Juvenile Sardine Production in Ecological Culture System: Opportunities for Restocking and Coastal Sustainability

Abstract

Small pelagic fish, including sardines, are essential to global fisheries and aquaculture feed production. However, these species are increasingly exposed to intense exploitation. In Chile, the common sardine (Strangomera bentincki), endemic to the Humboldt Current System, supports major industrial and artisanal fisheries. Landings are expected to reach 300,000 tons by 2025, mostly for fishmeal production. As a keystone species, S. bentincki is highly sensitive to environmental variability during early development, which can reduce recruitment and threaten long-term population sustainability. This interdisciplinary approach integrates ecological and biotechnological perspectives to assess the feasibility of controlled juvenile sardine production in land-based Ecological Aquaculture (EA) systems, including Recirculating Aquaculture Systems (RAS) and Integrated Multi-Trophic Aquaculture (IMTA), which are designed to reduce environmental impacts. These systems enable precise control of temperature, feeding regimes, and water quality, facilitating investigations into larval and juvenile survival, growth performance, and physiological responses under variable thermal and nutritional conditions. Emphasis is placed on fatty acid metabolism during ontogeny, particularly docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), which are essential for somatic growth, reproductive development, and thermal tolerance. Developing standardized protocols for juvenile S. bentincki culture addresses key gaps in husbandry and physiology (temperature threshold, nutrient density, larval growth rate, etc.) while introducing a novel ecological–aquaculture integration framework. This approach links early-life ecology with applied rearing techniques to support stock enhancement, strengthen artisanal fisheries, and promote sustainable aquaculture diversification under increasing environmental variability.

1. Introduction

Small marine pelagic fish, such as sardines, play a critical role in global marine ecosystems and support some of the most economically significant fisheries worldwide [1]. These species are a vital source of protein for human consumption and are also widely used as feed in aquaculture, particularly for high-value species such as salmonids [1]. However, increasing global demand has placed immense pressure on wild stocks. It is estimated that the global catch of small pelagic fish has reached several million metric tons annually, with a significant portion used for fishmeal and fish oil production [2,3]. Over the past decades, catch and landing data have shown declining trends, with many sardine populations now categorized as overexploited [1,4]. This overfishing threatens not only the sustainability of these species but also the livelihoods of communities that depend on them and the stability of marine food webs [5]. These challenges highlight the urgent need for alternative, sustainable approaches to sardine production, such as Ecological Aquaculture-based restocking supported by innovative technologies such as Recirculating Aquaculture (RAS) and Integrated Multitrophic Aquaculture (IMTA) systems. In this context, ecological aquaculture of sardines is conceptually transformative because it integrates the ecophysiological attributes of sardines (rapid growth, mid-trophic position, and high nutritional value) with biotechnological aspects of their rearing in sustainable culture systems that mimic natural ecosystems [6,7]. These systems enable nutrient recycling and minimize impacts on coastal ecosystems [8,9]. Accordingly, ecological sardine aquaculture can be used as a compensatory tool to support the supply of small marine pelagic fish threatened by overfishing in different regions of the world [3,4]. Therefore, the objective of the present study was to explore the potential for juvenile sardine production in land-based Ecological Aquaculture (EA) systems, evaluating its implications for restocking and coastal sustainability.

1.1. The Common Sardine (Strangomera bentincki): Biological and Economic Importance

The common sardine (S. bentincki) is a small pelagic fish endemic to the southern Humboldt Current System and plays a central role in the coastal marine ecosystems of south-central Chile. It supports one of the most significant fisheries in the region, both industrial and artisanal, particularly between 34° S and 40° S [10]. Nationally, landings of common sardines are projected to reach approximately 300,000 tons by 2025, the majority of which is processed into fishmeal [11]. In addition to its commercial value, S. bentincki is recognized as a keystone species within the upwelling-driven pelagic food web, occupying an intermediate trophic level. It feeds on phytoplankton and zooplankton [10,12] and serves as a major prey item for a variety of higher predators, including fish (Cilus gilberti), cephalopods (Dosidicus gigas), marine mammals (Otaria flavescens), and seabirds (Spheniscus humboldti) [13,14,15,16].

