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This study was aimed to optimise the Alcalase® enzymatic hydrolysis extraction of Asiatic hard clam (AHC) (Meretrix meretrix) protein hydrolysate in terms of hydrolysis time, hydrolysis temperature, hydrolysis pH, and concentration of enzyme. Protein hydrolysate produced from AHC (M. meretrix) meat was used to determine the optimum hydrolysis conditions. Hydrolysis of AHC meat was optimised using the Central Composite Design Response Surface Methodology (RSM) (CCD). The relationship between four parameters such as temperature (45 – 65°C), enzyme to substrate concentration (1 – 2%), hydrolysis time (60 – 180 mins), and pH (7.5 – 9.5) to the degree of hydrolysis was investigated. The optimum conditions for enzymatic hydrolysis of AHC meat to achieve the maximum degree of hydrolysis (DH) were observed at 65°C, enzyme to substrate concentration of 1%, hydrolysis time of 60 mins, and pH 7.5. The enzymatic protein hydrolysis of AHC meat was predicted using a two factors interaction (2FI) model. Under these optimum conditions, DH's predicted value was 97.41%, which was close to the experimental value (97.89%). The freeze-dried protein hydrolysate powder was characterized concerning the proximate composition. Proximate analysis revealed that the AHC meat contains 7.92±1.76% of moisture, 2.23±0.89% of crude fat, 1.98±0.82 of ash, and 10.53±0.04% of crude protein. While the Asiatic hard clam protein hydrolysate (AHCPH) composed 9.12±0.02% of moisture, 0.80±0.29% of crude fat, and 27.76±0.10% of ash. The protein hydrolysate produced also contained high protein content (50.09±0.88%) and may serve as a good protein source.

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 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.

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.

The present study was conducted in the Bakkhali river estuary, Cox’s Bazar, Bangladesh from September 2012 to July 2013. Percentage of protein was the main component of the biochemical composition in the mussels followed by carbohydrate, ash, and lipid.

Organophosphorus pesticides (OPs) play a certain role in promoting the development of agriculture and forestry, but they may cause potential harm to aquatic life when entering rivers and polluting water sources. Previous researches have shown that OPs participate in the regulation mechanism of aquatic organisms. Here, our aim is to determine the underlying mechanisms of one OP (dimethoate) at the transcriptional level using the clam Meretrix meretrix. 4119 DEGs were obtained from high-throughput RNA sequencing data. Then, expression profiles of some genes were verified by qPCR, which showed a positive correlation with the RNA sequencing results. 14,481 simple sequence repeats were also identified and could be further used as molecular markers. In addition, some oxidative, immune, and stress-related genes were further discussed and could also be used as biomarkers to indicate the biological response of dimethoate. This study will help to better understand the clam's response mechanism to dimethoate stress.

Paralytic shellfish toxins (PSTs) are notorious neurotoxins that threaten public health and food safety worldwide. Although PST monitoring programs have recently been established throughout China, the profiles and variation of PSTs in important commercial clams (e.g., Mactra veneriformis, Ruditapes philippinarum, and Meretrix meretrix) along the Jiangsu Province coastline remain largely unexplored. In this study, a validated hydrophilic interaction liquid chromatography–tandem mass spectrometry (HILIC-MS/MS) method was used to examine PST profiles and levels in 540 clam samples from natural production areas along Jiangsu Province coastline during 2014–2016. Although the PST levels (≤6.38 μg saxitotoxin equivalents (eq)/kg) were consistently below European Union regulatory limits (≤800 μg saxitotoxin eq/kg) during this time period, saxitotoxin, decarbamoylsaxitotoxin, and gonyautoxins 1 and 4 were detected, and nearly 40% of the samples were saxitotoxin-positive. The PST levels also varied significantly by seasons, with peak values observed in May during 2014–2016. This is the first systematic report of PSTs in clams from Jiangsu Province, and additional research and protective measures are needed to ensure the safety of clams harvested in this area.

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.

Benthic animal populations inhabiting intertidal flats provide important ecosystem functions and services that may be disrupted by physical disturbances such as tropical cyclones, which are predicted to increase in frequency and intensity under future climate change. However, the spatial reach at which tropical cyclones impact macrobenthos populations in intertidal flats remains poorly understood. We examined whether a typhoon with a center that remained more than 1400 km away from the study site could trigger severe erosion of intertidal flats and adversely affect macrobenthos populations. We undertook simultaneous measurements of hydrodynamics (waves, currents), morphodynamics (erosion, accretion) and density and biomass of the macrobenthic bivalve Meretrix meretrix during the passage of this typhoon, on an intertidal flat on the Chinese coast. Our results showed that, in spite of the considerable distance from the storm center, the bed shear stress greatly exceeded the critical value for erosion, resulting in rapid erosion of approximately 10 cm and a nearly 50% reduction in both the density and the biomass of the clam species. Our findings suggest that if storms become more frequent and more intense in a future warmer climate, they may increase physical disturbances to intertidal flats and their benthic animal populations, even at great distances from storm centers.

