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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. [ABSTRACT FROM AUTHOR]

Meretrix meretrix is one of the economical shellfish that has been exploited in Kendari Bay, Indonesia. Several studies have been done, but its growth pattern and condition index are not fully known. This study aims to determine its growth pattern and condition index at the Kambu River estuary, Kendari Bay. This research was conducted for 6 months from August 2021 to January 2022. Clams were collected using a rake, cleaned, and brought to the laboratory to be measured for length and weight using calipers and scales with an accuracy of 0.1 mm and 0.01g, respectively. Furthermore, the clam meat was dried using an oven and weighed. Data on growth and condition index were analyzed using simple regression and the Mann-Whitney test, respectively. The results showed that the growth of M. meretrix was in negative allometric conditions, with b values in males and females in the range of 2.20-3.00 and 1.86-2.73, respectively. The condition index of male and female clam ranged from 1.86-2.62 and 1.66-2.41, respectively, and differed significantly by month. The results of the Mann-Whitney test on clam showed that there was no significant difference between August-November and December-January. In conclusion, male and female clam had relatively different patterns based on the observation period, while the condition index was in the skinny and medium category. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

• Post-stress recovery assays separate Meretrix meretrix into proactive and reactive. • Nano-TiO 2 exposure impaired clams' survival and physiological conditions. • High survival rate in proactive clams might change ecosystem population structure. • Proactive clams had better adaptability under nano-TiO 2 exposure. Nano-TiO 2 is inevitably released into aquatic environment with increasing of nanotechnology industries. Study pointed that different individuality showed divergent behavioral and physiological response when facing environmental stress. However, the effects of nano-TiO 2 on tolerance of bivalves with different individualities remain unknown. In the study, clams were divided into two types of individuality - proactive and reactive by post-stress recovery method. It turned out that proactive individuals had quicker shell opening level, stronger burrowing behavior, faster feeding recovery, higher standard metabolic rate and more rapid ammonia excretion ability than reactive individuals after exposed to air. Then, the survival rate, hemocytes response and oxidase activity of classified clams were evaluated after nano-TiO 2 exposure. Results showed that after 30 d exposure, proactive individuals accelerated burrowing behavior with higher survival rate. Moreover, proactive clams had better adaptability and less hemocytes response and oxidative damage than reactive clams. The study highlights the individualities of marine shell fish determine individual capacity to adapt to environmental changes, play important roles in aquaculture and coastal ecosystem health. [ABSTRACT FROM AUTHOR]

In this study, the accumulation, depuration and methylation of mercury in Crassostrea gigas and Meretrix meretrix were analysed and evaluated using the two‐compartment kinetic model through exposure in mercury chloride (HgCl2) solution and depuration procedure in seawater. The results showed that the accumulation and depuration of mercury in organisms were related to the dissolved inorganic Hg(II) content with accumulation delay. It was suggested that the two organisms formed methylmercury (MeHg) when exposed to Hg(II) that is not only formed by anaerobic bacteria in marine sediments. The peak value of MeHg appeared in the depuration phase. The accumulation of C. gigas was stronger than that of M. meretrix, with a peak value of 37.86 ± 3.29 μg/g and 14.48 ± 0.29 μg/L respectively. Crassostrea gigas also had a stronger methylate ability. According to the reference dose for MeHg determined by the United States Environment Protection Agency along with model calculations, when the concentration of Hg in the water reaches 0.2 μg/L, the cultured M. meretrix would be safe for consumption, while cultured C. gigas should be depurated before marketing due to the higher content of MeHg (0.50 mg/kg). Therefore, the two‐compartment kinetic model could be used to monitor the Hg and MeHg content of bivalves when the concentration of Hg in seawater is known. [ABSTRACT FROM AUTHOR]

Odor is an important factor influencing the acceptance of clams by the consumer. In order to better understand the flavor characteristics of different clams, the volatiles in raw and cooked Meretrix meretrix with three shell colors (mottled shell, red shell, and yellow shell) were investigated by electronic nose and gas chromatography-mass spectrometry (GC-MS). A total of 69 volatiles, dominated by alcohols (32.10–41.02%) and 25 odor-active compounds, were identified in the raw samples, while 73 volatiles, dominated by aldehydes (55.18–58.22%) and 27 odor-active compounds, were determined in the cooked samples. Compared to raw samples, cooked samples had higher concentrations and odor activity values (OAVs) of volatiles. Among the raw clams, OAVs of volatiles in red shell clams were significantly higher than yellow shell clams. According to both electronic nose and GC-MS, all the samples could be distinguished, and 3-octanone, (Z)-1,5-octadien-3-ol, linalool, 1-octen-3-one, 1-octen-3-ol, 2-nonanone, (E,E)-2,4-heptadienal, and undecanal were the key volatiles to distinguish the odor profile of Meretrix meretrix with different shell colors. [ABSTRACT FROM AUTHOR]