1.2. Life Cycle, Population Dynamics and Coastal Fisheries

The ontogeny of the common sardine (S. bentincki) includes the following successive developmental stages: (i) egg, (ii) yolk-sac larva, (iii) first feeding larva (“pre-postflexion” stage), (iv) juvenile, and (v) adult [17,18]. S. bentincki is a short-lived species with rapid growth and early sexual maturation [19]. Reproduction occurs mainly during the winter months, with spawning concentrated off the coasts of central and south-central Chile [20]. This species typically inhabits shallow coastal areas, such as bays, at depths ranging from 0 to 70 m, where it forms large schools [21]. Adults can reach a maximum size of approximately 280 mm, with first sexual maturity generally reached within the first year of life, at a size of 130–150 mm [22]. The recruitment of juvenile individuals takes place 4 to 5 months post-spawning, usually between November and December [23]. Ecologically and economically, the common sardine—alongside the anchovy (Engraulis ringens)—represents one of the most important pelagic resources along the south-central Chilean coast. It is a cornerstone species for both the artisanal and industrial fisheries, particularly in the Biobío and Ñuble regions [21]. Given its rapid life cycle, high ecological and commercial value, and the current state of overexploitation of natural populations, there is a clear need to develop culture technologies aimed at producing juvenile sardines for restocking purposes. Advancing such technologies would support the recovery and sustainable management of wild stocks, contributing to the long-term resilience of regional fisheries.

1.3. Climate Change and Phenology

In the context of climate change, a series of environmental changes have emerged along coastal regions, potentially affecting both the abundance and nutritional status of species that constitute key fishery resources [24,25]. Among these changes are marine heatwave events characterized by abnormally high sea surface temperatures persisting for several days or even weeks and often spanning extensive coastal areas [26]. These heatwaves are already impacting coastal ecosystems in Chile [27] and may have significant consequences for marine species of high ecological and economic importance [28,29]. The common sardine, for instance, may be particularly vulnerable to these extreme thermal events. Elevated sea temperatures can disrupt the phenology of small pelagic fish such as sardines, leading to a mismatch in the timing of predator-prey interactions [30]. Many sardine species synchronize their reproductive cycles with periods of optimal temperature and peak availability of planktonic food (i.e., phyto- and zooplankton), which are critical for the successful development of their offspring—an ecological relationship described by the “match-mismatch theory” [31]. However, marine heatwaves can reduce both the quantity and quality of available plankton, causing a temporal mismatch between sardine reproduction and plankton abundance [32]. This mismatch can negatively impact the nutritional condition of sardines, thereby affecting their reproductive success, growth, and long-term population viability [31,32,33].

In turn, reproductive traits such as gonadal maturation and subsequent spawning of S. bentincki may be gradually adjusted to oceanographic–coastal phenomena, such as the seasonal upwelling events that occur along the central–southern coast of Chile [21]. In this context, it has recently been described that the common sardine exhibits a partial capital-breeding strategy characterized by two spawning periods: (i) late summer and (ii) late winter to early spring [34]. These spawning events are energetically supported by female feeding activity and the accumulation of nutrient reserves over an extended period within the annual cycle [20,34]. Moreover, under an environmental changing scenario, it would be of particular interest to determine whether recruitment variability in this species is associated with the different seasonal spawning events, and whether these are modulated by key environmental factors such as temperature, salinity, and food availability, among others. This information, considered a nature-based solution (for concept see [34,35]), is valuable for understanding how environmental parameters—applied here to culture conditions—can ensure successful reproduction and the completion of the life cycle of this species in captivity [36].

On the other hand, the development of fish aquaculture in coastal and land-based environments has been largely based on monoculture systems, primarily involving trout and salmonids [1,37]. As a mono-specific form of aquaculture (for concept see [37]), these systems may be particularly vulnerable under climate change scenarios—such as increased water temperatures, extreme and unpredictable weather events, and drastic changes in productivity—which could negatively affect coastal aquaculture production [25,33]. It is therefore urgent to diversify fish farming, particularly by adjusting which species are produced in different regions, and to promote the cultivation of native species with commercial and economic potential, such as the common sardine S. bentincki.

