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MicroRNAs (miRNAs) are a class of non-coding RNAs that modulate gene expression at the post-transcriptional level. Characterized by their dynamic expression patterns, miRNAs play a crucial role in regulating a multitude of biological processes, including metabolism and autophagy. For fishermen, enhancing the growth performance of the Asian hard clam, Meretrix meretrix, is vital for increasing yields and their income. To elucidating the regulatory mechanisms underlying clam growth, a comparative analysis of the miRNA and mRNA transcriptomes was undertaken for M. meretrix specimens exhibiting disparate growth rates. The results showed that a total of 32 differentially expressed miRNAs (DEMs) and 1049 differentially expressed mRNAs (DEGs) were identified. Furthermore, an integrated miRNA-mRNA expression analysis enabled the identification of 459 differentially predicted target genes (DETGs) associated with the DEMs. A significant enrichment in multiple functional categories related to metabolism and autophagy was observed among the DETGs. We constructed an intricate regulatory network that encompasses the metabolic and autophagy pathways influenced by 11 pivotal DEMs and 15 DETGs, which differ across the growth rates of M. meretrix. The results indicate that variations in growth rates elicit complex responses in both miRNA and mRNA expression, profoundly influencing the metabolic and autophagy processes within M. meretrix.

Carotenoids, the most widespread biological pigments, are responsible for the coloration of animal tissues and surfaces. Yet, little is known about the mechanism of how carotenoids affect the color of clam shells. The hard clam, Meretrix meretrix, exhibits genetic polymorphism leading to diverse shell colors, making it an ideal model for studying carotenoid-based coloring. Cultured strains of M. meretrix with distinct shell colors (red and white) were selected to explore the relationship between carotenoids and shell color. Raman spectroscopy and pigment content analysis revealed that carotenoids primarily contributed to the red shell. The β-carotene-15,15'-monooxygenase 1 (BCMO1) in M. meretrix was cloned, and a phylogenetic analysis was performed. Expression studies showed that Mm-BCMO1 mRNA was consistently expressed during early development, with a notable increase in umbo larvae. High levels of Mm-BCMO1 expression were observed in the hepatopancreas and mantles, particularly in the red strain compared to the white strain. In addition, protein analysis via western blotting (WB) and immunofluorescence (IF) confirmed that Mm-BCMO1 protein levels corresponded to mRNA levels, mainly localized in epithelial cells of the mantle. Moreover, 12 significant single nucleotide polymorphisms (SNPs) were identified in the promoter and coding sequence (CDS) regions of Mm-BCMO1, potentially explaining the color variation between the two shell color strains. These findings indicate that carotenoids, influenced by Mm-BCMO1, play a crucial role in the pigmentation of red shell color. The study provides insights into carotenoid metabolism in M. meretrix and offers valuable information for molecular marker-assisted breeding in clam aquaculture.

Cadmium (Cd) is a toxic heavy metal that, when present as a pollutant in the marine environment, is readily accumulated by marine bivalves, causing oxidative stress and tissue damage. This study explored whether short-term depuration could reverse Cd2+-induced toxicity in the ovary of the clam Meretrix meretrix. Clams exposed to 3 mg·L-1 Cd2+ for three days showed increased accumulated Cd2+ in their ovaries with obvious tissue damage as shown by loose structure and some apoptotic cells compared with non-exposed clams. Increased oxidative stress in the ovarian tissue was also obvious, as revealed by increased levels of oxidative indicators such as reactive oxygen species (ROS), malondialdehyde (MDA), DNA-protein crosslinking (DPC), and protein carbonylation (PCO) and increased expression levels of genes related to oxidative stress and apoptosis, which included the Bax, Bcl-2, caspase-3, HO-1, Hsp70, NQO1, Nrf2, and MT genes. When the clams were exposed to Cd2+ for three more days, the accumulated Cd2+ level in the ovary increased to more than 10-fold the level in the control clams, accompanied by more severe damage and cell death as well as oxidative stress. However, when the initial three-day Cd2+ exposure was followed by three days of depuration in Cd2+-free seawater, the Cd2+ level in the ovary was reduced by as much as 20%, accompanied by some recovery of tissue damage and reduced oxidative stress, suggesting that short-term depuration may mitigate Cd2+-induced toxicity in M. meretrix, allowing the clams to recover and potentially reducing the risk of Cd2+ exposure from consuming contaminated clams.

