Perkinsus spp. are pathogenic protistan parasites that pose a significant threat to the aquaculture of the Hong Kong oyster (Crassostrea hongkongensis). This study investigated the transcriptional response of the Hong Kong oyster digestive gland to natural Perkinsus spp. infection. The parasite species was identified via PCR, while infection prevalence, tissue-specific abundance, and infection grade were assessed using Ray's Fluid Thioglycollate Medium (RFTM) culture. Transcriptomic analysis was performed to compare gene expression profiles among uninfected (Neg), lightly infected (L), and light-to-moderately infected (LM) oyster digestive glands. Results confirmed the presence of P. beihaiensis, with an overall infection prevalence of 85.5%. The digestive gland exhibited the highest infection prevalence (80.1%) and abundance (1880.0 ± 144.2 cells/g) compared to other tissues (gills, mantle, and siphon). Transcriptomic analysis of 12 samples (4 biological replicates per Neg, L, and LM group) using an Illumina Novaseq 6000 platform generated 102,827 unigenes. A total of 531 differentially expressed genes (DEGs) were common to both infected groups relative to the Neg group. GO and KEGG enrichment analyses highlighted key biological processes and pathways: up-regulated DEGs were associated with the cell cycle, antigen processing and presentation, and signal transduction, while down-regulated DEGs were linked to cholesterol metabolism, phagosome function, and fat digestion and absorption. qRT-PCR validation of 8 DEGs confirmed consistent expression patterns with RNA-seq data. These findings elucidate the tissue-specific infection patterns of P. beihaiensis in Hong Kong oysters in the digestive gland and provide critical insights into host-parasite interactions.

Crassostrea hongkongensis is an economically important mariculture species in southern China, and hybrid breeding has been applied to improve its growth traits. However, the molecular mechanisms underlying growth heterosis remain poorly understood. In this study, inter-population hybrid (HG) and intra-population (IG) groups of C. hongkongensis were compared using integrated transcriptomic and metabolomic analyses to investigate the regulatory basis of growth heterosis. Shell length and shell height were significantly greater in HG than in IG (p < 0.01). Transcriptomic analysis identified 474 false discovery rate (FDR)-supported significant differentially expressed genes (DEGs) (233 upregulated and 241 downregulated), which were treated as the primary statistically robust findings; a broader set of 3161 candidate DEGs, including genes associated with growth regulation and shell biomineralization, was retained for exploratory functional and multi-omics analyses. Metabolomic analysis detected 345 differential metabolites (DMs), which were mainly enriched in energy metabolism, nucleotide metabolism, and arachidonic acid metabolism. Exploratory pathway-level multi-omics integration revealed significant concordance between the transcriptomic and metabolomic profiles (M2 = 0.1962, p = 0.001) and highlighted the tricarboxylic acid cycle, oxidative phosphorylation, branched-chain amino acid degradation, nucleotide metabolism, and arachidonic acid metabolism. These findings suggest that growth heterosis in C. hongkongensis is associated with altered energy metabolism, biosynthetic processes, shell formation-related pathways, and potential changes in the growth-defense balance, providing molecular insights for genetic improvement and selective breeding.

The Polydora complex is a globally widespread polychaete parasite known for secreting acidic substances to bore tunnels into oyster shells. This process leads to the formation of dark brown crusts on the inner shell surface, a condition commonly referred to as "black shell disease". Not only does this disease degrade the quality of shellfish, but it also causes substantial mortalities, with the Hong Kong oyster (Crassostrea hongkongensis) being one of its primary hosts. In this study, an improved Deeplabv3+ semantic segmentation model integrated with an attention mechanism was developed to identify and classify the severity of Polydora-induced disease in oysters. First, through systematic data collection and enhancement techniques, a comprehensive dataset of 4590 shellfish disease images was constructed, fully meeting the training requirements of convolutional neural networks (CNNs). Second, transfer learning was employed by leveraging pre-trained model weights, which validated the suitability of the self-constructed dataset for model training. Comparative analysis of multiple segmentation models confirmed Deeplabv3+ as the optimal baseline, achieving a mean Intersection over Union (MioU) of 88.76% and an average precision of 94%. To further enhance performance, the Deeplabv3+ model was upgraded by incorporating the Convolutional Block Attention Module (CBAM), a dual-module mechanism integrating channel and spatial attention. Compared to the original model, the improved version exhibited significant performance gains: MioU increased by 1.19%, average precision rose by 1.78%, and mFscore improved by 0.68%. Finally, an efficient and user-friendly web-based system was designed for grading and identifying Polydora disease severity. This system can accurately segment the diseased regions on the inner oyster shell, calculate their proportion relative to the total inner shell area, and precisely grade the disease severity, thereby providing robust technical support for the monitoring and prevention of oyster black shell disease.