1.4. Physiological Ecology and Sustainable Coastal Aquaculture

The sustainability of this fishery is increasingly threatened by overexploitation and environmental variability. As an ectothermic organism, the common sardine is highly sensitive to changes in seawater temperature, which directly affect physiological processes such as growth, reproduction, and survival [38]. Recruitment success and population abundance are particularly influenced during early-life stages (eggs, larvae, juveniles), which develop in coastal habitats where environmental factors such as temperature, food availability, and water quality fluctuate significantly. Despite its importance, critical knowledge gaps remain regarding the specific environmental and nutritional requirements of juvenile sardines and their potential for production in confined systems. Addressing these gaps is essential for exploring alternative solutions to declining wild stocks. In this context, the development of controlled rearing technologies for juvenile sardines, particularly within IMTA systems, offers a promising strategy for restocking and resource recovery. IMTA allows for ecological balance and nutrient recycling by integrating species from different trophic levels, making it a sustainable model for producing fish species with ecological and economic significance [39,40]. Advanced technologies could help mitigate the impacts of overfishing, promote ecosystem resilience, and support the socioeconomic stability of coastal communities dependent on sardine fisheries.

In small pelagic fish such as the common sardine (S. bentincki), lipids represent the primary organic constituents and serve as essential bioenergetic reserves [41]. Among these, fatty acids (FAs), particularly highly unsaturated fatty acids (HUFAs) such as docosahexaenoic acid (DHA = C22:6n3) and eicosapentaenoic acid (EPA = C20:5n3)—play a central role in key physiological and life-history processes including growth, reproduction, and migration [42,43]. These biomolecules, stored in tissues such as the muscle, liver, and gonads, are biosynthesized primarily by marine phytoplankton [44], making their availability in fish highly dependent on dietary intake rather than endogenous synthesis [41,45]. Temperature is a critical factor influencing fatty acid composition in marine organisms [33], and ongoing ocean warming has been shown to reduce the availability of omega-3 HUFAs in marine food webs by decreasing phytoplankton biomass [46,47]. This poses a significant concern not only for ecosystem health but also for the nutritional quality of fishmeal derived from sardines, which is widely used in aquaculture feeds and human consumption [48].

Given these dynamics, investigating the fatty acid profile of S. bentincki under varying thermal conditions is essential for understanding how environmental change may impact sardine nutritional quality, reproductive potential, and ecological function. Moreover, fatty acids are recognized as valuable biological indicators in marine systems, reflecting both dietary sources and the physiological status of fish populations [44,49]. At the level of the marine food web, long-chain polyunsaturated fatty acids (LC-PUFAs) may decline in the abundance and/or quality of primary planktonic food sources in response to increasing temperatures [46,47]. In addition, LC-PUFA availability may vary due to ecological processes among taxonomic groups, leading to reductions in their productivity and/or transfer along the trophic chain [50,51,52]. Within FA profiles, highly unsaturated fatty acids (HUFAs) are of particular interest, as they contribute to cellular membrane fluidity and confer resilience to thermal stress [50,53]. Membrane flexibility, facilitated by high levels of unsaturated fatty acids, is crucial for maintaining homeostasis and cellular function in fluctuating marine environments—a phenomenon known as homeoviscous adaptation [54,55,56]. Consistently, in small marine pelagic fish, LC-PUFAs have also been shown to play a critical role in key physiological processes at the individual level, including growth, reproduction, and nutrition [42,43]. These processes ultimately influence larval survival and the recruitment of juveniles into the adult population [42,45].

Understanding these lipid-related physiological mechanisms is therefore critical in the context of land-based juvenile sardine production within Integrated Multitrophic Aquaculture (IMTA) systems, where temperature and nutrition can be managed to enhance both fish health and product quality. In this context, IMTA can be evaluated in omnivorous species such as S. bentincki by experimentally testing whether common sardine individuals exhibit the capacity for conservative storage of LC-PUFAs or for their biosynthesis from PUFAs precursors present in the diet (for details, see the Sprecher metabolic pathway) [57]. In addition, this approach allows assessment of whether these presumably adaptive biochemical mechanisms are modulated by key factors such as temperature, diet, and salinity [58], which may ultimately reveal changes in PUFAs composition in specific tissues and/or organs [59]. Particularly, in marine ectotherms such as fishes the metabolic pathways of PUFA biosynthesis depend on the specific expression of genes and enzymatic capacity, and the fact that their degree of activation (on/off) is strongly modulated by key environmental factors (e.g., temperature, food quality, salinity), type of feeding (i.e., deposit- feeder, herbivore, omnivore, carnivore) [50,60,61].