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 effect 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, 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 malonaldehyde (MDA) content, caused by increased lipid peroxidation. The activities of superoxide dismutase (SOD) and catalase (CAT) also increased, peaking at different Cd2+ concentrations, depending on the tissue. Glutathione peroxidases (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) andoxidized 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.

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).

Microplastic pollution is a problem that is currently attracting the attention of various groups, from scientists to ordinary people. This type of pollution can have a negative impact on aquatic biota, especially organisms that have filter feeder behavior. Asiatic hard clam (Meretrix meretrix) is a filter feeder organism that has a considerable risk of being exposed to microplastics. This study aims to analyze the concentration of microplastics in Asiatic hard clam (M. meretrix) at Lemo Beach, Burau District, East Luwu Regency, South Sulawesi. Sampling was performed using purposive random sampling method. The number of samples of Asiatic hard clam was 118 which were divided into three groups of shell length, namely class A (2.75 - 3.40 cm), class B (3.41 - 4.21 cm), class C (4.22 - 5.24 cm). Observation of microplastic particles is carried out using a stereo microscope equipped with a camera (Miconos optical lab). The results of the frequency analysis of the presence of microplastics in the clam showed that class A was the class with the highest frequency, namely 95.67%. The observed microplastics were in the form of fibers, fragments, and films with a predominantly black and transparent color. The size of the observed microplastics ranged from 0.033-0.88 mm. The results of the microplastic concentration analysis showed that size class A had a greater concentration than class B and class C.

The objective of this study was to develop an analytical method for protecting Jiaozhou Bay clam (Ruditapes philippinarum) with Protected Designation of Origin (PDO). The R. philippinarum samples were collected from three major producing areas (Jiaozhou Bay, Nantong coast, and Dalian coast) in China, and the Meretrix meretrix samples were from Nantong coast in May and September 2014. The contents of 46 elements in all clam samples were determined by inductively coupled plasma mass spectrometry. The obtained data were analyzed using analysis of variance, principal component analysis, and stepwise linear discriminant analysis. The results showed that both the geographical origin and season affected elemental contents in R. philippinarum. Seven elements (Mg, Cd, Sn, Sb, Cs, Ba, and U) independent of seasonal variation were selected as good indicators for discriminating the geographical origin of clams. Based on the discriminant models built with these seven elements, the predictions of the geographic origin gave an overall correct classification rate of 100.0 % and a cross-validation rate of 97.2 %. In addition, R. philippinarum and M. meretrix had their own elemental fingerprinting patterns and could be distinguished. Therefore, the multi-element analysis combined with multivariate statistics can be used for the identification of Jiaozhou Bay clam with PDO.

Bivalvia is one of the organisms that is able to accumulate heavy metal content in the body. Lead heavy metal (Pb) is a heavy metal that is toxic if the level exceeds the safe limit that has been set both on the body of an organism or in humans. The purpose of this study was to determine the various types of bivalves found in Bangkalan Coastal Madura Island, and to analyze the content of lead heavy metals (Pb) in bivalve bodies found in the region. This research is observational. Sampling was carried out by hand sorting, then identified the type of bivalves that were obtained and then the samples were taken to the laboratory for testing using the Atomic Absorption Spectrophotometer (AAS). The results of the study are known that, the types of bivalves found and identified in the Bangkalan Coastal area of Madura Island are Bamboo Scallops (Solen sp.), Blood Scallops (Anadara granosa), Sweet Scallops (Meretrix meretrix), and Stone Scallops (Placamen isabellina). Laboratory test results of lead heavy metal content (Pb), it is known that each clam accumulates lead heavy metal (Pb) with different amounts of concentration, wherein the heavy metal content of lead (Pb) in Bamboo / Lorry Shells (0.168-0.208 ppm) , Blood Shells (0.152-0.231 ppm), Sweet Shells (0.161-0.288), and Stone Shells (0.143-0.169 ppm), and it is known that the heavy metal content of lead (Pb) of the four bivalves is still below the threshold level of metal contamination according to Kep. Ditjen POM No. 03725/B/SK/VII/1989 which determines that the maximum limit of lead (Pb) heavy metal content in marine organisms is 2 ppm.

