Search Results (143)

This study investigated seasonal variation in tissue growth, reproductive status, energy reserves, and digestive tubule condition in the Pacific oyster, Magallana gigas, cultured in an off-bottom intertidal rack system in Garorim Bay on the west coast of Korea. Monthly samples of adult oysters were collected from February 2009 to December 2010. Condition index (CI), total carbohydrate content, reproductive stage, female reproductive effort estimated by indirect enzyme-linked immunosorbent assay (ELISA), and digestive tubule atrophy (DTA) were measured concurrently in individual oysters. Gametogenesis was largely synchronized between sexes and was strongly associated with seasonal sea surface temperature ($r=0.84$, $p<0.0001$). Carbohydrate content peaked in early spring and declined during the spawning season. In females, carbohydrate content was negatively correlated with gonad somatic index (GSI) ($r=-0.30$, $p<0.0001$), suggesting that oysters investing more heavily in egg production tended to have lower remaining carbohydrate reserves. GSI showed interannual variation in spawning timing, peaking at 37.9% in June 2009 and 37.0% in July 2010. DTA showed temporal variation, with relatively elevated values in late summer–early autumn 2009 and mid-winter 2010. The late-summer 2009 increase in DTA coincided with a marked decline in salinity; however, monthly mean analyses did not establish a causal relationship between salinity and DTA. Together, these results indicate that the seasonal physiological condition of intertidal rack-cultured oysters reflects a dynamic balance between reproductive investment, carbohydrate reserves, and digestive gland condition, with this balance potentially modified by seasonal environmental variability. These results provide a cross-sectional, multi-parameter baseline for seasonal monitoring of reproductive status, energy reserves, and digestive tubule condition in intertidal rack-cultured oysters in Garorim Bay. Full article

Despite the recognized antioxidant properties of phycobiliproteins (PBPs) from Limnospira platensis, their potential application in bivalve aquaculture—particularly regarding their modulation of endogenous antioxidant defenses—remains largely unexplored. This study evaluated the effects of an aqueous PBP extract at concentrations of 2, 20, and 80 µg/mL on antioxidant parameters in the Pacific oyster Magallana gigas following 24, 48 and 96 h exposure periods. Activities of superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx), levels of lipid peroxidation (TBARS) and protein oxidation, and expression of corresponding genes in gills and hepatopancreas have been evaluated. PBPs elicited significant effects on prooxidant–antioxidant balance in oyster tissues. Low concentrations (2–20 µg/mL) enhanced SOD and CAT activities and reduced protein oxidation, indicating protective effects. The highest concentration (80 µg/mL) suppressed enzyme activities—particularly GPx—while elevating TBARS, suggesting prooxidant effects at excessive doses. Tissue-specific responses were observed, with hepatopancreas more vulnerable to oxidative stress than gills. Notably, GPx transcription was upregulated at 80 µg/mL of PBP extract despite suppressed activity, implying its post-transcriptional regulatory properties. These findings demonstrate that L. platensis PBPs modulate oyster antioxidant status in a biphasic manner, with moderate doses conferring stimulation and high doses inducing oxidative stress. This study provides the first integrative evidence of PBP effects on enzymatic, and transcriptional antioxidant defenses in a commercially important bivalve, underscoring their promise as functional bioactive additives while emphasizing the need for careful dose optimization. Full article

