resilience. Similar benefits have been documented in periphyton-based systems, where carp polyculture yielded annual maxima of 9 t/ha without supplementary feed, substantially outperforming monoculture [50]. These findings collectively demonstrate that polyculture not only increases biomass output but also improves ecological stability and nutrient retention.

4.2. Food Web Dynamics and the Role of Microbial Pathways

Polyculture capitalizes on the full spectrum of the aquatic food web. The microbial loop, from bacteria and small phytoplankton to protists, constitutes a crucial trophic base for higher-level consumers [88]. Incorporating unselective grazers into polyculture systems allows for the efficient utilization of microbial resources, particularly under high nutrient presence where small particles dominate.

By including species from diverse feeding guilds (e.g., herbivores, omnivores, benthivores, zooplanktivores, and carnivores), polyculture systems channel energy and nutrients more efficiently across trophic levels while maintaining system resilience against resource fluctuations [86,87,89]. The ability of fish to adaptively shift their feeding habits further amplifies their role as regulators of plankton composition and water quality [89]. In a prawn–tilapia–rohu pond polyculture system, the abundance of periphytic algae and periphyton biomass was negatively regulated by tilapia, indirectly improving the system’s FCR by 16% [90]. The addition of tilapia and periphyton substrates in a C/N controlled system benefited freshwater prawn culture practices by (1) reducing toxic inorganic nitrogenous compounds in water, (2) enhancing the utilization of natural foods, and (3) improving survival, production, and economic benefit.

Recent studies have shown that feeding management strategies, such as adjusting feed pellet size ratios, buoyancy, and stocking density, can be used to steer food web dynamics, favor the production of one species at the expense of another, and regulate the overall fish biomass in polyculture systems [91,92].

Polyculture is a scientifically validated framework for ecological intensification in aquaculture. By enhancing nutrient recovery, energy transfer efficiency, microbial food web utilization, and water quality regulation, polyculture achieves higher productivity with reduced environmental impact. Studies have consistently demonstrated that production gains can be realized without increasing nitrogen and phosphorus discharge, making polyculture central to sustainable aquaculture development [50,84,87]. This exemplifies how ecological design anchored in food web dynamics can maximize aquaculture output while reinforcing ecosystem stability and resilience.

Despite being a traditional practice, polyculture in aquaculture faces several interconnected challenges, including ensuring species compatibility to avoid competition, predation, or conflicting environmental requirements, as well as increased management complexity due to the need for careful control of stocking densities, feeding strategies, and water quality. Differences in growth rates and harvest timing among cultured species can complicate production planning, while disease management becomes more difficult because pathogens may transfer between species, and treatments suitable for one species may adversely affect another. Additionally, poorly balanced trophic interactions can lead to inefficient nutrient use, where natural food resources are either underutilized or depleted, and the successful implementation of polyculture is further constrained by limited species-specific ecological knowledge and technical expertise.

5. Conclusions

Harnessing the trophic dynamics of pond food webs offers substantial advantages for sustainable aquaculture. By stimulating primary production and promoting efficient trophic transfer, farmers can more effectively capture the energy fixed by phytoplankton, thereby reducing their dependence on expensive, formulated feeds.

This review underscores the critical role of understanding and actively managing pond food web dynamics for sustainable aquaculture. Demand-oriented feeding, the nutritious pond concept, and polyculture strategies collectively offer a paradigm shift towards ecological intensification, reducing reliance on external inputs, enhancing nutrient-use efficiency, and mitigating environmental impacts. In combination, these strategies suggest a multilevel ecological intensification model characterized by enhanced energy transfer, reduced nutrient leakage, and improved feed conversion efficiency. This integrative approach operationalizes circular bioeconomy principles in aquaculture and holds the potential to transform ponds into functional ecosystems that simultaneously sustain productivity, environmental integrity, and economic viability.

Future research should prioritize comprehensive life cycle assessments, economic viability studies (including overhead or operational costs) across diverse production scales, and the development of standardized, low-cost food web monitoring tools applicable to various species and environmental conditions. Farm-scale mathematical models are needed to apply food web dynamics for assessing carrying capacity and designing feed formulations. Furthermore, interdisciplinary efforts are needed to integrate ecological, socioeconomic, and policy perspectives to facilitate the widespread adoption of these promising sustainable aquaculture practices.