Meretrix meretrixwas found to be a very abundant waste at Amal Beach, Tarakan City. M. meretrixwaste can reduce heavy metals, especially heavy metals copper (Cu2+), by the adsorption process. Research has been carried out on M.meretrixas an adsorbent of heavy metals copper (Cu2+) using the adsorption method of Shacker through chemical activation using NaOH bases. The SEM resultsshowed that M.meretrixbefore activation had a rough pore surface that was still closed but M. meretrix after activation had a open pore surface that is whyit could be used as an adsorbent. M.meretrixcontains Al (Aluminum), which can be used as an adsorbent. The adsorption results showed that M.meretrixwith activation in the Freundlich isotherm had the highest ability to absorb Cu2+as much as 9,108 mg/g compared to without activation only 0.051 mg/g. It can be concluded that M.meretrixwaste can be used as an absorbent of Cu2+heavy metals.

Cadmium (Cd) is one of the most common pollutants in the environment. It can cause irreversible tissue damage and apoptosis in invertebrates. This study investigated the relationship between Cd exposure and oxidative damage and apoptosis in the ovarian cell of the clam Meretrix meretrix. The clams were exposed to different concentrations of Cd2+ (0, 1.5, 3, 6 and 12 mg L−1) for 5 days, and the accumulated level of Cd2+ in the ovarian tissue, and the degree of oxidative damage, changes in morphology and the response of apoptosis-related factors in the ovarian cell were determined. The bioaccumulation of Cd2+ and the levels of reactive oxygen species (ROS), malondialdehyde (MDA), protein carbonylation (PCO), and DNA-protein crosslinking (DPC) in the ovary were found to increase significantly when the clams were exposed to increasing concentrations of Cd2+. The structure of the ovarian tissue was severely damaged, and the ovarian cells displayed an irregular arrangement. The results of AO/EB staining and flow cytometry showed that the apoptotic rate of the ovarian cells increased with increasing Cd2+ concentrations. The activities of caspase-3, -8, -9, and the mRNA levels of p53, Bax and Caspase-3 in the ovary were also significantly increased. Furthermore, the level of p53 mRNA was positively correlated with the levels of MDA, PCO, DPC and ROS, but negatively correlated with the levels of total antioxidant capacity (T-AOC) and Bcl-2 mRNA. Taken together, these results indicated that Cd2+ exposure would result in oxidative damage and apoptosis for the ovarian cells, suggesting that Cd2+ toxicity could negatively affect the reproductive capacity of M. meretrix, thus threatening the reproductive development of the shellfish.

Vibrio as one of the main pathogens of shellfish diseases can cause serious human seafoodborne gastroenteritis and even death. In this study, we analyzed the bacterial communities from the clam, and compared the resistance phenotypes and genotypes of Vibrio spp. from Meretrix meretrix at different growth stages. High-throughput sequencing analysis revealed the predominance of Proteobacteria (50%) in the bacterial community and Vibrio was one of the dominant genera in the clam hepatopancreas in the summer. Vibrio abundance in Meretrix meretrix positively correlated with the water temperature (p

Background: Two suspected shellfish poisoning events were reported in Cuddalore District in Tamil Nadu, India, between January and April 2015. Objectives: The study was conducted to confirm the outbreaks and to identify the source and risk factors. Methods: For both outbreaks, a case was defined as a person with nausea, vomiting, or dizziness. Sociodemographic details and symptoms were noted down. Data were also collected in a standard 3-day food frequency questionnaire, along with a collection of clam samples. A case–control study was initiated in the April outbreak. Stool samples were collected from cases, and clam vendors were interviewed. Results: In an outbreak that happened in January, all the twenty people reported to be consumed clams were diagnosed as cases (100% attack rate, 100% exposure rate). In the April outbreak, we identified 199 cases (95% attack rate). In both outbreaks, the clams were identified as genus Meretrix meretrix. The most common reported symptoms were dizziness and vomiting. The clams heated and consumed within 30–60 min. No heavy metals or chemicals were detected in the clams, but assays for testing shellfish toxins were unavailable. All 64 selected cases reported clam consumption (100% exposure rate) as did 11 controls (17% exposure rate). Illness was associated with a history of eating of clams (odds ratio = 314, 95% confidence interval = 39–512). Of the six stool samples tested, all were culture negative for Salmonella, Shigella, and Vibrio cholerae. The water at both sites was contaminated with garbage and sewage. Conclusion: Coordinated and timely efforts by a multidisciplinary team of epidemiologists, marine biologists, and food safety officers led to the outbreaks' containment.