Microplastics ingested by two bivalve species Perna viridis and Meretrix meretrix collected from three estuaries viz. Ariyankuppam, Panithittu, and Chunnambar in Pondicherry, India was analysed for the first time in this research. Nile Red dye was used for microplastic detection. A survey of 50 local families was conducted to determine the frequency and quantity in which they consume mussels/clams. On an average, the number of microplastics per gram of soft tissue (wet weight) is 0.18 ± 0.04, 1.84 ± 0.61, and 1.76 ± 0.48; and the number of microplastics per bivalve is 0.50 ± 0.11, 1.75 ± 0.35, and 4.80 ± 1.39 respectively for Ariyankuppam, Panithittu, and Chunnambar. 61.02% and 77.42% of the particles belonged to the size group of100 μm in M. meretrix and P. viridis respectively. A moderate positive correlation of r (18) = 0.6985, p 0.05 was calculated between bivalve weight and microplastic particles. An average person belonging to the local community is likely to ingest 3917.79 ± 144.71 microplastic particles per year through mussel consumption.

High temperature has significant effects on the survival and immunity of organisms. In order to conduct a detailed investigation into the response of the saltwater clam Meretrix meretrix from different geographical populations (GuangXi, JiangSu, ShanDong, LiaoNing) to high temperatures, we examined the survival rates and antioxidant enzyme activities of these clams that were exposed to different temperature treatments (25°C, 35°C, 37.5°C, 40°C). Results showed that the survival rate of clams from GuangXi was highest at 40°C, followed by JiangSu. SOD and CAT activities of all the clams increased with the increasing temperatures, and then gradually decreased at 40°C over time. The expression levels of Hsp70 of M. meretrix from four populations were analyzed by qPCR sampled from the hepatopancreas after 72 h under different temperatures. Higher Hsp mRNA expression of GuangXi at 40°C indicated that clams of GuangXi have stronger high temperature resistance than those of the other geographical populations. Our findings provide a basis for the choice of cultured clams with a high temperature tolerance.

In this study, a sensitive and rapid method for the simultaneous quantification of 17 nucleosides and nucleobases and 23 free amino acids in clam samples using ultra-fast liquid chromatography coupled with tandem mass spectrometry (UFLC-MS/MS) was developed. Sufficient separation of 40 analytes was achieved on an Acquity BEH Amide column (2.1 mm × 100 mm, 1.7 μm) in a single run of 15 min. The overall limits of detection (LODs) and limits of quantification (LOQs) were between 0.05~38.8 and 0.15~128 ng/mL for the 40 analytes, respectively. The newly developed method was validated and subsequently applied for the analysis of the content variation of 40 analytes in four commercial clam species (Mactra veneriformis, Ruditapes philippinarum, Meretrix meretrix, and Cyclina sinensis) collected monthly from January to December 2014 at the coast of Jiangsu, China. Significant seasonal variation was observed for most analytes. Major nucleosides and nucleobases were at their highest contents in June or July, the contents of free amino acids showed the same pattern. Thus, if high concentrations of these functional small molecules are desired, Jiangsu native clams should be harvested in early summer. The results suggest that the present UFLC-MS/MS method could be employed as a useful tool for quality assessment of the clam samples as well as other food samples using nucleobases, nucleosides, and free amino acids as markers.

Color polymorphism has received much attention due to its strong implications for speciation and adaptation. In contrast to body color, little is currently known about the molecular mechanism of shell color formation. This study represents the first analysis of the relationship between whole-scale gene expression and shell color variations in the marine bivalve mollusks via comparative transcriptome analyses. Three clam Meretrix meretrix strains with different and monotonous shell color patterns, which were developed by our 10-year artificial selection, combined with clams with nearly white shell color were used in the analyses. The results supported the idea that there was a relationship between gene expression and shell pigmentation in the clam M. meretrix, and complex signal transduction were involved. It was proposed that Notch signaling pathway played a crucial role in shell pigmentation in a gene-dosage dependent pattern and also potentially involved in the shell color patterning. Calcium signaling process may equally be implicated in shell color formation via activation of Notch pathway. Other differentially expressed genes (e.g., Myl, Mitf) potentially implicated in shell color pigmentation were also noticed. This study provides information on the expression profiles of clams with different shell color morphs and sheds light on color formation mechanism of shell.

