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Final culture of Magallana gigas (~40 mm) was evaluated in lantern nets at densities of 60, 80, and 100 oysters per floor over 6 months in the Chone River estuary, Ecuador. At the end of the experiment, oysters cultured at 60 oysters per floor exhibited significantly higher survival rates (75%) and growth (111 mm height) compared to those at 80 and 100 oysters per floor (64% survival and 102 mm and 92 mm growth). Oysters at the lower density reached commercial size (80 mm) within 3 months, while at higher densities reached this size after 4 and 5 months. Economic analyses indicated high profitability (58 to 67%), with maximum values at the higher density, although with a notable decline in soft tissue. Therefore, densities of 60–80 oysters per lantern net floor are recommended for the optimal culture of M. gigas in the Chone River estuary. [ABSTRACT FROM AUTHOR]

The increase in marine diseases, particularly in economically important mollusks, is a growing concern. Among them, the Pacific oyster (Crassostrea gigas) production faces challenges from several diseases, such as the Pacific Oyster Mortality Syndrome (POMS) or vibriosis. The microbial education, which consists of exposing the host immune system to beneficial microorganisms during early life stages is a promising approach against diseases. This study explores the concept of microbial education using controlled and pathogen-free bacterial communities and assesses its protective effects against POMS and Vibrio aestuarianus infections, highlighting potential applications in oyster production. We demonstrate that it is possible to educate the oyster immune system by adding microorganisms during the larval stage. Adding culture based bacterial mixes to larvae protects only against the POMS disease while adding whole microbial communities from oyster donors protects against both POMS and vibriosis. The efficiency of immune protection depends both on oyster origin and on the composition of the bacterial mixes used for exposure. No preferential protection was observed when the oysters were stimulated with their sympatric strains. Furthermore, the added bacteria were not maintained into the oyster microbiota, but this bacterial addition induced long term changes in the microbiota composition and oyster immune gene expression. Our study reveals successful immune system education of oysters by introducing beneficial microorganisms during the larval stage. We improved the long-term resistance of oysters against critical diseases (POMS disease and Vibrio aestuarianus infections) highlighting the potential of microbial education in aquaculture. [ABSTRACT FROM AUTHOR]

Tetraploids play a crucial role in the large-scale production of all-triploid Pacific oyster, Crassostrea gigas by mating with diploids. For nursery farms, research related to larval tolerance to the environment appears to be extremely important. For this goal, fertilization, embryonic development, growth, and settlement from fertilization stage to metamorphosis stage of the diploid, triploid, and tetraploid larvae of C. gigas "Haida No. 2" strain were studied under controlled conditions of temperature (20, 24, 28, and 32 ℃) and salinity (18, 21, 24, 27, and 30 psu). The results showed that increasing temperature and lowering salinity reduced survival time of sperm while increasing temperature and raising salinity accelerated the germinal vesicle breakdown (GVBD) ratio of stripped eggs in diploids and tetraploids for the first time. The appropriate condition for hatching of four crosses (DD, DT, TD, and TT, males were listed first, D for diploid, T for tetraploid) were listed as follows: 20–28 ℃/27–30 psu for DD, 24 ℃/27–30 psu for DT, 24–28 ℃/27–30 psu for TD, and 24 ℃/27–30 psu for TT. Diploids and triploids had similar performance but were all better than tetraploids under different temperature and salinity. The settlement rate increased with rising temperature while salinity and ploidy had little influence on settlement. The information obtained in this study can contribute to increasing the yield of triploid and tetraploid "Haida No. 2" of C. gigas. [ABSTRACT FROM AUTHOR]

Tetraploid oysters are valuable germplasm resources for the production of triploid oysters. However, the broodstock condition and gonadal development of tetraploid oysters are poorly understood. To assess the effects of temperature on gamete quantity and quality, tetraploid and diploid oysters were held at controlled temperatures of 18, 20 and 22 °C for 120 days. The gametogenesis process in tetraploid and diploid oysters showed an accelerated trend in response to increased conditioning temperatures. Nonetheless, the gonadal development of tetraploid oysters was slower than that of diploid oysters. Histomorphometric analysis of gonadal tissues showed variations in observed sex ratio under different conditioning temperatures. The proportions of tetraploid and diploid males increased with elevated temperature. However, survival rates of tetraploid and diploid oysters at 22 °C were significantly lower than those at 18 and 20 °C (P < 0.05). In terms of the number of oocytes and spermatozoa, tetraploid oysters were fewer than diploid oysters. Overall, these results demonstrated the differences in broodstock conditioning and gonadal development between tetraploid and diploid oysters, suggesting the need for specialized broodstock cultivation strategies for tetraploid oysters. [ABSTRACT FROM AUTHOR]

PIWI-interacting RNAs (piRNAs) are crucial for silencing transposable elements, germ cell development, and gametogenesis. Triploid Pacific oysters (Crassostrea gigas) are vital in the oyster aquaculture industry due to reduced fertility and rapid growth. This study integrates piRNA and mRNA expression analyses to elucidate their potential contributions to the sterility of triploid C. gigas. Bioinformatics analysis reveals a distinct U-bias at the 5′ terminal of oyster piRNAs. The abundance of piRNA clusters is reduced in triploid gonads compared to diploid gonads, particularly in sterile gonads, with a significant decrease in piRNA numbers. A specific piRNA cluster is annotated with the PPP4R1 gene, which is downregulated in infertile female triploids and exhibits a negative correlation with three piRNAs within the cluster. Differential expression analysis identified 46 and 88 piRNAs in female and male comparison groups, respectively. In female sterile triploids, the expression of three target genes of differentially expressed piRNAs associated with cell division showed downregulation, suggesting the potential roles of piRNAs in the regulation of cell division-related genes, contributing to the gonad arrest observed in female triploid oysters. In male triploid oysters, piRNAs potentially interact with the target genes associated with spermatogenesis, including TSSK4, SPAG17, and CCDC81. This study provides a concise overview of piRNAs expression in oyster gonads, offering insights into the regulatory role of piRNAs in triploid sterility. [ABSTRACT FROM AUTHOR]

Glycans containing fucose play crucial roles in cell biology, particularly in recognition processes. In humans, fucose found in H-blood group antigens is recognized by various pathogens, thereby influencing host-pathogen interactions. However, in invertebrate biology the specific functions of these modifications and the corresponding glycosyltransferases are not fully elucidated. Therefore, cloning these glycosyltransferases from different model systems will provide valuable insights into this process. Little is known about fucosyltransferases in molluscs. For this study, a sequence of the Pacific oyster, Crassostrea gigas, based on amino acid sequence homologies with rabbit and human α-1,2-fucosyltransferases, was chosen. The recombinant enzyme (350 amino acids) was able to transfer fucose from GDP-fucose to the galactose residue of type II disaccharides, terminal galactoses in complex N-glycan structures and several linear and branched galactans which were tested using a glycan microarray. The α-1,2-linkage formed was confirmed by NMR analysis. The enzyme was active in a broad pH-range, it was relatively stable upon storage conditions and its activity was not dependent on the presence of divalent cations. In this study, we were able to clone, express and characterise a novel α-1,2-fucosyltrasferase from Crassostrea gigas (CgFUT2). [ABSTRACT FROM AUTHOR]

Mollusca first evolve primitive immune cells (namely, haemocytes), which assemble a notable complex innate immune system, which are continuously produced through proliferation and differentiation and infused in the haemolymph. As a typical E3 ligase, CHIP is critical for immune cell turnover and homeostasis in vertebrates. In this study, a CHIP homolog (CgCHIP) with a high expression in haemocytes was identified in oysters to investigate its role in the proliferation and differentiation of ancient innate immune cells. CgCHIP exhibited a widespread distribution across all haemocyte subpopulations, and the knockdown of CgCHIP altered the composition of haemocytes as examined by flow cytometry. Mechanistically screened with bioinformatics and immunoprecipitation, a key haematopoietic transcription factor CgRunx was identified as a substrate of CgCHIP. Moreover, amino acids in the interacted intervals of CgCHIP and CgRunx were determined by molecular docking. Experimental evidence from an in vitro culture model of an agranulocyte subpopulation and an in vivo oyster model revealed that the knockdown of CgCHIP and CgRunx had opposing effects on agranulocyte (precursor cells) differentiation and granulocyte (effector cells) proliferation. In summary, CgCHIP negatively regulated agranulocyte differentiation and granulocyte proliferation by mediating the ubiquitination and degradation of CgRunx in oysters. These results offer insight into the involvement of ubiquitylation in controlling haemocyte turnover in primitive invertebrates. [ABSTRACT FROM AUTHOR]