Although the Pacific oyster (Crassostrea gigas) is a premium marine protein source, its neuroprotective peptidome remains largely uncharacterized. This study established an integrated in silico and in vitro pipeline to discover acetylcholinesterase (AChE)-targeting peptides with cellular AChE-regulating and neuroprotective peptides from simulated gastrointestinal digests of oyster. Peptidomic profiling identified 18,292 sequences, which were filtered down to seven candidates predicted to have favorable blood–brain barrier (BBB) permeability and to be non-toxic and non-allergenic (VPYPR, VPVHF, HHTF, PVHF, GPKPW, HWF, and KYW) via multi-step virtual screening. In cellular assays, simulated H₂O₂ injury (500 μM) reduced PC12 cell viability to 47.53 ± 4.53%. Compared with the model group, pretreatment with the three most potent candidates—HHTF, VPYPR, and VPVHF (200 μM)—significantly rescued injured cells, restoring cell viability to 88.31 ± 7.83%, 85.12 ± 3.35%, and 82.00 ± 3.47%, respectively (p < 0.05). These peptides effectively fortified cellular antioxidant defenses by increasing glutathione (GSH) levels to 24.24, 30.11, and 26.83 nmol/mg protein (from 20.22 nmol/mg protein in the model group) and superoxide dismutase (SOD) activity to 151.41, 153.97, and 151.96 U/mg protein (from 119.33 U/mg protein), while suppressing malondialdehyde (MDA) accumulation to 0.088, 0.064, and 0.086 nmol/mg protein (from 0.193 nmol/mg protein). Crucially, the peptides alleviated cholinergic dysfunction by normalizing the H₂O₂-induced elevation of intracellular AChE activity (11.39 nmol/min/mg protein) down to 7.02, 6.22, and 7.14 nmol/min/mg protein, respectively. Specifically, VPYPR (200 μM) restored AChE activity to a level (6.22 nmol/min/mg protein) that was not significantly different from that in the normal control group (p > 0.05). Molecular dynamics (MD) simulations (100 ns) and molecular mechanics Poisson–Boltzmann surface area (MM-PBSA) calculations identified VPYPR as the leading candidate with a remarkably low binding free energy of −49.74 ± 3.58 kcal/mol. This study demonstrates that oyster gastrointestinal digests are valuable reservoirs of multi-target neuroprotective ingredients and provides an efficient strategy for marine bioactive peptide discovery. Full article

Whether zinc (Zn) and copper (Cu) bioaccumulation in the Pacific oyster (Magallana gigas) reflects toxicological stress or is an incidental consequence of growth remains unclear. We cultured three commercial triploid M. gigas stocks for approximately one year, sampling gill and hepatopancreas at the start and end of this period, when Zn/Cu burden was naturally low and high, respectively. Pooled samples from both time points were profiled by whole-transcriptome sequencing, enzyme activity and oxidative damage assays, qPCR validation, and protein–protein interaction network analysis. Transcriptome-wide changes in both tissues tracked the culture period, but growth and Zn/Cu burden were too highly collinear (r = 0.92–0.98) to separate statistically. Critically, of the four metals measured (Zn, Cu, iron [Fe], and manganese [Mn]), only Zn and Cu increased with growth, whereas Fe and Mn did not, indicating metal-specific rather than generalized accumulation. Superoxide dismutase (SOD) activity and the transcript abundance of its copper/zinc isoform (Cu/Zn-SOD) increased with growth in both tissues, whereas catalase (CAT) activity was unchanged and glutathione peroxidase (GPX) activity rose only in gill. Malondialdehyde (MDA), a marker of oxidative damage, increased in both tissues. Gill mounted a broader response than hepatopancreas, including upregulation of KEAP1 alongside downregulation of detoxification, proteostasis, and ribosome-related genes. Stock-level qPCR further revealed stock-dependent regulation of antioxidant genes in hepatopancreas. Together, these results indicate that Zn/Cu bioaccumulation in M. gigas co-varies with growth in a metal-specific manner, consistent with cofactor demand for Cu/Zn-SOD. The accompanying oxidative and proteostatic changes therefore more plausibly reflect growth physiology than an independent pollutant signal. Full article

Bacterial disease is a major constraint on Magallana gigas larval production, yet hatchery microbiology has been characterised almost exclusively through the lens of Vibrio, and rarely across the whole production chain. We tracked bacterial communities throughout an entire larval rearing cycle at a commercial hatchery in northern China. A total of 78 samples were collected from the full production chain, from water intake to larvae. Bacterial communities were characterised using 16S rRNA (V4–V5) amplicon sequencing and culture-based isolation, with larvae sampled from three replicate tanks at six developmental stages. A protracted mortality event began at the D-veliger stage, with cumulative losses of roughly 40% before sinking ceased; ostreid herpesvirus 1 was not detected. The only taxon that rose above its healthy baseline during larval mortality was a single undescribed a single undescribed amplicon sequence variant (ASV) of the family Cryomorphaceae. Its relative abundance increased to a mean of 41% (with a tank-to-tank range of 33.7–51.6%) before disappearing once the mortality event concluded. No described species exceeds 92.2% 16S rRNA gene sequence identity to it, whereas its closest environmental relatives (97–98%) are, without exception, uncultured bacteria associated with marine invertebrates. It was an order of magnitude more abundant in larvae than in the surrounding water. Vibrio rose transiently at the onset of mortality but fell below its healthy-stage abundance while larvae were still dying. Tenacibaculum, by contrast, was the dominant genus of the rearing water yet was never recovered on Vibrio-selective medium and showed no association with mortality. Chlorination of the feed-room supply removed Tenacibaculum while leaving Vibrio uncontrolled. These findings reveal the limitations of the Vibrio-targeted, culture-based paradigm that has long dominated hatchery microbiology, as it overlooks both prevailing water-column organisms and mortality-linked taxa. Our results highlight the need for whole-community, culture-independent surveillance to better understand larval disease. Full article