Molluscs, apart from being a food ingredient, animals belonging to this class, also can be used as a source of potentially bioactive compounds. Shellfish are generally often used to treat liver disease. Thus, clam Meretrix meretrix may become a hepatoprotector. This research was conducted to determine the phytochemical components and hepatoprotective activity by measuring the levels of SGPT and SGOT from experimental animals that had been intervened by using ethanol extract of fresh and fermented clam Meretrix meretrix. The results of phytochemical screening showed the ethanol extract of the fresh sample only contained alkaloid compounds, and the ethanol extract of the fermented sample contained alkaloids, steroids, and saponins. The measurement of the SGPT value after treated with the sample extracts at concentrations of 100 ppm, 150 ppm, and 200 ppm for three days varied of 19.49 - 22.97 IU. The same also found in SGOT measurements after-treatment of the sample extracts at concentrations of 50 ppm, 100 ppm, and 150 ppm for three days, varied of 28.08 - 34.60. Our study revealed that ethanol extract from fresh and fermented clams showed a potential hepatoprotective activity, as seen from the effect of reducing SGPT and SGOT values after treatment for three days. [ABSTRACT FROM AUTHOR]

This study applies a translog cost function model to analyze the culture costs and the use of input factors among three groups of hard clam farmer households in Yunlin County, Taiwan, with different survival rates (low‐intermediate, intermediate‐high, and high). The study found that farmer household production in the three observed groups all exhibited economies of scale and could significantly expand the scale of production to lower the average cost. For farmer households with high survival rates, production cost could be reduced by 2.16% by a 10% increase in output. Moreover, the study shows that the survival rate–cost interaction values of farmer households in the intermediate‐high and low‐intermediate survival rate clusters were negative. Therefore, any increase in the survival rate could help lower the culture cost of farmer households. For low‐intermediate farmers, the survival rate–cost interaction value was the most negative; any increase in the survival rate by 10% would decrease the cost per hectare by NT$23,424. For high survival‐rate households, seeding and capital were substitutes, and seeding and feed were complements. As such, farmers would reduce the use of seeding factors when increasing the use of capital and decreasing the use of feed. [ABSTRACT FROM AUTHOR]

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, 5'-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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract Tetraspanins belong to the transmembrane 4 superfamily (TM4SF), and play crucial roles in immune responses. In the present study, a novel tetraspanin gene (designated MmTSPAN) was cloned and characterized from the hard clam Meretrix meretrix. The complete cDNA sequence of MmTSPAN contained an open reading frame (ORF) of 816 bp, which encoded a protein of 271 amino acids. Mm TSPAN exhibited highly similarity with previously identified tetraspanins from other species. It contained four transmembrane domains (12–35 aa, 69–92 aa, 99–123 aa and 238–261 aa), characteristic CCG motif and four conservative cysteine residues. The mRNA transcripts of MmTSPAN were ubiquitously detectable in all the tested tissues, with the highest expression level in hepatopancreas. Temporal transcriptional levels in the hepatopancreas revealed significant up-regulation of MmTSPAN by Vibrio splendidus stimulation, with a 3.14-fold increase at 6 h compared to the control, and reaching 32.98-fold at 24 h. These results provide useful information for further study of the function of tetraspanin in the innate immune system of M. meretrix , and may offer a new therapeutic target for diseases of M. meretrix. Highlights • A novel tetraspanin gene (MmTSPAN) was identified and characterized from Meretrix meretrix. a. • MmTSPAN was highly expressed in hepatopancreas and gill. • Significant induction of MmTSPAN was detected post Vibrio splendidus stimulation. [ABSTRACT FROM AUTHOR]

