Siberian Sturgeon (Acipenser baerii, Brandt, 1869) The Relationship Between Genetic Resources and Acclimatization: Ecology, Conservation, and the Nutritional Significance of Meat and Caviar

1. Introduction

Sturgeons are among the oldest and most evolutionarily distinct vertebrate lineages alive today. The order Acipenseriformes stands apart from all other bony fishes through a set of primitive traits that has been kept largely intact. These include a cartilaginous skeleton, a heterocercal tail, skin without true scales and a notochord that remains functional even in adulthood [1,2,3,4]. The family Acipenseridae itself counts 27 living species spread across four genera, Acipenser, Huso, Scaphirhynchus and Pseudoscaphirhynchus, a group that has changed remarkably little over more than 200 million years [2,5,6,7]. That evolutionary staying power has not translated into resilience in the modern era. Nearly every sturgeon species alive is now considered threatened or critically endangered, putting the family among the most at risk vertebrate groups on the planet [8,9,10]

Interest in sturgeon biology has picked up noticeably over the last approximately thirty years. This has been pushed along by conservation urgency, by efforts to rebuild depleted wild stocks and by the fast growth of sturgeon aquaculture worldwide [7,10,11]. Early work on Acipenser baerii stayed largely confined to the Ob and Irtysh basins, mostly because Siberian habitats are remote and the wild populations there were already sparse. It was not until 1961 that anything like systematic research on the eastern populations got underway, with long term studies in the Lena River basin providing the first real picture of the species’ ecology and life history [12.13]. Since then, the field has broadened considerably. Europe and Asia in particular have produced a steady stream of work on genetics and genomics, reproductive physiology, nutrition, immunology, environmental tolerance and aquaculture methods [8,14,15,16].

From a nutritional point of view, A. baerii behaves in the natural environment as an opportunistic benthic feeder, consuming insect larvae, oligochaetes, mollusks, crustaceans, and small fish [17,18]. This dietary flexibility carries over well into captivity. The species can grow efficiently on diets high in plant derived protein without any real loss in performance, so long as essential amino acid needs are covered [19,20,21]. That has made it an attractive candidate for sustainable feed development, meaning feeds that cut back on fishmeal without sacrificing growth or welfare in intensive systems [8,22,23]. Despite being critically threatened in its natural range, A. baerii adapts unusually well to farming, which is precisely why it has become one of the main species used in commercial sturgeon production globally [3,4,11,24,25]. Fast growth, tolerance of a wide range of environmental conditions, reliable artificial reproduction and compatibility with recirculating systems all make a strong biological model for a more broadly sturgeon farming [8,11,16].

This narrative review synthesizes current knowledge on the ecology, reproductive biology, aquaculture production systems, meat and caviar quality, and conservation of A. baerii, while identifying current knowledge gaps and highlighting future research priorities for sustainable sturgeon production and management.

2. Material and Methods

A narrative analysis was conducted by systematically searching major international scientific databases and authoritative institutional sources, including Google Scholar, ScienceDirect, Web of Science, Scopus, PubMed and ResearchGate, as well as technical reports and datasets published by the Food and Agriculture Organization of the United Nations (FAO) and the International Union for Conservation of Nature (IUCN). The searches combined predefined keywords such as Acipenser baerii, Siberian sturgeon, sturgeon aquaculture, caviar production, sturgeon meat, reproductive biology, conservation, polyunsaturated fatty acids, no-kill technology and sustainable aquaculture, using connectors to refine the results. Duplicate records were first removed. The remaining titles and abstracts were then checked against the scope of this analysis, and anything unrelated to the ecology, reproduction, conservation or nutritional value of A. baerii was removed at this stage. A study was excluded if it was only a conference abstract without a full paper behind it or if the methodology was not reported clearly enough to assess its quality. The year of publication was not restricted, the fundamental studies on sturgeon biology date back to 1993 and these remain relevant alongside the most recent works available at the time of writing, so both were retained. After this process, 177 studies were included in the final analysis.

A bibliometric analysis was also performed using VOSviewer (v.1.6.20; Leiden University) to complement the narrative synthesis with a quantitative perspective on current research trends on Acipenser baerii. Although the broader bibliographic search above included fundamental studies without a lower date limit, this analysis was deliberately limited to Web of Science data from 2023–2026, in order to capture only the most recent changes in research focus. Author keywords appearing at least three times were included in a co-occurrence analysis, which produced 19 keywords with the strongest links. The resulting network, shown in Figure 1, indicates the main research clusters and publication trends in the field.

3. Ecology of the Siberian Sturgeon

The Siberian sturgeon (Acipenser baerii, Brandt, 1869) is a potamodromous freshwater species characterized by remarkable ecological and morphological plasticity, capable of surviving in habitats with highly variable thermal and trophic conditions [4,7,8,18,26]. Its native range spans a vast region of northeastern Eurasia, from the Ob River basin in the west to the Kolyma River in the east, between approximately 48°–74° N latitude and 70°–97° E longitude, encompassing all major Siberian rivers draining into the Arctic Ocean [4,7,8,26]. This extensive distribution reflects the remarkable environmental adaptability of the species, which has contributed to its successful establishment in commercial aquaculture under diverse production conditions [11]. The Ob River holds ecological significance for the species, representing the most extensively studied and productive habitat within its range [4,27]. Beyond the Siberian River systems, A. baerii is also found in the tributaries of the Angara River and in the Bratsk reservoir, where it is widely distributed [28].

The Siberian sturgeon was introduced to Romania relatively recently, alongside the development of intensive aquaculture technologies, and has become widespread on Romanian farms due to its high growth potential, disease resistance, and adaptability to various production systems [29]. Delayed sexual maturation is a common trait throughout the genus Acipenser, but A. baerii exhibits a high degree of plasticity in the relationship between growth rate and age at first reproduction, primarily mediated by food availability and water temperature [29,30].