1.5. Human Nutrition and Food Safety

In the context of human nutrition, fish is widely recognized as a healthy food [62]. Moreover, it represents one of the most efficient sources of animal protein in terms of feed conversion: approximately one kilogram of feed is required to produce one kilogram of fish meat, whereas pigs require around three kilograms and cattle up to eight kilograms to produce the same amount [63]. This factor is expected to become increasingly important as the global population continues to grow. The United Nations projects that the world population will increase from the current 7.7 billion to 9.7 billion by 2050 [64,65]. Given the limited availability of arable land, aquaculture is emerging as a key alternative to ensure future food security. Currently, approximately half of the fish traded globally comes from large-scale aquaculture operations. However, this is not always an ecologically viable option, as open-sea aquaculture can lead to environmental degradation due to the accumulation of uneaten feed and fish waste compounds (e.g., ammonia and feces). These wastes represent a major source of aquatic ecosystem contamination through excess nutrients (i.e., nitrogen and phosphorus) and organic matter [66,67], which degrade water quality, promote harmful algal blooms, and reduce oxygen availability [66,67]. This situation poses significant challenges to the sustainability of the sector and highlights the need for efficient management strategies to mitigate environmental impacts [65]. Considering this scenario, the present research perspective aims to develop sustainable, land-based aquaculture systems of sardines using closed-loop water recirculation and multitrophic systems. This system not only contributes to the treatment of aquaculture wastewater but also generates additional high-value products, thus enhancing the economic sustainability of the model [35,37].

1.6. RAS and IMTA

Recirculating Aquaculture Systems (RASs) provide a highly suitable platform for the intensive culture of juvenile sardines by ensuring stable and controlled rearing conditions. The external biofilter, which combines a surface water zone with an anaerobic environment, supports nitrifying microbes that regulate ammonia and nitrogenous waste—factors particularly critical for the survival of delicate early life stages [68]. Suspended particles are removed with solid filters, while sterilization methods such as UV treatment minimize pathogen loads and improve overall water quality [69]. Continuous recycling of water through biological and drum filters maintains consistent environmental conditions, reduces water consumption, and promotes robust fish health. Compared to traditional outdoor systems, RASs are more compact and resource-efficient [70], allowing sardine juveniles to be reared year-round under optimized conditions with reduced environmental impact [70,71]. For juvenile production, additional benefits include improved waste management, enhanced nutrient recycling, stricter disease control, and minimized risks of biological contamination—factors that directly support high survival rates and uniform growth [72]. Ongoing advancements, such as the integration of artificial wetlands and coastal habitat analogs, further enhance nutrient recycling and water quality stability within RASs [73].

In turn, the Integrated multi-trophic aquaculture (IMTA) is an innovative and ecologically balanced approach that combines species from different trophic levels, where the by-products (e.g., waste nutrients) of one species serve as inputs (e.g., food, fertilizer) for another [74,75]. In land-based systems, IMTA provides a controlled environment in which key parameters—such as temperature, water quality, and feeding regimes—can be precisely managed to optimize the growth and survival of sensitive species like juvenile sardines (S. bentincki). By integrating primary producers (e.g., algae) and filter feeders (e.g., mussels) with sardines, nutrient recycling is enhanced, water quality is improved, and ecological impacts are minimized. This closed-loop system not only increases production efficiency and sustainability but also reduces risks related to disease, pollution, and environmental variability that commonly affect open-water systems. The land-based IMTA model therefore offers a promising platform for the reliable, scalable production of juvenile sardines for restocking programs, supporting the recovery of overexploited populations and strengthening the resilience of coastal fisheries. Finally, the success of sardine hatchery also depends on careful site selection, with facilities located in areas that minimize environmental impact while ensuring accessibility, production efficiency, and proximity to restocking or market destinations [76].

