24 DECEMBER • WORLD AQUACULTURE • WWW.WAS.ORG processes. Importantly, no mortality was observed within the first 72 hours following surgery, indicating that the surgical and anesthetic protocols were well tolerated by all individuals. Ethical and Welfare Considerations This experiment followed ethical guidelines for invertebrate handling. Anesthetic application minimized discomfort and prevented reflex responses. No harmful agents were used at any stage, and oysters were allowed to recover fully postsurgery. The use of MgSO4 ensured non-lethal, reversible immobilization, enabling repeated procedures if needed for longitudinal studies. The comparative evaluation between Batch 1 and Batch 2 revealed marked differences in survival rate, graft retention, and pearl quality — primarily influenced by the degree of environmental control, microbial connectivity, and nutritional strategies employed. The pearls were harvested after 247 days of onshore rearing, allowing for a full gestation cycle under monitored conditions. Batch 1 exhibited a moderate survival rate of approximately 55%. While the setup ensured physicochemical stability, the pearl outcomes were suboptimal. Many pearls from this batch showed irregular shapes, surface blemishes, and inconsistent nacre layering. Elevated tissue rejection was observed during the post-operative recovery phase, possibly linked to physiological stress caused by confinement, mechanical water processing, and reduced microbial exposure. Despite adequate aeration, the absence of native microbial cues and ecological complexity may have compromised the oysters’ immune modulation and tissue integration capacity. In contrast, Batch 2, transitioned post-surgically into a seminatural, unfiltered seawater system with ambient light and continuous natural flow-through circulation, exhibited superior biological performance. Mortality was limited to only 2%, and 119 pearls were harvested, of which approximately 60% were graded as high-quality based on their intense luster, symmetry, and uniform nacre thickness (Figure 3). The success of Batch 2 is attributed to the natural thermal range (19–23°C), sustained by ambient seawater, and the presence of in-situ photosynthesizing microalgae and native microbial communities, including beneficial bacteriophages. These microbiota are hypothesized to have provided post-surgical immunological support and pathogen control, mimicking the biological advantages observed in offshore environments. Importantly, despite being fed with non-mediumbased algae cultivated through photosynthesis in natural seawater (without nutrient enrichment), the oysters in Batch 2 did not exhibit any decline in pearl quality compared to those in Batch 1 (Figure 4). This finding challenges conventional dependency on nutrient-enriched culture media and introduces a viable, cost-effective alternative for sustainable feed production — particularly relevant for resource-constrained farming systems. In summary, this 247- day rearing trial demonstrated that the integration of microbial exposure, natural food webs, and ambient environmental dynamics significantly enhances oyster survival, immune resilience, and pearl biomineralization. The seminatural rearing environment of Batch 2 functioned as a bio-intelligent system, aligning with the oysters’ evolutionary physiology and leading to consistent production of premium pearls with minimal intervention. These findings strongly advocate for a paradigm shift in onshore pearl production — moving away from over-engineered, sterile systems toward ecologically enriched, self-regulating environments that not only improve biological outcomes but also promote long-term sustainability in pearl production. Environmental Observations Wave dynamics and oxygenation were found to be critical for both systems. Wave makers installed in each tank successfully enhanced dissolved oxygen levels and simulated mild tidal flows, mimicking natural estuarine conditions. These devices prevented the formation of stagnant zones and sedimentation, both of which can compromise the health and function of oysters. The stable hydrodynamic conditions achieved through these interventions contributed significantly to the physiological well-being of the grafted oysters, ensuring that oxygenation and nutrient distribution remained consistent. Another major advantage observed across both onshore systems was the complete absence of predation and biofouling—two common and costly challenges in traditional offshore pearl culture. The secure, enclosed nature of the onshore tanks effectively eliminated the risk posed by marine predators. Additionally, the tanks showed no signs of FIGURE 3. Approximately 60% of the pearls produced in Batch 2 were graded as high-quality. FIGURE 4. Despite being fed with algae cultivated through photosynthesis in natural seawater oysters in Batch 2 did not exhibit any decline in pearl quality.
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