The migratory behavior of A. baerii differs significantly from that of purely anadromous sturgeons and is strictly adapted to local ecological conditions [30,31]. In the Ob River, both juveniles and adults migrate upstream from the Gulf of Ob to feed. However, only the adults continue on to the spawning grounds located downstream, a process occurring between late May and early June at temperatures of 8–11 °C and ceasing at 18–19 °C [30]. The Lake Baikal population is exclusively potamodromous and travels long distances, as the lake’s feeding grounds are spatially separated from the spawning grounds [18,30].

This characteristic allows the species to sustain intense reproductive activity even under suboptimal nutritional conditions [12]. From a feeding ecology perspective, behavioral and trophic adaptations are evident from the earliest ontogenetic stages, both under natural and laboratory conditions [19,20,21,30]. In particular, empirical studies have shown that A. baerii can maintain somatic growth rates equivalent to those achieved on diets completely devoid of animal protein, provided that the requirement for essential amino acids is fully met a finding that suggests a significant physiological predisposition toward utilizing plant-derived nutrients, consistent with the species’ general classification as omnivorous [18,30].

The Siberian sturgeon (Acipenser baerii) is classified as Critically Endangered on the IUCN Red List, a classification that reflects the dramatic collapse of wild populations throughout its Siberian range [31,32,33,34]. The decline is due to a combination of factors such as overfishing and poaching, driven by international demand for caviar, despite international bans and protective regulations in the Ob and Yenisei River basins [35,36]. Furthermore, habitat fragmentation caused by the construction of hydroelectric dams has blocked migration routes and led to the loss of up to 40% of spawning grounds [28,37], while pollution from industrial activities has caused severe reproductive abnormalities (affecting 80–100% of females in some cases) in populations of the Ob, Kolyma, and Indigirka rivers [38,39]. The species’ intrinsic biological vulnerability, such as late sexual maturity and long intervals between reproductive cycles, severely limits the ability of populations to recover naturally in low-productivity northern ecosystems [10,28,33,39].

Legally, the species is protected under CITES (Appendix II, 1997–1998) and various regional restrictions, but enforcement remains inconsistent, and poaching continues to threaten wild populations [34,36,40,41,42]. Integrated strategies are therefore needed, combining in situ conservation with living gene banks and rigorous genetic monitoring, such as that at Konakovo [43,44,45]. Advances in environmental monitoring, animal welfare, and physiological indicators are expected to support both conservation and commercial production, particularly in the context of increasingly frequent chronic heat stress [16,46].

4. Reproductive Biology of Acipenser baerii

4.1. Sexual Maturation and Gonadal Development

The Siberian stork adopts a stage-based life strategy that prioritizes extensive somatic growth before energy is redirected toward reproductive metabolism [18,47]. Sexual maturity occurs late, and the timing of its onset varies considerably depending on the environmental temperature and food availability [18]. Natural populations reach sexual maturity relatively late, females between 11 and 22 years of age, males between 9 and 19 years of age, and the slowest growth rates have been documented in populations in the cold waters of northern Russia [18,33]. Under aquaculture conditions, however, optimized temperature regimes and continuous feeding significantly shorten this interval: males reach maturity at 3–6 years, and females reach reproductive maturity at 6–8 years, with controlled reproduction allowing for the synchronization of gonadal development with production cycles [15,32,48]. Gonadal differentiation can be observed around 18 months of age, while sexual differentiation at the molecular level sometimes begins much earlier, as early as 3–6 months after hatching [49], analyses conducted on the offspring of gynogenetic females have allowed for a more precise structural characterization of this process [50].

The absence of external sexual dimorphism in A. baerii means that sex identification and maturity assessment, for both wild and aquacultured specimens, depend on gonadal biopsies, plasma hormone assays, and ultrasound examinations [15,32,51]. Ultrasound examination has proven particularly effective for sex determination in young specimens, offering a noninvasive alternative to biopsy [52], and the ovarian structure, including the organization of oocyte nests, has been described in detail in farmed females through histomorphological analyses [53]. In females, the progressive increase in 17β-estradiol during vitellogenesis remains one of the most reliable biochemical markers of approaching puberty [32]. Testosterone concentrations may also increase considerably toward the end of maturation, as estradiol is actively involved in processes of sexual differentiation, including experimentally induced sexual transdifferentiating [54,55]. The final maturation of oocytes is controlled by progestins, particularly 17,20β-dihydroxy-4-pregnen-3-one, while spermatogenesis is controlled by androgens, specifically testosterone and 11-ketotestosterone [15,32]. Sperm morphology and biochemical changes during short-term storage provide additional markers of reproductive status [56,57]. The reproductive process is triggered by GnRH, which stimulates pituitary secretion of gonadotropins and gonadal steroidogenesis [32], and reproductive performance can be predicted by the in vitro ovulation rate of isolated follicles [58]. Phytoestrogens in the diet, especially those from soy, can induce vitellogenin synthesis in immature individuals or males, disrupting hormonal sex determination [16,18].