A 3×3 complete diallel cross comprising three families of the clam Meretrix meretrix (P1, P2 and P3) was used to determine the combining ability of parental families and heterosis of F1 under indoor and openair environments for growth traits. Analysis of variance for shell length and whole body weight indicated highly significant cross effects, environment effects and the interaction of cross by environment. General combining ability (GCA) and specific combing ability exhibited great variation among crosses and between two environments. Pooled over environments, P2 was the top combiner among the three parental families for both traits studied. The cross of P1 and P3 had the highest SCA. Additionally, significant reciprocal effects were observed. For individual environment, about half of the crossbred combinations showed favorable Mid-parent heterosis (MPH) (>1%) for the shell length and whole body weight. Our data has shown that non-additive genetic and reciprocal effects constituted the major sources of genetic variation for both shell length and whole body weight, which indicates that crossbreeding among selective families could further explore the heterotic effects.

Unbalanced parental contribution and small effective population size (N (e)) are common issues during the artificial breeding of marine bivalves. The impact of hatchery-spawning practices on parental contribution, effective population size, the N (e)/N ratio, and genetic diversity are largely unknown. To address this, we conducted a parentage analysis on a complete 3x3 diallel cross of clam M eretrix meretrix using eight microsatellite markers. The genetic diversity of the parents was higher than that of their respective offspring in most crosses (8/9). Sires or dams from the same family contributed unequally to the pool of offspring from a particular cross, and the same parent clam exhibited large variation in parental contribution among different crosses. The variance in male contribution was higher than that of the female contribution in most crosses, suggesting that male contribution was more skewed than for females. The N (e)/N ratio for nine crosses ranged from 0.58 to 0.86. There was no linear relationship between the sex ratio and the N (e)/N ratio (P > 0.05). Moreover, a sex ratio closer to one-to-one does not necessarily mean a larger effective population size. A solution to small effective population size in commercial breeding programs is increasing broodstock numbers and attempting to maintain a balanced sex ratio.

Carbonated hydroxyapatite (CHAp) derived from three different shells, Cerastoderma edule, Paphia undulata, and Meretrix meretrix shells, have been synthesized by precipitation method. Calcium oxide from extracting shells, diammonium hydrogen phosphate, and ammonium bicarbonate was used to synthesis as the starting precursors. The CHAp materials were analyzed by Energy Dispersive Spectroscopy (EDS), Fourier Transform Infrared (FT-IR), and X-Ray Diffractometer (XRD). EDS analysis showed that the Ca/P ratio of CHAp powders were around 1.75-1.77 (bigger than the Ca/P ratio of HAp) and carbonate content of the powder CHAp was 3.10-4.05wt%. XRD data has produced diffraction patterns from the three different shells similar to the apatite structure. The position of the main peak (2θ) diffraction patterns detected at 31.99°, 32.23°, and 31.95°. The lattice parameter of a-axis and c-axis were obtained around 9.37 Å and 6.89 Å. Crystallite size of CHAp samples was 30-40 nm. The FTIR spectra showed that there are functional groups of OH-, PO4 3-, and CO3 2- at wave number around 3447, 571, and 873 cm−1. Based on the results of the analysis, it shows that the CHAp characteristics that had successfully produced from Cerastoderma edule, Paphia undulata, and Meretrix meretrix shells were B-type CHAp.

Asiatic hard clam (Meretrix meretrix) was one of molluscs (bivalve) with economical value. However, fishing activities were presumed to cause a decline in population. This condition was strengthened by the size of the clam which became smaller nowadays. The purpose of this study was to determine spatial distribution of M. meretrix, length distribution, and length-weight relationship. The study was conducted at 3 stations, consisted of Station I at Asahan River estuary which was located by mangrove forest, Station II at the sea and Station III at the waters near mainland of Batu Bara Regency. Estimation growth of M. meretrix was examined following FISAT II method. The density of M. meretrix was dominant at Station I which was low in salinity and high in organic matter. The class interval of 23-34 mm at station I dominated length distribution. Length-weight relationship was found to be very strong with determinant value approaching

A breeding-selection program for the clam, Meretrix meretrix, was conducted since 2004. Two of the selection populationswere generated with the shell color pattern as an additional selection criterion and named as SP (purple stripes) population and SB (black dots) population. The third-generation SP and SB populations (08G3SP and 08G3SB, respectively) were cultured at two commercial clam farms and a nursery pond and their shell lengths were compared. 08G3SB clams had significantly larger sizes than 08G3SP clams at commercial clam farms (p < 0.05), yet 08G3SB individuals were significantly smaller than 08G3SP individuals at the nursery pond (p < 0.05). Then, we examined the growth of the fourth-generation SP and SB populations (10G4SP and 10G4SB, respectively) at a commercial farm, and found that the shell lengths of the 10G4SB clams increased at a significantly higher growth rate than the 10G4SP clams (p < 0.05) from May to September, when the water temperature was between 24.2-27.5A degrees C, while 10G4SB lost the growth advantage in the other months. These results indicated that SP and SB populations responded differently to environmental factors, so it is beneficial for the clam farmers to select a suitable population according to the culture environment. Furthermore, a diallel mating of the SB and SP populations was designed to investigate whether their hybrid population would show heterosis. However, the heterosis was not shown in this study, whichmight result from the slight genetic divergence between SB and SP populations.