Antibiotic resistance genes (ARGs) have emerged as critical environmental pollutants, posing a substantial threat to public health. However, the distribution patterns and driving factors of ARGs—particularly high-risk ARGs—in the gut microbiota of freshwater snails remain poorly understood. This study collected gut samples from 48 cultured and wild individuals of Sulcospira hainanensis, a species inhabiting pristine aquatic environments (e.g., high-quality mountain streams), from six sampling locations in China. High-throughput sequencing and quantitative PCR (HT-qPCR) techniques were employed to investigate the distribution characteristics and potential risks of ARGs in S. hainanensis. Results revealed that although gut microbial community structure was relatively simple and compositionally similar between cultured and wild groups, ARGs were extensively prevalent in S. hainanensis guts. Notably, the high-risk ARG dfrA12 and floR were frequently detected. The abundance of dfrA12 showed a significant positive correlation with the abundance of Pseudomonas, suggesting a potential ecological association that warrants experimental validation.The presence of these ARGs in cultured S. hainanensis suggests the need for further assessment of their potential for food-chain transmission. This study provides baseline data on ARG distribution in S. hainanensis guts offering insights for the sustainable management of freshwater aquaculture systems. Further studies integrating quantitative risk assessment are needed to evaluate potential public health implications.

Lead (Pb) is a persistent aquatic pollutant that disrupts redox homeostasis in fish. This study investigated hepatic Pb accumulation, reactive oxygen species (ROS) production, antioxidant responses, lipid peroxidation, and transcriptomic alterations in juvenile pufferfish (Takifugu obscurus) exposed to waterborne Pb. Juvenile pufferfish were exposed to 5.98 mg/L waterborne Pb, corresponding to 10% of the 96 h LC50, for 96 h. Liver, blood, and hepatocyte samples were collected at 0, 12, 24, 48, and 96 h, with four biological replicates at each sampling time point. Hepatic Pb accumulation increased over time and reached the highest level at 96 h. ROS levels in blood cells and hepatocytes increased rapidly and peaked at 12 h. Superoxide dismutase (SOD) and catalase (CAT) activities showed early activation followed by late suppression, whereas glutathione peroxidase (GSH-Px) displayed partial adaptive recovery. Malondialdehyde (MDA) content increased progressively and reached approximately 2.8-fold of the control level at 96 h, indicating persistent lipid peroxidation. RNA-seq analysis identified 167, 460, 1398, and 2580 differentially expressed genes at 12, 24, 48, and 96 h, respectively. Enrichment, temporal trend, and weighted gene co-expression analyses indicated that Pb exposure shifted hepatic responses from early redox regulation to later metabolic adaptation, protein processing in the endoplasmic reticulum, proteasome function, and oxidative phosphorylation. qRT-PCR validation of 12 hub genes supported the RNA-seq results. These findings provide integrated biochemical and transcriptomic evidence for oxidative-stress-mediated hepatic toxicity in pufferfish exposed to waterborne Pb.

Sulcospira hainanensis, an emerging and potential aquatic food resource, exhibits significant phenotypic plasticity that critically affects its quality attributes. This study aimed to systematically analyze population differences and environmental adaptation mechanisms. We present the first comprehensive analysis of five populations in Southern China, innovatively integrating traditional morphometrics, large-scale targeted metabolomics (504 metabolites), and advanced machine learning approaches to elucidate quality variation and geographic origin. Morphological analysis revealed substantial variation, ranging from extremely slender (length/width: 3.31) to robust (2.36) shell forms, reflecting adaptive differentiation to hydrodynamic environments. Metabolomic profiling demonstrated clear population separation (PLS-DA: R2Y = 0.903, Q2 = 0.705). Free amino acid analysis revealed bitter-dominant profiles (52.92% of total FAAs) and a critical "yield-versus-palatability" trade-off: highyield Yunfu exhibited maximum bitter amino acids, while wild Huizhou1 showed a 12-fold glycine enrichment, potentially linked to osmotic adaptation. Cultured Huizhou2 reduced both bitter and sweet components, potentially leading to a perceived flavor imbalance based on its metabolic profile. Through multi-algorithm feature selection, we identified 14 high-accuracy molecular biomarkers achieving 96% classification accuracy (ROC-AUC = 0.998), with quinic acid identified as the strongest discriminator. These findings establish a reliable molecular basis for the geographic authentication and quality certification of S. hainanensis, and provide crucial guidance for aquaculture optimization to balance yield, palatability, and nutritional quality.

