Pacific Oyster Crassostrea Research Articles

Toxic effects of exposure to Polymethyl methacrylate and polyvinyl chloride microplastics in Pacific oysters (Crassostrea gigas)

Increasing attention has been directed toward the toxic effects of microplastics (MP) on marine mollusks in recent years. To evaluate these effects, Pacific oysters (Crassostrea gigas) were acclimated and cultured in a 140-liter container, where two types of MP, polymethyl methacrylate (PMMA) and polyvinyl chloride (PVC), were introduced into their feed. MP concentrations in the water were maintained at 300 μg/L, 600 μg/L, and 900 μg/L to assess oxidative stress, DNA damage, and metabolic disorders in these organisms. Significant alterations in antioxidant enzyme activities were detected in C. gigas exposed to these pollutants. After 30 days of exposure to high concentrations of PMMA, superoxide dismutase (SOD) activity in the adductor muscle was reduced by 59% compared to the control group, while catalase (CAT) activity increased by 67%. DNA damage assessments revealed that NF-κB expression levels reached a maximum value of 2.46 in the high-concentration PMMA group after 30 days, the highest among all experimental groups. Additionally, metabolic pathway alterations in the hepatopancreas of C. gigas were observed, including reduced expression levels of uridine and methylmalonic acid (MMA), alongside significantly elevated expression levels of glutamic acid and asparagine. This study offers essential toxicological data for understanding and quantifying the impacts of PMMA and PVC MP on marine mollusks.

Multi-scale influences on Escherichia coli concentrations in shellfish: From catchment to estuary.

Sustainability of bivalve shellfish farming relies on clean coastal waters, however, high levels of faecal indicator organisms (FIOs, e.g. Escherichia coli) in shellfish results in temporary closure of shellfish harvesting beds to protect human health, but with economic consequences for the shellfish industry. Active Management Systems which can predict FIO contamination may help reduce shellfishery closures. This study evaluated predictors of E. coli concentrations in two shellfish species, the blue mussel (Mytilus edulis) and the Pacific oyster (Crassostrea gigas), at different spatial and temporal scales, within 12 estuaries in England and Wales. We aimed to: (i) identify consistent catchment-scale or within-estuary predictors of elevated E. coli levels in shellfish, (ii) evaluate whether high river flows associated with rainfall events were a significant predictor of shellfish E. coli concentrations, and the time lag between these events and E. coli accumulation, and (iii) whether operation of Combined Sewer Overflows (CSO) is associated with higher E. coli concentrations in shellfish. A cross-catchment analysis gave a good predictive model for contamination management (R2=0.514), with positive relationships between E. coli concentrations and river flow (p=0.001), turbidity (p=0.002) and nitrate (p=0.042). No effect was observed for catchment area, the number of point source discharges, or agricultural land use type. 64% of all shellfish beds showed a significant relationship between E. coli and river flow, with typical lag-times of 1-3 days. Detailed analysis of the Conwy estuary indicated that E. coli counts were consistently higher when the CSO had been active the previous week. In conclusion, we demonstrate that real-time river flow and water quality data may be used to predict potential risk of E. coli contamination in shellfish at the catchment level, however, further refinement (coupling to fine-scale hydrodynamic models) is needed to make accurate predictions for individual shellfish beds within estuaries.

GABA mitigates mitochondrial apoptosis induced by high temperature stress in the Pacific oyster (Crassostrea gigas).

