Search Results (183)

Marine heatwaves repeatedly trigger summer mortality of the farmed Pacific oyster (Crassostrea gigas), forcing its haemocytes to reprogramme metabolism under thermal stress. The metabolic nodes governing this adaptation remain poorly defined. Integrating publicly available transcriptomics, single-cell analysis, enzyme inhibition, and molecular dynamics simulation, we identify argininosuccinate synthetase (CgASS) as a key node of this response. Heat stress drove sustained metabolic remodelling of the haemocyte transcriptome, and network analysis placed CgASS at the centre, where it was preferentially expressed in haemocytes and developmentally regulated. Single-cell virtual knockout selectively reshaped minor haemocyte populations, markedly expanding a stress-activated effector population while contracting immunomodulatory and cytoskeletal populations. In vivo inhibition with α-methyl-DL-aspartate raised citrulline, lowered argininosuccinate, and further suppressed respiration and feeding under heat, confirming that CgASS activity sustains aerobic performance. CgASS inactivation constricts arginine supply, thereby depriving both the nNOS–NO pathway that sustains respiration and feeding and the AMD–polyamine pathway that supports cytoprotection. Molecular dynamics revealed that CgASS collapses into an abnormally compact, rigid conformation at 30 °C, constraining the flexibility required for catalysis. Together, these results suggest CgASS as a potential key node of a metabolic compensation–decompensation axis and a molecular target for breeding thermally resilient shellfish. Full article

Heat stress causes severe oxidative damage and immune cell death in marine bivalves, but its upstream regulators remain unclear. This study identified regulators linking heat stress to oxidative damage in Pacific oyster haemocytes. Under 30 °C exposure, the apoptosis rate of oyster haemocytes increased from ~4.54% to 17.40% at 24 h, accompanied by elevated ROS, malondialdehyde, and lipid hydroperoxide and reduced SOD activity. GSEA and protein interaction analysis of the haemocyte transcriptome pinpointed protein disulfide isomerase A6 (CgPDIA6) as the hub gene linking endoplasmic reticulum stress, apoptosis, and oxidative stress. Single-cell in silico knockout placed CgPDIA6 at the head of a coupled SOD–peroxiredoxin relay (CgSOD1, CgSOD2, CgPRDX6) and shifted haemocytes toward a stress-activated state. This prediction was confirmed by RNAi knockdown, in which silencing CgPDIA6 aggravated heat-induced oxidative injury, reduced the expression of antioxidant-related genes (CgSOD1, CgSOD2, and CgPRDX6), and further suppressed SOD activity. Molecular dynamics simulations showed that heat destabilized its catalytic thioredoxin domains, compromising its protective function. These results demonstrate that CgPDIA6 protects haemocytes against heat-induced oxidative damage by sustaining antioxidant enzyme activity, providing insights into redox regulation and heat adaptation in mollusks. Full article

Oysters, as sessile organisms, are highly influenced by environmental conditions affecting their growth and reproduction. Therefore, unfavorable conditions can directly compromise the effectiveness of oyster reef restoration efforts. The study applied the dynamic energy budget (DEB) theory to model the growth of the Suminoe oyster (Crassostrea ariakensis) and estimated the model’s main parameters through linear and nonlinear regression methods. Meanwhile, the parameters of the existing DEB models for the Pacific oyster (Crassostrea gigas) and the Portuguese oyster (Crassostrea angulata) were optimized to improve the model performance. Model accuracy was confirmed by comparing the simulated and observed values of shell height and wet weight for three oyster species. The validated models were subsequently applied to three distinct habitats: Qianhu Bay, the Yangtze River Estuary, and Jiaozhou Bay, to simulate the individual dynamic growth and survival processes of the three oyster species. The simulations of shell height and wet weight for the three oyster species showed strong agreement with observations, with a mean coefficient of determination (R²) of 0.98. The mean NRMSE value of the three models was 0.16, indicating low model-prediction error. The simulation of various habitat scenarios suggested that C. ariakensis exhibited faster growth in the Yangtze River Estuary and Qianhu Bay, and C. gigas in the Yangtze River Estuary. Additionally, C. angulata experienced mortality in the Yangtze River Estuary (February) and Jiaozhou Bay (January). The findings of this study can provide scientific guidance on selecting species for oyster reefs across various marine environments to effectively enhance their ecological restoration outcomes. Full article