Highlight • Identify the Vibrio bacteria • Diversity of shellfish Vibrio bacteria (Meretrix Meretrix) • Relationship similarity of Vibrio bacteria with MVSP 3.1 Program produces Dendogram Abstract Meretrix meretrix is one type of shellfish that is potential, and economic value, which high animal protein content as well as seafood that is widely consumed in Indonesia. This study aims to determine the diversity and similarity of Vibrio in M. meretrix at eduwisata mangrove Cengkrong Beach, Trenggalek. Isolation and identification of Vibrio was conducted by using the media TCBSA (Thiosulfate Citrate Bile Salt Sucrose Agar) streat plate through morphological observation, physiological and biochemical tests based Bergey's Manual of Systematic Bacteriology conducted in the laboratory of Microbiology Faculty of Biology, Universitas Gajah Mada. Data analysis was performed using the MVSP (Multivariate Statistical Package) 3.1 in the form of a dendrogram showing the similarity relationship Vibrio bacteria. The results of the identification of Vibrio bacteria in M. Meretrix are V. herveyi, V. parahemolyticus, V. nereis and V. proteolyticus. V. herveyi has similarities with V. parahemolyticus 66% and 62% with V. proteolyticus while with V. nereis bacterium 54%.

The ichthyotoxic raphidophyte Heterosigma akashiwo is associated with harmful algal blooms (HABs). Although the influence of H. akashiwo on fish has been reported, little is known of its effects on other marine organisms, such as shellfish. In this study, the physiological and transcriptomic responses of the Asiatic hard clam Meretrix meretrix to H. akashiwo were investigated. The results showed that clam survival was not influenced by H. akashiwo (at a concentration of 2 × 104 cells/mL), and M. meretrix eliminated the alga effectively after 48 h in co-culture. H. akashiwo did not alter the antioxidant capacity of the clams. However, 544 unigenes were found to be differentially expressed between the control and H. akashiwo-treated clams. Interestingly, the significant up-regulation of lysosome-related genes and transport proteins suggested remodeling of the clam metabolism possibly for digestion of H. akashiwo. In summary, our results indicate that the clam M. meretrix can effectively feed on H. akashiwo, and intensification of shellfish farming may be helpful to control and mitigate H. akashiwo blooms.

Meretrix meretrix with three shell colors (mottled shell, red shell, yellow shell) were analyzed for nutritive and taste attributes. Additionally, the influence of cooking on the taste active components was also evaluated. The three kinds of clams had higher crude protein contents. Alanine, glutamic acid, arginine, 5ʹ-adenosine monophosphate, Cl−, Na+, K+ and PO43- were the major taste compounds of Meretrix meretrix. In addition to PO43-, the contents of all major taste compounds decreased after cooking. Among raw samples, red shell clams had the highest value of equivalent umami concentration (EUC) and contents of Cl− and Na+, along with the lowest content of PO43-. In cooked samples, the value of EUC and the contents of Na+ and K+ in red shell clams were higher than those of yellow shell clams and lower than those of mottled shell clams. Furthermore, the contents of PO43- in red and yellow shell clams were higher than that in mottled shell clams. However, there were no significant differences in the amount of K+ among different raw samples and the amount of Cl− among different cooked samples.