Biochar (BC) and activated carbon (AC) amendments have been applied to remediate contaminated sediments because of their benefits in reducing toxicity and/or the bioavailability of contaminants. However, their ecotoxicity to benthic organisms, which are not well understood, should be carefully considered before their practical application. Therefore, a wood-derived BC (WBC) or a coconut shell-derived AC (CAC) was incorporated into a marine sediment at 5% (dw%) to investigate their effects on the growth and nutritional quality of a marine clam ( Meretrix meretrix ). CAC and WBC had no effect on the pH and calcium content of the sediment, but significantly increased the electrical conductivity (EC) and total organic carbon (TOC), and decreased the dissolved organic carbon (DOC). After 28 days of cultivation, WBC reduced the shell growth of the clam by 36.4%, and CAC reduced the soft tissues of the clam by 9.05%. This was probably because WBC and CAC adsorb organic matters and the feeding algae may colonize within their pores, thus, reducing food bioavailability for the clams. Water extracts of CAC and WBC had negligible effects on soft tissue growth, whereas the CAC extract inhibited the growth of clam shells by 57.9%. WBC and CAC had little influence on the nutritional quality of clams, including moisture, crude protein, and crude lipid contents. These findings are helpful to understand the ecotoxicological risks of BC and AC amendments to benthic organisms when used for the remediation of contaminated marine sediments. [ABSTRACT FROM AUTHOR]

Even trace amounts of cadmium (Cd), a non-essential metal, are known to be toxic to aquatic organisms. Here we investigated the relationship between cadmium ion (Cd) exposure and oxidative damage and apoptosis in the hepatopancreas of the clam Meretrix meretrix. Clams were exposed to different concentrations of Cd (0, 1.5, 3, 6 and 12 mg L) for 5 days. We monitored both antioxidant enzyme activity, including that of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidases (GPx), and levels of malondialdehyde (MDA), glutathione (GSH) and glutathione disulfide (GSSG). Apoptosis of hepatopancreatic cells was detected by DNA laddering and AO/EB double fluorescent staining. The results show that the rate of apoptotis, MDA levels, and caspase-3 activity, increased with Cd concentration, whereas GPx activity and the ratio of GSH/GSSG, decreased. SOD and CAT enzyme activity first increased, then decreased, with increasing Cd concentration; peak activity of these enzymes was recorded in the 3 mg L Cd-treatment group. These results show that Cd-induced oxidative damage can both induce, and aggravate, apoptosis in the hepatopancreatic cells of clams, even at Cd concentrations far below the semi-lethal dose for adult clams. The observed changes in caspase-3 activity enhanced significantly at lower Cd concentrations, indicating that caspase-3 is a suitable biomarker for heavy metal pollution, especially cadmium pollution, in marine organisms. [ABSTRACT FROM AUTHOR]

This study aimed to evaluate the potential impacts of an introduced clam Mercenaria mercenaria on estuarine ecosystem, and implications for the niche competition with a native clam Meretrix meretrix. The biodeposition, respiration, and excretion rates of M. mercenaria were determined seasonally using a sediment trap and a closed respirator in field. The biodeposition rates of M. mercenaria were 0.06-0.37 g/ (ind.·d), and the respiration rates were 0.31-14.66 mg/(ind.·d). The ammonia and phosphate excretion rates were 0.18-36.70 and 1.44-14.87 μg/(ind.·d), respectively. The hard clam M. mercenaria may discharge dry deposits up to 2.1×10 t, contribute 18.3 t ammonia and 9.0 t phosphate to culture ponds, and consume 7.9×10 t O from ponds annually. It suggested that the hard clam M. mercenaria might play an important role in pelagic-benthic coupling in pond ecosystem through biodeposition and excretion. A comparison of the key physiological parameters of the introduced clam M. mercenaria and the native clam Meretrix meretrix suggested that M. mercenaria had a niche similar to that of Meretrix meretrix in Shuangtaizi estuary and might have a potential competition with Meretrix meretrix for habitat and food if M. mercenaria species escaped from the culture pond or artificially released in estuarine ecosystem. [ABSTRACT FROM AUTHOR]