High temperature is a critical environmental factor leading to mass mortality in oyster aquaculture in China. Recent advancements highlight the physiological regulation function of γ-aminobutyric acid (GABA) in the adaptation of environmental stress. This study examined the physiological responses of the Pacific oyster (Crassostrea gigas) upon high temperature exposure, focusing on the histopathological changes in gill, the GABA concentration, the mRNA expression and activities of apoptosis-related genes. Following 24h of exposure to seawater at 28°C, notable histopathological changes, including cellular swelling and vacuolization, along with an increase in TUNEL-positive cells were observed in the oyster gill, compared to the control group maintained at 18°C. Moreover, there was a significant increase in CgCaspase-3 transcripts, Caspase-3 and Caspase-9 activities in the gills, glutamate decarboxylase CgGAD transcripts in the haemocytes, and GABA concentrations in the haemolymph supernatant. Intervention with GABA markedly ameliorated these responses, including reducing the mRNA expression levels of CgBax, CgBak, CgCaspase-3, and CgCaspase-9, as well as the activities of Caspase-3/9. Furthermore, after the treatment with GABAA and GABAB receptor antagonists, the activities and expression levels of Caspase-3 and Caspase-9 significantly up-regulated under hightemperature stress. GABA treatment also significantly diminished the increased Caspase-3 activity by mitochondrial pathway apoptosis inducers. High temperature induced mitochondrial pathway apoptosis via increased caspase activities. The transcripts of CgGAD in haemocytes and GABA concentration in hemolymph supernatant also increased after high-temperature stress. GABA countered these effects through the activation of GABAA and GABAB receptors, reducing both caspase activity and expression of apoptosis-related genes.

General and Specific Combining Abilities of Pacific Oyster (Crassostrea gigas) and Fujian Oyster (C. angulata) for Growth, Survival and Thermal Tolerance of Their Reciprocal Hybrids

General and Specific Combining Abilities of Pacific Oyster (Crassostrea gigas) and Fujian Oyster (C. angulata) for Growth, Survival and Thermal Tolerance of Their Reciprocal Hybrids

The utility of selective breeding to increase resistance against OsHV-1 µVar for Pacific oyster Crassostrea (Magallana) gigas farming in Galicia is called into question by infection with Vibrio aestuarianus

The utility of selective breeding to increase resistance against OsHV-1 µVar for Pacific oyster Crassostrea (Magallana) gigas farming in Galicia is called into question by infection with Vibrio aestuarianus

CgmiR307 involved in the regulation of Nrf2-dependent oxidative response in the Pacific oyster Crassostrea gigas under high-temperature stress.

miRNA, a type of endogenous small non-coding RNA, is involved in the response to various environmental stresses through post-transcriptional regulation. In the present study, the role of CgmiR307 in the regulation of oxidative response under high-temperature stress by targeting CgNrf2 was investigated in the Pacific oyster Crassostrea gigas. The binding site of CgmiR307 were predicted at 1,799-1,818 bp in the 3'-UTR of CgNrf2, and the binding activity of CgmiR307 with the mRNA of CgNrf2 was further proved by the dual-luciferase reporter assay. The expression levels of CgmiR307 and CgNrf2 in gill were significantly higher than in other tissues, and exhibited significant fluctuations and variations after exposure to 28°C. There was a significant reduction in the expression levels of CgSOD, and CgCAT in gill, as well as the activities of SOD, CAT, and T-AOC, while ROS and MDA contents significantly increased in CgNrf2-RNAi oysters. After CgmiR307 agomir injection and high-temperature stress, the expression levels of CgNrf2, CgSOD and CgCAT in gill, the activities of SOD and CAT and T-AOC decreased significantly, while ROS and MDA content significantly increased. After CgmiR307 antagomir injection and high-temperature stress, the changes in the parameters of oxidative response shown exactly the opposite trend. These results demonstrated that CgmiR307 was involved in the regulation of oxidative response by inhibiting the mRNA expression of CgNrf2 under high-temperature stress.

Role of Filter-Feeding Bivalves in the Bioaccumulation and Transmission of White Spot Syndrome Virus (WSSV) in Shrimp Aquaculture Systems.

White spot syndrome virus (WSSV) poses a major risk to shrimp aquaculture, and filter-feeding bivalves on shrimp farms may contribute to its persistence and transmission. This study investigated the bioaccumulation and vector potential of WSSV in Pacific oysters (Crassostrea gigas), blue mussels (Mytilus edulis), and manila clams (Venerupis philippinarum) cohabiting with WSSV-infected shrimp. Sixty individuals of each species (average shell lengths: 11.87 cm, 6.97 cm, and 5.7 cm, respectively) cohabitated with WSSV-infected shrimp (Penaeus vannamei, average body weight: 16.4 g) for 48 h. In the experiments, bivalves accumulated WSSV particles in both the gill and digestive gland tissues, with the digestive glands exhibiting higher viral load (average viral load, 3.91 × 104 copies/mg), showing that the viral concentrations in bivalve tissues are directly influenced by seawater WSSV concentrations, reaching levels sufficient to induce infection and 100% mortality in healthy shrimp using tissue homogenates. After a 168 h release period in clean water, the WSSV levels in bivalve tissues decreased below the detection thresholds, indicating reduced transmission risk. These results highlight the role of bivalves as temporary reservoirs of WSSV in aquaculture settings, with the transmission risk dependent on the viral concentration and retention period. Our findings suggest that the management of bivalve exposure in WSSV-endemic environments could improve the biosecurity of shrimp farms.