This study aimed to assess the impact of microalgal concentrations in diets on the settlement and metamorphosis stages of pediveliger larvae and spat of Crassostrea gigas oysters. Diets containing microalgal concentrations of 8, 12, and 16×104 cells mL-1 were administered for seven days during the larval settlement phase of pediveliger larvae. In the metamorphosis and postlarval cultivation phases, diets with microalgal concentrations of 8, 16, 24, and 32×104 cells mL-1 and a control group without food were tested for 14 and 21 days, respectively. Growth, yield, and survival were assessed every seven days. The diet comprised 30% Isochrysis galbana and 70% Chaetoceros muelleri microalgae. In the metamorphosis phase, the results revealed no significant differences in larval metamorphosis rate and survival across the tested diets. The concentrations exhibited similar survival in the spat with an initial average shell height of 0.657 ± 0.05 mm, with a significant difference only in growth. In the spat with an initial average shell height of 0.830 ± 0.12 mm, no differences in survival were observed among the tested concentrations. We concluded that diets of 12 and 16×104 cells mL-1 provide high rates of larval metamorphosis and spat yield during the larval settlement and metamorphosis phases. During the spat cultivation phases, diets of 32 and 24×104 cells mL-1 could optimize the cultivation time and yield of C. gigas spat in the laboratory. However, when considering survival alone, no advantage was found in providing a diet with a microalgal concentration above 8×104 cells mL-1 across all C. gigas oyster cultivation phases. [ABSTRACT FROM AUTHOR]

Abstract The increase in marine diseases, particularly in economically important mollusks, is a growing concern. Among them, the Pacific oyster (Crassostrea gigas) production faces challenges from several diseases, such as the Pacific Oyster Mortality Syndrome (POMS) or vibriosis. The microbial education, which consists of exposing the host immune system to beneficial microorganisms during early life stages is a promising approach against diseases. This study explores the concept of microbial education using controlled and pathogen-free bacterial communities and assesses its protective effects against POMS and Vibrio aestuarianus infections, highlighting potential applications in oyster production. We demonstrate that it is possible to educate the oyster immune system by adding microorganisms during the larval stage. Adding culture based bacterial mixes to larvae protects only against the POMS disease while adding whole microbial communities from oyster donors protects against both POMS and vibriosis. The efficiency of immune protection depends both on oyster origin and on the composition of the bacterial mixes used for exposure. No preferential protection was observed when the oysters were stimulated with their sympatric strains. Furthermore, the added bacteria were not maintained into the oyster microbiota, but this bacterial addition induced long term changes in the microbiota composition and oyster immune gene expression. Our study reveals successful immune system education of oysters by introducing beneficial microorganisms during the larval stage. We improved the long-term resistance of oysters against critical diseases (POMS disease and Vibrio aestuarianus infections) highlighting the potential of microbial education in aquaculture.

The Pacific oyster, Crassostrea gigas, is an important cultured species in the northern coastal areas of China. In recent years, the triploid oyster was popular worldwide because of its fast growth and high meat quality and has rapidly occupied a large portion of the oyster market. As a multi-generation selection strain, "Haida No.2" of C. gigas has good growth performance. At the same time, we have successfully obtained the triploid and tetraploid "Haida No.2." This study was conducted to evaluate the performance of the triploid of "Haida No.2" under different rearing environments. The results showed that there was no significant difference in fertilization rate and hatching rate between diploids and triploids, and so did the survival rate at the larval stage, while the cumulative survival rate of triploids was significantly lower than that of diploids. At grow-out stage, the growth and survival rate of triploids were significantly higher than diploids on day 420 at two sites; meanwhile, the triploid rate was slight decline but still kept a high level (96–98%) on 420 days at two sites. However, high gametogenesis and subsequent mass spawning of triploid females were observed at two sites (32% at Rongcheng and 54% at Rushan), and the fecundity of triploid females relative to diploid females was high (23.73% at Rongcheng and 41.15% at Rushan) under different rearing environments. Our results showed that the triploid of "Haida No.2" had better performance at grow-out stage than diploids. However, the phenomenon of high gametogenesis of triploid and spawning is not favorable for the industrialization of triploid oysters, and the mechanism of high gametogenesis of triploids needs further study. [ABSTRACT FROM AUTHOR]

As human activities increase and environmental changes persist, increased ultraviolet B (UVB) radiation in aquatic ecosystems poses significant threats to aquatic life. This study, through transcriptomic analysis of the mantle tissue of Crassostrea gigas following UVB radiation exposure, identified and validated two key transcription factors, CgRunx1 and CgCBFβ. The highest expression levels of CgRunx1 and CgCBFβ in the mantle suggest their pivotal roles in this tissue. Co-immunoprecipitation experiments revealed that CgRunx1 and CgCBFβ could form heterodimers and interact with each other. Furthermore, this study assessed the impact of UVB radiation on the levels of reactive oxygen species of the C. gigas, speculating that CgRunx1, as a potential redox-sensitive transcription factor, might be regulated by intracellular ROS. Through screening and binding site prediction analysis of target genes, coupled with dual-luciferase reporter assays, we verified that CgRunx1 might participate in regulating the biomineralization and autophagy processes in C. gigas by activating the transcriptional expression of target genes Transport and Golgi organization 1 and V-type proton ATPase catalytic subunit A. These findings provide new insights into the molecular response mechanisms of the C. gigas to UVB radiation and lay an important foundation for studying the adaptive evolution of bivalves to environmental stress. [ABSTRACT FROM AUTHOR]

Crassostrea gigas, also known as Pacific oysters, are economic shellfish with the widest range of cultivation, the highest yield in the world, and the most important type of mariculture shellfish in China. However, many C. gigas have died during summer in coastal areas worldwide in recent decades. In 2008, the mortality rate of C. gigas cultured in France reached 40%–100%. In 2009, the mortality rate of C. gigas in some area of Sanggou Bay reached 51%. In 2019, the mortality rate of the Rushan area reached 50%–90%, with the death peak occurring in middle and late August. There were many reasons for the large-scale death of C. gigas, such as temperature, dissolved oxygen, salinity, disease, food availability, and reproduction levels, among which high temperature was the most important abiotic stress factor. The high temperature in summer disturbed the enzyme metabolism of C. gigas, resulting in slow or impeded growth. Furthermore, the reproduction and spawning of C. gigas caused a large amount of protein consumption, and physical weakness combined with high-temperature stress induced many deaths. Therefore, considering the problems faced by C. gigas culture during high summer temperatures, the introduction of new varieties will increase the economic benefits to the industry.Due to its high sterility, triploid C. gigas has attributes such as a fast growth rate, resilience excellent economic characteristics, and high energy conversion efficiency. In recent years, a certain farmed scale has formed in China, especially in northern coastal areas. There have been many studies on the biological and physiological differences between triploid and diploid C. gigas worldwide, mainly focusing on the differences in growth characteristics, soft tissue components, gonadal development, disease resistance, and gill structure. However, comparisons between triploid and diploid C. gigas feeding, metabolic physiology, energy budget, and carbon budget have not been reported. Focusing on the specific period of high temperatures in summer, this study investigated the feeding and metabolic physiological characteristics of triploid and diploid C. gigas using the field flow method, and compared and analyzed their energy allocation strategies in response to a high-temperature environment. The study provide data support for revealing the physiological differences caused by the ploidy effect of C. gigas in order to assist with evaluating the culture capacity.Triploid and diploid C. gigas were selected as research objects in August 2022 to analyze the differences in feeding and metabolic physiology and energy/carbon allocation strategies during high temperatures in summer. Physiological parameters related to intake and metabolism, such as water filtration rate, absorption efficiency, oxygen consumption rate, and ammonia discharge rate, were determined based on the field flow method in Sanggou Bay, Rongcheng, Shandong Province, and energy allocation and carbon allocation were estimated based on the principle of the energy budget. The results revealed that the water filtration rate and assimilation efficiency of triploid C. gigas were higher than those of diploid C. gigas, but there were no significant differences (P > 0.05). There were significant differences in the oxygen consumption rate and ammonia discharge rate between triploid and diploid C. gigas (P < 0.05). The oxygen consumption rate of triploid C. gigas was significantly lower than that of diploid C. gigas (P < 0.05), but ammonia discharge rate was significantly higher than that of diploid C. gigas (P < 0.01). The results of the energy and carbon budget analyses showed that the feeding energy/carbon and assimilation energy/carbon values of triploid C. gigas were higher than those of diploid C. gigas, but there was no significant difference (P > 0.05). There were significant differences in respiratory energy/carbon, excretion energy/carbon, and growth power between triploid and diploid C. gigas (P < 0.05). Respiratory energy/carbon values of triploid C. gigas were significantly lower than those of diploid C. gigas (P < 0.05), but excretion energy/carbon and growth power values were significantly higher than those of diploid C. gigas (P < 0.05). The oxygen/nitrogen ratio of triploid and diploid C. gigas fluctuated in the range of 7.91–14.11 and 59.81–94.19, respectively. Moreover, the main energy supply substances of triploid C. gigas were proteins, while the main energy supply substances of diploid C. gigas were carbohydrates and fats. These results revealed the differences in energy allocation patterns associated with the ploidy effect of C. gigas during high temperatures in summer.From the perspective of individual physiology and ecology, this study found that, compared with diploid C. gigas, triploid C. gigas showed certain advantages in energy allocation strategies by adjusting feeding and metabolic physiological behaviors during the high-temperature summer. However, the internal molecular mechanism of response strategies adopted by triploid C. gigas to cope with an adverse environment is still unclear. Further interpretation at the molecular level needs to be combined with omics and other systems biology techniques.