The hard clam (Meretrix meretrix) is a commercially important maricultured shellfish in China. The transcriptome data of M. meretrix provided a valuable resource to mining large amount of EST-SSR markers quickly and cost-effectively. Here we isolated and characterized 53 novel polymorphic EST-SSR markers in 30 individuals. The number of alleles varied from 2 to 8, with an average of 4.19 alleles per locus. The observed and expected heterozygosities ranged from 0.040 to 1.000 and from 0.040 to 0.799, respectively. Thirty-one loci significantly deviated from HWE (P < 0.01) after Bonferroni correction. Interspecific transferability revealed that 19 polymorphic loci in Meretrixlamarckii and 10 in Meretrix lyrata were firstly characterized. These novel polymorphic SSR markers will be particularly useful for further diversity analysis, evolutionary studies, genetic trait mapping and marker assisted selection.

The research goal was to compare the shells types of Kapah (Meretrix meretrix; M. lyrata; Geloniacoaxans) that found in the Coast Binalatung area, Tarakan and to assess the growth of shellfishallometri. Sampling is done by making a transect along the coast Binalatung as much as 12 transects.Each transect arranged lengthwise along the beach with 25 meters of each transect. Sampling wascarried out in the absence of repetition with an area of 25 x 25 meters transect. Sampling was done byusing tools such as Kapah’ rakes. The result showed the M. meretrix constistes of 63 % of Kapah’spopulation while M. lyrata and G. coaxans represent 27 % and 10 % respectively. Growth comparisonbetween shell length and weight was considered as positive allometri while comparison between thickshells and weight of shellfish Kapah was allometri negative.Keywords: shellfish kapah, allometri growth, Binalatung, Tarakan

We identified the species of “kerang kapah” (hard clam) using the Gel Electrophoresis SDS Page, inorder to clarify the species of kerang kapah those found living along the East Coast of TarakanIsland. The study was conducted from July to December 2014. The kerang kapah were collectedfrom the several parts of East Coast Tarakan Island. Eight group samples of kerang kapah were used for Gel Electrophoresis SDS Page and scanned using the IMAGE software. Generally, thekerang kapah those found at the shouth part of East Coast of Tarakan Island have very similarmorphologies and shell colors, making species identification difficult. Four species of kerang kapahwere identified. Three species belong to Veneridae and one species belong to Corbiludae. Thespecies of Veneridae were Meretrix meretrix, Meretrix lyrata, and Meretrix sp. The species karangkapah belong to Corbiludae is Polymesoda erusa.Keywords: kerang kapah, meretrix, polymesoda, gel electrophoresis.

This study investigated accumulation of Escherichia coli and aerobic colony count in three types of shellfish species. The results indicated that the capability of accumulating E. coli and aerobic colony count for Sinonovacula constricta was stronger than that for Meretrix meretrix and Tegillarca granosa, and capability of accumulating E. coli for M. meretrix was slightly stronger than that for T. granosa. However, no significant difference was observed in the capability of accumulating aerobic colony count between M. meretrix and T. granosa. Moreover, accumulation of E. coli in S. constricta is affected by contaminated seawater and E. coli were accumulated much faster and more in S. constricta when the seawater contaminated more serious. Meanwhile, the results suggested that the populations of E. coli in S. constricta changed in accordance with the weather. This is the first study to investigate the differences of accumulating E. coli in three types of shellfish species.

Mere15 is a novel antitumor polypeptide purified from Meretrix meretrix Linn. (Veneridae). Previous studies have shown that the polypeptide induced cell death via intrinsic mitochondrial pathway.In the present study, the effects of Mere15 on cell adhesion, migration, invasion, as well as secretion and expression of matrix metalloproteinases (MMPs) were studied in human lung adenocarcinoma A549 cells.The effect of Mere15 on cell adhesion, migration and invasion were studied by cell adhesion and transwell assay. The expression of MMPs was determined by gelatin zymography and RT-PCR analysis.The ability of cell adhesion was decreased by 86.74% at the concentration of 12.0 μg/mL of Mere15. And the migration and invasion of A549 cells were decreased with the inhibition ratio of, 69.22 and 53.84% when treated with 15.0 μg/mL of Mere15. Further study also revealed that treatment of the cancer cells with Mere15 (15.0 μg/mL), the secretion of MMP-2 and MMP-9 were down-regulated with the inhibition ratio of 72.00 and 93.24% and the inhibition rate of mRNA expression of MMP-2 and MMP-9 was 57.54 and 91.22%, respectively.The study demonstrates that Mere15 inhibits tumor growth via both pro-apoptotic and antimetastasis pathways, and the polypeptide has potential to be developed as a multi-target therapeutic agent for the treatment of human lung cancer.