Sex-specific mRNA alternative splicing patterns and Dmrt1 isoforms contribute to sex determination and differentiation of oyster.

Alternative splicing (AS) of pre-mRNA is a crucial mechanism that regulates the expression of genes involved in sex determination and differentiation. Despite its importance, AS has been rarely characterized in molluscs. In this study, PacBio Iso-Seq was employed to obtain full-length transcriptome and unveil AS patterns of gonads in the Pacific oyster Crassostrea gigas. A total of 24,783 AS events were identified across 6259 genes, with many enriched in phosphorylation-related processes. Splicing factors were found to drive a high frequency of AS events in gonads. Significant sex-based differences in isoform abundance and the incidence of AS events were observed. Comparative analysis of mature female and male gonads revealed a subset of overlapping differential alternative splicing genes and differentially expressed genes enriched in processes related to microtubule function and cell motility. In addition, the expression levels of sex-biased genes were found correlated with their isoform number in both female and male gonads. A novel isoform of Dmrt1 was identified with male specific expression in mature gonads. This study provides the first comprehensive understanding of full-length transcriptome and AS patterns in molluscan gonads, shedding light on the post-transcriptional regulatory mechanisms underlying sex determination and differentiation in molluscs and potentially across other animals.

Glutamate induces larval settlement of the pacific oyster Crassostrea gigas

Glutamate induces larval settlement of the pacific oyster Crassostrea gigas

An ultra-high-performance liquid chromatography-quadrupole-orbitrap mass spectrometry based metabolomics investigation on pacific oysters (Crassostrea gigas) during depuration and anhydrous living-preservation

Depuration and anhydrous living-preservation are essential steps in the cold chain process for bivalves. However, the mechanisms by which these steps affect the quality of Pacific oysters (Crassostrea gigas) remain inadequately understood. In this study, the metabolic changes in Crassostrea gigas during these processes were investigated. Ultra-high-performance liquid chromatography-quadrupole-Orbitrap mass spectrometry (UHPLC-QE-Orbitrap/MS) was utilized, and multivariate statistical analysis was performed to extract and identify differential metabolites. A comprehensive analysis of the associated metabolic pathways was subsequently conducted, leading to the identification of differential metabolites, including amino acids, organic acids and fatty acids were identified. Among these, 10 key differential metabolites, primarily comprising tyrosine, glutamic acid, glutamine, citrate, succinic acid, arginine, malic acid, L-isoleucine, L-valine and fumaric acid were highlighted. Furthermore, alanine, aspartate and glutamate metabolism, valine, leucine and isoleucine biosynthesis, phenylalanine, tyrosine and tryptophan biosynthesis, tricarboxylic acid (TCA)cycle, nitrogen metabolism and pyruvate metabolism were delineated. These findings reveal the key metabolites and metabolic pathways responsible for quality changes in Pacific oysters during depuration and anhydrous living-preservation. This study provides a theoretical basis for the quality control of Pacific oysters in cold chain circulation, which will help promote the development of the Pacific oyster industry chain.

Sublethal impacts of Hebei Spirit oil spill on the growth and reproductive physiology of the Pacific oyster Crassostrea gigas at Taean on the West Coast of Korea (2008–2010)

Following the Hebei Spirit oil spill (HSOS) in December 2007, benthic organisms of the Taean coast on the west coast of Korea were heavily affected. A month after HSOS, the alkyl PAHs in the oyster body elevated to 13,500 ng/g dry wt, although it dropped to 5335 ng/g dry wt in December 2008, and returned to the levels before the accident (547–858 ng/g dry wt) by 2010. In 2008 spring, the damaged oysters exhibited deteriorated growth and reproduction, exhibiting signs of physiological stress. However, a year after the accident, oysters exhibited signs of recovery from the stresses. Gonad maturation, reproductive effort, and carbohydrate content recorded in 2010 were comparable to the levels in 2009 and the levels in undamaged oysters. Our study suggested that the Pacific oysters recovered from the HSOS stresses within a year, although long-term monitoring of oyster health must be carried out to ascertain the recovery.