This study elucidated the time- and concentration-dependent effects of Cd exposure on adult Haliotis diversicolor through an integrated analysis of survival, physiological indices, and metabolomic profiles. Abalones were subjected to varying Cd concentrations for one and two months. While one-month exposure yielded no significant mortality, prolonged exposure to high Cd concentrations for two months substantially elevated mortality risk (hazard ratio = 3.359). Integrated biomarker response values exhibited progressive elevation with both concentration and exposure duration, indicating cumulative perturbation of antioxidant defense and metabolic enzyme systems. Metabolomic analysis revealed distinct temporal and concentration-dependent responses. After one month of exposure, medium concentrations predominantly affected energy and amino acid metabolism with a shift toward anaerobic pathways, while high concentrations activated additional detoxification and stress response mechanisms; after two months of exposure, divergent metabolic strategies emerged, where low concentrations induced lipid remodeling, medium concentrations maintained basic metabolic adjustments, while high concentrations precipitated comprehensive cellular dysfunction. Notably, the observed metabolic focusing at two months represented a forced trade-off under allostatic overload rather than successful adaptation, particularly in high-concentration groups. Combined analysis demonstrated fundamental reorganization of cellular metabolism under prolonged exposure. These findings emphasize the importance of long-term, multi-parameter assessments in evaluating marine ecotoxicological impacts of metal pollution.

Water temperature stands as a crucial environmental element, exerting an impact on the survival and growth of organisms in aquaculture. Heat stress poses a significant threat to the survival and aquaculture of the Hong Kong oyster Magallana hongkongensis (also known as Crassostrea hongkongensis), yet the underlying physiological and molecular mechanisms remain poorly understood. This study investigated the effects of elevated temperatures (35 °C and 37 °C) on survival, DNA damage, antioxidant enzyme activities, and gene expression related to apoptosis, inflammation, and heat shock proteins (HSPs) in M. hongkongensis. The median lethal temperature (LT50) of M. hongkongensis was determined to be 37.09 °C, with significant mortality observed at 35 °C compared with the control (29 °C). Antioxidant enzyme activities (SOD, CAT, and GPx) and T-AOC were up-regulated initially but exhibited divergent patterns under prolonged stress, indicating a temperature-dependent threshold for oxidative defense. Comet assay results also showed that heat stress induced severe DNA damage in hemocytes. Moreover, heat stress significantly up-regulated mRNA expression of apoptosis-related genes (Caspase-2, Caspase-8, Bax, and P53), inflammatory genes (TNF, p38-MAPK, and AP-1), and HSP family members (Hsp70, Hsp90, Hsp27, and Hsp68). The expression peaks of these genes were generally earlier and more pronounced at 37 °C, reflecting intensified cellular damage and protective responses. Collectively, this study demonstrates that M. hongkongensis employs integrated antioxidant, apoptotic, inflammatory, and HSP-mediated mechanisms to counteract heat stress, but temperatures exceeding 35 °C disrupt these defenses, leading to survival impairment. These findings provide critical insights into the heat adaptation strategies of M. hongkongensis and serve as a scientific foundation for developing sustainable aquaculture practices to mitigate summer heat stress.

The duration of rapid salinity change (RSC) prevailing in estuarine and coastal regions is increasing due to extreme climate and weather events, posing significant challenges to marine bivalves. The Hong Kong oyster (Crassostrea hongkongensis), an ecologically and economically important species in tropical estuarine ecosystems, has experienced increasing mass mortality during prolonged periods of RSC, yet little is known about underlying physiological processes. Here, we investigated how physiological energetics of C. hongkongensis were affected by longer-lasting scenarios and four-week episodes of RSC. Compared with ambient conditions with seawater salinity ranging from 15 to 20, rapid salinity change by ± 10 units significantly decreased the survival of oysters, with RSC-induced hyposaline stress (-10) resulting in more serious consequences than that of hypersaline regime (+10). Continuing exposure of oysters to both RSC scenarios significantly affected their feeding activities, but the food absorption efficiency were still virtually unchanged. Significantly depressed respiration and increased excretion activities were observed in RSC-stressed oysters, resulting in significantly lowered O:N ratio. Overall, when exposed to RSC, oysters showed significantly decreased scope for growth, due to shifts in energy budget toward maintenance of essential physiological processes. Our results demonstrate the vulnerability of estuarine oysters to prolonged RSC events, and underscore the pressing need to develop strategies to enhance oyster tolerance under intensifying RSC conditions and safeguard oyster aquaculture in this era of unprecedented climate change.