The Pacific oyster (Crassostrea gigas) is well known for its pronounced umami taste. Here the interaction between the T1R1/T1R3 taste receptor and three oyster-based peptides, namely, FLNQDEEAR (FR-9), EEFLK (EK-5), and FNKEE (FE-5), was investigated via molecular docking and molecular dynamics (MD) simulations, as well as molecular mechanics Poisson–Boltzmann surface area (MM–PBSA) and residue–residue contact score (RRCS) analyses. A full-length human T1R1/T1R3 heterodimer was constructed with AlphaFold3. MD simulations indicated that the binding of FR-9 led to a large structural fluctuation, a large radius of gyration, and a large solvent accessible surface; on the contrary, FE-5 yielded the most stable receptor–ligand complex. The MM-PBSA analysis showed that the binding free energies of the three peptides were in the order of FR-9 > EK-5 > FE-5. The RRCS analysis indicated that RRCS values per residue were in the order of FR-9 < EK-5 < FE-5, in line with the reported umami score, and that the highest taste score of FE-5 originated from the hydrophobic interactions between Glu301 (receptor) and Phe1 (ligand) as well as the salt bridges between arginine (Arg277 and Arg307, receptor) and glutamic acid (Glu4 and Glu5, ligand) residues. These findings show that structural stability and residue contact density were more informative than binding affinity for distinguishing the taste intensity of umami peptides. Full article

Selenium-enriched yeast is an important organic selenium source for improving the nutritional value and physiological function of aquatic products. However, whether ploidy affects the molecular responses of Pacific oysters (Crassostrea gigas) under selenium supplementation conditions remains unclear. In this study, diploid, triploid, and tetraploid Pacific oysters were fed a selenium-enriched diet for 10 days. Hepatopancreas tissues were collected for antioxidant enzyme assays and transcriptomic analysis. The results showed that triploid oysters exhibited higher superoxide dismutase, glutathione peroxidase, and catalase activities, together with a relatively lower malondialdehyde level, suggesting stronger antioxidant defense under selenium supplementation conditions. Transcriptomic analysis revealed substantial numbers of differentially expressed genes across all groups compared, indicating pronounced ploidy-dependent transcriptional responses. Functional enrichment analysis showed that these genes were mainly associated with metabolic processes, oxidative stress responses, membrane components, endocrine-related pathways, lipid metabolism, and signal transduction. Several redox-related genes, including glutathione S-transferase family genes, CHAC1, superoxide dismutase family genes, and NRX1, showed ploidy-dependent expression patterns. In particular, triploid oysters appeared to rely more on enzymatic antioxidant defense and glutathione turnover, whereas tetraploid oysters showed a stronger tendency toward redox signal integration and homeostatic regulation. These findings provide new insights into ploidy-dependent selenium responses in Pacific oysters and offer a theoretical basis for the development and utilization of selenium-enriched oyster products. Full article

As an important aquaculture bivalve, the Pacific oyster (Crassostrea gigas) undergoes a metamorphosis process during its embryonic development. The mortality rate of the eye-spot larva during the metamorphosis and settlement stage is relatively high, which urgently needs to be solved. Glutathione (GSH), as a key antioxidant and immune regulator in organisms, plays an important role in the growth, development, and immune defense of marine invertebrates. Analysis of oyster transcriptome data revealed that the expression of key enzyme-producing GSH, Glutathione S-transferase Kappa 1, reached the highest level at the pediveliger larvae (the stage just before eye-spot larvae), suggesting its important role in the larval settlement process. This study investigated the effects of reduced glutathione supplementation in pediveliger larvae on the settlement metamorphosis and immune capacity of eye-spot larvae. The results showed that high concentrations of glutathione (100 μmol/L, 500 μmol/L) significantly reduced the larval eye-spot rate and settlement rate, with larvae in the 500 μmol/L group nearly all dead after 48 h. Meanwhile, low-concentration GSH (7 μmol/L) could significantly increase the settlement rate of larvae, which was 1.17 times (p < 0.05) that of the control group. When the larvae developed to 1-month-old eye-spot larvae, the survival rate of larvae in the low GSH group significantly increased (38.42 ± 15.98%) after Vibrio splendidus stimulation, while they were almost all dead in the control group. Low GSH could also significantly increase lysozyme LZM activity (by 1.39 times, p < 0.05) and Cu/Zn-SOD activity (by 1.15 times, p < 0.05). Gene expression analysis found that low GSH promoted expressions of larval settlement and metamorphosis-related genes, including ecdysone receptor, P450, and calmodulin. Treatment with low GSH also enhanced the expressions of immune genes of SOD, CAT, and LZM. In summary, a low glutathione supplement can promote the settlement process of oyster eye-spot larvae and enhance disease resistance. These findings reveal the role of glutathione in the metamorphosis and settlement of oyster larvae, providing a scientific basis for optimizing techniques for oyster seedling cultivation. Full article