Simple Summary: With the acceleration of global industrialization, marine heavy metal pollution is becoming increasingly severe, posing significant threats to marine ecosystems and human health. To comprehensively understand the response mechanisms of mollusks to cadmium (Cd) stress, we selected the Pacific oyster (Crassostrea gigas) as the research species. We aim to delve into the molecular mechanisms underlying the response of oysters to cadmium exposure. Our results indicate that Cd exposure significantly increases Cd concentration in oyster gill tissues, eliciting strong physiological and metabolic reactions, including enhanced oxidative stress response and disrupted energy metabolism, signaling the oyster's biological response to acute Cd stress. This study provides new insights into the signal transduction and metabolic pathways involved in the acute biological response of bivalves and other marine organisms to heavy metals. Marine mollusks, including oysters, are highly tolerant to high levels of cadmium (Cd), but the molecular mechanisms underlying their molecular response to acute Cd exposure remain unclear. In this study, the Pacific oyster Crassostrea gigas was used as a biological model, exposed to acute Cd stress for 96 h. Transcriptomic analyses of their gills were performed, and metabolomic analyses further validated these results. In our study, a total of 111 differentially expressed metabolites (DEMs) and 2108 differentially expressed genes (DEGs) were identified under acute Cd exposure. Further analyses revealed alterations in key genes and metabolic pathways associated with heavy metal stress response. Cd exposure triggered physiological and metabolic responses in oysters, including enhanced oxidative stress and disturbances in energy metabolism, and these changes revealed the biological response of oysters to acute Cd stress. Moreover, oysters could effectively enhance the tolerance and detoxification ability to acute Cd exposure through activating ABC transporters, enhancing glutathione metabolism and sulfur relay system in gill cells, and regulating energy metabolism. This study reveals the molecular mechanism of acute Cd stress in oysters and explores the molecular mechanism of high tolerance to Cd in oysters by using combined metabolomics and transcriptome analysis. [ABSTRACT FROM AUTHOR]

Large-scale production of triploid oysters requires tetraploids as broodstock; hence, tetraploidy is a key asset for the triploid oyster industry. To explore the possibility of obtaining new allotetraploid strains with improved traits through hybridization and polyploidization, we conducted a comparative study for growth, survival, and gonadal development of tetraploid Crassostrea gigas, tetraploid C. angulata, and four allotetraploids. Firstly, allotriploid GGA (C. gigas ♀ × C. angulata ♂) and AAG (C. angulata ♀ × C. gigas ♂) were obtained from the hybridization between diploid C. gigas and diploid C. angulata by inhibiting the polar body II. Subsequently, allotetraploid GGGA (triploid C. gigas ♀ × diploid C. angulata ♂), allotetraploid AAAG (triploid C. angulata ♀ × diploid C. gigas ♂), allotetraploid GGAG (allotriploid GGA ♀ × diploid C. gigas ♂), allotetraploid AAGG (allotriploid AAG ♀ × diploid C. gigas ♂), autotetraploid GGGG (triploid C. gigas ♀ × diploid C. gigas ♂), and autotetraploid AAAA (triploid C. angulata ♀ × diploid C. angulata ♂) were obtained by inhibiting polar body I. The growth, survival, and gonad development of six groups (GGGA, AAAG, GGAG, AAGG, GGGG, and AAAA) were assessed. There were no detectable differences in fertilization and hatching rates among the six groups. Flow cytometry analysis showed that the tetraploid ratios of the four allotetraploid groups exceeded 88% on day 20. At larval stage, the allotetraploids GGGA and GGAG groups had higher growth rates and cumulative survival rates than the autotetraploid groups. Field-based phenotyping at three sites indicated that certain allotetraploid groups exhibited higher growth and survival compared to the autotetraploid groups. In particular, the best group over 9 months of testing was the allotetraploid GGAG, which significantly outperformed the autotetraploid groups in growth and survival. Furthermore, most of the individuals from the four allotetraploids were fully mature, with morphologically normal oocytes or sperm. The establishment of these four allotetraploids offers new germplasm resources for oyster genetic improvement and commercial production. [ABSTRACT FROM AUTHOR]

Carotenoids play crucial physiological roles in animals. A comprehensive investigation into the mechanism of carotenoid metabolism in oysters will establish a theoretical foundation for further development of its carotenoid-rich traits. However, the information on the function of miRNA in β-carotene metabolism in oysters is limited. To elucidate the mechanisms underlying miRNA regulation of carotenoid metabolism in oysters, we compared the expressions of miRNA in digestive gland tissues of Pacific oyster (Crassostrea gigas) fed with a β-carotene supplemented diet and a normal diet, respectively. A total of 690 candidate miRNAs in the Pacific oyster digestive gland tissues were identified, including 590 known miRNAs and 111 unknown miRNAs. Three differentially expressed miRNAs were obtained in the carotenoid-fed and normal groups, associated to 137 differentially expressed target genes. Moreover, the GO enrichment analysis revealed that the differentially expressed target genes were mainly involved in transmembrane transport activity. KEGG enrichment showed that the differentially expressed target genes were involved in ABC transport. Analysis of the mRNA-miRNA network revealed that novel0025 played a central role in carotenoid metabolism, and it was negatively correlated with the expression of 46 mRNAs. In addition, down-regulated expression of novel0025 upregulated the expression of the lipoprotein gene LOC105342186, suggesting a potential regulatory role in carotenoid metabolism. Our results provide useful information for elucidating the miRNA regulation mechanism during carotenoids metabolism in the Pacific oyster. [ABSTRACT FROM AUTHOR]

To evaluate the combined effect of temperature and cadmium on the molecular responses of heat shock protein 70 (hsp70) and P-glycoprotein (P-gp) in mantle, digestive gland and gills of Crassostrea gigas, oysters were exposed to combinations of five temperature levels (10, 15, 20, 25, and 30°C) and 10 µg L−1 cadmium for 21 days. Oysters were sampled for mRNA quantification by qPCR, and the results showed that the P-gp gene expression changed significantly after treatment at different temperatures and different treatment times. The P-gp gene expression was the highest in the digestive gland. Compared with the control group, the P-gp gene expression in cadmium treatment groups at all the different temperatures were significantly higher than the control group. The control oysters (kept at 10° during the whole experiment without cadmium) expressed low levels of hsp70, but the groups treated with cadmium displayed somewhat higher levels. The present study demonstrated hsp70 and P-gp played an important role in the detoxification of Cd in C. gigas, and confirmed temperature should be considered for the assessment of Cd-induced toxicity in oysters. [ABSTRACT FROM AUTHOR]

Near-infrared spectroscopy (NIR) has become an essential tool for non-destructive analysis in various fields, including aquaculture. This study presents a pioneering application of portable NIR spectrometers to analyze glycogen content in the gonadal tissues of the Pacific oyster (Crassostrea gigas), marking the first instance of developing quantitative models for glycogen in tetraploid C. gigas. The research also provides a comparative analysis with models for diploid and triploid oysters, underscoring the innovative use of portable NIR technology in aquaculture. Two portable NIR spectrometers were employed: the Micro NIR 1700 (908–1676 nm) and the Micro PHAZIR RX (1624–2460 nm). Near-infrared spectra were acquired from the gonadal tissues of diploid, triploid, and tetraploid C. gigas. Quantitative models for glycogen content were developed and validated using cross-validation methods. Additionally, qualitative models for different ploidies and genders were established. For the Micro NIR 1700, the cross-validation correlation coefficients (Rcv) and cross-validation relative predictive errors (RPDcv) for glycogen were 0.949 and 3.191 for diploids, 0.915 and 2.498 for triploids, and 0.902 and 2.310 for tetraploids. The Micro PHAZIR RX achieved Rcv and RPDcv values of 0.781 and 2.240 for diploids, 0.839 and 2.504 for triploids, and 0.717 and 1.851 for tetraploids. The Micro NIR 1700 demonstrated superior quantitative performance, with RPD values exceeding 2, indicating its effectiveness in predicting glycogen content across different ploidy levels. Qualitative models showed a performance index of 91.6 for diploid and 95 for tetraploid genders using the Micro NIR 1700, while the Micro PHAZIR RX achieved correct identification rates of 99.79% and 100% for diploid and tetraploid genders, respectively. However, differentiation of ploidies was less successful with both instruments. This study's originality lies in establishing the first quantitative models for glycogen content in tetraploid C. gigas using portable NIR spectrometers, highlighting the significant advancements in non-destructive glycogen analysis. The applicability of these findings is substantial for oyster breeding programs focused on enhancing meat quality traits. These models provide a valuable phenotyping tool for selecting oysters with optimal glycogen content, demonstrating the practical utility of portable NIR technology in aquaculture. [ABSTRACT FROM AUTHOR]