The relationship between carotenoid and shellfish shell color has gained increasing attention. β, β-carotene-9′,10′-oxygenase 2 (BCDO2) is a key enzyme in animal carotenoid metabolism, and its accumulation affects the change in body color, as demonstrated in mammals, birds, and fish. However, it is unclear whether BCDO2 is involved in the formation of the red shell color of clam. To explore the molecular structure and biological function of BCDO2 gene in the process of carotenoids accumulation, in this study, the BCDO2 from hard clam Meretrix meretrix (designated as Mm-BCDO2) was cloned and characterized, and the single-nucleotide polymorphisms (SNPs) associated with shell color were detected. The results of qRT-PCR indicated that Mm-BCDO2 gene was expressed in all six tested tissues, and the expression of mantle was significantly higher than other tissues (P < 0.05). The association analysis identified 20 SNPs in the exons of Mm-BCDO2, among which three loci (i.e., c.984A > C, c.1148C > T, and c.1187A > T) were remarkably related (P < 0.05) to the shell color of clam. The western blot analysis revealed that the expression level of Mm-BCDO2 in the mantle of red shell clams was stronger than that of white shell clams (P < 0.05). Further, the immunofluorescence analysis indicated that the single-layer columnar cells at the edge of the mantle were the major sites for the Mm-BCDO2 secretion. This study explored the potential impacts of BCDO2 gene on the shell color of M. meretrix, which provided a theoretical basis for a better understanding of the important role of BCDO2 in carotenoid metabolism.

In this study, the release effects of the buried clam Meretrix meretrix in a northern estuary of China (Shuangtaizi Estuary) was assessed in terms of population ecology and genetic variability by using longer-term monitoring data from 2011 (used as the baseline data) to 2018. A total of 2.4 × 108 hatchery juveniles were released from 2012 to 2014, and follow-up monitoring survey of the growth, distribution, density, and biomass of M. meretrix population was carried out. Results showed a temporary spike in the population of M. meretrix, and the population underwent considerable year-to-year fluctuations in total abundance and biomass. Meanwhile, the age structure of the populations from 2011 to 2018 is still an unstable expanding type. Genetic analysis based on 10 polymorphic microsatellite markers revealed no significant genetic differentiation and weak genetic structures between years but higher genetic diversities in 2014–2018 than in the initial period (2013) of stock restoration. Our study suggests that effective policies for management and conservation to restore M. meretrix population by local governments are still needed in the long run.

Cadmium (Cd) has been widely used in industry and can accumulate in the water, soil, and food. Meretrix meretrix is one of the marine shellfishes cultivated for economic purpose in China. The increasing Cd levels in coastal marine water could adversely affect the economic benefits of shellfish cultivation. In the present study, M. meretrix were exposed to different Cd2+ concentrations (0, 1.5, 3, 6, and 12 mg L-1) for 5 d to evaluate the effects of Cd on spermatogenic cell. The Cd accumulation, survival rate and the indices of oxidative stress and apoptosis were determined in the spermatogenic cells of M. meretrix. The expression levels of p53 and metallothionein (MT) mRNA were also measured in the spermatogenic cells. Cd accumulation and the mortality rate of spermatogenic cells were found to increase in a dose-response manner with Cd2+ concentrations. Histopathology changes, especially the damage of membranous structure, were more severe as the Cd2+ levels in the testis became higher. The indexes of oxidative stress, including reactive oxygen species, malondialdehyde, protein carbonyl derivates and DNA-protein crosslinks all increased after exposure to Cd2+. However, the total antioxidant capacity gradually decreased with the increasing Cd2+ concentration. In addition, exposure to Cd2+ increased the apoptotic rate and caspase-3 and 9 activities but decreased the level of mitochondrial membrane potential and cytochrome C oxidase in the spermatogenic cells. MT mRNA expression increased in lower Cd2+ concentration treated groups whereas decreased in higher groups, while the p53 mRNA expression increased in a dose-response manner with Cd2+ and was positively correlated with the oxidative damage indices. These results indicated that Cd2+ caused oxidative stress and p53 induced apoptosis in the spermatogenic cells, and thus decreased the survival rate of sperm cells. This finding highlights that Cd can reduce the reproductive capacity of M. meretrix, thus threatening to wild shellfish populations and reducing the efficiency of shellfish farming.

The substrate is the key environmental factor that affects the growth, survival, population and distribution of dwelling mollusks in mudflat settings. To clarify the effect of the substrate grain size on soft substrate preference, burrowing ability and behavior during the selection process of juvenile Meretrix meretrix, four different grain size substrates (coarse sand, medium sand, fine sand, and natural substrate) were set up for comparison. The results indicated that: (1) the burrowing ability of juvenile specimens in fine sand was the strongest; (2) the degree (from high to low) of the juvenile’s preference for the four substrates was in the order of fine sand > natural substrate > medium sand > coarse sand; and (3) the selection process of the substrate by the juveniles could be divided into four stages: preparation, selection, burrowing and end stages. These stages showed the behavioral characteristics of a longer selection time and higher percentage of movement in coarse sand. Therefore, our results demonstrated that sea areas or ponds with fine sand as the main component are more suitable for stock enhancement with M. meretrix. These results provide basic data for habitat selection and suitability evaluations for the aquaculture of M. meretrix.