The small abalone ( Haliotis diversicolor) is an economic shellfish cultured in the south coast of China. In recent years, the frequent occurrence of the disease has led to significant mortality in abalone farms. Deleted in malignant brain tumors 1 (DMBT1), a member of the scavenger receptor cysteine-rich (SRCR) protein family, plays an important role in host defense. However, its function in H. diversicolor remains unknown. In order to evaluate the immune priming effect after secondary infection and elucidate possible regulatory mechanism, a novel DMBT1 from the small abalone H. diversicolor (designated as HdDMBT1) was cloned and characterized in this study. The open reading frame of HdDMBT1 was 2331 bp encoding 776 amino acids with a molecular weight of 84.73 kDa. HdDMBT1 contained conserved active sites with DMBT1 from other species, detected in all tested tissues and had higher expression levels in hepatopancreas. The temporal expression profiles of HdDMBT1 after two challenges of Vibrio harveyi were examined to evaluate priming response in the small abalone. The expression level of HdDMBT1 mRNA in hepatopancreas increased significantly after V. harveyi challenge. Meanwhile, the expression level of HdDMBT1 after the second challenge was significantly higher than that after the first challenge (4.23-fold). RNA interference (RNAi) experiments were conducted to examine the role of HdDMBT1 in response to V. harveyi infection. Knocking down HdDMBT1 decreased the hemocytes phagocytosis (0.48-fold). In addition, the bacterial density in hemolymph and the mortality of abalone raised, when infected with V. harveyi after dsHdDMBT1 injection. These results indicated that HdDMBT1 might play an important role in tolerance to bacterial infection.

This study investigated the effects of selenium nanoparticles (Se NPs) on the physiological responses of Crassostrea hongkongensis during high salinity exposure, which threatens this commercially important species. Oysters were pretreated with Se NPs (0, 0.4, 4, and 40 μg/L) for 14 days, followed by high salinity (30 psu) exposure for 7 days. Antioxidant, metabolic, and immune parameters were analyzed in gill and hepatopancreas tissues. Results revealed tissue-specific responses to Se NPs under salinity stress, with medium concentrations (4 μg/L) showing significant protective effects. In gills, medium Se NPs enhanced selenium-dependent antioxidant systems (glutathione peroxidase, GSH-PX and glutathione S-transferase, GST) and regulated metabolic enzymes (acid phosphatase, ACP; alanine aminotransferase, ALT; aspartate aminotransferase, AST). The hepatopancreas demonstrated increased antioxidant capacity (decreased malondialdehyde, MDA; increased superoxide dismutase, SOD) and metabolic adaptations (increased ALT). High Se NPs concentrations (40 μg/L) exacerbated physiological stress. These findings advance our understanding of nanomaterial-environment interactions with aquaculture implications.

The Kumamoto oyster (Crassostrea sikamea), an indigenous species in southern China, is ecologically and aquaculturally significant. To explore the associations between oyster-associated bacteria and their environment, we analyzed bacterial communities in oyster gills, seawater, and sediment from Techeng Island (TCCS, TCW, TCS) and Longtousha (LTSCS, LTSW, LTSS) using Illumina MiSeq sequencing of the 16S rRNA gene V3–V4 region. Alpha diversity showed the highest richness and diversity in sediments (Shannon index: 6.40–6.52), followed by seawater (4.15–4.58) and gills (2.64–2.99). Taxonomic analysis revealed 75 phyla, with Pseudomonadota (23.23–49.32%) dominant across all habitats. Habitat-specific patterns were observed: Spirochaetota was enriched in gills (45.31–46.43%), Bacteroidota in seawater (6.70–14.05%), and Thermodesulfobacteriota in sediments (0.31–0.91%). At the genus level, norank_f_Spirochaetaceae, Marinococcus, and Woeseia showed significant differences among groups (p ≤ 0.001). Venn and PCoA analyses indicated closer similarity between gill and seawater communities than between gill and sediments, likely linked to oyster filter-feeding. This study clarifies the association between oyster gill bacteria and their environment, providing a basis for understanding microbial dynamics in oyster aquaculture.