Suspended oysters employ physiological strategies to adjust their metabolic needs with the available food resources. Using the biodeposition method, the feeding and processing behavior of Pacific oysters (Crassostrea gigas) was investigated with a field study comparing four periods (May, July, October, and December 2016) with different upwelling intensities in the coastal lagoon of San Quintin Bay (Mexico). We calculated physiological feeding responses throughout the culture cycle, including the clearance rate (CR), filtration rate (FR), net organic ingestion rate (NOIR), net organic absorption rate (NOAR), net organic selection efficiency, net absorption efficiency, and the ammonium excretion rate (AER). The dietary quality predictors showed large fluctuations in terms of total particulate material, organic fraction of seston, and chlorophyll concentration. Unlike the pumping activity, FR, NOIR, and NOAR were related to upwelling conditions, and C. gigas removed twofold, ingested fourfold, and assimilated fivefold more of the organic suspended material during the upwelling season compared with periods of weak upwelling. C. gigas showed the potential of depositing nearly twice the organic biodeposits to the sediments during the intense upwelling events. The highest AER was recorded in July and October, suggesting that seasonal temperature variation is the most important exogenous factor regulating nitrogen metabolism, even in a subtropical environment. Also, mechanistic models incorporating dietary quality predictors to the feeding and processing response functions of C. gigas were performed. We conclude that coastal upwelling plays an important bottom-up control on oysters' feeding and processing activity, and our results facilitate further studies of the carrying capacity of embayments influenced by eastern boundary current systems. [ABSTRACT FROM AUTHOR]

Tetraploid oysters are of rising aquacultural importance because they can be used to produce 100% triploid seeds. Nevertheless, notable gaps in the understanding of the environmental preferences of tetraploid oyster larvae still exist. To investigate the combined effects of temperature and salinity on the growth, survival and metamorphosis of larvae of tetraploid Crassostrea gigas (GGGG), tetraploid C. angulata (AAAA) and two allotetraploid oysters (GGAG and AAGG), a total of 192 independent experiments were established, including 4 temperatures (21, 24, 27 and 30 ℃) × 4 salinities (22, 25, 28 and 31) × 4 populations (GGGG, AAAA, GGAG and AAGG) treatment combinations. Results showed that both temperature and salinity significantly affected growth, survival and metamorphosis of tetraploid oyster larvae and there was a significant interaction between salinity and temperature on survival and metamorphosis. The highest specific growth rate (SGR) of AAAA (7.61%), GGAG (8.47%) and AAGG (8.33%) occurred at a salinity-temperature combination of 25/27 °C, and that of GGGG (8.07%) occurred at a salinity-temperature combination of 25/24 °C. The highest accumulative survival rate (ASR) of AAAA (22.72%), GGAG (33.88%) and AAGG (31.10%) occurred at a salinity-temperature combination of 25/24 °C, and that of GGGG (27.51%) occurred at a salinity-temperature combination of 25/21 °C. The largest metamorphosis rate (MR) of AAAA (25.50%), GGAG (33.27%) and AAGG (32.73%) were found at a salinity-temperature combination of 28/27 °C, and that of GGGG (27.60%) were found at a salinity-temperature combination of 28/24 °C. In general, the larval performance of allotetraploid oysters was superior to that of autotetraploid oysters, with an allotetraploid superiority ranging from 3.57 to 9.39% in SGR, 32.82 to 103.26% in ASR and − 12.08 to 28.79% in MR. The optimum larval rearing salinity-temperature condition recommended for GGGG, GGAG and AAGG is 25–28 at 21–24 °C, while for AAAA is 25–28 at 24–27 °C; a temperature range of 24–27 °C and a salinity range of 28–31 are suggested to improve spat production of these four tetraploid oysters. [ABSTRACT FROM AUTHOR]

Tetraploid oysters are artificially produced oysters that do not exist in nature. The successful breeding of 100% triploid oysters resolved the difficulties of traditional drug-induced triploids, such as the presence of drug residues and a low triploid induction rate. However, little is known concerning the biochemical composition and nutrient contents of such tetraploids. Therefore, we investigated compositional differences among diploid, triploid, and tetraploid Crassostrea gigas as well as between males and females of diploids and tetraploids. The findings indicated that glycogen, EPA, ∑PUFA, and omega-3 contents were significantly higher in triploid oysters than in diploids or tetraploids; tetraploid oysters had a significantly higher protein content, C14:0, essential amino acid, and flavor-presenting amino acid contents than diploids or triploids. For both diploid and tetraploids, females had significantly higher levels of glutamate, methionine, and phenylalanine than males but lower levels of glycine and alanine. In addition, female oysters had significantly more EPA, DHA, omega-3, and total fatty acids, a result that may be due to the fact that gonadal development in male oysters requires more energy to sustain growth, consumes greater amounts of nutrients, and accumulates more proteins. With these results, important information is provided on the production of C. gigas, as well as on the basis and backing for the genetic breeding of oysters. [ABSTRACT FROM AUTHOR]

ABSTRACT The Pacific oyster is the most widely cultured shellfish worldwide, but production has been affected by mortality events, including in hatcheries that supply the seed for growers. Several pathogens cause disease in oysters, but in many cases, mortality events cannot be attributed to a single agent and appear to be multifactorial, involving environmental variables and microbial interactions. As an organism’s microbiome can provide resilience against pathogens and environmental stressors, we investigated the microbiomes in cohorts of freshly settled oyster spat, some of which experienced notable mortality. Deep sequencing of 16S rRNA gene fragments did not show a significant difference among the microbiomes of cohorts experiencing different mortality levels, but revealed a characteristic core microbiome comprising 74 taxa. Irrespective of mortality, the relative abundance of taxa in the core microbiomes changed significantly as the spat aged, yet remained distinct from the microbial community in the surrounding water. The core microbiome was dominated by bacteria in the families Rhodobacteraceae, Nitrosomonadaceae, Flavobacteriaceae, Pirellulaeceae, and Saprospiraceae. Within these families, 14 taxa designated as the “Hard-Core Microbiome” were indicative of changes in the core microbiome as the spat aged. The variability in diversity and richness of the core taxa decreased with age, implying niche occupation. As well, there was exchange of microbes with surrounding water during development of the core microbiome. The shift in the core microbiome demonstrates the dynamic nature of the microbiome as oyster spat age.IMPORTANCEThe Pacific oyster (Magallana gigas, also known as Crassostrea gigas) is the most widely cultivated shellfish and is important to the economy of many coastal communities. However, high mortality of spat during the first few days following metamorphosis can affect the seed supply to oyster growers. Here, we show that the microbiome composition of recently settled oyster spat experiencing low or high mortality was not significantly different. Instead, development of the core microbiome was associated with spat aging and was partially driven by dispersal through the water. These findings imply the importance of early-stage rearing conditions for spat microbiome development in aquaculture facilities. Furthermore, shellfish growers could gain information about the developmental state of the oyster spat microbiome by assessing key taxa. Additionally, the study provides a baseline microbiome for future hypothesis testing and potential probiotic applications on developing spat.