Despite mass mortality, hard clams remain among the main cultured shellfish in Taiwan. Using cross-sectional data, this study applies threshold regression modeling with stocking density and feed costs as the threshold variables to explore the nonlinear relationship between input and output factors. The findings show that the production output levels may be increased by different combinations of factor inputs and variations in input factors. More specifically, the higher output levels may be achieved by increasing labor input while reducing capital input factors in farming households with a higher stocking density (HSD > 1,087,870 inds/ha) or higher feed cost (HFC > 13,889 NTD/ha). Farming households with a lower stocking density (LSD ≤ 1,087,870 inds/ha) may enhance production output levels by increasing feed input while reducing capital inputs. Moreover, the maximum output level of HSD and HFC farming households was estimated to reach 9255 kg/ha and 9807 kg/ha, respectively. Results of the production output simulation suggest that the feeding cost per hectare in LSD households should not exceed 25,119 NTD to avoid overfeeding, which may cause culture deterioration and lower survival rates. As such, farmers are advised to adjust their feed costs according to the stocking density to maximize production output.

Polychlorinated biphenyls (PCBs) are well-known persistent organic pollutants; they have toxic effects on the immune system, reproductive system, and endocrine system by changing the metabolism of the body. To elucidate the underlying molecular mechanism, the clam Meretrix meretrix was exposed to 10 and 1000 ng/L Aroclor 1254 and natural seawater (control). Samples from clams exposed to natural seawater and those exposed to Aroclor 1254 for 1 and 3 days were individually collected for transcriptome analysis. After assembly, more than 535,157 transcripts with a mean length of 949 bp and an N50 length of 1279 bp were obtained; a final set of 177,142 unigenes was generated. In the present study, 5101 differentially expressed genes were identified. The differentially expressed genes were related to detoxification metabolism, oxidative stress, immune response, and endocrine system disruption. Of these genes, under the Aroclor 1254 exposure, cytochrome P450 20A1 (2.06–4.46 folds), glutathione S-transferase (2.25–3.80 folds), multidrug resistance-associated protein 1-like (1.49–2.92 folds), peroxidase-like protein (1.33–4.26 folds), lysozyme (1.61–2.05 folds), bcl-2 like 1 protein (1.14–2.29 folds) and vitellogenin (1.09–1.19 folds) showed been significantly induced expressed. At the same time, some genes were down regulated, including cytochrome P450 2J5 (−1.20 ~ −2.86 folds), cytochrome P450 3A24 (−1.40 ~ −4.08 folds), C1q (−1.27 ~ −1.66 folds), Sulfotransferase (−1.51 ~ −1.84 folds), monocarboxylate transporter 10 (−1.30 ~ −4.70 folds), 3-beta hydroxysteroid dehydrogenase (−1.43 ~ −2.81 folds) and beta-galactosidase (−1.23 ~ −2.23 folds). Furthermore, it showed that the expression levels of CYP2J5, glutathione S-transferase, 3-beta hydroxysteroid dehydrogenase and beta-galactosidase had time responses and dose responses. The present study provided insights into the toxic effects of Aroclor 1254 exposure in M. meretrix.