The mortality rate of first- to second-instar horseshoe crabs during molting is extremely high under culture conditions (pH of 7.6 ± 0.1, salinity of 27 ± 2, temperature of 26–32 °C), and we preliminarily speculate that it is related to disease. Our team found that Ectoplana limuli was attached to the ventral limbs of adult horseshoe crabs during culture. Parasite samples were collected from the external appendages and mouthparts of adult Tachypleus tridentatus for classification and identification. The primary objective of this experiment was to identify the species of this parasite and determine its taxonomic status. To this end, the experiment employed a combination of morphological methods and 18S rDNA gene molecular markers. The obtained sequences showed over 99% homology with Ectoplana limuli. Sequence alignment and phylogenetic tree results indicated that Ectoplana limuli showed a closer genetic relationship with Nerpa fistulata, but more distant relationships with Paucumara and Baikalobia. This is the first time that this parasite has been found in China, providing additional information for the study of horseshoe crab diseases.

Perkinsus olseni is a highly pathogenic protozoan parasite affecting mollusks worldwide, posing a significant threat to Manila clam (Ruditapes philippinarum) aquaculture. This study investigated the impact of natural P. olseni infection abundance on the gill lipid metabolism of clams collected from Dandong City, Liaoning Province. The parasite species was identified via Polymerase Chain Reaction (PCR), while infection prevalence, abundance, and infection grade classification were assessed using Ray's Fluid Thioglycolate Medium (RFTM) culture. Lipid metabolomics analysis was performed to compare lipid profiles among uninfected (Neg), lightly infected (L), and moderately infected (M) clam gills. Results confirmed the presence of P. olseni with an overall prevalence of 91%. The infection abundance was significantly higher in the gills and digestive gland than in the mantle and siphon tissues. Lipidomic analysis of 18 samples (6 biological replicates per Neg, L, and M group) using a Liquid Chromatography-Mass Spectrometry (LC-MS) platform identified 1,561 metabolites, with significant differences observed across infection groups. 28 differential lipid metabolites were common to both the L and M groups when compared to the Neg group. KEGG pathway enrichment and correlation network analysis highlighted two key metabolites: diacylglycerol (DG) (16:0/18:2) and triacylglycerol (TG) (18:0/18:1/18:2). These metabolites were associated with 13 pathways, including T cell receptor signaling, fat digestion and absorption, and regulation of lipolysis in adipocytes. These findings elucidate tissue-specific infection patterns and reveal lipid metabolic reprogramming in clam gills in response to P. olseni, providing insights into host-parasite interactions and potential metabolic biomarkers for perkinsosis.

Dried oysters are widely valued in Asian cuisine for their unique flavor profiles and nutritional benefits. However, as a newly developed variety characterized by rapid growth, the effects of different drying methods triploid Fujian oysters remain unexplored. In this study, we investigated the effects of different drying methods on the flavor profile of triploid Fujian oyster. Oysters processed by hot air drying (HAD), natural drying (ND), vacuum drying (VD), and vacuum freeze-drying (VFD) were compared with blanched controls (BC). Drying significantly increased the types and concentrations of non-volatile metabolites and flavor substances, with HAD yielding optimal results. The HAD-treated oysters contained the highest contents of key nutritional compounds (N-acetyl-L-aspartic acid: 2.2-fold the mean value across all drying treatments), antioxidants (2-pyrrolidone: fold), and flavor substances (pyrazines: 2.0-fold; 2-furanmethanol: 2.8-fold, ethyl acetate: 1.3-fold). Thus, HAD treated oysters had a rich and balanced aroma profile with excellent umami, sweet, and fruity flavors. compounds contributing to flavor enhancement (odor activity value > 1) were (E)-2-nonenal, (E)-2-octenal, heptanal, 2-methylbutyraldehyde, and 2-undecanone. Correlation analysis revealed complex relationships tween non-volatile compounds and flavor substances. This study provides guidance for optimizing drying techniques and standardizing dried oyster production.