The identification and use of probiotic bacterial stains is a practical approach to protect clams grown in aquaculture farms from disease. The inhibition of the pathogenic bacterium Vibrio alginolyticus was used as a trait to select a candidate probiotic bacterial strain in this study. An ideal bacterial strain, SW-1, was isolated from sea water from a clam farm. The selected isolate SW-1 was identified based on its physiological, morphological, and biochemical characteristics and its 16S rDNA sequence. The experiments showed that strain SW-1 had a high similarity to Pseudoalteromonas piscicida and could inhibit the growth of V. alginolyticus (V.-MP-1). SW-1 also improved the survival of clams following challenge with the pathogenic V.-MP-1. The mortality of clams was 100% after infection with 108CFU/mL of V. alginolyticus, whereas mortality was only 11% when clams were infected with 108CFU/mL of V.-MP1 while simultaneously exposed to the same concentration of Pseudoalteromonas SW-1, indicating that Pseudoalteromonas SW-1 could be used as a probiotic to protect farmed clams, and thus reduce the effects of antibiotics on aquatic environment. [ABSTRACT FROM AUTHOR]

Abstract: The clam Meretrix meretrix is an important commercial bivalve distributed in the coastal areas of South and Southeast Asia. In this study, marker–trait association analyses were performed based on the stock materials of M. meretrix with different vibrio-resistance profile obtained by selective breeding. Forty-eight EST-SSR markers were screened and 27 polymorphic SSRs of them were genotyped in the clam stocks with different resistance to Vibrio parahaemolyticus (11-R and 11-S) and to Vibrio harveyi (09-R and 09-C). Allele frequency distributions of the SSRs among different stocks were compared using Pearson's Chi-square test, and three functional EST-SSR markers (MM959, MM4765 and MM8364) were found to be associated with vibrio-resistance trait. The 140-bp allele of MM959 and 128-bp allele of MM4765 had significantly higher frequencies in resistant groups (11-R and 09-R) than in susceptive/control groups (11-S and 09-C) (P < 0.01), which suggested that the clams carrying these two alleles have stronger resistance against vibrio. Clam individuals of 11-S were divided into three subgroups based on the survival time post-challenge, and the multi-dimensional scaling (MDS) analysis showed that clusters generated by genetic similarity revealed by the three SSR markers were consistent with the three subgroups distinctions. The putative functions of contig959, contig4765 and contig8364 also suggested that the three SSR-involved genes might play important roles in immunity of M. meretrix. All these results supported that EST-SSR markers MM959, MM4765 and MM8364 were associated with vibrio-resistance and would be useful for marker-assisted selection (MAS) in M. meretrix genetic breeding. [Copyright &y& Elsevier]

Abstract: Inhibitor of NF-κB (IκB) is an important member of Rel/NF-κB signaling pathway, which is an important mediator of immune responses in innate immune system. In this study, the IκB cDNA of hard clam Meretrix meretrix (designated as Mm-IκB) was cloned and characterized. The full-length cDNA of Mm-IκB was of 2098 bp, containing a 5′ untranslated region (UTR) of 123 bp, a 3′ UTR of 810 bp with a poly (A) tail, and an open reading frame (ORF) of 1164 bp encoding a polypeptide of 387 amino acids. The high similarity of Mm-IκB with other IκBs from invertebrates indicated that Mm-IκB should be a member of IκB family. Similar to most IκBs, Mm-IκB possessed all conserved features critical for the fundamental structure and function of IκBs, such as five ankyrin repeats and a conserved degradation motif (DS44RYSS48). Two PEST domains and a phosphorylation site motif (S367EEE370) at the C-terminus of Mm-IκB were identified. By quantitative real-time RT-PCR analysis, mRNA level of Mm-IκB was found to be most abundantly expressed in the tissues of mantle, gill and hepatopancreas, weakly expressed in muscle, foot and haemocyte. The Mm-IκB gene expression was significantly up-regulated at 24 h in haemocyte and at 12 h in gill after Vibrio anguillarum challenge, respectively. The results suggested the involvement of Mm-IκB in response against bacterial infection and further highlighted its functional importance in the immune system of M. meretrix. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

A total of 2,970 EST--SSRs (2.38%) were identified by transcriptome sequencing of clam Meretrix meretrix (751,970 reads, ~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. [ABSTRACT FROM AUTHOR]