Both ecological culture systems (RAS and IMTA) have been tested in a wide range of marine organisms, including algae, bivalves, crustaceans, and fish [77]. These organisms are commonly used as model species in such systems because they exhibit key characteristics, such as relatively low nutritional requirements associated with mid- to lower-trophic levels, high physiological flexibility and tolerance, high commercial value, and, in some cases, overexploitation by coastal fisheries [77,78]. Comparatively, these culture systems may present some minor disadvantages, including dependence on water with appropriate salinity and stable temperature conditions to ensure individual maintenance and survival [79]. In addition, high mortality due to cannibalism has been reported in some cases, often associated with inadequate stocking densities and insufficient feed supply [79]. From an aquaculture nutrition perspective, given the high commercial value of cultured species, it is necessary to explore not only essential fatty acids in their diets but also other essential nutrients, such as amino acids and vitamins [59,80]. Together, these nutrients play an important role in shaping the nutritional profile of the edible tissues of aquatic resources [58].

1.7. Husbandry Conditions and Production Cycle

This perspective article proposes a dual approach and valuable practical details to secure a reliable supply of juvenile sardines (S. bentincki) for experimental and restocking purposes by combining wild collection with controlled tank-based production. Wild specimens should be obtained from coastal waters using standardized plankton nets and juvenile traps, in collaboration with local fisheries and under appropriate environmental permits, before acclimation and rearing under laboratory conditions. Simultaneously, broodstock should be maintained in recirculating aquaculture systems (RAS) to induce natural spawning, providing a continuous, year-round source of eggs, larvae, and juveniles. Rearing densities and culture conditions should follow established methodologies for small pelagic fish [6,7,36] and be informed by detailed descriptions of the morphological and developmental stages of S. bentincki [17,81,82]. In this context of ontogeny and the production cycle, particular emphasis should be placed on the husbandry conditions, rearing practices, and developmental timing of each ontogenetic stage of S. bentincki, which are considered “bottleneck” phases in the culture of small pelagic fishes. For details on each developmental phase and the duration of ontogeny—from embryogenesis through larval and juvenile stages to first sexual maturity—see [17,18].

1.8. Future Work

Finally, to support integrated ecological aquaculture, a conceptual plan with key objectives should be include: (i) developing and evaluating broodstock and early-stage rearing systems within RAS; (ii) identifying environmental and biological factors affecting larval growth and survival; (iii) establishing a pilot-scale integrated multi-trophic aquaculture (IMTA) system for juvenile sardines; (iv) assessing nutrient dynamics and species interactions; and (v) monitoring growth, survival, and health to define best husbandry practices. By combining controlled production with ecological integration, this approach provides a framework for sustainable juvenile sardine cultivation, supporting both research and restocking initiatives. For details of conceptual model, see infographic (Figure 1).

2. Conclusions

This perspective offers an innovative scientific and technological approach by establishing foundational knowledge that links environmental variability—specifically water column temperature in coastal ecosystems—with the biological performance and economic viability of the common sardine (S. bentincki) fishery. By connecting environmental drivers to extraction timing and post-harvest processing, the research covers the way for evidence-based conservation strategies such as environmentally adaptive fishing closures, which could optimize both the biological sustainability and economic return of the fishery.

From a technological standpoint, this interdisciplinary proposal breaks new ground by evaluating the physiological responses of common sardines reared in land-based, controlled aquaculture systems, under varying stressors and water quality conditions. The future research project will generate critical data on growth, feeding behavior, water quality tolerance, and system management—forming the technical basis for the development of novel confined aquaculture technologies for this ecologically and economically significant species. Such farming systems may help reduce fishing pressure, enhance year-round availability, and support targeted restocking strategies, contributing to the rebuilding of depleted natural populations.

Furthermore, this interdisciplinary perspective explores the integration of the common sardine into land-based Integrated Ecological Aquaculture Systems (RAS, IMTA), capitalizing on its mid-trophic position and high nutritional value. This approach introduces a new model for ecological efficiency and nutrient recycling in aquaculture, positioning S. bentincki as a strategic species for diversifying sustainable production systems. The implementation of small-scale IMTA and restocking units in artisanal fishing covers offers a socio-technological innovation that empowers coastal communities by creating employment, reducing income vulnerability, and promoting the co-management and ecological stewardship of local marine resources. Collectively, these approaches support policy strategies focused on sustainable exploitation, stock rebuilding, reduced fishing pressure, and strengthened socio-economic resilience of artisanal coastal communities, contributing to marine biodiversity conservation, food security, and long-term fisheries sustainability.