Cadmium (Cd), one of the most toxic metals found in inshore sediments of China, is a persistent environmental contaminant capable of exerting irreversible toxic effects on aquatic organisms and their associated ecosystems. Although Cd is known to be toxic to marine animals, the underlying mechanism of this toxicity is not clear. In this study, Meretrix meretrix, a commercially and ecologically important species of clam, was exposed to different concentrations of cadmium chloride (0, 1.5, 3, 6, and 12 mg L–1) for 5 days, and the levels of Cd accumulation, antioxidant enzyme activity, and expression of metallothionein (MT) in the hepatopancreas, gill, foot, and mantle were evaluated. The results revealed a sharp increase in Cd accumulation in the tissues in response to increased Cd2+ concentrations in the water, and significant differences in Cd accumulation were observed among the different tissues. Increased Cd2+ level in the tissues also led to a significant increase in malondialdehyde content, caused by increased lipid peroxidation. The activities of superoxide dismutase and catalase also increased, peaking at different Cd2+ concentrations, depending on the tissue. Glutathione peroxidase (GPx) activity in the gill and mantle initially increased but then decreased with increasing external Cd2+ concentration. In the hepatopancreas and foot, GPx activity was inhibited by Cd2+, even at low concentrations. Furthermore, Cd2+ also stimulated the expression of MT in all four tissues. However, the levels of reduced glutathione (GSH) and oxidized glutathione (GSSG) in the gill and mantle, as well as the GSH/GSSG ratios in all four tissues, decreased with increasing external Cd2+ concentrations. Taken together, the results suggested that in M. meretrix, response to the toxic effect of Cd2+ might occur through a combination of mechanisms, which involve both enhanced antioxidant enzyme activities and the ability to bind and sequester Cd2+ via cysteine-rich molecules such as GSH and MT, both of which would eventually lead to the reduction of heavy metal-induced oxidative stress.

The hard clam Meretrix meretrix is ecologically and economically important in the coastal regions of China. We evaluated the genetic diversity and population structure among eight M. meretrix samples from the Yellow Sea (YS) and South China Sea (SCS) using nine microsatellite DNA loci. Both conventional and model-based population genetic analyses suggested significant genetic divergence between YS and SCS regions (pairwise FST values ranging from 0.014 to 0.056). Samples within each region were not genetically different, except for Zhanjiang which clearly differed from other the four SCS samples. Membership coefficients, estimated by STRUCTURE, suggested some genetic admixture of the two genetic clusters in ZJ. Population genetic structure was detected in SCS region. We detected moderate levels of genetic variation in all eight samples (mean A = 16.111–22.111, mean Ar = 14.512–19.029, mean Ho = 0.736–0.843, mean He = 0.823–0.868) and two genetic clusters (mean A = 27.167–29.833, mean Ae = 8.834–9.471, mean Ar = 26.032–27.005, mean Ho = 0.824–0.839, and mean He = 0.821–0.850). Low levels of Ne estimates were detected in M. meretrix populations. None of the genetic populations had signs of recent genetic bottlenecks. Knowledge on genetic variation and population structure of M. meretrix populations along the Chinese coasts will support the aquaculture management and conservation of M. meretrix, and will provide insights for stock selection in selective breeding programs for these species and delineating management units.

It has been demonstrated that the sekelsky mothers against decapentaplegic homolog 3 (Smad3) plays an important role in the growth and development of vertebrates. However, little is known about the association between the Smad3 gene and the growth traits of mollusks. In this study, Smad3 from the hard clam Meretrix meretrix (Mm-Smad3) was cloned, characterized, and screened for growth-related single nucleotide polymorphisms (SNPs) in its exons. The full-length cDNA of Mm-Smad3 was 1938 bp, encoding a protein with 428 amino acid residues. The protein sequence included an MH1 (27–135 aa) and MH2 domain (233–404 aa). Promoter analysis showed that the promoter sequence of Mm-Smad3 was 2548 bp, and the binding sites of Pit-1a, Antp, Hb, and other transcription factors are related to the growth and development of hard clams. The phylogenetic tree was divided into two major clusters, including mollusks and vertebrate. The expression level of Mm-Smad3 was predominantly detected in the mantle and foot, while extremely less expression was observed in the digestive gland. The low expression level of Mm-Smad3 was detected at the stages of unfertilized mature eggs, fertilized eggs, four-cell embryos, blastula, gastrulae, trochophore, and D-shaped larvae, whereas an opposite trend was observed regarding the highest expression at the umbo larvae stage (p < 0.05). In the mantle repair experiment, the time-course expression profiles showed that compared to the expression level at 0 h, Mm-Smad3 significantly decreased at 6 h (p < 0.05) but increased at 12 and 48 h. Further, the association analysis identified 11 SNPs in the exons of Mm-Smad3, of which three loci (c.597 C > T, c.660 C > T, c.792 A > T) were significantly related to the growth traits of clam (p < 0.05). Overall, our findings indicated that Mm-Smad3 is a growth-related gene and the detected SNP sites provide growth-related markers for molecular marker-assisted breeding of this species.