Because of the high frequencies of null alleles at microsatellite loci in mollusks, it is difficult to enhance the accuracy of parentage assignment in closely related families by increasing the number of loci. To develop an effective approach, microsatellite markers combined with mitochondrion COI marker were used for parentage assignment with computer simulations and experimental verification in the clam, Meretrix meretrix. In the present study, simulations based on allele frequency data from the candidate parents (sample II) demonstrated that combined exclusion probability of the five microsatellite loci (0.991 for Excl 1 and 0.995 for Excl 2) were not much lower than that of the seven loci (0.993 and 0.999). After discarding the two loci that deviated from Hardy-Weinberg equilibrium in experimental verification, accurate probability of progeny assigned to their fathers and mothers with both parents unknown was 68% and 59% in CF (closely related families), and 76% and 68% in DF (distant related families), respectively, which were much lower than those predicted by the simulations. When the COI marker was used in combination with microsatellite markers, 32 out of 39 offspring that were not previously assigned to their correct parents were assigned to their correct mothers, and 29 doubtful offspring could be assigned to their correct fathers. Consequently, with the combination of the two kinds of markers, the accurate probability of progeny that can be correctly assigned to their true fathers and mothers was increased to 89% and 92% respectively. We suggest that the use of microsatellite markers and COI marker will greatly improve the efficiency of parentage determination in closely related families in the clam. (C) 2011 Elsevier B.V. All rights reserved.

We described and characterized 17 expressed sequence tag (EST)-derived simple sequence repeats (SSR) and 16 genomic-derived SSRs for the clam Meretrix meretrix. The EST-SSRs comprised 17.6% dinucleotide repeats, 35.3% trinucleotide repeats, and 47.1% tetranucleotide repeats; whereas the majority of the G-SSRs were dinuleotide repeats (75.0%). The number of alleles for the 33 SSR markers varied from 6 to 15, with a mean of 10.3 alleles per locus. Observed and expected heterozygosity (Ho and He) varied from 0.613 to 0.824, and 0.687 to 0.850, respectively. Polymorphic information content (PIC) ranged from 0.645 to 0.842. The mean values of number of alleles, Ho, He, and PIC of G-SSRs were higher than those of the EST-SSRs. No significant deviations from Hardy-Weinberg equilibrium or linkage disequilibrium were observed in the 33 loci. These loci are the first to be characterized in M. meretrix and should be useful in the investigation of genetic evaluation for conservation.

A total of 2,970 EST-SSRs (2.38%) were identified by transcriptome sequencing of clam Meretrix meretrix (751,970 reads, similar to 310.82 Mbp), using 454 Genome Sequencer FLX next-generation sequencing platform. Dinucleotide SSR was the dominant repeat type (40.2%), followed by trinucleotide (37.8%), tetranuleotide (12.0%) and pentanucleotide (2.0%) SSR. The dominant repeat motif was AT (71.3%) in the dinucleotide SSR type and AAC (45.6%) in the trinucleotide SSR type. Nearly 79% of all microsatellites had flanking sequences suitable for PCR primer design. Half of PAL were found to be polymorphic in a subset of 40 primer pairs randomly selected. Specifically, the density of dinucleotide, trinucleotide and tetranucleotide repeats showed significant variation among four development stages (trochophore, D-veliger, pediveliger and postlarva). The results suggested that dinucleotide, trinucleotide and tetranucleotide SSRs may play an important role in contributing to the different expression profiles in larval stages.