4.2. Ovarian Cycle, Fecundity, and Reproductive Ecophysiology

A defining reproductive characteristic of A. baerii is asynchronous gonadal development: females do not produce eggs annually, and the extended intervals between egg-laying serve to replenish energy reserves depleted between reproductive events [53,59,60]. In natural habitats, the resting interval between successive spawning events averages 3–5 years, whereas under optimized aquaculture conditions this interval may be reduced to 1–2 years [18,60,61]. Histological analyses of farmed broodstock indicate that the biennial ovarian cycle is the most commonly observed pattern, though annual and triennial cycles have also been recorded within the same population, reflecting substantial individual variability [60,62]. With respect to fecundity, A. baerii produces eggs of intermediate diameter (3.0–3.6 mm), with individual mature oocyte mass ranging from 10.8 to 25.0 mg slightly lower than values recorded for related ponto-caspian species, a characteristic inversely correlated with the large clutch sizes that enhance offspring survival in the harsh Siberian environment [18,63]. The gonadosomatic index may exceed 20% in cultured individuals and reach up to 67% in certain wild populations [18,64]. In natural spawning habitats, females select hard substrates of rock or gravel in deep fluvial zones with moderate current velocity, conditions that facilitate secure egg adhesion while preventing siltation-induced asphyxiation [30,65,66]. Optimal water temperature ranges for natural reproduction and hatching exhibit a clinal pattern, ranging from 8–18 °C in the Lena River to 16–21 °C in the Kolyma system [67].

4.3. Embryonic Development and Early Life Stages

Embryogenesis in A. baerii proceeds through well-defined sequential stages, including asymmetric holoblastic cleavage, blastulation, gastrulation, neurulation, and organogenesis, with gastrulation representing a particularly sensitive phase susceptible to developmental abnormalities [50,67,68,69]. Developmental rate is strongly temperature-dependent, with elevated incubation temperatures accelerating hatching while potentially compromising embryonic survival and modulating the yolk-sac absorption rates [50,70,71]. Upon hatching, the prolarvae emerge approximately 10–12 mm in length, with their mouths still closed, relying exclusively on the endogenous reserves of the yolk sac for nutrition, a stage during which energy is produced through an intense fatty acid metabolism [15,66,67]. Hatchlings initially exhibit positive phototaxis and vertical swimming behavior (swim-up and drift), transitioning to benthic locomotion and shoaling as yolk absorption progresses [30,66].

The shift to exogenous feeding occurs approximately 9–11 days post-hatching at 18 °C and represents a critical developmental threshold and a recognized mortality bottleneck for larval survival [15,32,48,70]. Introduction of live feeds such as Artemia nauplii at this stage significantly enhances early growth and survival rates, though gradual transition to microdiets is feasible [51,70]. Skeletal and digestive anomalies may emerge under suboptimal nutritional or environmental conditions, such as sustained elevated temperatures, during early ontogeny [28,48], while high stocking densities may reduce juvenile growth performance through competition and stress responses, despite the species’ relatively high-density tolerance [51,72,73,74].

4.4. Artificial Reproduction and Hatchery Management

Acipenser baerii does not reproduce spontaneously in captivity and therefore requires controlled broodstock management incorporating both thermal conditioning and hormonal stimulation [15,32,76]. A mandatory pre-spawning wintering phase (vernalization) requires maintaining broodstock at 2–8 °C for a minimum of one to three months, a thermal cue essential for completing gametogenesis and ensuring gamete quality prior to the spring spawning induction [15,32,58,75]. Water temperature is subsequently raised progressively to 15–16 °C to initiate the ovulatory response [58,76]. Selection of reproductively competent females for hormonal induction represents the principal technical challenge in hatchery operations, as operators must prevent ovarian follicular atresia [59]. In vivo oocyte biopsy is used to confirm follicle diameter exceeding 2.8 mm, while the polarization index of the germinal vesicle serves as the key indicator for determining optimal induction timing [32,50,58,59,60].

Ovulation and spermination are induced using carp pituitary extract or synthetic GnRH analogues (such as LHRHa), the latter increasingly preferred due to superior egg quality outcomes and reduced physiological stress; females typically receive two injections (a priming dose and a resolving dose) while males receive a single dose, sometimes combined with dopamine antagonists to enhance response [15,32,76,77]. Gamete collection may be performed through minimally invasive approaches such as the Podushka technique, involving a small incision of the oviduct wall, key-hole microsurgery, which circumvents the need to sacrifice mature broodstock females, or via surgical laparotomy depending on individual size and developmental stage [15,78,79,80]. Fertilization is carried out using the semi-dry method, followed by egg de-adhesion with clay, milk, talc suspensions, tannin solutions, or diluted sodium hypochlorite, and subsequent incubation in Weiss or Osetr-type incubators at optimal temperatures of 12–16 °C for A. baerii [15,23,50,81]. Finally, sperm cryopreservation offers an important tool for genetic resource conservation and broodstock optimization, though sperm quality (DNA integrity, motility, oxidative stress) varies considerably among individual males and standardized protocols, such as optimal cryoprotectants like methanol or dimethyl sulfoxide (DMSO), remain an active area of development [32,82,83,84].

5. Products Derived from Acipenser baerii: Production Systems, Quality, and Market Positioning

5.1. Production Systems and Resource Efficiency

Production systems and resource efficiency Sturgeon aquaculture relies on a mix of production technologies, and their share differs a lot from one region to another. Table 1 summarizes rearing conditions across the wild environment and the main aquaculture systems used for A. baerii. Globally, flow-through systems still lead with 36% of production, followed by recirculating aquaculture systems (RAS) at 21%, floating cages at 18%, and earthen ponds at 6%, the rest coming from hybrid setups [3,85]. Local resources play a big role in which technology dominates: cages cover about a quarter of production in China and two thirds in Russia, while earthen ponds are the norm across Western and Central Europe [3]. However, recent environmental regulations have begun to restrict open cage culture in inland waters, notably in China, driving a shift towards land-based systems [48]. RAS is growing fast worldwide because of its high water-reuse rates, which typically range from 80% to 99% depending on management practices [51]. Stricter environmental rules and limited water availability push producers toward these closed systems, which give tighter control over oxygen, temperature, and nitrogenous compounds, all critical for A. baerii physiology [86,87,88].