Systematic surveillance of World Organization for Animal Health (WOAH)-listed protozoan parasites is essential for maintaining the sanitary status of seafood exports and detecting the introduction of exotic pathogens into coastal ecosystems. In 2023, we examined wild Mediterranean mussels Mytilus galloprovincialis and Pacific oysters Crassostrea gigas collected from small harbors adjacent to ten major trading ports along the west and south coasts of Korea to assess the occurrence of WOAH-listed protozoan parasites and emerging Perkinsus species. A total of 1080 mussels and 1080 oysters from 18 sites were sampled in spring and autumn, and gill and digestive gland tissues were pooled from six individuals for DNA extraction. Species-specific PCR assays targeting Perkinsus marinus, P. olseni, P. beihaiensis, Bonamia ostreae, B. exitiosa, and Marteilia refringens were performed using previously validated primer sets and positive controls. All PCR assays were negative for the six protozoan parasite species in both host species across all sampling sites, indicating no detectable infections in port-adjacent wild mussel and oyster populations during the survey period. These negative results contrast with recent reports of P. marinus in wild C. gigas and B. ostreae in Ostrea denselamellosa on the west coast of Korea, suggesting that infections may currently be focal, transient, and host-specific rather than widespread in port-associated M. galloprovincialis and C. gigas populations. The present study provides baseline data on the distribution of protozoan parasites in bivalves inhabiting high-risk harbor environments and underscores the need for continued surveillance of transboundary shellfish diseases that is closely coupled with environmental monitoring. Full article

V. alginolyticus (VAlg) is one of the three Vibrio species causing human vibriosis. Its presence in shellfish constitutes a potential health risk. Thus, this investigation aimed to determine the prevalence and distribution of VAlg in 18,544 shellfish across geographies using standard protocols and random intercepts/mixed-effects regressions. The global VAlg prevalence in shellfish was 19.70% (95% CI: 13.54–27.75). VAlg pooled prevalence was significantly different (p < 0.0001) by shellfish type (${\chi }_{20}^2$ = 238.48), species (${\chi }_{74}^2$ = 440.34), genus (${\chi }_{51}^2$ = 414.37), VAlg detection methods (${\chi }_{10}^2$ = 150.43), nation (${\chi }_{30}^2$ = 632.27), and continent (${\chi }_4^2$ = 33.81). Europe and South America showed the highest pooled VAlg contaminated rates in shellfish (27% and 32%, respectively) but Asia had a low rate (~4%). By shellfish type, gastropods (snails) topped the list with 50%, followed by bivalves (29%). Among shellfish species, the VAlg rate declined from 67% to 5% (k ≤ 6), but with a more stable prevalence in Litopenaeus vannamei (19.02%, k = 11) and Crassostrea gigas (15.18%, k = 9). Edible oysters and clams had lower VAlg pooled rates (4–15%). Targeted culture with MALDI-TOF or species-specific qPCR detected VAlg in 100% of tested shellfish samples. By contrast, conventional phenotypic tests detected less VAlg in shellfish yielding 20% by general biochemical/API tests, 8.8% by generic PCR, and near-zero (0.3–3%) by multiplex PCR or MALDI-TOF/PCR. Both the multiplicative (${\beta }_0=-3.28\pm 3.76, F_{54;125}$ = 3.01, p = 0.001) and additive (${\beta }_0=-1.89\pm 1.47, F_{31;148}$ = 3.83, p = 0.001) interactions of nation and sample size explained 73.14% and 58.04% of the true variance in VAlg prevalence in shellfish. Other factors include detection techniques ($R^2$ = 46.59%, ${\beta }_0=-1.63\pm 0.83, F_{10;169}=11.16$, p = 0.001), nation ($R^2=37.72$ = 1.89, p = 0.006), medium $R^2$ = 19.42%, ${\beta }_0=2.24\pm 1.85, F_{15;164}$ = 1.69, p = 0.03), shellfish type ($R^2$ = 16.99%, ${\beta }_0=-3.90\pm 1.32, F_{20;159}$ = 1.34, p = 0.12), and continent ($R^2$ = 15.29%, ${\beta }_0=-1.81\pm 0.41, F_{4;175}$ = 5.90, p = 0.001). In conclusion, the study reveals substantial occurrence of VAlg in shellfish worldwide, with notable regional and species-specific hotspots. Harmonized and molecular-based surveillance of VAlg in shellfish linked to food safety criteria will be essential to manage its emerging threat. Full article