The hard clam (Meretrix meretrix) is a popular edible shellfish in South and Southeast Asia, being heavily exploited by hand dredging in Marudu Bay, Malaysia. The current study was performed to evaluate the shell damages caused by this artisanal dredging gear. Samplings were conducted in triplicates at two sites using both hand dredging and hand collecting (control) sampling methods. The shell length and total weight, damage areas and breakage patterns of each clam were recorded. A questionnaire survey was conducted with local bivalve harvesters to gather information on the fishing pressure in Marudu Bay. Results revealed that the efficiency (fishing yield) of hand dredging gear was three times higher than hand collecting. However, hand dredging gear causes lethal shell damages to small hard clams (

Wild clams of Meretrix meretrix and Cyclina sinensis were collected from intertidal flats of Shuangtaizi estuary during low tide in 2016. Morphometric traits including shell length (SL), shell height (SH), shell width (SW), and total body weight (TW) of the clams were measured. Correlation, path, and regression analyses were conducted to evaluate the relationship between morphometric traits and total body weight and determine the optimal indices for artificial breeding of M. meretrix and C. sinensis. Significant differences in correlation coefficient among various characteristics were found. Shell height and SW showed the strongest influence on total body weight. The optimal regression equation of the measured traits was established in both clams by using a stepwise regression method: TW = –27.404 + 0.948 SW + 0.422 SH + 0.291 SL for M. meretrix and TW = –36.965 + 1.107SH + 0.564SW for C. sinensis. These results provide baseline information for selective breeding and conservation management of the two commercially important clam species in Shuangtaizi estuary.

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.

Three wild populations of Meretrix meretrix sampled from Dongxing, Beihai, and Shankou along the coast of Guangxi, China, were investigated with morphometry and karyometry. Six morphological indices (shell length, shell height, shell width, hinge length, total wet weight and shell weight) were measured. Differences in all morphological indices except hinge length were significant among the three populations (P 0.05). However, the order of metacentric, submetacentric and subtelocentric chromosome pairs was variable among the three populations. The results indicate a high level of inter-population variation in morphology and karyotype.

Polysaccharides from marine clams perform various biological activities, whereas information on structure is scarce. Here, a water-soluble polysaccharide MMPX-B2 was isolated from Meretrix meretrix Linnaeus. The proposed structure was deduced through characterization and its immunological activity was investigated. MMPX-B2 consisted of d-glucose and d-galctose residues at a molar ratio of 3.51:1.00. The average molecular weight of MMPX-B2 was 510 kDa. This polysaccharide possessed a main chain of (1→4)-linked-α-d-glucopyranosyl residues, partially substituted at the C-6 position by a few terminal β-d-galactose residues or branched chains consisting of (1→3)-linked β-d-galactose residues. Preliminary immunological tests in vitro showed that MMPX-B2 could stimulate the murine macrophages to release various cytokines, and the structure-activity relationship was then established. The present study demonstrated the potential immunological activity of MMPX-B2, and provided references for studying the active ingredients in M. meretrix.

Meretrix meretrix L. was held in the laboratory under simulated natural conditions to measure specific physiological parameters of its energy budget. O2 consumption rate, NH3 excretion rate (NR), ingestion rate, faeces excretion rate and scope for growth (SFG) were negatively related in an exponential manner to the fresh weight of the clams at all water temperatures, while almost all metabolic rates of the clams were positively related in an exponential or e-exponential manner with water temperature. However, the co-relationship between metabolic rates and water temperature was not as close as that between metabolic rates and fresh weight of the clam. The combined effect of fresh weight and water temperature was observed on all metabolic rates except for NR and SFG. At all culture temperatures and for all fresh weights of clams used, respiration took the largest percentage of ingested energy (41.5–51.2%), faeces excretion was second (31.0–42.3%), growth third (12.1–15.5%) and urine production last (2.1–5.6%).

A nature-simulating culture system was used to explore the influence of salinity, the diurnal cycle and daylength on ingestion rate (IR) and assimilation efficiency (AE) of Meretrix meretrix . The clams used in the experiments were grouped into three sizes: small, with a shell length of 2.70 ± 0.10 cm and a dry fresh weight of 0.35 ± 0.04 g; medium, with a shell length of 4.00 ± 0.05 cm and a dry fresh weight of 1.25 ± 0.05 g; and large, with a shell length of 5.00 ± 0.10 cm and a dry fresh weight of 2.45 ± 0.10 g. The clams in all size groups demonstrated a common response pattern in IR and AE under salinities ranging from 18 to 34 ppt. The clams achieved the greatest IR within the salinity range 27 to 30 ppt. There was a marked reduction in IR outside this range. Of the salinities tested 18 ppt was the harshest stress to the feeding of M. meretrix . Between the salinities 24 to 34 ppt, changes in AE of the clam were the inverse of those observed in IR, suggesting that M. meretrix is able to compensate for the loss of IR by an increase in AE. Although the effect of both salinity and body size of the clam was significant on both IR and AE, salinity had evidently stronger influence than body size. All sizes of clam showed a three-phase diurnal feeding pattern: a high ingestion phase from 00:00 to 08:00, a low ingestion phase from 12:00 to 20:00, and a changing phase between low and high ingestion phases. The IR response to daylength comprised a high and constant feeding phase at daylengths from 0 to 16 h (longer darkness) and a declining and unstable feeding phase as daylength increased from 16 to 24 h (shorter darkness). All sizes of clams demonstrated an inverse adaptation to AE compared with IR, indicating that the clam is able to achieve a stable feeding physiology by compensating for daylength-induced variations in IR by changing AE. The ANOVA analysis also showed that both diurnal cycle and daylength affected IR and AE of the clam very significantly, body size did not, however.