RAS does demand more energy, but it cuts water use and effluent discharge substantially compared to flow-through or pond systems, which explains why it keeps expanding, especially where water is scarce [3,87]. A. baerii is now the main species used for caviar in several countries, including France, China, Italy, and Uruguay, with China leading global production of farmed sturgeon caviar [11,61,89,90].

Beyond the choice of system, integration into multitrophic setups like aquaponics looks promising when water quality is tightly controlled, although alternative diets, such as full-fat insect-based meals, still need work on palatability and growth performance [20,91]. Stocking density also matters directly for welfare and productivity, higher densities slow growth and raise stress levels in early life stages by inducing chronic stress and impairing the antioxidant system [51,73,91,92]. Juvenile A. baerii can recover from this: after periods of feed restriction followed by re-feeding, they show compensatory growth, which points to a real metabolic capacity to bounce back after nutritional stress [93,94].

5.2. Caviar Harvesting Methods and No-Kill Technology

Caviar is produced through two main methods: conventional harvesting, which sacrifices females after 6–10 years for premium malossol caviar with strong stability and shelf life [11,15], and no-kill technology, which allows five to seven harvest cycles over 15+ years per female, improving asset utilization, stabilizing output, and lowering long-term costs [11,104,105,106].

No-Kill relies on ovulated eggs, whose soft, adhesive membranes require post-harvest stabilization (e.g., thermal coagulation, tannin cross-linking, patented molecular treatments, or pH-adjusted cold-water processing) to match conventional caviar’s texture and stability [63,104,107,108,109]. Extraction uses minimally invasive techniques such as the Podushka (oviduct incision), the minimally invasive surgical technique (MIST), and abdominal stripping methods [15,78,110]. Codex Alimentarius permits labeling such products as caviar when methods are declared, and strictly requires that any hormones used to induce ovulation be approved by the competent authorities, supporting market integration [11,111].

However, repeated hormonal induction, surgical incisions, and handling raise unresolved welfare concerns, including the risk of muscular stress, suture ruptures, infections, and even mortality [79,105]. Furthermore, ovulated-egg caviar may show reduced bead integrity, a heterogeneous texture, and altered mouthfeel versus conventional product. This occurs because the eggs ripen and form a shell (chorion) which hardens upon contact with water, significantly impairing the typical melting sensation associated with the traditional egg membrane [63,107,112,113,114]. Overall, No-Kill boosts efficiency and scalability at the cost of trade-offs between sustainability, standardization, and welfare [104,105].

5.3. Sensory Quality and Technological Determinants

The sensory characteristics of A. baerii caviar are directly influenced by post-harvest processing, diet, and oocyte maturity stage [63,115]. Premium caviar is valued for its delicate buttery, nutty, and subtle oceanic aromas, complemented by a balanced texture combining slight resistance on the palate with a creamy finish, driven by free amino acids and specific nucleotides (e.g., inosinic acid) that impart a strong umami taste [115,116].

Siberian sturgeon caviar is frequently compared to Acipenser gueldenstaedtii (Osetra) in terms of egg size and coloration, though its sensory profile is characterized by buttery and yeasty notes with mild sweetness and earthy nuances, in contrast to the more pronounced marine or anchovy-like aromas typical of wild-caught sturgeons [63,107]. Recent advanced aroma profiling further describes the scent of both species with “fatty”, “fishy”, “seawater-like”, and “green/grassy” notes, which are primarily driven by aldehydes and alcohols derived from lipid oxidation during maturation [117].

A major technological challenge in quality control is the prevention of off-flavors, particularly the earthy or muddy taste caused by the volatile compounds geosmin and 2-methylisoborneol (MIB) produced by cyanobacteria and actinomycetes present in the rearing water, which rapidly accumulate in adipose tissue and roe [118,119]. To mitigate this defect, producers implement a pre-harvest purification protocol, in which sturgeons are kept in clean freshwater without being fed for several weeks prior to roe harvesting [119,120,121]. Additionally, seasonality and the duration of maturation heavily impact the volatile profile; for instance, spring-harvested caviar often exhibits higher levels of desirable “milky” or “buttery” flavors, while an optimal cold-storage maturation period of 6 to 9 months is critical for proper flavor development [119].

Post-harvest processing parameters also substantially influence the quality of the final product: for example, rinsing the eggs with cold water at an adjusted pH produces caviar that is darker in color, firmer, and glossier with a distinct “popping” sensation, compared to washing with hot water which can induce a slimier texture and a stronger seaweed odor [109].

5.4. Market Positioning

The global sturgeon market was fundamentally restructured following the collapse of wild Caspian stocks and the introduction of strict CITES conservation regulations in 1997, which effectively redirected nearly all commercial caviar production toward aquaculture [36,64,122]. Caviar retains its status as a global luxury commodity with premium pricing; however, the rapid international expansion of sturgeon farming, an industry dominated by China, which accounts for over 84–85% of global output [25,123,124] has generated a clear overproduction trend and a supply-demand imbalance, exerting sustained downward pressure on wholesale prices [3,90,125].

In response, industry analysts are increasingly anticipating the need for strategies to reposition luxury products in order to expand accessibility to middle-class consumers in emerging economies. Through the adoption of “masstige” (mass-prestige) marketing strategies, producers aim to absorb excess production while preserving brand value [90.104]. Sturgeon meat, in parallel, benefits from established domestic markets in Russia, China, and Eastern Europe, where it has longstanding cultural traditions and is commonly consumed [11,125] while achieving commercial success in Western markets through premium niche positioning as smoked fillets and luxury preserves [63,125].

