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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]

Simple Summary: As a filter-feeding and sessile invertebrate living in estuaries and intertidal areas, Crassostrea gigas must cope with and adapt to a dynamic and changeable environment. Vibrio alginolyticus is a Gram-negative bacterium that is widespread in oceans and estuaries, and is one of the main Vibrio species that cause oyster disease. In this study, we used transcriptome sequencing to help us better understand how the giant oyster adapts to pathogen-rich environments. By focusing on the gills, which play a crucial role in the immune response, we aimed to shed light on the molecular processes underlying the interaction between the oyster and the pathogen. Over the years, oysters have faced recurring mass mortality issues during the summer breeding season, with Vibrio infection emerging as a significant contributing factor. Tubules of gill filaments were confirmed to be in the hematopoietic position in Crassostrea gigas, which produce hemocytes with immune defense capabilities. Additionally, the epithelial cells of oyster gills produce immune effectors to defend against pathogens. In light of this, we performed a transcriptome analysis of gill tissues obtained from C. gigas infected with Vibrio alginolyticus for 12 h and 48 h. Through this analysis, we identified 1024 differentially expressed genes (DEGs) at 12 h post-injection and 1079 DEGs at 48 h post-injection. Enrichment analysis of these DEGs revealed a significant association with immune-related Gene Ontology (GO) terms and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. To further investigate the immune response, we constructed a protein–protein interaction (PPI) network using the DEGs enriched in immune-associated KEGG pathways. This network provided insights into the interactions and relationships among these genes, shedding light on the underlying mechanisms of the innate immune defense mechanism in oyster gills. To ensure the accuracy of our findings, we validated 16 key genes using quantitative RT-PCR. Overall, this study represents the first exploration of the innate immune defense mechanism in oyster gills using a PPI network approach. The findings provide valuable insights for future research on oyster pathogen control and the development of oysters with enhanced antimicrobial resistance. [ABSTRACT FROM AUTHOR]

In this study, diploid, triploid, and tetraploid Crassostrea gigas samples were subjected to gas chromatography and ion mobility (GC-IMS) to identify and analyze volatile compounds and flavor fingerprints under conditions of high-temperature incubation. The GC-IMS technology identified a total of 54 volatile components in C. gigas. The contents of 1-octen-3-ol, butyl pentanoate, p-methyl anisole, and 2-methyl-2-hepten-6-one in male oysters were significantly higher than in females, while the contents of phenylacetaldehyde, benzaldehyde, 2-ethyl-3-methylpyrazine, 2-ethylfuran, and 2,4-hexadienal in female oysters were significantly higher than in males. The contents of non-3-en-2-one-M and 1-pentanol in diploids were significantly higher than in triploids and tetraploids, while the content of 2,4-hexadienal in tetraploids was significantly higher than in diploids and tetraploids. The contents of ethyl acetate, ethyl-2-butenoate, and butanal in tetraploids were significantly higher than those in diploids and triploids. The results of a principal components analysis showed that different samples were relatively independently clustered, allowing the ability to distinguish different oyster samples. The chemical fingerprints of volatile compounds of C. gigas with different ploidy and gender under high-temperature incubation were established, and the volatile substance contours of C. gigas were visualized. The results provide a reference for distinguishing the ploidy and gender of C. gigas under conditions of high-temperature incubation. [ABSTRACT FROM AUTHOR]

In this study, GC-IMS was used to analyze the volatile component and flavor profiles of Crassostrea gigas individuals of different ploidy and gender. Principal component analysis was used to explore overall differences in flavor profiles, and a total of 54 volatile compounds were identified. The total volatile flavor contents in the edible parts of tetraploid oysters were significantly higher than in diploid and triploid oysters. The concentrations of ethyl (E)-2-butenoate and 1-penten-3-ol were significantly higher in triploid oysters than in diploid and tetraploid oysters. In addition, the volatile compounds propanoic acid, ethyl propanoate, 1-butanol, butanal, and 2-ethyl furan were significantly higher in females than in males. The volatile compounds p-methyl anisole, 3-octanone, 3-octanone, and (E)-2-heptenal were present in higher levels in male than in female oysters. Overall, different ploidy and gender of oysters are connected with different sensory characteristics, providing new insights for understanding the flavor characteristics of oysters. [ABSTRACT FROM AUTHOR]