Marine biomucus, a complex biomolecular gel, plays a pivotal role in defense against biofouling, mitigation of environmental stress, and regulation of biomineralization. This study conducts a comparative analysis of the physicochemical properties of mucus secreted by three distinct tissues—labial palps, mantle, and gills—of the Pacific oyster (Crassostrea gigas), alongside their freeze-dried counterparts. By integrating amino acid profiling, scanning electron microscopy (SEM), and Fourier-transform infrared spectroscopy (FTIR), we explored potential correlations between chemical composition, microstructure, and hypothesized macroscopic functional properties. Our findings inspire distinct tissue-specific structural characteristics that suggest potential structure–function relationships: The structure of labial palps mucus leads to the hypothesis that it may act as a viscous barrier-like property; mantle mucus shows features that could potentially support the formation of continuous films by a dense hydrogen-bond network; and gill mucus exhibits a porous three-dimensional network that potentially facilitates the process of respiratory and feeding. This work not only explores the material basis and potential structure–function relationships of C. gigas mucus as a natural biopolymer but also provides a potential theoretical framework for the design of novel marine-inspired biomimetic materials. Full article

The discharge of effluents from shrimp farms into coastal lagoons can alter food availability, water quality, and pollutant load, potentially affecting the biological performance and safety of farmed bivalves. This study evaluated the influence of shrimp farm effluents on the growth, total weight, and condition index of the Pacific oyster Crassostrea (Magallana) gigas. Two oyster cultivation zones were established in the coastal lagoon of Los Melagos (Sonora, Mexico): one near a shrimp effluent zone (EZ) and the other in a reference effluent-free zone (FZ). Shell height and length, total weight, and condition index were measured monthly, along with environmental variables, including chlorophyll “a” concentration and sea surface temperature obtained from satellite imagery. Oysters cultivated in EZ showed significantly higher total weight, condition index, and growth rates compared to those in FZ. Seasonal fluctuations in chlorophyll “a” were observed, reflected in growth patterns, suggesting greater food availability in waters influenced by effluents. However, these environments pose health risks that require continuous, integrated environmental and health monitoring. Full article

This study examined the effects of hydrodynamic conditions on the growth performance and nutritional quality of Pacific oysters (Crassostrea gigas) in raceway flumes. Oysters were reared under three flow velocities—low (LV, 5 cm/s), medium (MV, 10 cm/s), and high (HV, 20 cm/s)—using three replicate flumes per treatment, each containing 100 individuals. Results indicated that while shell morphology remained unaffected by flow rate, MV significantly enhanced soft tissue weight and meat yield compared to LV. Physiologically, HV upregulated the activities of trypsin and amylase, with trypsin levels significantly exceeding those in LV. Furthermore, MV exhibited the highest crude protein and glycogen content. Notably, both MV and HV improved the accumulation of total and essential amino acids. Fatty acid profiles showed clear separation among treatments, primarily driven by C16:0, C18:0, C20:5n3, C22:1n9, and C20:2. Collectively, moderate flow velocity (10 cm/s, MV) resulted in a well-balanced enhancement of growth, biochemical composition, and nutritional value compared to low or high velocities, highlighting the potential value of controlled hydrodynamic conditions in oyster farming. Full article