Siberian sturgeon (Acipenser baerii) caviar occupies an accessible luxury segment priced significantly below Beluga (Huso huso) and premium Osetra (Acipenser gueldenstaedtii) [124], yet offering consistent quality, reliable supply, and strong consumer acceptance, making it a cornerstone of the legal global caviar market and accounting for approximately 31% of the total global caviar volume [11]

5.5. Meat and Nutritional Composition

Acipenser baerii meat is highly valued for its firm texture, absence of intramuscular bones, and favorable nutritional profile [63]. It is generally classified as a moderate-to-high fat, protein-rich food product with high biological and nutritional value [126].

Proximate composition. The flesh of A. baerii is characterized by high protein content and moderate lipid levels. Reported protein concentrations range from approximately 15.0% to 20.0%, while lipid content varies between 2.3% and 12.5%, depending on species, age, body size, and culture system [126,127]. Moisture content ranges between 70% and 78% [126]. Specimens reared in recirculating aquaculture systems (RAS) may exhibit higher protein (e.g., 23.74% dry matter) and fat concentrations compared with wild-caught individuals, reflecting efficient feed utilization under controlled conditions [128].

Amino acid profile and protein quality. The protein fraction exhibits high biological value, with a balanced profile of essential and non-essential amino acids [129]. The most abundant amino acids include glutamic acid, aspartic acid, lysine, and leucine. Lysine concentrations range from approximately 9.69 to 10.02 g per 100 g protein, and chemical scores generally exceed FAO/WHO reference patterns for most essential amino acids, confirming the high nutritional quality of sturgeon meat protein [130].

Lipid profile. Sturgeon meat is a valuable dietary source of polyunsaturated fatty acids (PUFAs), which may represent 40–50% of total fatty acids [63]. The omega-3 fatty acids EPA and DHA are particularly noteworthy, and the n-3/n-6 ratio falls within the optimal range for human health [126,131]. The fatty acid composition is, however, strongly influenced by feed formulation: partial replacement of fish oil and fishmeal with plant-based ingredients increases the proportion of omega-6 fatty acids, particularly linoleic acid, relative to omega-3 fatty acids compared with wild populations [126,129]. Early dietary programming with long-chain n-3 highly unsaturated fatty acids (n-3 HUFA) has been shown to influence growth, antioxidant response, and lipid metabolism in A. baerii [132], further underscoring the importance of feed formulation during early ontogeny. Despite this shift, the meat remains a meaningful source of EPA and DHA [129]. Additionally, sturgeon meat supplies essential minerals (magnesium, phosphorus, iron, zinc) and important B-complex vitamins, including vitamin B12, niacin, and pyridoxine [126].

Color and texture. The flesh color is species-specific, generally exhibiting achromatic tones perceived as varying shades of gray, with intermediate lightness (L*) values [63]. Instrumental analysis reveals slightly negative redness (a*) values and positive yellowness (b*) values, the latter differing significantly between Siberian and white sturgeon [63]. Color varies along the fillet: the cranial and medial zones appear whiter and more luminous, while the caudal region is darker, more reddish, and more yellowish due to higher intramuscular fat content and the presence of red muscle fibers [133]. Hybridization and fish age also influence color parameters. In Siberian × Russian sturgeon hybrids, lightness (L*) decreases and redness (a*) increases with advancing age (5 to 7 years), whereas Russian sturgeon meat maintains high lightness regardless of age [134]. Texture is firm, dense, and free of intramuscular bones, making sturgeon meat an excellent substitute for chicken breast, pork, or veal [125]. Textural parameters including hardness, gumminess, and chewiness are key determinants of consumer acceptance [123]. Hybridization can further enhance textural properties through heterosis. The Siberian × Amur sturgeon hybrid demonstrates markedly superior hardness and chewiness compared with parental species, attributed to muscle fiber hyperplasia [123].

Sensory profile. In fresh condition, sturgeon meat exhibits a fresh odor with floral, fruity, or sweet notes derived from certain esters (e.g., methyl hexanoate) and alcohols [135]. The aromatic profile may also include marine, fatty, or grassy attributes produced by aldehydes (e.g., hexanal, nonanal, heptanal) and alcohols (e.g., 1-octen-3-ol) formed via enzymatic breakdown of fatty acids [136]. A significant sensory defect in aquaculture specimens is a muddy flavor caused by the accumulation of geosmin and 2-methylisoborneol in adipose tissue, which are produced by cyanobacteria and actinomycetes present in the rearing water. [64,104].

Microbiological safety and shelf life. The shelf life of chilled sturgeon fillets under aerobic packaging is limited to approximately 8 days at 4 °C, after which total aerobic colony counts (ACC) exceed the safety threshold of 7.0 log CFU/g and total volatile basic nitrogen (TVB-N) surpasses 20 mg/100 g [135]. The dominant spoilage microorganisms are Pseudomonas fluorescens, P. mandelii, and Shewanella putrefaciens, which metabolize proteins and lipids, generating volatile malodorous metabolites (e.g., hexanenitrile, thiazole, ammonia derivatives) and bitter-tasting hypoxanthine [135,137].

Market forms. Although often considered a co-product of the caviar industry, sturgeon meat is commercially vital for farm profitability and is marketed fresh, frozen, or smoked, as whole fish, steaks (medallions), or fillets [125,138]. Within the European Union, the majority of farmed sturgeon meat is frozen and exported to Eastern European and Russian markets, where strong culinary traditions support high consumer demand [63,125]. Smoked fillets command premium prices in specialized retail, while boneless meat is increasingly used in fish paste products, stuffed pastries, and raw preparations such as sashimi, sushi, and the traditional Russian stroganina [125]. The market is dominated quantitatively by males, which are slaughtered shortly after sex determination and sometimes fetch higher prices than females retained for caviar production [125].