Triploid oysters have provided the oyster industry with many benefits, such as fast growth rates, meat quality improvement, and increased oyster production and economic benefits, since the first report on triploid oysters was published. The development of polyploid technology has remarkably increased the output of triploid oysters to meet the increasing demand of consumers for Crassostrea gigas in the past decades. At present, research on triploid oyster has mainly focused on breeding and growth, but studies on the immunity of triploid oysters are limited. According to recent reports, Vibrio alginolyticus is a highly virulent strain that can cause disease and death in shellfish, shrimp, as well as serious economic losses. V. alginolyticus may be a reason why oysters die during summer. Therefore, using V. alginolyticus to explore the resistance and immune defense mechanisms of triploid oysters against pathogens presents practical significance. Transcriptome analysis of gene expression was performed in triploid C. gigas at 12 and 48 h after infection with V. alginolyticus , and the respective 2257 and 191 differentially expressed genes (DEGs) were identified. The results of GO and KEGG enrichment analyses showed that multiple significantly enriched GO terms and KEGG signaling pathways are associated with immunity. A protein–protein interaction network was constructed to investigate the interaction relationship of immune-related genes. Finally, we verified the expression situation of 16 key genes using quantitative RT-PCR. This study is the first to use the PPI network in exploring the immune defense mechanism of triploid C. gigas blood to fill the gap in the immune mechanism of triploid oysters and other mollusks, and provide valuable reference for future triploid farming and pathogen prevention and control. • This study is the first transcriptome analysis based on protein interaction network in triploid Crassostrea gigas. • It provides valuable gene resources for further study of the immune responses in invertebrate blood. • The data serve as a foundation for further research on invertebrates against to pathogen. [ABSTRACT FROM AUTHOR]

Tetraploid oysters hold a significant position in the global oyster industry, particularly as core germplasm resources for the production of triploids. Triploids exhibit desirable characteristics such as reduced gonadal development, larger adult size, and superior flesh quality compared with diploids. However, tetraploids often face challenges of slow growth and chromosomal instability during the breeding process, and the mechanisms underlying the formation of these polyploid characteristics remain unclear. This study aimed to elucidate these mechanisms by constructing a polyploid oyster system and comparing the differences in growth-related phenotypes and gene expression among diploids, triploids, and tetraploids. We identified 1404 differentially expressed genes (DEGs) between diploids and triploids, 1814 DEGs between triploids and tetraploids, and 933 DEGs between diploids and tetraploids. Furthermore, we observed distinct gene expression patterns related to innate immunity response and biomineralization between different ploidy levels. Through trend analysis, we clustered genes with similar expression level changes across different ploidy levels and conducted gene ontology (GO) enrichment analysis on genes with different expression profiles. The results indicated that genes associated with the innate immunity response exhibited significantly upregulated expression with increasing ploidy, while genes related to biomineralization showed higher or lower expression levels in triploid oysters. As biomineralization is closely linked to oyster shell growth, this highlights the crucial role of genes associated with biomineralization in regulating the rapid shell growth observed in triploid oysters. Confronted with environmental challenges, tetraploid oysters may display a stronger innate immune response than diploids and triploids. Our study provides valuable resources for investigating the functional aspects of genes related to polyploid phenotype differences and offers new insights into the molecular mechanisms of existing issues in tetraploid oyster breeding. • Triploid oysters show enhanced calcium transport, regulation, and protein degradation. • Chromosomal duplication affects polyploid oysters' growth and adaptability. • Gene replication exhibits detrimental dosage effects following duplication. [ABSTRACT FROM AUTHOR]