A Zinc Uptake Transporter ZIP1-II Is Involved in Zinc Accumulation in the Hepatopancreas of Pacific Oyster Crassostrea gigas.

The Pacific oyster Crassostrea gigas is known to have an exceptional ability to accumulate zinc, which endows it with robust resistance to pathogens and makes it an excellent source of dietary zinc. ZIP1 has been identified as an important zinc uptake protein in other species, but its role in oysters remains unclear. In the present study, a ZIP1 homologue (CgZIP1-II) of the Zrt/Irt-like protein (ZIP) family was identified in C. gigas. The mRNA transcripts of CgZIP1-II were constitutively expressed in examined tissues of C. gigas, with higher levels in the hepatopancreas and gill. After zinc exposure, the mRNA transcripts of CgZIP1-II in the hepatopancreas showed a significant decline from 12 h to 14 d, while those in the gill significantly decreased at 72 h, followed by a recovery to basal level at 7 to 14 d. Immunocytochemical analysis revealed that the CgZIP1-II protein was mainly located at the plasma membrane of oyster hemocytes. Compared to the control cells, overexpression of CgZIP1-II in the transfected HEK293 cells resulted in a 2.44-fold (p < 0.05) increase in zinc content after incubation with 100 μM zinc for 24 h. Inhibition of endogenous CgZIP1-II expression with siRNAs led to a 42% reduction in zinc content in the hepatopancreas of oysters. Similarly, in vivo blocking of CgZIP1-II with anti-CgZIP1-II antibody caused a 43% decrease in zinc content in the hepatopancreas. These results collectively indicated that CgZIP1-II functioned as a zinc uptake transporter in C. gigas and played a certain role in zinc accumulation.

SNP Fingerprinting for Germplasm Identification of the Fast-Growing Pacific oyster (Crassostrea gigas) "Haida No. 1" Variety.

The Pacific oyster (Crassostrea gigas) is a global aquaculture species of economic significance. Selective breeding programs have been conducted to produce multiple strains with fast growth as well as other desirable traits. However, due to the phenotypic plasticity of oysters, challenges existed for precise germplasm identification among selectively bred strains. In this work, we identified selection signatures of three fast-growing Pacific oyster strains originated from wild populations collected from China, Japan, and Korea, respectively, which were used for development of SNP-based molecular fingerprinting for precise identification of germplasm. We performed whole-genome resequencing of 59 oysters from three selectively bred strains and a wild population for genome-wide SNP analyses. Population structure analysis with these SNPs revealed significant genetic differentiation among the selectively bred strains. Based on the FST index, we identified 41, 49, and 36 strain-specific SNPs from the three selectively bred strains. Taking into account the "hitch-hiking effect" that occurs in the genome during positive selection, we identified two, three, and two molecular fingerprints for the three strains, respectively. We validated the molecular fingerprints of the China selectively bred strain (i.e., "Haida No. 1" variety) with a separate population of 42 oysters with diverse genetic background, demonstrating the accuracy of germplasm identification of over 96%. This work provides a reliable tool for precise germplasm identification of the "Haida No. 1" variety as well as other two selectively bred strains, which is valuable in germplasm conservation and breeding design in the C. gigas.

QTL mapping reveals predominantly nonadditive genetic architecture of heterotic growth traits in yearling Pacific oysters Crassostrea gigas