5.6. Caviar. Nutritional Composition, Sensory Properties, and Food Safety

Caviar, defined as the unfertilized, salted roe of sturgeon, remains the primary commercial product and continues to dominate the market. It is colloquially known as “black gold” due to its gastronomic prestige and high economic value, as well as its exceptional nutritional density, with an energy value of approximately 202–271 kcal/100 g, depending on the sturgeon species and processing method [118,139,140].

Proximate composition. The physicochemical composition of sturgeon caviar is characterized by a moisture content ranging from 47.7% to 59.5%, crude protein ranging from 23.8% to 29.3%, fat between 14.2% and 19.7%, and an ash content (strongly influenced by the degree of salting) ranging from 1.9% to 3.9% [63,89,140].

Protein and amino acid profile. Caviar constitutes an excellent source of high-quality protein, with a complete and balanced essential amino acid profile exceeding FAO/WHO reference standards [89]. The most abundant amino acid is glutamic acid (7.29%–7.69%), followed by aspartic acid, leucine, and lysine [92]. These amino acids fulfill important metabolic and functional roles, supporting immune function and cellular development. The ratio of essential to total amino acids (EAA/TAA) is particularly favorable, averaging approximately 37%–38% [89].

Lipid profile and fatty acids. The lipid fraction of caviar is rich in biologically active fatty acids. Monounsaturated fatty acids (MUFAs) represent the dominant group (approximately 38%–43%), with oleic acid (C18:1n-9) as the predominant component [63,89,141]. Of particular nutritional significance are the polyunsaturated fatty acids (PUFAs), which constitute between 29% and 35% of total fatty acids [92]. Caviar is notably rich in long-chain omega-3 fatty acids, particularly EPA and DHA, which are widely recognized for their cardiovascular and neuroprotective benefits [118,140]. The omega-6 profile including linoleic and arachidonic acids is directly influenced by diet; farmed caviar typically exhibits a higher linoleic acid content compared with wild-sourced caviar [63,141]

Vitamins and minerals. Caviar is a rich source of both fat-soluble vitamins (A, D, E) and water-soluble vitamins, particularly B12, B1, B2, and B6 [140]. Its mineral composition is equally noteworthy, comprising significant concentrations of phosphorus, calcium, magnesium, iron, zinc, and copper, all of which are essential for energy metabolism and cellular function [118].

Sensory profile. The sensory experience of caviar consumption involves a complex interaction between texture, taste, and aroma. Texture is a primary quality criterion: during mastication, the characteristic “popping” phenomenon occurs, whereby the egg membrane ruptures under mechanical pressure, releasing a fine, creamy, and unctuous internal content [109,116]. Post-harvest processing significantly influences textural properties: cold-processed caviar treated with pH-adjusted water exhibits superior firmness, popping intensity, and surface gloss, whereas mild thermal treatment (pasteurization) may yield a slightly stickier and less elastic texture [109,115].

Due to elevated salt and free amino acid concentrations, the primary taste profile of caviar is a harmonious combination of saltiness, mild sweetness, slight acidity, and pronounced umami [109,116]. The umami character is primarily driven by nucleotides (including inosinic acid and AMP) and glutamic acid [115,116]. In premium caviar (e.g., Huso huso), elevated concentrations of gamma-glutamyl peptides contribute an additional complex, round gustatory dimension known as “kokumi” [115].

The aromatic profile is largely mediated by volatile organic compounds (VOCs) derived from enzymatic degradation and oxidation of free fatty acids, including aldehydes (hexanal, nonanal, heptanal), alcohols (1-octen-3-ol), and ketones [116,117]. The optimal aromatic profile is characterized by notes of sea breeze, marine algae, oyster, butter, and hazelnut [109,115,117]. Off-flavor defects arise primarily from the accumulation of geosmin, which imparts an undesirable earthy or muddy taste the same compound responsible for sensory defects in sturgeon meat, as discussed in section 3.5 [117].

The sensory characteristics of A. baerii caviar are also directly influenced by post-harvest processing, diet, and oocyte maturity stage [63]. Siberian sturgeon caviar is frequently compared with Acipenser gueldenstaedtii (Osetra) in terms of egg size and coloration, though its sensory profile is distinguished by buttery and yeasty notes with mild sweetness and earthy nuances, in contrast to the more pronounced marine or anchovy-like aromas typical of wild-caught specimens [63,107].

Microbiological safety and quality management. Freshly extracted roe is nearly sterile; however, it is highly susceptible to contamination during processing due to its high water content, near-neutral pH (5.78–6.46), and rich nutrient composition [63]. The predominant specific spoilage organisms (SSOs) identified in sturgeon caviar belong to the genera Pseudomonas (P. fluorescens, P. mandelii), Shewanella putrefaciens, and Acinetobacter [139]. These bacteria metabolize proteins and lipids, leading to the accumulation of total volatile basic nitrogen (TVB-N), biogenic amines (histamine, cadaverine), and thiobarbituric acid reactive substances (TBARS), with concomitant deterioration of the volatile compound profile and development of rancid off-odors [118,139].

Microbial growth including that of hazardous pathogens such as Clostridium botulinum and Listeria monocytogenes is controlled through a combination of salting (3%–6% NaCl), maintenance of water activity (aw) below 0.97, and cold-chain storage at −2 °C to +4 °C [66]. To extend shelf life and maintain total viable counts (TVC) below the rejection threshold of 6.0 log CFU/g, producers may apply permitted preservatives such as sodium tetraborate (E285), which effectively inhibits spoilage bacteria within EU-regulated limits or mild pasteurization [63,115,139]. Natural antimicrobial agents, including nisin, lysozyme, and polyphenols, have also demonstrated efficacy in suppressing psychrophilic bacterial growth under refrigerated storage conditions [139].

