Oyster health is important for aquaculture productivity and sustainability. In Thailand, the white scar oyster, Crassostrea belcheri, is being promoted for cultivation, yet its health status has not been compared between research breeding and community farming sites. This study evaluated histopathological features, ultrastructure, apoptosis, and defender against apoptotic death 1 (dad1) gene expression in sexually mature C. belcheri collected from these two sites. Gill tissues were examined by histology, transmission electron microscopy, TUNEL assay, and gene expression analysis, while organ condition was assessed using a Health Assessment Index (HAI). The proportion of TUNEL-positive cells in the gills and mantle differed significantly between sites (p < 0.05), with higher levels in oysters from the farming site. In contrast, TUNEL-positive cells in the digestive gland did not differ significantly between sites, although brown cells were observed only in the digestive gland of oysters from the breeding site, suggesting possible physiological stress. To assess the expression level of dad1 in oysters cultured under different conditions, RT-qPCR revealed no significant difference between the two sites. The breeding site also had lower temperature and salinity than the farming site. Overall, these findings suggest that site-specific environmental conditions may influence gill health and stress-related responses in C. belcheri, providing baseline information for oyster health assessment and aquaculture management.

The induction of diploid gynogenesis in the Tropical oyster, Crassostrea belcheri 1873, was carried out through two main experiments: 1) the destruction of spermatozoa DNA using ultraviolet (UV) irradiation, and 2) the induction of gynogenetic diploids. UV light source was placed 30 cm over the sperm for various durations, including 0 (control), 30, 60, 90, and 120 seconds. The study revealed that the highest survival rate was observed in trochophore at 90 minutes (42.5 ± 2.50%) compared to the normal control C. belcheri (p>0.05). Based on cytogenetic study, haploid (n=10), diploid (2n=20), and aneuploid were observed in all trials, while only diploid (2n=20) could be seen in the control group. Diploid gynogenesis was induced using 100 µmol 6-DMAP for 10 minutes. The study found that the survival rate and developmental stages in both trochophore and D-shape were gradually decreasing as the duration of UV rays increased. The highest survival rate of trochophore in the control group was 75.20 ± 4.84%, while survival rates in other experimental groups ranged from 52.22 ± 4.82% to 59.33 ± 13.57%. However, regarding the survival rate of D-shape larvae, their survival rates were relatively low across all trials. They displayed abnormal embryo development, distorted shape, unnatural swimming, and were smaller than normal (40-50 µm). Moreover, haploid (n=10), diploid (2n=20), triploid (3n=30), tetraploid (4n=40), and aneuploid were observed in all trials, while only diploid (2n=20) could be discovered in the control group. However, gynogenesis in this tropical oyster is still limited at this time. Therefore, suitable conditions for inducing gynogenesis in oysters should be further developed.

This study develops and validates a Design-for-Circularity approach for sustainable marine aquaculture infrastructure using recycled high-density polyethylene (r-HDPE). To assess material suitability for tropical marine applications, virgin and recycled HDPE blends were systematically characterized at weight ratios of 70:30, 50:50, and 30:70. Comparative mechanical and thermal analyses were conducted to identify the optimal formulation and to evaluate molecular stability, structural performance, and chemical durability. The 50:50 r-HDPE blend exhibited synergistic molecular stabilization and satisfied ISO 1133 and ISO 6259 performance criteria (maximum stress: 21.42 MPa; elongation: 683.97%; oxidation induction time >35 min), indicating sufficient ductility and durability for dynamic marine environments. Field validation further confirmed the structural and hydrodynamic stability of the prototype aquaculture cage under tropical monsoon conditions, with buoyancy deviation below 0.01% relative to theoretical displacement, demonstrating precise density control in recycled extrusions. The system maintained structural integrity under cyclic wave and current loading, verifying the fatigue resistance of welded joints and structural brackets. Aquatic biosafety assessments using Nile tilapia (Oreochromis niloticus) as a bioindicator species confirmed no detectable Pb or Cd accumulation in fish tissues (<0.01 mg kg⁻¹), indicating material inertness and minimal ecotoxicological risk. In addition to structural reliability, the circular material strategy reduces production costs by 35–40% and mitigates approximately 1.6 t CO₂ emissions per cage annually. These results provide an experimentally validated pathway for integrating recycled polymer materials into resilient and environmentally responsible coastal aquaculture infrastructure.