Meretrix meretrix, Pholas dactylus and Babylonia spirata are potential fisheries commodity, but information about their nutritional values is still limited. This research was aimed to determine the chemical compositions of Meretrix meretrix, Pholas dactylus and Babylonia spirata. Proximate of Meretrix meretrix, Pholas dactylus and Babylonia spirata were analyzed using thermogravimetric, soxhlet and kjeldahl methods. Their amino acid composition and taurine content were analyzed using High Performance Liquid Chromatografy (HPLC). The moisture, ash, fat, protein and carbohydrate contents of Meretrix meretrix were 79.98%, 1.37 0.11 9.39 and 9.02 respectively; Pholas dactylus were 83.78%, 1.19, 0.11, 11.37 and 3.55 respectively; while Babylonia spirata 78.44, 1.20, 0.33, 17.38 and 2.65 respectively. Arginine was the highest essential amino acid found in Meretrix meretrix, Pholas dactylus and Babylonia spirata meat with values of 1.12%, 0.93 dan 2.50 respectively. Glutamic acid was the most abundant non-essential amino acid with the highest value of 2.24, 2.14 and 3.76. The limiting amino acid was histidine with the value of 0.25%, 0.18 and 0.34, respectively. The taurine content of Pholas dactylus meat (0.085%) was higher than the Babylonia spirata and Meretrix meretrix (0.067 and 0.062%, respectively).

The present study describes the molecular characterization and transcriptional features of a tumor suppressor QM protein gene, MmQM, in Meretrix meretrix. The full-length cDNA (819 bp) of MmQM consists of a 657 bp opening reading frame (ORF) encoding a 218 amino acid protein with a calculated molecular mass of 25.3 kDa and theoretical isoelectric point of 10.2. A ribosomal protein L10 signature, an SH3-binding motif, an antibiotic binding site, an amidation site and two protein kinase C phosphorylation sites were revealed from the MmQM sequence. Phylogenetic analysis showed that MmQM is clustered with previously identified mollusk QM proteins. MmQM mRNA transcripts were detectable in all of the examined tissues in a constitutive manner, and were significantly different from each other. After bacterial stimulation, the mRNA transcripts of MmQM in the hepatopancreas significantly increased. Hence, we conclude that MmQM could respond to pathogenic infections and it might play an important role in the innate immunity against microorganisms in the clam M. meretrix.

The hard clam (Meretrix meretrix) is a commercially and ecologically important benthic mollusk in South and Southeast Asia. Growth is one of the most important and complex traits affecting clam breeding. Therefore, identification of key growth factor genes and their association with growth traits are the primary prerequisites for in-depth study of the mechanisms of growth regulation and molecular marker-assisted selection of the hard clam. In the present study, we generated the full-length cDNA sequences of the growth-related genes BMP2 and BMP7 in M. meretrix (MmBMP2 and MmBMP7) and then investigated their gene expression patterns and associations with growth traits. The full-length cDNA of MmBMP2 was 2641 base pairs (bp), with a 1395 bp open reading frame (ORF) encoding 464 amino acids. The full-length MmBMP7 cDNA was 3161 bp, with a 1257 bp ORF encoding 418 amino acids. In adult clams, expression of MmBMP2 and MmBMP7 were significantly higher in the mantle than in the other five tested tissues (p < 0.05). Among the seven developmental stages of M. meretrix, expression of MmBMP2 was the highest in juveniles (p < 0.05), and expression of MmBMP7 was very low in 4-cell embryo and eyespot larva stages (p < 0.05). Two hundred and sixty-three individuals from two populations were screened for MmBMP2 and MmBMP7 polymorphisms, and single nucleotide polymorphisms (SNPs) associated with growth traits in MmBMP2 was found in both populations. Subsequent analysis revealed that two SNPs in MmBMP2 were shared between the populations. One was A726G, for which individuals with genotypes AG had significantly higher growth traits than those with genotype AA (p < 0.05). The other was A732T, for which individuals with genotype AT had significantly higher growth traits than those with genotype AA (p < 0.05). These results suggest that BMP2 markers may have potential value in molecular selective breeding to improve clam growth.