5.7. By-Products. Collagen, Gelatin, Oils, and Bioactive Compounds

Sturgeon processing generates substantial quantities of by-products, including skin, swim bladder, viscera, and cartilage, which can be valorized to improve economic efficiency and environmental sustainability [61].

Skin and leather. Sturgeon skin can be tanned into high-quality leather (shagreen), used in luxury leather goods. This practice has recently been revitalized in Europe, particularly in France, as part of circular economy initiatives in aquaculture [61,102].

Swim bladder and isinglass. The swim bladder is the traditional raw material for isinglass, a highly purified collagen historically used as a clarifying agent in wine and beer production and in art conservation and cabinet-making due to its superior adhesive properties [24,49].

Oils and lipids. Oils extracted from viscera or liver are rich in unsaturated fatty acids and may be exploited for food supplements or pharmaceutical applications [126].

Gelatin, collagen, and cartilage. Skin and cartilaginous tissues are rich in collagen, with soluble collagen representing a significant fraction of total muscle collagen [126]. Cartilage is a natural source of chondroitin sulfate, widely used in nutraceutical formulations targeting joint health [143].

5.8. Applications in the Nutraceutical, Cosmetic, and Biomedical Industries

Cosmetic applications. Caviar extracts are widely incorporated into high-end cosmetic products, including anti-aging creams and serums, due to their rich content of proteins, lipids, vitamins, and minerals. These formulations are marketed for their moisturizing and regenerative properties, with luxury brands such as La Prairie and Dermastir using caviar as a symbolic and functional ingredient [11].

Nutraceutical applications. Sturgeon-derived oils rich in EPA and DHA contribute to cardiovascular health and cognitive development, supporting their use in functional foods and dietary supplements [129]. Additionally, protein hydrolysates obtained from meat or by-products may exhibit antioxidant activity and potential health-promoting properties [63].

Biomedical applications. Chondroitin sulfate extracted from sturgeon cartilage has demonstrated immunomodulatory effects, including increases in thymus mass and mast cell numbers in experimental animal models, indicating potential therapeutic relevance [143]. Isinglass also retains technical and biomedical relevance due to its exceptional purity and collagen structure [49].

6. Knowledge Gaps and Future Research Priorities

Although Acipenser baerii has attracted increasing scientific attention in recent decades, owing to its rapid adaptation to commercial aquaculture, and is often described as a ‘living fossil,’ substantial knowledge gaps still persist across multiple biological and applied domains. Addressing these gaps requires multidisciplinary approaches integrating molecular biology, behavioral ecology, reproductive physiology, and advanced monitoring technologies, in order to ensure both the success of conservation programs and the long-term sustainability of aquaculture production systems.

6.1. Sex Determination and Early Genetic Diagnostics

The genetic mechanism underlying sex determination in A. baerii remained unclear for a long time. Although a WZ-type model had been proposed, until recently no major gene had been identified, nor were there any reliable molecular markers for early diagnosis [54]. The prolonged rearing of males, which do not produce caviar, generates additional costs estimated at up to 30% of rearing expenses [48,144], and current methods, ultrasound and endoscopy, become effective only after 3–5 years [101,145].

The research priority was early sex determination (ESD) through the identification of molecular markers during the window of sexual differentiation [54], implementing ESD at the juvenile stage (~0.5 years) offers a clear economic advantage, allowing for the early separation of males and the optimization of rearing space [145]. However, the development of reliable PCR markers, such as AllWSex2, has been hampered by the genomic complexity of sturgeons, which retain an evolutionary octoploid karyotype of ~250 chromosomes and sex chromosomes that are poorly differentiated microscopically [34,45,146].

Despite these structural challenges, a major recent discovery identified a female specific genomic region dating back 180 million years, confirming the conserved ZZ/ZW sex-determination system in Acipenseridae [146]. As a result, the AllWSex2 marker has been validated as an effective tool for qualitative PCR based genetic sex determination, enabling high accuracy sex identification well before any morphological gonadal differentiation [55,146].

6.2. Early-Life Behavioral Ecology

The behavior of prolarvae and juveniles in the wild remains poorly understood, particularly their substrate and feeding preferences [47]. Post-release survival is affected by maladaptive behaviors acquired in hatcheries; surface feeding accustoms sturgeons, which are naturally benthic, to swimming in the upper water column, increasing the risk of predation [147].

Research focuses on “survival training” prior to release: exposure to chemical signals from predators triggers avoidance reflexes [148,149], and enriching the environment with sand or gravel reduces stress and promotes natural benthic behavior [30,150,151]. Laboratory tests provide useful data, but extrapolating these findings to natural environments remains difficult [30].

6.3. Reproductive Physiology and Endocrine Disruption

The mechanisms that regulate sexual maturity and ovarian cyclicity remain essential for the management of breeding stock [0,61]. The hypothalamic-pituitary-gonadal axis is sensitive to contaminants: nitrates in RAS systems abnormally increase sex steroid levels in females, disrupting oogenesis [152,153], and thermal stress reduces gonadotropin gene expression and vitellogenin synthesis, potentially inhibiting gonadal development [154].

6.4. Cryopreservation and Genetic Resource Banking

Standardizing cryopreservation protocols remains a priority for genetic conservation [56]. Methanol, used as a cryoprotectant in place of DMSO, has improved post-thaw motility and fertilization of sperm, but the cryopreservation of oocytes and embryos remains unfeasible due to the large size of the oocytes and variability in sperm quality limits the reliability of cryopreserved material [56].