The increase of the frequency and severity of marine diseases affecting farmed marine mollusks are currently threatening the sustainability of this aquaculture sector, with few available prophylactic or therapeutic solutions. Recent advances have shown that the innate immune system of invertebrates can develop memory mechanisms allowing for efficient protection against pathogens. These properties have been called innate immune memory, immune priming or trained immunity. Previous results demonstrated the possibility to elicit antiviral immune priming to protect Pacific oysters against the ostreid herpes virus 1 (OsHV-1), currently plaguing M. gigas production worldwide. Here, we demonstrate that UV-inactivated OsHV-1 is also a potent elicitor of immune priming. Previous exposure to the inactivated virus was able to efficiently protect oysters against OsHV-1, significantly increasing oyster survival. We demonstrate that this exposure blocked viral replication and was able to induce antiviral gene expression potentially involved in controlling the infection. Finally, we show that this phenomenon can persist for at least 3 months, suggesting the induction of innate immune memory mechanisms. This study unravels new ways to train the Pacific oyster immune system that could represent an opportunity to develop new prophylactic strategies to improve health and to sustain the development of marine mollusk aquaculture. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the effect of neutral protease treatment on the biochemical properties of various parts of Pacific oysters (Crassostrea gigas) under different storage conditions. The mechanism of quality degradation in the mantle, adductor muscle, gill, and trunk of treated oysters stored at −1.5 °C (superchilling) or 4 °C (refrigeration) for several days using different storage methods was studied. The results showed that the oyster treated with the enzyme exhibited higher glycogen content, flavor nucleotide content, and sensory scores compared to the control group. Superchilling at −1.5 °C was observed to slow the increase in total volatile basic nitrogen (TVB-N), total viable count (TVC), and pH, while maintaining sensory scores better than refrigeration at 4 °C. Both wet superchilling (WS) and dry exposed superchilling (DeS) methods effectively preserved freshness and quality at −1.5 °C. The freshness of the oysters' body trunk changed most significantly. K value, K′ value, and AEC value, as the evaluation indexes of oyster freshness, were affected by the storage medium. Therefore, neutral protease enhances the flavor of oysters in a short time, and oysters stored in wet superchilling or dry exposed superchilling conditions have an extended shelf life. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Dalian Ocean University is the property of Journal of Dalian Ocean University Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Hydrobiology is the property of Editorial Department of Journal of Hydrobiology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Shell color is one of the shell traits of molluscs, which has been regarded as an economic trait in some bivalves. Pacific oysters (Crassostrea gigas) are important aquaculture shellfish worldwide. In the past decade, several shell color strains of C. gigas were developed through selective breeding, which provides valuable materials for research on the inheritance pattern and regulation mechanisms of shell color. The inheritance patterns of different shell colors in C. gigas have been identified in certain research; however, the regulation mechanism of oyster pigmentation and shell color formation remains unclear. In this study, we performed transcriptomic and physiological analyses using black and white shell oysters to investigate the molecular mechanism of melanin synthesis in C. gigas. Several pigmentation-related pathways, such as cytochrome P450, melanogenesis, tyrosine metabolism, and the cAMP signaling pathway were found. The majority of differentially expressed genes and some signaling molecules from these pathways exhibited a higher level in the black shell oysters than in the white, especially after l-tyrosine feeding, suggesting that those differences may cause a variation of tyrosine metabolism and melanin synthesis. In addition, the in vitro assay using primary cells from mantle tissue showed that l-tyrosine incubation increased cAMP level, gene and protein expression, and melanin content. This study reveals the difference in tyrosine metabolism and melanin synthesis in black and white shell oysters and provides evidence for the potential regulatory mechanism of shell color in oysters. [ABSTRACT FROM AUTHOR]

Exposure to tert-butyl hydroperoxide (t-BHP) leads to cytotoxicity and oxidative stress in various organs and cell types. The bioactive peptides extracted from Oysters exhibit marked antioxidant activity. The impacts of Crassostrea gigas peptides on t-BHP-triggered oxidative stress remain largely unknown. The protective and antioxidant activity of a C.gigas peptide, PEP-1, on t-BHP-treated HepG2 cells, was investigated. PEP-1, this peptide is arginine kinase in oysters. This enzyme functions as a catalyst for the chemical reaction and serves as a phosphate transferase. Since it was the most expressed protein in the adductor muscle of oysters. Our determination showed the lowest level of a toxic concentration of t-BHP (200 µM) and the resting concentration of PEP-1 (0–1000 ng/ml). PEP-1 exerted a protective effect against t-BHP-induced apoptosis by modifying the expression of pro-and anti-apoptotic proteins. PEP-1 administration reduced nitric oxide and ROS levels while restoring levels of antioxidant proteins in t-BHP-induced cells. PEP-1 exhibited the capacity to enhance the translocation of nuclear factor erythroid 2-related factor 2 (Nrf2). Therefore, the C. gigas peptide PEP-1 has demonstrated its ability to protect HepG2 cells against oxidative stress induced by t-BHP. [ABSTRACT FROM AUTHOR]

Molluscs are intermediate hosts for several parasites. The recognition processes, required to evade the host's immune response, depend on carbohydrates. Therefore, the investigation of mollusc glycosylation capacities is of high relevance to understand the interaction of parasites with their host. UDP-N-acetylglucosamine:α-1,3-D-mannoside β-1,2-N-acetylglucosaminyltransferase I (GnT-I) is the key enzyme for the biosynthesis of hybrid and complex type N-glycans catalysing the transfer of N-acetylglucosamine from UDP-N-acetylglucosamine to the α-1,3 Man antenna of Man5GlcNAc2. Thereby, the enzyme produces a suitable substrate for further enzymes, such as α-mannosidase II, GlcNAc-transferase II, galactosyltransferases or fucosyltransferases. The sequence of GnT- I from the Pacific oyster, Crassostrea gigas, was obtained by homology search using the corresponding human enzyme as the template. The obtained gene codes for a 445 amino acids long type II transmembrane glycoprotein and shared typical structural elements with enzymes from other species. The enzyme was expressed in insect cells and purified by immunoprecipitation using protein A/G-plus agarose beads linked to monoclonal His-tag antibodies. GnT-I activity was determined towards the substrates Man5-PA, MM-PA and GnM-PA. The enzyme displayed highest activity at pH 7.0 and 30 °C, using Man5-PA as the substrate. Divalent cations were indispensable for the enzyme, with highest activity at 40 mM Mn2+, while the addition of EDTA or Cu2+ abolished the activity completely. The activity was also reduced by the addition of UDP, UTP or galactose. In this study we present the identification, expression and biochemical characterization of the first molluscan UDP-N-acetylglucosamine:α-1,3-D-mannoside β-1,2-N-acetylglucosaminyltransferase I, GnT-I, from the Pacific oyster Crassostrea gigas. Illustration of GnT-I activity. (a) Transfer of GlcNAc to Man5-PA, creating Man5GlcNAc3-PA. (b) Transfer of GlcNAc to MM-PA, creating MGn-PA. (c) Transfer of GlcNAc to GnM-PA, creating GnGn-PA. Blue squares represent N-acetylglucosamine, green cycles depict mannose. Graphic illustration of N-glycans were created using bioRENDER. [ABSTRACT FROM AUTHOR]

Understanding temporal changes in reproductive conditions and physicochemical environmental factors governing the variation is vital in the management and ecology of oysters. This study investigated the annual gametogenesis and reproductive effort of the Pacific oyster Crassostrea gigas in Incheon Bay using histology and indirect enzyme-linked immunoassay (ELISA). Seasonal changes in the reproductive condition were closely associated with the changes in sea surface temperature (SST), as a rapid increase in SST from April (10.1 °C) to early June (18.7 °C) coincided with the growth and maturation of the eggs. Histology indicated that the spawning was synchronous, as both males and females initiated the spawning in late June, which continued until early August. Gonad-somatic index (GSI), a ratio of the egg mass to the tissue weight determined by ELISA, showed a dramatic decline from late June (47.3%) to August (3.9%), suggesting that the females discharged a substantial amount of eggs through spawning, which accounted for approximately 40% of the body weight. The condition index (CI) of oysters determined in this study was comparable to those of oysters reported from the south coast, where oysters were raised in subtidal using suspended long lines, suggesting that the off-bottom culture of the Pacific oysters near the low tide line in Incheon Bay is a promising culture technique in the tidal flat environment. [ABSTRACT FROM AUTHOR]