Abstract: In the present study, a 71.43kDa heat shock protein cDNA was cloned from Asiatic hard clam Meretrix meretrix. The cDNA was 2292bp, containing an open reading frame (ORF) of 1959bp, which encodes a protein of 652 amino acids with a theoretical molecular weight of 71.43kDa and an isoelectric point of 5.32. Based on the amino acid sequence analysis and phylogenetic analysis, this hsp70 cDNA is a member of cytoplasmic hsc70 (constitutive genes) subfamily in the hsp70 family, and is designated as MmeHsc71. Quantitative RT-PCR was carried out to compare the spatial and temporal expression patterns of MmeHsc71 in the mRNA level between control clams and Vibrio parahaemolyticus-infected clams. Spatially, MmeHsc71 mRNA was found in all tested tissues, including foot, hepatopancreas, mantle and gill. MmeHsc71 mRNA expression level in hepatopancreas and gill displayed a significant increase in vibrio-challenged clams at 24h post-infection compared to control clams (P <0.05). Temporally, there was a significant increase of MmeHsc71 mRNA level in hepathopancreas of vibrio-challenged clams compared to control clams at 6, 12, and 24h post-challenge, respectively. The result of quantitative immunofluorescence also indicated that there was obvious increase of MmeHsc71 in hepatopancreas of vibrio-challenged clams compared to control clams in protein level at 24h post-infection. The results suggested that MmeHsc71 may play an important role in mediating the immune responses of M. meretrix to bacterial challenge. [Copyright &y& Elsevier]

Abstract: MM5 was a bacterial strain isolated from moribund clam (Meretrix meretrix) collected from a farm with mass mortality outbreak. Primary genotypic and phenotypic identification including 16S rDNA sequence analysis, multilocus sequence analysis (MLSA) of four housekeeping genes (gapA, ftsZ, mreB and topA) and biochemical tests suggested that strain MM5 was a Vibrio species closest to but different from Vibrio furnissii. Our previous study indicated that MM5 could induce a high mortality of M. meretrix (). Quantitative challenge test was performed in this study to further evaluate the pathogenic potential of MM5, which showed that at 84h post-inoculation, the cumulative mortalities of the MM5-injected group were significantly higher than those of control groups (P <0.05). Cytopathological and histopathological features of the clam infected by MM5 were carried out by transmission electron microscopy (TEM) and Hematoxylin and Eosin (H&E) staining, respectively. Cytopathologically, foci of MM5 were found in hepatocytes of the clam infected by MM5. In addition, cytopathological lesion was detected in foot of infected clam. Histopathologically, MM5 was detected in different tissues of infected clam, including hepatopancreas, mantle and gill. Challenge test combined with pathological features indicated that MM5 was virulent to M. meretrix. [ABSTRACT FROM AUTHOR]

The extracted unfractionated glycosaminoglycans (GAGs) obtained from the marine clam Meretrix meretrix were fractionated by ion-exchange (Amberlite IRA-900 and 120) chromatography. The fractionated sample activity was determined through azure-A by metachromatic activity and agarose gel electrophoresis. The active fractionated sample molecular mass was determined through gradient polyacrylamide gel electrophoresis (PAGE). The structural characterization of low-molecular-weight GAGs was analyzed by Fourier transform infrared (FT-IR) and 1H-nuclear magnetic resonance (NMR) spectroscopy. The Activated partial thromboplastin time (APTT) of fractionated heparin-like glycosminoglycan is 72 IU/mg and it has a molecular mass of 15,000 Da. The disaccharide profiles, such as uronic acid 15.31%, hexosamine 24.61%, and sulfate content 11.7%, were also determined. The results of this study suggest that the GAGs from M. meretrix could be an alternative source of heparin. [ABSTRACT FROM AUTHOR]

Abstract: Shell formation is one of the important events during larval development and metamorphosis in bivalves. However, the molecular mechanisms and environmental cues regulating shell initiation and growth are unclear. Here, we report that ferritin, a principal protein for biological iron storage and metabolism, might play a role in larval shell development of the bivalve mollusk Meretrix meretrix. A full-length ferritin subunit cDNA, named as MmeFer, was cloned and characterized. The MmeFer mRNA expression in different developmental stages, from trochophore to post larvae, was analyzed by real-time reverse transcription polymerase chain reaction (RT-PCR). MmeFer mRNA expression in larvae of later developmental stages increased at least 8-fold following trochophores. Moreover, the temporal and spatial expressions of MmeFer mRNA were examined by whole mount in situ hybridization. In the trochophore stage, MmeFer was detectable where it was supposed to be for shell initiation. In the later developmental stages, MmeFer was found near digestive glands and mantle that secret larval shell. MmeFer expression was also detected in larvae cultured in artificial seawater with different iron concentrations ranging from 0 to 100 µM. These results suggest that ferritin may play a role in the shell formation of mollusks. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]