Promising approaches include the cryopreservation of somatic cells via nuclear transfer [155] and the transplantation of primordial germ cells into surrogate species, such as the cega [156,157,158].

6.5. Environmental Monitoring and Non-Invasive ASSESSMENT Technologies

The need to assess sturgeon populations and products without sacrificing the fish has driven the development of noninvasive monitoring technologies. Acoustic telemetry (VEMCO Positioning System) allows for tracking migration routes and behavioral responses to hydroelectric flow regulation [159,160], it is also essential to assess the impact of these implanted microtransmitters on the physiology and swimming ability of juveniles [161]. Furthermore, the analysis of stable isotopes (oxygen, hydrogen, carbon, nitrogen, along with sulfur and strontium) complements genetic markers in distinguishing farmed caviar or meat from poached ones [34,36,162,163].

For quality control in aquaculture, the analysis of volatile organic compounds (SIFT-MS, GC-IMS) provides a rapid and non-destructive assessment of caviar freshness, including the early detection of flavor defects and dynamic quality assessment during cold storage [119,135,136].

7. Sustainability and Future Directions

Despite the significant advances achieved in the understanding and cultivation of Acipenser baerii, several scientific and technological challenges remain to be addressed. Future research should focus on improving genetic tools for sex determination, optimizing cryopreservation protocols, developing sustainable feed formulations, enhancing animal welfare in no-kill caviar production systems, and increasing the valorization of sturgeon-derived by-products. Drawing on the evidence synthesized throughout this review, a conceptual framework is proposed to illustrate the interconnected pathways linking the natural ecology of A. baerii, aquaculture development, product valorization, and conservation outcomes (Figure 2).

As illustrated in Figure 2, the sustainable management of A. baerii requires an integrated approach that connects ecological knowledge, reproductive management, aquaculture innovation, food production, and conservation strategies. Such a framework may support both the long-term viability of the species and the economic sustainability of the sturgeon industry.

7.1. Environmental Impact and Life Cycle Assessment

Long production cycles and intensive use of resources result in a significant ecological footprint for sturgeon aquaculture, which is higher than that of other fish farming systems [164]. LCA studies indicate a global warming potential of 53.4–82.9 kg CO₂ equivalent per kilogram of caviar, depending on the species and the length of the growth cycle to maturity [90], with feed often accounting for over 70% of total emissions [90,165,166]. Strategies such as early sex determination (ESD) or the transition to renewable energy can reduce the impact by 3.7–21% [90].

Economic allocation of the impact through the utilization of meat and byproducts reduces caviar’s carbon footprint by 6–14%, aligning the industry with the principles of the circular economy [90,167,168]. There remains a need to develop new protein conversion efficiency indicators tailored to long-cycle species, given the increasingly acute competition between feed and food [169] at the production system level [61,90].

7.2. Animal Welfare and Ethical Considerations

The principles of the “Five Freedoms” are being applied with increasing frequency in sturgeon aquaculture as well [32], and the slaughter of females after years of rearing, while technically efficient, raises growing ethical concerns [105]. No-Kill technology (abdominal massage, “key-hole” microsurgery/MIST) is promoted as an ethical alternative, but research shows that the entire process, recurrent anesthesia (agents such as MS-222 or clove oil can themselves induce severe stress), repeated invasive handling, and mandatory preoperative fasting, generates severe chronic stress, undermining these claims [105,170,171,172,173]. Refusal to eat, which is common in the postoperative period, suggests persistent pain and suffering throughout the healing process [83].

Transparent regulatory and labeling standards are needed, as well as humane slaughter methods (electrical stunning, percussive stunning or ice slurries) that comply with WOAH and EFSA guidelines [104,174,175]. However, the lack of scientifically validated indicators for assessing unconsciousness in sturgeon remains a critical issue, this combined with inconsistent practices among farms, exposes the fish to the risk of prolonged and inhumane deaths [176].

7.3. Balancing Conservation and Market Demand

The listing of Acipenseridae species in the CITES Appendices has shifted commercial supply toward aquaculture, but the fraudulent substitution of cheaper roe from over 38 non-sturgeon species as genuine caviar remains a persistent problem in a competitive global market [64,118,177]. Advanced molecular methods, such as DNA barcoding (including COIBar-RFLP) and stable isotope analysis, enable the differentiation of wild caviar from farmed caviar and the rapid detection of fraudulently traded batches [34,36,122]. The expansion of the middle class and “masstige” marketing strategies have led to a significant increase in consumer demand for organic certification, animal welfare, and supply chain transparency [11,104].

8. Conclusions

Acipenser baerii (Brandt, 1869) has undergone a fundamental transition, from a heavily exploited wild resource to a species whose commercial viability depends almost entirely on aquaculture. The severe decline of natural populations in Siberian basins has rendered wild harvesting insufficient, shifting production almost exclusively to controlled systems. China, Russia, and several European countries have established themselves as leading producers, supported by the species’ remarkable ecological plasticity. Being predominantly freshwater and potamodromous, A. baerii avoids the physiological constraints of salinity transitions and tolerates temperature fluctuations and high stocking densities well, making it suitable for RAS systems, ponds, or cages.

The sector’s sustainability depends on several interconnected factors, such as identifying viable alternative protein sources capable of reducing the environmental footprint of production, managing genetic risks, and the potential for hybridization resulting from accidental escapes from aquaculture farms. Overall, the industry’s ability to balance economic profitability with environmental responsibility, genetic conservation, and ongoing technological innovation remains a key challenge. A. baerii thus remains a species of strategic importance for global luxury aquaculture, and its future development, including within the specific context of Romanian aquaculture, will depend on the balance between production efficiency, environmental protection, and ethical standards in an increasingly regulated market.