Bivalves are affected by various stressors, such as global warming and microplastics, in the marine environment. Microplastics are one of the most concerning pollutants worldwide, and high seawater temperatures caused by global warming influence the survival of marine organisms. However, little is known about the combined effects of elevated temperature and microplastics (MPs) on marine organisms, and most studies conducted in recent years have investigated the two factors, respectively. Thus, it is necessary to investigate the combined effects of elevated temperature and MP exposure on marine life. The Pacific oyster Crassostrea gigas is a widely distributed marine mollusk, and has very important economic value. The aim of the current study was to explore the toxic effects of elevated temperature and microplastic co-exposure on the hemocyte function, immune-related gene expression, and energy metabolism of C. gigas. In the current study, oysters were exposed to three levels of microplastics (no microplastics, 6 μm microplastics: SPS-MPs, and 50~60 μm microplastics: LPS-MPs) and two temperature levels (20 ℃ and 25 ℃) for 21 days, and the phagocytosis rate and reactive oxygen species (ROS) content of hemocytes, glycogen content in digestive glands, and immune-related gene expression in digestive glands and gills were examined on the 21st day. 2', 7'-Dichlorodihydrofluorescein diacetate and fluorescent microspheres were used to measure the ROS content and phagocytosis ratein hemocytes of C. gigas by flow cytometry, respectively. The glycogen content was measured using detection kits. Total RNA was isolated by TRIzol reagent, and the concentration was measured by Nanodrop. M-MLV Reverse Transcriptase was used for cDNA synthesis. The expressions of immune-related genes [inhibitor of NF-κB (IκB), p53, and heat shock protein 90 (HSP90)] were examined by quantitative real-time PCR in the digestive glands and gills of oysters from each treatment group. Two-way ANOVA was used to analyze the interactive effects of elevated temperature and microplastics on tested parameters of oysters using SPSS software. The results showed that exposure to SPS-MPs could elevate ROS content and reduce phagocytosis in hemocytes, but no significant interaction was found between elevated temperature and microplastic effects on ROS content and phagocytosis rate in hemocytes (P > 0.05). The 25 ℃+LPS-MPs exposure significantly decreased phagocytosis in hemocytes compared with single LPS-MPs and elevated temperature exposures (P < 0.05). Single SPS-MPs exposure significantly decreased phagocytosis in hemocytes compared with single LPS-MPs exposure (P < 0.05). In digestive glands, there was a significant interaction between elevated temperature and microplastics in glycogen content (P < 0.05), and the combined exposure could increase the glycogen content compared with other treatments. In digestive glands, the 25 ℃+LPS-MPs exposure significantly increased glycogen content compared with single elevated temperature and single LPS-MPs exposure (P < 0.05). In digestive glands and gills, there was a significant interaction between elevated temperature and microplastics in the expressions of HSP90, IκB, and p53 genes (P < 0.05). The 25 ℃+SPS-MPs exposure significantly upregulated the expression of HSP90, IκB, and p53 genes in the digestive glands of oysters compared with single SPS-MPs and single elevated temperature exposures (P < 0.05). The 25 ℃+SPS-MPs exposure significantly downregulated the expression of the HSP90 gene in the gills of oysters compared with single SPS-MPs exposure (P < 0.05). Single elevated temperature and single microplastics exposure significantly upregulated the expression of the IκB gene compared with the control in gills (P < 0.05). The combined exposure of elevated temperature and microplastics showed a significant antagonistic effect on the expression of the p53 gene in gills. Microplastics exposure downregulated p53 gene expression compared with the control at 20 ℃, while it upregulated p53 gene expression compared with single elevated temperature at 25 ℃. These results indicated that the p53 gene plays an important role in regulating the immune response in both digestive glands and gills. The interaction between elevated temperature and microplastics on the mRNA expression of HSP90 and IκB genes in digestive glands of C. gigas was size-dependent: A synergistic effect was found between SPS-MPs and elevated temperature, and an antagonistic effect was found between LPS-MPs and elevated temperature. A significant antagonistic effect was found between elevated temperature and microplastics on the mRNA expression of the IκB gene in gills, and the regulation pattern was different from that in the digestive glands, indicating that the regulation effect of the IκB gene was tissue-specific. In conclusion, the combined exposure of elevated temperature and microplastics can increase the glycogen content in the digestive glands of C. gigas, induce an immune response in digestive glands and gills, and trigger the oxidative stress response in hemocytes. Microplastics can cause stronger oxidative stress in hemocytes than elevated temperature. Moreover, a significant interactive effect was found between elevated temperature and microplastics on glycogen content in digestive glands and the expression of immune-related genes (HSP90, p53, and IκB) in digestive glands and gills. The results of this study provide valuable information for evaluating the toxic effects of microplastics on marine organisms under a global warming background.

Warm water temperature is a risk factor for recurrent mass mortality in farmed Pacific oysters Crassostrea gigas caused by Ostreid herpesvirus-1, but there is little information on environmental conditions when the disease first appears in a region—the index case. Environmental conditions between four index cases in Australia (2010, 2013, 2016 and 2024) were compared to provide insight into possible origins of the virus. Each index case was preceded by unusually low rainfall and higher rates of temperature change that could increase oyster susceptibility through thermal flux stress. Water temperature alone did not explain the index cases, there being no consistency in sea surface, estuary or air temperatures between them. Tidal cycles and chlorophyll-a levels were unremarkable, harmful algae were present in all index cases and anthropogenic environmental contamination was unlikely. The lack of an interpretable change in the estuarine environment suggests the recent introduction of OsHV-1; however, viral emergence from a local reservoir cannot be excluded. Future events will be difficult to predict. Temperature flux and rainfall are likely important, but they are proxies for a range of undetermined factors and to identify these, it will be necessary to develop comprehensive protocols for data acquisition during future index cases.

Mollusca first evolve primitive immune cells (namely, haemocytes), which assemble a notable complex innate immune system, which are continuously produced through proliferation and differentiation and infused in the haemolymph. As a typical E3 ligase, CHIP is critical for immune cell turnover and homeostasis in vertebrates. In this study, a CHIP homolog (CgCHIP) with a high expression in haemocytes was identified in oysters to investigate its role in the proliferation and differentiation of ancient innate immune cells. CgCHIP exhibited a widespread distribution across all haemocyte subpopulations, and the knockdown of CgCHIP altered the composition of haemocytes as examined by flow cytometry. Mechanistically screened with bioinformatics and immunoprecipitation, a key haematopoietic transcription factor CgRunx was identified as a substrate of CgCHIP. Moreover, amino acids in the interacted intervals of CgCHIP and CgRunx were determined by molecular docking. Experimental evidence from an in vitro culture model of an agranulocyte subpopulation and an in vivo oyster model revealed that the knockdown of CgCHIP and CgRunx had opposing effects on agranulocyte (precursor cells) differentiation and granulocyte (effector cells) proliferation. In summary, CgCHIP negatively regulated agranulocyte differentiation and granulocyte proliferation by mediating the ubiquitination and degradation of CgRunx in oysters. These results offer insight into the involvement of ubiquitylation in controlling haemocyte turnover in primitive invertebrates.

In order to investigate the differences of volatile flavor components in different tissues of Crassostrea gigas, and reveal the source and formation mechanism of the overall flavor of oysters, the volatile flavor components in the adductor muscle, hepatopancreas, gills and gonads of Crassostrea gigas were detected by using SPME-GC-MS technique combined with the method of multivariate statistical analysis. The results showed that 18 substances were detected in the adductor muscle, 11 substances were detected in the hepatopancreas, 8 substances were detected in the gills and 6 substances were detected in the gonads. The main components in the adductor muscle, gills and gonads were aldehydes, and the main components in hepatopancreas were alcohols. A total of 28 volatile flavor components were detected in the four tissues, most of which were aldehydes, ketones and alcohols, etc. The clustering heat map analysis, screening of key flavor components and principal component analysis were used to compare the volatile flavor components of the four different tissues, and the results showed that there were obvious differences in the flavors of the various tissues of Crassostrea gigas, and the main substances that affected the flavors of Crassostrea gigas were aldehydes and ketones. The various flavor substances in the different tissues of Crassostrea gigas coordinated with each other to create the unique marine fresh flavor of Crassostrea gigas. The results of this study were of great significance in guiding the research on the flavor of Crassostrea gigas and the processing and utilization of Crassostrea gigas products. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Dalian Ocean University is the property of Journal of Dalian Ocean University Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Heterosis has been exploited to enhance the yield and adaptability in various shellfish species; however, the molecular basis of it remains unclear. The Pacific oyster Crassostrea gigas is one of the most economically important aquaculture species, and its productive traits can be improved by hybridization. Here, an intraspecific cross between orange shell (O, 10th generation) and 'Haida No. 1' (H, 13th generation) of C. gigas was performed to assess the heterosis of survival trait. Survival rates of hybrid family (OH) and inbred families (HH and OO) were compared at larval stage, and eyed-pediveliger larvae of three families were subjected to transcriptome analysis. The analysis results of best-parent heterosis and mid-parent heterosis showed that the hybrid family exhibited a high heterosis in survival relative to the parental families. The OH-M (OH vs. OO) and OH-P (OH vs. HH) had 425 and 512 differentially expressed genes (DEGs), respectively. Functional enrichment analysis of these DEGs revealed that the significantly enriched genes function in virion binding, C-type lectin receptor signaling pathway, cellular defense response and other immune-related processes, which involves perlucin-like protein, CD209 antigen-like protein, ZNFX1, caspase-3 and acan genes. These differentially expressed genes in OH-M and OH-P, together with the immune-related processes mentioned above may play an important role in the larval survival of C. gigas. In addition, three genes (CYP450, fucolectin and perlucin-like) are associated with the orange shell and low survival of maternal oyster OO. These findings provide support for the application of hybrid with superior survival and will facilitate the understanding of heterosis formation in the Pacific oyster. [ABSTRACT FROM AUTHOR]