C-type lectins (CTLs), a member of pattern recognition receptors, play an important role in the innate immunity by recognizing invading microorganisms. In this study, a novel perlucin gene (designated as HdPer 3), a typical CTLs was cloned and characterized from the small abalone Haliotis diversicolor. The open reading frame of HdPer 3 was 471 bp, encoding a protein of 156 amino acids that included a single carbohydrate-recognition domain. HdPer 3 was widely expressed in all tested tissues and developmental stage. HdPer 3 expression was significantly up-regulated after Vibrio harveyi infection, suggesting that HdPer 3 was activated in response to bacterial infection. The encapsulation ability of hemocytes could be significantly enhanced by the recombinant protein HdPer 3 (rHdPer 3). To understand the regulation mechanism of the HdPer 3, HdPer 3 was silenced in vivo by RNAi. Knocking down HdPer 3 decreased the hemocytes phagocytosis. Meanwhile, knocking down HdPer 3 can reduce the expression of 2 phagocytosis-related genes (Rab and Dynamin), TNF-α, and 2 MAPK pathway-related genes (MAPK-X1 and Ras) after V. harveyi infection. Moreover, HdPer 3 interference could increase the bacterial load in the hemolymph and the mortality of abalones after V. harveyi infection. All these results suggested that HdPer 3 played a crucial role in the defense against V. harveyi infection by recognizing bacterial pathogens and activating the expression of immune-related genes.

The structure of fish intestines does not have a clear regional division, while the function of the intestines may be related to their structure. Therefore, in this study, the delimitation of intestinal segments in pufferfish (Takifugu obscurus) was achieved by morphological analysis. Subsequently, enzyme activity, intestinal microbiota, and gene expression were examined to compare the differences among the pufferfish various segments. According to four morphological parameters: height of mucosa folds (HF), width of mucosa folds (WF), thickness of muscularis (TM), and cross-sectional area (CSA), the pufferfish's intestine was divided into anterior intestine (AI), middle intestine (MI), and posterior intestine (PI). The activity levels of amylase, lipase, and trypsin in the AI and MI were significantly higher than these in the PI. According to the analysis of 16S rDNA, the dominant microbiota at the phylum level in the different segments were Epsilonbacteraeota, Spirochaetes, and Proteobacteria. At the genus level, there were variations observed in the relative abundance of Brevinema, Mycobacterium, Bradyrhizobium, and Microvirga. α diversity analysis revealed that the richness indexes (Ace and Chao1) were the lowest in the MI, while β diversity analysis revealed significant difference in intestinal microbial community composition among the three intestinal segments. Furthermore, RNA-Seq was used to identify differential expression genes (DEGs) and biological pathways among the different intestinal segments. The DEGs between the AI and MI were enriched in pancreatic secretion and protein digestion and absorption, those between AI and PI were involved in ascorbate and aldarate metabolism and glutathione metabolism, and those between MI and PI were involved in steroid biosynthesis, fat digestion and absorption, vitamin digestion and absorption, and glycine, serine and threonine metabolism. In conclusion, the presented results compare and analyze the differences in various intestinal segments of pufferfish, which will be conductive to future exploration of the functions of these different segments.

Post-harvest air exposure is unavoidable during oyster transportation and storage, yet the physiological tolerance limits and underlying metabolic responses of commercially important oyster species remain poorly understood. While previous studies have focused on immediate post-harvest quality changes, there is limited knowledge about the time-dependent metabolic adaptations that determine product quality during extended air exposure. This study investigated the physiological and metabolic responses of Crassostrea hongkongensis during air exposure at 4 °C, focusing on identifying the optimal period for quality preservation. Using a combination of survival analysis, enzyme activity assays, and metabolomic profiling, we examined oysters exposed to air for up to 18 days, with particular emphasis on the critical first three days. Survival analysis showed 100 % survival rate at 4 °C through day 7, with mortality beginning thereafter, compared to significant mortality observed at 25 °C (complete mortality by day 7) and 37 °C (complete mortality by day 2). Analysis of antioxidant enzyme activities revealed complex, time-dependent changes, with robust responses observed within the first three days, indicating effective stress management. Metabolomic analysis identified 38 differentially abundant metabolites throughout the exposure period. Notably, the metabolic profile at day 3 showed a tendency to revert towards the control state, suggesting a temporary adaptive response. Key findings included stability in total antioxidant capacity (T-AOC) levels during the initial three days and subtle changes in flavor-related compounds, such as slight decreases in glutamate and aspartate levels. Correlation analyses revealed intricate interactions between enzyme activities and metabolites, highlighting complex stress response mechanisms. The relationship between T-AOC and key osmolytes underscored their critical role in maintaining cellular redox balance during the initial exposure period. Our findings suggest that the optimal window for maintaining C. hongkongensis quality during air exposure at 4 °C is within the first three days. During this period, oysters demonstrate effective adaptive responses, maintaining key quality attributes and nutritional value. Beyond this timeframe, the risk of quality degradation increases significantly. These results have important implications for the oyster industry, providing evidence-based guidelines for post-harvest handling, transportation, and storage practices. We recommend limiting air exposure during cold storage to no more than 3 days to ensure optimal product quality and consumer satisfaction.