Paralytic shellfish toxins (PSTs) contamination of seafood has become a growing global problem. However, the molecular response of bivalves, some of the most popular seafoods, to PSP toxins has seldom been reported and the underlying molecular mechanisms of the interactions between Meretrix meretrix bivalves and PSTs-producing dinoflagellates are scarcely known. This study compared the protein expression profiles between PSP toxin-contaminated and non-PSP toxin contaminated M. meretrix, determined proteome responses and identified potential biomarkers based on feeding experiments. Results showed that the content of total PSP toxins in contaminated bivalves was 40.63 ± 4.08 μg saxitoxin (STX) equivalents per gram, with 95.3% in hepatopancreas, followed by gill (1.82%) and foot (1.79%). According to two-dimensional gel electrophoresis (2-DE), 15 differentially expressed proteins (at least 2-fold difference) between the hepatopancreas of bivalves with and without PSP toxins were detected. Eight of them were successfully identified by MALDI-TOF MS. These were catalase, protein ultraspiracle homolog, G2 and S phase-expression protein, paramyosin, Mn-superoxide dismutase, response regulator receiver domain-containing protein, sarcoplasmic calcium-binding protein and major facilitator superfamily transporters. The differences in the expression levels of the last three proteins involving in cell signaling, structure and membrane transport were 4.2, 5.3 and 4.9-fold, respectively. These proteins could be further developed as potential biomarkers. The other two up-regulated proteins, Mn-superoxide dismutase and catalase, were involved in cell defence mechanisms against oxidative stress, suggesting PSP toxin acts as xenobiotics and poses oxidative stress in bivalves. This study gives insights into the response of bivalves to PSP toxin-producing dinoflagellate at the proteomic level and the potential of using 2-DE to develop specific protein markers in bivalves.

α-Amylase is a major digestive enzyme in phytophagous animals that catalyzes the hydrolysis of starch into sugars so that it affects the carbohydrate metabolism and growth of many species. In the present study, the full-length cDNA and intron sequences of α-amylase (MmAmy) were investigated by rapid amplification of cDNA ends (RACE) method. The genomic DNA sequence of MmAmy is 6689 bp, which contains 7 exons and 6 introns. The cDNA of MmAmy is 1783 bp, with a 1569 bp of open reading frame (ORF) encoding 522 amino acids. No expression was detected in the early stages of unfertilized mature eggs, fertilized eggs, 4-cell embryo, blastula, gastrulae, trochophore, whereas it was detected after D-shaped larva showing the highest expression in umbo larvae. The quantitative expression of six different tissues in adults showed that expression of MmAmy was enriched in visceral mass, while no expression was detected in other tissues. Furthermore, gene expression and enzyme activity of MmAmy in visceral mass were highly correlated with the growth rates of four shell color strains. The positive correlation between MmAmy and growth traits suggested that α-amylase gene could be used as a candidate gene in the molecular breeding programs to improve clam growth.

The hard clam Meretrix meretrix, which has been traditionally used as medicine and seafood, was used in this study to isolate antioxidant peptides. First, a peptide-rich extract was tested for its protective effect against paraquat-induced oxidative stress using the nematode model Caenorhabditis elegans. Then, three novel antioxidant peptides; MmP4 (LSDRLEETGGASS), MmP11 (KEGCREPETEKGHR) and MmP19 (IVTNWDDMEK), were identified and were found to increase the resistance of nematodes against paraquat. Circular dichroism spectroscopy revealed that MmP4 was predominantly in beta-sheet conformation, while MmP11 and MmP19 were primarily in random coil conformation. Using transgenic nematode models, the peptides were shown to promote nuclear translocation of the DAF-16/FOXO transcription factor, a pivotal regulator of stress response and lifespan, and induce the expression of superoxide dismutase 3 (SOD-3), an antioxidant enzyme. Analysis of DAF-16 target genes by real-time PCR reveals that sod-3 was up-regulated by MmP4, MmP11 and MmP19 while ctl-1 and ctl-2 were also up-regulated by MmP4. Further examination of daf-16 using RNA interference suggests that the peptide-increased resistance of C. elegans to oxidative stress was DAF-16 dependent. Taken together, these data demonstrate the antioxidant activity of M. meretrix peptides, which are associated with activation of the stress response factor DAF-16 and regulation of the antioxidant enzyme genes.