The fecundity of triploid female Crassostrea gigas exhibited significant variation and was lower compared to diploid individuals. Previous studies categorized mature stage triploid female C. gigas into two groups: female α, characterized by a high number of oocytes, and female β, displaying few or no oocytes. To investigate the molecular mechanisms underlying irregular oogenesis and fecundity differences in triploid C. gigas, we performed a comparative analysis of gonad transcriptomes at different stages of gonadal development, including female α, female β, and diploids. During early oogenesis, functional enrichment analysis between female diploids and putative female β triploids revealed differently expressed genes (DEGs) in the ribosome and ribosome biogenesis pathways. Expression levels of DEGs in these pathways were significantly decreased in the putative female β triploid, suggesting a potential role of reduced ribosome levels in obstructing triploid oogenesis. Moreover, to identify regulatory pathways in gonad development, female oysters at the early and mature stages were compared. The DNA repair and recombination proteins pathways were enriched in female diploids and female α triploids but absent in female β triploids. Overall, we propose that decreased ribosome biogenesis in female triploids hinders the differentiation of germ stem cells, leading to the formation of a large number of abnormal germ cells and ultimately resulting in reduced fecundity. The variation in fertility among triploids appeared to be related to the degree of DNA damage repair during female gonad development. This study offers valuable insights into the oogenesis process in female triploid C. gigas. [ABSTRACT FROM AUTHOR]

Increasing evidence confirms that histone modification plays a critical role in preserving long-term immunological memory. Immune priming is a novel form of immunological memory recently verified in invertebrates. Toll-like receptor (TLR) signaling and cytokines have been reported to be involved in the immune priming of the Pacific oyster Crassostrea gigas. In the present study, the expression of Toll-like receptor 3 (CgTLR3), myeloid differentiation factor 88-2 (CgMyd88-2) and interleukin 17-1 (CgIL17-1) was found to be elevated in the hemocytes of C. gigas at 6 h after the secondary stimulation with Vibrio splendidus, which was significantly higher than that at 6 h after the primary stimulation (p < 0.05). A significant increase in histone H3 lysine 4 trimethylation (H3K4me3) enrichment was detected in the promoter region of the CgTLR3 gene at 7 d after the primary stimulation with inactivated V. splendidus (p < 0.05). After the treatment with a histone methyltransferase inhibitor (5′-methylthioadenosine, MTA), the level of H3K4me3 at the promoter of the CgTLR3 gene decreased significantly at 7 d after the primary stimulation with inactivated V. splendidus (p < 0.05), and the expression of CgTLR3, CgMyD88-2 and CgIL17-1 was significantly repressed at 6 h after the secondary stimulation with V. splendidus (p < 0.05). Conversely, the treatment with monomethyl fumarate (MEF, an inhibitor of histone demethylases) resulted in a significant increase in H3K4me3 enrichment levels at the CgTLR3 promoter at 7 d after the primary stimulation (p < 0.05), and the expression of CgTLR3, CgMyD88-2 and CgIL17-1 was observed to increase significantly at 6 h after the secondary stimulation (p < 0.05). These results suggested that H3K4me3 regulated MyD88-dependent TLR signaling in the hemocytes of C. gigas, which defined the role of histone modifications in invertebrate immune priming. [ABSTRACT FROM AUTHOR]

CGL1 is a mannose-specific lectin isolated from the Pacific oyster Crassostrea gigas , and it belongs to the DM9 domain protein family. Each subunit of the CGL1 dimer consists of a tandem repeat of DM9 motifs, which were originally found in the Drosophila melanogaster genome. The CGL1 protomer contains two carbohydrate-binding sites: a high-affinity site A and a low-affinity site B. An assay using dendrimers containing oligomannose from yeast (Saccharomyces cerevisiae) revealed that CGL1 exhibited significantly higher affinity for mannotetraose (Man 4 ) compared to mannobiose (Man 2 ) and mannotriose (Man 3 ). To investigate its oligomannose-recognition mechanism, X-ray crystallographic analyses of CGL1/oligomannose complexes were performed. In the CGL1/Man 2 and CGL1/Man 3 complexes, Manα1–2Man and Manα1–2Manα1–2Man, respectively, were primarily bound to site A, interacting with the non-reducing mannose residue. On the other hand, in the CGL1/Man 4 crystal, Man 4 (Manα1–2Manα1–2Manα1–6Man) was bound at both site A and site B at the non-reducing and reducing ends, thus linking adjacent CGL1 molecules with crystallographic symmetry. These findings suggest that CGL1 can recognize both the non-reducing and reducing mannose residues of mannose oligosaccharides at its two distinct carbohydrate-binding sites. This enables efficient complex formation, making CGL1 a pattern-recognition molecule capable of recognizing diverse structures of mannose-containing carbohydrate chains. [ABSTRACT FROM AUTHOR]

As the world's largest farmed marine animal, oysters have enormous economic and ecological value. However, mass summer mortality caused by high temperature poses a significant threat to the oyster industry. To investigate the molecular mechanisms underlying heat adaptation and improve the heat tolerance ability in the oyster, we conducted genome-wide association analysis (GWAS) analysis on the F2 generation derived from the hybridization of relatively heat-tolerant Crassostrea angulata ♀ and heat-sensitive Crassostrea gigas ♂, which are the dominant cultured species in southern and northern China, respectively. Acute heat stress experiment (semi-lethal temperature 42 °C) demonstrated that the F2 population showed differentiation in heat tolerance, leading to extremely differentiated individuals (approximately 20% of individuals die within the first four days with 10% survival after 14 days). Genome resequencing and GWAS of the two divergent groups had identified 18 significant SNPs associated with heat tolerance, with 26 candidate genes located near these SNPs. Eleven candidate genes that may associate with the thermal resistance were identified, which were classified into five categories: temperature sensor (Trpm2), transcriptional factor (Gata3), protein ubiquitination (Ube2h, Usp50, Uchl3), heat shock subfamily (Dnajc17, Dnaja1), and transporters (Slc16a9, Slc16a14, Slc16a9, Slc16a2). The expressional differentiation of the above genes between C. gigas and C. angulata under sublethal temperature (37 °C) further supports their crucial role in coping with high temperature. Our results will contribute to understanding the molecular mechanisms underlying heat tolerance, and provide genetic markers for heat-resistance breeding in the oyster industry. [ABSTRACT FROM AUTHOR]

Polyploidy has been suggested to negatively impact environmental stress tolerance, resulting in increased susceptibility to extreme climate events. In this study, we compared the genomic and physiological response of diploid (2n) and triploid (3n) Pacific oysters (Crassostrea gigas) to conditions present during an atmospheric heatwave that impacted the Pacific Northwestern region of the United States in the summer of 2021. Climate stressors were applied either singly (single stressor; elevated seawater temperature, 30°C) or in succession (multiple stressor; elevated seawater temperature followed by aerial emersion at 44°C), replicating conditions present within the intertidal over a tidal cycle during the event. Oyster mortality rate was elevated within stress treatments with respect to the control and was significantly higher in triploids than diploids following multiple stress exposure (36.4% vs. 14.8%). Triploids within the multiple stressor treatment exhibited signs of energetic limitation, including metabolic depression, a significant reduction in ctenidium Na+/K+ ATPase activity, and the dysregulated expression of genes associated with stress response, innate immunity, glucose metabolism, and mitochondrial function. Functional enrichment analysis of ploidy‐specific gene sets identified that biological processes associated with metabolism, stress tolerance, and immune function were overrepresented within triploids across stress treatments. Our results suggest that triploidy impacts the transcriptional regulation of key processes that underly the stress response of Pacific oysters, resulting in downstream shifts in physiological tolerance limits that may increase susceptibility to extreme climate events that present multiple environmental stressors. The impact of chromosome set manipulation on the climate resilience of marine organisms has important implications for domestic food security within future climate scenarios, especially as triploidy induction becomes an increasingly popular tool to elicit reproductive control across a wide range of species used within marine aquaculture. [ABSTRACT FROM AUTHOR]

Artificial light at night (ALAN) constitutes a growing threat to coastal ecosystems by altering natural light cycles, which could impair organisms' biological rhythms, with resulting physiological and ecological consequences. Coastal ecosystems are strongly exposed to ALAN, but its effects on coastal organisms are poorly studied. Besides ALAN's intensity, ALAN's quality exposure may change the impacts on organisms. This study aims to characterize the effects of different ALAN's spectral compositions (monochromatic wavelength lights in red (peak at 626 nm), green (peak at 515 nm), blue (peak at 467 nm), and white (410–680 nm) light) at low and realistic intensity (1 lx) on the oyster Crassostrea gigas daily rhythm. Results reveal that all ALAN's treatments affect the oysters' daily valve activity rhythm in different manners and the overall expression of the 13 studied genes. Eight of these genes are involved in the oyster's circadian clock, 2 are clock-associated genes, and 3 are light perception genes. The blue light has the most important effects on oysters' valve behavior and clock and clock-associated gene expression. Interestingly, red and green lights also show significant impacts on the daily rhythm, while the lowest impacts are shown with the green light. Finally, ALAN white light shows the same impact as the blue one in terms of loss of rhythmic oysters' percentage, but the chronobiological parameters of the remaining rhythmic oysters are less disrupted than when exposed to each of the monochromatic light's treatments alone. We conclude that ALAN's spectral composition does influence its effect on oysters' daily rhythm, which could give clues to limit physiological and ecological impacts on coastal environments. [ABSTRACT FROM AUTHOR]