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

The number of alien species recorded in the Black Sea has increased over recent decades, raising concerns regarding their long-term ecological consequences. Among the taxa currently extending their distribution within the basin are the Pacific oyster, Magallana gigas, and the Chesapeake blue crab, Callinectes sapidus. This study presents new records of both species from the Romanian Black Sea coast obtained through citizen-reported observations. Five specimens of M. gigas collected from Constanța and Mangalia harbours were examined, together with one ovigerous female specimen of C. sapidus collected from Vadu Beach. In addition, two male C. sapidus records from Sinoe Lake were documented and validated based on photographic evidence. The finding of M. gigas in Mangalia Harbour extends the known distribution of the species along the Romanian coastline and suggests that the species is more widespread than previously documented. The occurrence of an ovigerous C. sapidus female confirms that reproduction is taking place in Romanian Black Sea waters. Morphometric measurements and reproductive traits were within the ranges reported from other Black Sea and Mediterranean populations. While none of these species can currently be regarded as invasive in Romanian coastal waters due to the absence of documented ecological impacts, the increasing frequency of records suggests that both warrant continued monitoring. The results further indicate that citizen-reported observations, when validated by specialists, can complement conventional surveys and provide valuable information on the occurrence and spread of conspicuous alien marine species, thereby supporting sustainable marine biodiversity monitoring and informed ecosystem management. 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

Sustainable management of intensive aquaculture areas requires a profound understanding of the feeding interactions between cultured species and their environment. This study compared the seasonal feeding performance of the Pacific oyster Magallana gigas and the bay scallop Argopecten irradians on the southern coast of Korea using the biodeposition method. Our results demonstrated significant interspecific differences: M. gigas adopted a ‘high-throughput’ strategy with superior filtration rates, whereas A. irradians exhibited a ‘pre-ingestive selective’ strategy characterized by higher pseudofeces production and particle rejection. Based on these findings, we propose three core spatial management strategies: (1) horizontal re-arrangement to optimize food utilization by positioning high-efficiency filter feeders upstream; (2) a dynamic vertical positioning strategy to mitigate metabolic stress during environmental shifts; and (3) an environmental management model incorporating species-specific biodeposition loads. These strategies provide a scientific foundation for maximizing growth efficiency while ensuring the ecological sustainability of intensive aquaculture systems. 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

The physiological performance of the Pacific oyster Magallana gigas in subtropical lagoon systems is shaped by the interaction between environmental variability, reproductive dynamics, and oxidative stress. This study quantified monthly changes in the growth and proximate composition of oysters cultivated in Estero La Cruz, Sonora, and evaluated their relationship with temperature and chlorophyll-a as proxies for thermal stress and trophic availability. Shell growth was continuous, while somatic biomass increased markedly during winter, indicating high thermal tolerance and metabolic flexibility. Proximate composition showed pronounced seasonal oscillations, with energy reserves accumulating during periods of high primary productivity and declining sharply in December, coinciding with peak gametogenic activity. Antioxidant enzyme activities (SOD, CAT, GPx) increased toward winter, reflecting elevated oxidative stress. Correlation and regression analyses revealed consistent relationships among environmental variables and biological responses, identifying temperature as the main factor associated with growth variability. Overall, these results demonstrate a strong coupling between environmental forcing, energy allocation, and oxidative stress, providing an integrative framework for understanding oyster performance and supporting aquaculture management in subtropical coastal systems. 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