Near-infrared (NIR) spectroscopy is a vital non-destructive analytical tool in the food and aquaculture industries. This study pioneers the application of portable NIR spectrometers for evaluating selenium (Se) content in the Pacific oyster (Crassostrea gigas). We developed quantitative and qualitative models to predict selenium levels in oyster tissue, representing a novel application for monitoring trace elements in marine organisms. Quantitative models were developed using partial least squares (PLS) regression on spectra collected with two portable spectrometers (Micro NIR 1700, Micro PHAZIR RX) and a benchtop FT-NIR instrument, with validation via cross-validation and an independent set. Qualitative models were also constructed to categorize Se content into three levels: 0–1, 1–3, and >3 mg/kg. For quantitative analysis, the Micro NIR 1700 model performed robustly in external validation (RP = 0.932; RMSEP = 0.392; RPD = 2.46). The Micro PHAZIR RX model achieved the highest RC (0.988) and the lowest RMSEC (0.233), yet cross-validation indicated a potential risk of overfitting. In contrast, the FT-NIR instrument yielded the best external predictive ability for powdered samples (RP = 0.954, RPD = 2.60), highlighting its high precision under laboratory conditions. For qualitative discrimination, the Micro PHAZIR RX’s classification module achieved a 100% correct recognition rate (AUC = 0.937). The models based on the Micro NIR 1700 and FT-NIR instruments showed cumulative contribution rates (CCR) of 98.61% and 97.59%, respectively, with high performance indices (PI) of 89.3 and 90.2, confirming their effective discrimination capability. The models established in this study enable the rapid, on-site detection of Se content in oyster samples, underscoring the significant potential of portable NIR spectroscopy for selenium analysis in shellfish. Full article

Widespread in coastal environments, artificial light at night (ALAN) is suspected to disrupt organisms’ biological rhythms by altering natural light cycles and thus constitutes a growing threat to these ecosystems. This study evaluates the effects of ALAN exposure at low and realistic intensity (~1 lx) on a coastal keystone species, the oyster Crassostrea gigas. The results reveal that ALAN significantly impairs the expression of core circadian clock genes (CgClock and CgBmal1) as well as the valve opening behavior, affecting rhythmic characteristics such as its robustness and daily profile. At the same time, ALAN leads to a decrease in daily shell growth and to a disruption of the gill microbiota, associated with an obliterated day/night difference in microbial alpha diversity. A direct correlation between a decrease in daily rhythm robustness, limitation of shell growth, and some microbial strands is shown, suggesting that biological rhythm disruption caused by ALAN might have harmful physiological consequences in oysters. Full article

Background: Clostridium perfringens is an infectious agent of concern in wild/farmed shellfish. Hence, this study assessed shellfish-borne Clostridium perfringens (ShbCp) prevalence. Methods: A total of 1469 ShbCp from 2336 shellfish were modelled using hierarchical generalized linear and 1000-permutation-based-mixed-effects, meta-regression models. Results: The overall ShbCp prevalence was 54.12% (19.73–84.99) with a 32.02% (14.52–56.64) toxigenic rate and a higher estimate in 2020–2025 (41.01%, 17.00–70.23) versus 1970–2019 (20.01%, 4.49–57.08). Culture media significantly affect ShbCp recovery, with cooked meat medium and thioglycollate medium registering higher estimates (77% and 25.15%, respectively) than selective agars (<7%). The molluscans had a higher ShbCp rate (60.68%) than crustaceans (1.57%) and cephalopods (0.14%); oysters (85.97%) than mussels (71.81%), clams (50.38%), slug/snails (48.23%), scallops (16.24%), crabs (11.91%), shrimps (1.05%), and squids (0.42%); and Crassostrea gigas (89.27%) versus Ruditapes philippinarum (45.92%) versus Mytilus galloprovincialis (30.14%). ShbCp differed significantly by nations but not by continent with Spain (87.79%) having the highest rate, then China (47.01%), Japan (43.91%), the USA (10.44%), and Greece (0.00%); South America (51.36%), then Asia (44.77%), Europe (21.97%), and North America (10.44%). Sample size, growth medium, nation, and shellfish class significantly explained 27.58%, 72.30%, 67.52%, and 28.51% ($R^2$) variance in ShbCp prevalence, respectively. Conclusions: The present study estimated a high ShbCp prevalence, suggesting a significant public health risk. It recommends that C. perfringens should be incorporated as a supplemental indicator into shellfish safety/shellfish water quality monitoring alongside traditional indicators. Also, geographical data gaps from Africa, Latin America, the Middle East, and Oceania underline the need for national and global monitoring attention and priority on C. perfringens in shellfish/shellfish beds. Full article