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The Pacific oyster Crassostrea gigas is one of the most important cultured marine species around the world. Production of Pacific oysters in China has depended primarily on hatchery produced seeds since 2016, with the successful introduction and development of triploid oysters. However, the seed supply of Pacific oysters is threatened by recurring mass mortality events in recent years. Vibriosis is the most commonly encountered disease associated with intensive oyster culture in hatcheries and nurseries. Vibrio alginolyticus and Bacillus hwajinpoensis were the two strains with pathogenic and probiotic effects, respectively, identified during the Pacific oyster larvae production. To monitor their colonization process in Pacific oyster larvae, green fluorescent protein (GFP) and red fluorescent protein (RFP) were labeled to the pathogenic V. alginolyticus and the probiotic B. hwajinpoensis stain, respectively. The pathogenic and probiotic effects of the two strains during the colonization process were then assessed. Stabile expression of GFP and RFP were observed in corresponding stains, and the capabilities of growth, biofilm formation and in vitro adhesion of GFP- and RFP- tagged stains were not significantly different from those of the wild-type strains. Usage of probiotics of 105 CFU/mL significantly inhibited the growth of pathogenic V. alginolyticus and reduced the mortality of D-sharped larvae. Both the pathogenic and probiotic strains employed a similar route to enter and colonize the oyster larvae, which indicates that competing with pathogens for binding and spreading sites were one of the mechanisms of B. hwajinpoensis to provide the probiotic effects to oyster larvae. In summary, employment of fluorescence-tagged pathogenic and probiotic strains simultaneously provides us with an excellent bioassay model to investigate the potential mechanisms of probiotics. [ABSTRACT FROM AUTHOR]

Three groups of mollusks of the triploid Pacific oyster Crassostrea gigas differing in morphometric parameters—fast-growing (FG) with a shell height of over 40 mm; medium-growing (MG), 15 mm < H < 40 mm; and slow-growing (SG), H < 15 mm—have been studied from the Donuzlav estuary (Black Sea). Stable differences have been revealed in the growth rates of juveniles of the same age. Mollusks of the FG group are dominant in weight gain and linear dimensions throughout the study. The average daily increase in the shell height of the studied mollusks ranges from 0.1 to 0.35 mm/day, with maximum values in June and September. The weight increases with different rates: on average, 0.051 g/day in the SG groups, 0.168 g/day in the MG group, and 0.287 g/day in the FG group. The peaks of this parameter have been recorded in August and September, reaching 0.12, 0.26, and 0.43 g/day, respectively. The shell height of slow-growing polyploid oysters has a negative allometry (b = 2.17), while the other two groups are characterized by a clear positive allometry (b = 3.23 for MG and 3.80 for FG); i.e., the increase in weight is faster than the linear growth in juveniles of the species. It has been suggested that polyploidy (triploidy) determines the differences in the growth rates of the same-aged mollusks. The allometry index b can be used to identify growth features at the early stages of oyster development. [ABSTRACT FROM AUTHOR]

The increase of the frequency and severity of marine diseases affecting farmed marine mollusks are currently threatening the sustainability of this aquaculture sector, with few available prophylactic or therapeutic solutions. Recent advances have shown that the innate immune system of invertebrates can develop memory mechanisms allowing for efficient protection against pathogens. These properties have been called innate immune memory, immune priming or trained immunity. Previous results demonstrated the possibility to elicit antiviral immune priming to protect Pacific oysters against the ostreid herpes virus 1 (OsHV-1), currently plaguing M. gigas production worldwide. Here, we demonstrate that UV-inactivated OsHV-1 is also a potent elicitor of immune priming. Previous exposure to the inactivated virus was able to efficiently protect oysters against OsHV-1, significantly increasing oyster survival. We demonstrate that this exposure blocked viral replication and was able to induce antiviral gene expression potentially involved in controlling the infection. Finally, we show that this phenomenon can persist for at least 3 months, suggesting the induction of innate immune memory mechanisms. This study unravels new ways to train the Pacific oyster immune system that could represent an opportunity to develop new prophylactic strategies to improve health and to sustain the development of marine mollusk aquaculture.

Ambient ultraviolet radiation (UVB) from solar and artificial light presents serious environmental risks to aquatic ecosystems. The Pacific oyster, Crassostrea gigas, perceives changes in the external environment primarily through its mantle tissue, which contains many nerve fibers and tentacles. Changes within the mantles can typically illustrate the injury of ambient UVB. In this study, a comprehensive analysis of phenotypic, behavioral, and physiological changes demonstrated that extreme UVB radiation (10 W/m²) directly suppressed the behavioral activities of C. gigas. Conversely, under ambient UVB radiation (5 W/m²), various physiological processes exhibited significant alterations in C. gigas, despite the behavior remaining relatively unaffected. Using mathematical model analysis, the integrated analysis of the full-length transcriptome, proteome, and metabolome showed that ambient UVB significantly affected the metabolic processes (saccharide, lipid, and protein metabolism) and cellular biology processes (autophagy, apoptosis, oxidative stress) of the C. gigas mantle. Subsequently, using Procrustes analysis and Pearson correlation analysis, the association between multi-omics data and physiological changes, as well as their biomarkers, revealed the effect of UVB on three crucial biological processes: activation of autophagy signaling (key factors: Ca2+, LC3B, BECN1, caspase-7), response to oxidative stress (reactive oxygen species, heat shock 70, cytochrome c oxidase), and recalibration of energy metabolism (saccharide, succinic acid, translation initiation factor IF-2). These findings offer a fresh perspective on the integration of multi-data from non-model animals in ambient UVB risk assessment.

Marine mollusks, including oysters, are highly tolerant to high levels of cadmium (Cd), but the molecular mechanisms underlying their molecular response to acute Cd exposure remain unclear. In this study, the Pacific oyster Crassostrea gigas was used as a biological model, exposed to acute Cd stress for 96 h. Transcriptomic analyses of their gills were performed, and metabolomic analyses further validated these results. In our study, a total of 111 differentially expressed metabolites (DEMs) and 2108 differentially expressed genes (DEGs) were identified under acute Cd exposure. Further analyses revealed alterations in key genes and metabolic pathways associated with heavy metal stress response. Cd exposure triggered physiological and metabolic responses in oysters, including enhanced oxidative stress and disturbances in energy metabolism, and these changes revealed the biological response of oysters to acute Cd stress. Moreover, oysters could effectively enhance the tolerance and detoxification ability to acute Cd exposure through activating ABC transporters, enhancing glutathione metabolism and sulfur relay system in gill cells, and regulating energy metabolism. This study reveals the molecular mechanism of acute Cd stress in oysters and explores the molecular mechanism of high tolerance to Cd in oysters by using combined metabolomics and transcriptome analysis.

Near-infrared spectroscopy (NIR) has become an essential tool for non-destructive analysis in various fields, including aquaculture. This study presents a pioneering application of portable NIR spectrometers to analyze glycogen content in the gonadal tissues of the Pacific oyster (Crassostrea gigas), marking the first instance of developing quantitative models for glycogen in tetraploid C. gigas. The research also provides a comparative analysis with models for diploid and triploid oysters, underscoring the innovative use of portable NIR technology in aquaculture. Two portable NIR spectrometers were employed: the Micro NIR 1700 (908–1676 nm) and the Micro PHAZIR RX (1624–2460 nm). Near-infrared spectra were acquired from the gonadal tissues of diploid, triploid, and tetraploid C. gigas. Quantitative models for glycogen content were developed and validated using cross-validation methods. Additionally, qualitative models for different ploidies and genders were established. For the Micro NIR 1700, the cross-validation correlation coefficients (Rcv) and cross-validation relative predictive errors (RPDcv) for glycogen were 0.949 and 3.191 for diploids, 0.915 and 2.498 for triploids, and 0.902 and 2.310 for tetraploids. The Micro PHAZIR RX achieved Rcv and RPDcv values of 0.781 and 2.240 for diploids, 0.839 and 2.504 for triploids, and 0.717 and 1.851 for tetraploids. The Micro NIR 1700 demonstrated superior quantitative performance, with RPD values exceeding 2, indicating its effectiveness in predicting glycogen content across different ploidy levels. Qualitative models showed a performance index of 91.6 for diploid and 95 for tetraploid genders using the Micro NIR 1700, while the Micro PHAZIR RX achieved correct identification rates of 99.79% and 100% for diploid and tetraploid genders, respectively. However, differentiation of ploidies was less successful with both instruments. This study’s originality lies in establishing the first quantitative models for glycogen content in tetraploid C. gigas using portable NIR spectrometers, highlighting the significant advancements in non-destructive glycogen analysis. The applicability of these findings is substantial for oyster breeding programs focused on enhancing meat quality traits. These models provide a valuable phenotyping tool for selecting oysters with optimal glycogen content, demonstrating the practical utility of portable NIR technology in aquaculture.