A survey of organotin compounds comprising tributyltin (TBT), dibutyltin (DBT) and monobutyltin (MBT) in sediment and clam (Meretrix meretrix) was undertaken in Vietnam in 2003. Samples were collected from dry docks and cargo harbours in Ho Chi Minh (south), Da Nang (centre) and Hai Phong (north) cities. Measurable amounts of TBT, DBT and MBT were found in all samples. The total concentration of the butyltin compounds (ΣBTs) in sediment from shipyards and vessel repair yards (Nam Trieu, Song Cam, Lach Tray and Ba Son) were always higher than those measured in cargo ports (Hai Phong, Da Nang, and Sai Gon). The highest ΣBTs concentration (as tin: 122 ng g−1 dry wt) was found in the sediment from Song Cam station, where seven shipyards are located. The lowest concentrations of ΣBTs occurred in sediments from the Da Nang and Hai Phong cargo ports (as tin: 21–22 ng g−1 dry wt). This implies that the major source of BTs in the marine environment in Vietnam is from the shipbuilding activities. The ratio of TBT to Σ(MBT + DBT) in sediment was 0.67 ± 0.03 for all the sampling sites, indicating the recent use of TBT in Vietnam. For the clam (M. meretrix), the concentration of ΣBTs (as tin) varied in the range 11.2–60.1 ng g−1 wet wt. There was a good correlation (R2 = 0.85) between total organic matter-normalized ΣBTs in sediment and hexane-extractable organic matter-normalized ΣBTs in clam soft tissue. The mean biota–sediment accumulation factors (organic carbon/lipid) for MBT, DBT and TBT in clam's soft tissue were found to be 1.83 ± 0.66, 1.44 ± 0.23 and 1.16 ± 0.47 respectively, indicating that sediment-bound BTs might be an important source of contamination for the clam. Copyright © 2005 John Wiley & Sons, Ltd.

This study describes the apicomplexa as well as other parasites infecting organs/tissues of the hard clam Meretrix meretrix Linnaeus, from Merambong Shoal, Western Johor Straits, Malaysia. Samples were collected randomly by hand picking, in November and December 2013. Histological techniques were performed, stained using Masson's Trichrome protocol and observed under light microscope. The results showed that gonad and gill were the most infected organs followed by digestive gland, intestine and adductor muscle. No pathology condition was observed in the mantle. Histophatological examination showed that the gregarine, Nematopsis, unidentified coccidian and Perkinsus were found in the gill and gonad, and also in the numerous hemocytes. Other pathological conditions such as bacteria-like inclusion and intracellular bacteria were also observed in the same organs. Further investigations are needed particularly on other molluscs present at the study area. Understanding the morphology and pathology of parasites ...

The hydrocarbon levels in the clam Meretrix meretrix at selected locations along the Saudi Arabian Gulf coastline for the period 1981–90 (prior to the 1991 Gulf War) are compared to those from the war and post-war periods. Five of the nine sites in the study were affected by the war oil spill. There was no significant impact in the n -alkane levels. However dibenzothiophenes and phenanthrenes increased significantly in the clam tissue during the war period. These values returned to pre-war levels after a short period of time (within two years). The data from the sites affected by the oil spill are compared with data from the other four unaffected sites in the study that are located further to the south.

Meretrix meretrix is a commercially important bivalve species in China. Due to overfishing for food, the wild stocks are decreasing rapidly. We reported the isolation and characterization of 10 polymorphic loci isolated from apartial genomic DNA library of Meretrix meretrix enriched for CA repeats. A total of 21 primers were designed with online software PRIMER3. We tested variability of these microsatellites on 30 individuals collected in Zhejiang Province. Ten microsatellites were polymorphic. The number of alleles ranged from 2 to 17. The observed heterozygosity was from 0.1667 to 0.9333 and the expected heterozygosity was from 0.1554 to 0.9322. Seven of 10 microsatellites conformed to Hardy–Weinberg equilibrium, and inherited independently. These polymorphic loci provide a valuable tool for assessing population genetic diversity of this species.