Heterosis, which has been applied to increase the yields of major crops over the past century, is also widely observed in many bivalves and, specifically, the Pacific oyster Crassostrea gigas. Understanding the genetic architecture of growth heterosis has implications for the design of optimal breeding strategies for this commercially important species. Historically, three main genetic explanations, dominance, overdominance, and epistasis, and several complementary hypotheses for heterosis have been proposed, but no single, unifying theory seems to explain heterosis. Quantitative trait locus (QTL) maps reveal the number, genomic location, magnitude of effect, and mode of action of genetic factors contributing to phenotypic variation, in general, and to heterotic traits, in particular. With this approach, we map growth QTL (gQTL) in six F2 families for a suite of 21 traits, derived from five, monthly live weights of over 1000, individually tagged, yearling oysters. Redundancy in data and results is reduced by correlations of traits with three underlying factors, size, growth rate, and growth-curve shape. Across the six families, we detect 37 gQTL evenly distributed over the three growth factors. These QTL explain from less than 1 % to nearly 25 % of phenotypic variance and exhibit predominantly nonadditive gene action, with over half showing positive dominance or overdominance for yield. All classical hypotheses for heterosis are supported, none excluded. Whereas genetic load causing early oyster mortality fits the classical model of normalizing selection against deleterious mutations, the diversity of genetic mechanisms underlying variation in the growth of sessile juvenile and adult stages fits the balance model of population genetic variation. Overall, our study supports crossbreeding, which can utilize both additive and nonadditive components of variation in yield, as an optimal strategy for improvement of farmed oysters.

Comparative analysis of growth and metabolism in diploid and triploid Pacific oysters Crassostrea gigas under different temperature and salinity

Comparative analysis of growth and metabolism in diploid and triploid Pacific oysters Crassostrea gigas under different temperature and salinity

Genetic diversity and genetic structure in successive mass selected generations of tetraploid Pacific oysters (Crassostrea gigas), diploid Portuguese oysters (C. angulata) and their allotriploid oysters

In bivalve aquaculture, tetraploids are commonly used to generate sterile triploids for commercial aquaculture. We obtained the allotriploid population (tetraploid C. gigas ♂ × diploid C. angulata ♀) through the hybridization of tetraploid male C. gigas with diploid female C. angulata for the first time. However, the genetic diversity and genetic structure in successive mass selected generations of tetraploid C. gigas, diploid C. angulata and their allotriploid offspring are currently unknown. In this study, nine polymorphic microsatellite markers were used to evaluate their genetic diversity and genetic structure. The trend of reduced genetic diversity was recorded in successive generations of mass selected tetraploid C. gigas and diploid C. angulata. However, the diversity of the allotriploid population was significantly higher than that of the male parent population and the female parent population. This indicates that the hybridization technique of tetraploid C. gigas + diploid C. angulata to produce triploids is beneficial for increasing the genetic diversity of the hybrid triploid. Little genetic differentiation was found within tetraploid C. gigas and diploid C. angulata (except A3, the third generation of C. angulata), which is most likely caused by the insignificant genetic structure of the selected lines. The large genetic differences between tetraploid C. gigas and diploid C. angulata are caused by subspecies differences and ploidy difference. In addition, allotriploids were found to be more closely related to the female population, suggesting that this genetic relationship is more consistent with phenotypic traits. The findings of this study offer useful information for further genetic improvement of oyster polyploidy breeding.

Microbial education plays a crucial role in harnessing the beneficial properties of microbiota for infectious disease protection in Crassostrea gigas.

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.

Overexpression of CDC42 causes accumulation of DNA damage leading to failure of oogenesis in triploid Pacific oyster Crassostrea gigas

Triploid Pacific oyster Crassostrea gigas exhibits notable differences in fecundity, with the majority being sterile individuals, referred to as female β, which produce few oocytes, while a minority are fertile individuals, referred to as female α, which produce abundant oocytes. However, the molecular mechanisms underlying these differences in triploid fecundity remain poorly understood. CDC42 has been implicated in processes related to increased DNA damage and genomic instability. Here, we investigate the crucial role of CDC42 in DNA damage repair during oogenesis in triploid C. gigas. Immunofluorescence analysis of γH2AX, a marker for DNA double-stranded breaks, showed significantly higher levels of DNA damage in gonadal cells of triploids compared to diploids, particularly in female β. Histological and ultrastructural analyses revealed abnormal germ cells, termed β gonia, characterized by giant nuclei condensed into irregular chromosome-like chromatin, present in triploid gonadal follicles. Analysis of mRNA and protein expression revealed significantly elevated CDC42 expression in triploid gonads compared to the diploids. Inhibition of CDC42 activity in triploids using ZCL278, a CDC42-specific inhibitor, resulted in a significant reduction in DNA damage, increased oocyte numbers, and a decrease in β gonia count. Transcriptome profiling revealed that CDC42 inhibition upregulated the PI3K-AKT signaling pathway along with DNA repair activation. Overall, our findings suggest that overexpression of CDC42 during oogenesis in triploid C. gigas impedes DNA repair, leading to the accumulation of DNA damage, and consequently, oogenesis blockade and abnormal germ cell differentiation. Conversely, inhibition of CDC42 activity activates the PI3K-AKT signaling pathway and promotes DNA repair, thereby mitigating DNA damage and facilitating oogenesis in triploids. This study provides new insights into the molecular mechanisms of sterility in female triploid C. gigas.