Zinc oxide nanoparticles, increasingly used in industrial and consumer products, and low salinity, exacerbated by climate change-induced alterations in precipitation patterns, represent significant environmental pressures in estuarine and coastal environments. This study advances previous research on their impacts on Hong Kong oysters (Crassostrea hongkongensis) by integrating metabolomics of hepatopancreas and gills with intestinal microbiomics. Employing advanced multi-omics integration methods, our analysis reveals novel insights into metabolic resilience under combined stress conditions. This resilience is characterized by coordinated, organ-specific adjustments in energy metabolism (d-glucose 1-phosphate in hepatopancreas, cytidine in gills), antioxidant defenses (glutathione, meso-2,6-diaminoheptanedioate, pimelic acid in hepatopancreas; indole, 3-(3-hydroxyphenyl)propanoic acid in gills), immune function (l-glutamine, ergocalciferol in hepatopancreas; argininosuccinic acid in gills), and membrane stability (lanosterin in hepatopancreas, allantoin in gills). Notably, under dual stressors, we observed a previously undescribed stabilization of microbial alpha diversity and certain phyla, an absence of distinctive biomarkers, and certain metabolic activity stabilization within the intestinal microbiota. These findings suggest robust compensatory mechanisms that maintain physiological homeostasis and microbial balance under stress, contrasting with primarily negative impacts reported in previous studies. Integration of metabolomic and microbiomic data revealed coordinated responses between microbial community changes and metabolic adjustments, particularly in osmoregulation, energy metabolism and antioxidant defenses, under dual stressors. This comprehensive approach provides a more realistic model of environmental challenges, revealing sophisticated adaptive strategies in Hong Kong oysters. Our study offers critical insights for understanding bivalve resilience, informing conservation strategies, and managing marine ecosystems in the face of increasing anthropogenic pressures.

Heavy metals in soil, water, and industrial production can affect the antibiotic resistance of bacteria. Antibiotic resistance in gut microbiota has been extensively researched. The effects of cadmium (Cd) was investigated on the gut microbiota and antibiotic resistance genes (ARGs) of Haliotis diversicolor, a commercially important abalone species. By exposing H. diversicolor to four concentrations of Cd (0 μg L-1 (control), 6.5 μg L-1 (low), 42.25 μg L-1 (medium), and 274.63 μg L-1 (high)) for 30 and 60 days, 16 types of ARG (aadA-01, aadA-02, cfr, dfrA1, ermB, floR, folA, mecA, sul2, tetB-01, tetC-01, tetD-01, tetG-01, tetM-02, tetQ, vanC-01), and 1213 genus and 27 phylum microbiomes were detected. ARGs can be resistant to aminoglycoside, beta-lactamase, macrolide-lincosamide-streptogramin B, multidrug, florfenicol, macrolide, sulfonamides, tetracyclines, and vancomycin. Cadmium exposure significantly alters the abundance of tetC-01, tetB-01, tetQ, sul2, and aadA-01. About 5% (61) of genus-level microorganisms were significantly affected by Cd exposure. Microbiota alpha and beta diversities in the 60-day 42.25 μg L-1 Cd treatment differed significantly from those in other treatments. In addition, 26 pathogens were detected, and two pathogens (Vibrio and Legionella) were significantly affected by Cd exposure. Significant correlations between pathogens and ARGs increased with increased Cd concentration after 60 days of Cd exposure. Cadmium exposure may cause gut microbiota disturbance in H. diversicolor and increase the likelihood of ARG transfer to pathogens, increasing potential ecological and economic risks.