KiNext: a portable and scalable workflow for the identification and classification of protein kinases

BackgroundProtein kinases are a diverse superfamily of proteins common to organisms across the tree of life that are typically involved in signal transduction, allowing organisms to sense and respond to biotic or abiotic environmental factors. They have important roles in organismal physiology, including development, reproduction, acclimation to environmental stress, while their dysregulation can lead to disease, including several forms of cancer. Identifying the complement of protein kinases (the kinome) of any organism is useful for understanding its physiological capabilities, limitations and adaptations to environmental stress. The increasing availability of genomes makes it now possible to examine and compare the kinomes across a broad diversity of organisms. Here we present a pipeline respecting the FAIR principles (findable, accessible, interoperable and reusable) that facilitates the search and identification of protein kinases from a predicted proteome, and classifies them according to group of serine/threonine/tyrosine protein kinases present in eukaryotes.ResultsKiNext is a Nextflow pipeline that regroups a number of existing bioinformatic tools to search for and classify the protein kinases of an organism in a reproducible manner, starting from a set of amino acid sequences. Conventional eukaryotic protein kinases (ePKs) and atypical protein kinases (aPKs) are identified by using Hidden Markov Models (HMMs) generated from the catalytic domains of kinases. Furthermore, KiNext categorizes ePKs into the eight kinase groups by employing dedicated Hidden Markov Models (HMMs) tailored for each group. The performance of the KiNext pipeline was validated against previously identified kinomes obtained with other tools that were already published for two marine species, the Pacific oyster Crassostrea gigas and the unicellular green alga Ostreoccocus tauri. KiNext outperformed previous results by finding previously unidentified kinases and by attributing a large proportion of previously unclassified kinases to a group in both species. These results demonstrate improvements in kinase identification and classification, all while providing traceability and reproducibility of results in a FAIR pipeline. The default HMM models provided with KiNext are most suitable for eukaryotes, but the pipeline can be easily modified to include HMM models for other taxa of interest.ConclusionThe KiNext pipeline enables efficient and reproducible identification of kinomes based on predicted amino acid sequences (i.e. proteomes). KiNext was designed to be easy to use, automated, portable and scalable.

Identification of a T-box transcription factor TBX2 and its negative regulatory role in melanin production in the Pacific oyster Crassostrea gigas

Oyster shells exhibit varying color patterns—black, white, or black and white striations—attributable to differences in melanin content and distribution. In this study, we identified a new homolog of TBX2, a member of the T-box transcription factor family, in the Pacific oyster (Crassostrea gigas) named CgTBX2. The mRNA expression of CgTBX2 was higher in tissues from white-shelled oysters than in those from black-shelled oysters. Knockdown of CgTBX2 in C. gigas significantly upregulated the expression of two key genes involved in melanin synthesis, CgTYR and CgTYR2. The tissue expression profile revealed that CgTBX2 is highly expressed in gill and mantle. CgTBX2 protein is mainly localized in the nucleus and can combine with TBX-binding elements (TBEs) present in the CgOCA2 promoter. CgTBX2 repressed the activity of the CgOCA2 promoter, with a strong transcriptional inhibition effect on the −2000 to −878 and −211 to −1 regions. Furthermore, the combination of CgTBX2 with GTTGACACCTT sequence is responsible for the transcriptional inhibition on the −211 to −1 region of the CgOCA2 promoter. Our findings reveal that CgTBX2, a novel regulator of melanin pigmentation in C. gigas, negatively regulates melanin deposition by inhibiting tyrosinase genes expression and repressing the transcriptional activity of the CgOCA2 promoter.