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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.

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. (C) 2013 Elsevier Ltd. All rights reserved.

The respiration and excretion rates of Meretrix meretrix at different salinities were studied at 20°C in laboratory in December 2008. 1) It was shown that the effects of salinity on oxygen consumption rate(OR) and ammonia excretion rate(NR) in Meretrix meretrix are extremely significant(pA0.05), when salinity changes from 8.2 to 28.1. 2) At the same time, the trend of ratio of O/N shows first increased and then decreased with the raise of salinity, moreover, and the ratio O/ N of the largest is 11.38 at 28.1.

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Ferric hydroxide and particulate organic matter are important pools of trace metals in sediments and control their accumulation by benthic animals. We investigated bioaccumulation of cadmium in bivalve Meretrix meretrix by using a simplified system of laboratory synthesized iron oxides and commercially obtained humic acids to represent the inorganic and organic matrix found in nature. The results showed that bioaccumulation characteristics were distinctly different for these two substrates. Bioaccumulation from ferric hydroxide was not observed at 70 and 140 mg/kg, while the clams started to absorb Cd at 140 mg/kg from organic matter and the bioaccumulation rate was faster than that from ferric hydroxide. Within 28 d, accumulation of Cd from organic matter appeared to reach a steady state after rising to a certain level, while absorption from ferric hydroxide appeared to follow a linear profile. The findings have implications about the assimilation of trace metals from sediments by benthic animals.

Clams (Meretrix meretrix) were collected during April–May 1991 (post-war period) from five locations along the Saudi Arabian coast of the Gulf. All the soft tissue from each clam was removed and digested separately at 120°C for 3 h in the nitric-perchloric acids mixture. Twenty metals were determined in the acid digests using an inductively coupled plasma analyser. Clams (Meretrix meretrix) were also collected from the same stations in April–May, 1985 (pre-war period) and analysed for Cd, Co, Cr, Mo, Ni, Pb, V, and Zn. Wherever appropriate, these data were compared with those collected in this study. Sediment and seawater samples were also collected during clam sampling. Concentrations of selected metals were determined in the sediment and seawater samples. Concentrations of Ba, Ca, K, Mg, P, and Sr were affected significantly (p

The objective of this study was to investigate Pb bioaccumulation in clams (Meretrix meretrix) living in different salinities. Several hundred clams and samples of sediment and seawater were collec...

In this study, we report that the steroid extract 5alpha, 8alpha-epidioxycholest-6-ene-3beta-ol (MME) from Meretrix meretrix has the ability to inhibit growth of hepatoma cells and to induce G1-phase cell cycle arrest in two human hepatoma cell lines, HepG2 and Hep3B. HepG2 cells were more sensitive than Hep3B to MME. The extract markedly up-regulated the expression of p53 and p21WAF1/CIP1 in HepG2, suggesting that MME-induced G1 phase cell cycle arrest in HepG2 might be p53-dependent. Therefore, the up-regulation of p27KIP1and p16INK4A in both cell lines indicates that a p53-independent pathway might be involved in the mechanism of MME inducing cell cycle arrest. In conclusion, MME induces G1 phase cell cycle arrest via both p53-dependent and p53-independent pathways.

The tidal rhythms for changes in morphology, length, dry weight and protein content of the crystalline style are studied in two venerid clams,Meretrix meretrix andKatelysia opima and in a donacid clam,Donax cuneatus. In the two venerid clams the style is housed in a sac conjoined with midgut and there is a tidal rhythm of feeding and extracellular digestion involving a partial dissolution of the style in the ebb tide and reformation in flood tide. But in the donacid clam where the style sac is completely separated from midgut, no detectable changes in the style parameters are recorded during a tidal cycle. However, the rhythmicity in feeding activity is indicated, by the presence of ‘mudcap’ and food particles in the style during flood tide and their subsequent absence during ebb tide. Hence the tidal rhythm of feeding and digestion inDonax cuneatus may be without corresponding changes in the crystalline style. Also this study throws light on the mode of style dissolution.

A comparative study of the pH of crystalline style, digestive diverticula and stomach fluid in six bivalve species,Anadara rhombea, Crassostrea madrasensis, Meretrix meretrix, M. casta, Katelysia opima andDonax cuneatus revealed that the digestive diverticula are more acidic while crystalline style is either slightly acidic or nearly neutral. The significance of this finding is discussed. In vitro dissolution of crystalline style of all the six species in buffer solutions of varying pH from 3·6 to 9·0 was observed and the study indicated that the optimum pH for style dissolution is around 8·0 in all species exceptingDonax cuneatus where some dissolution was recorded only at pH 9·0. Based on the physical changes observed in the style, a mechanism of style dissolution has been put forward.

Accumulation and excretion of crude- and prep'd-106Ru by the clam, Meretrix meretrix lusoria, were investigated under laboratory conditions. Accumulation of 106Ru by the clam reached equilibrium approximately 2 weeks after immersion in sea water. The radioactivity ratio of prepared ruthenium-106 complexes was higher than that of the crude ones. After 100 days of uptake experiment, radioactivity ratio of the edible part with both chemical forms showed less than 5.0. The highest radioactivity ratio was observed in mid gut gland, which was about an order of 40. And approximately 30% of the total radioactivity accumulated in whole soft tissues was concentrated in mid gut gland which occupies only 7% to the whole soft tissues in weight. The concept of the specific surface area should be taken into consideration for the tissues which contact directly with environmental sea water. In both chemical forms of prep'd-106Ru, approximately 25% of accumulated radioactivity was lost from the whole body of the living clam during 40 days of loss experiment. The biological half lives of the short component and the long component were 49 days and 167 days respectively for prep'd-106Ru•Clx, while 39 days and 121 days were for prep'd-106RuNO•Clx. The radioactivity loss from the whole body of the living clam observed in the initial stage was attributable to the physiological activity of the living clam through the metabolic pathway, because the affinity of 106Ru with the surface of the shell or the tissues seemed to be fairly tight.

1. The action of thiamine and related compounds on the isolated heart of clam (Meretrix meretrix lusoria) was investigated.2. S-benzoylthiamine (SBT) and thiamine propyl disulfide (TPD) among these related compounds displayed a very remarkable positive inotropic action, whereas thiamine, acetylthiamine, thiamine diphosphate, thiamine triphosphate, benzoylthiamine monophosphate and ATP did not practically display any clear action.3. SBT and TPD showed a remarkable antagonistic action against the negative inotropic action of acetylcholine, but have no effect on the action of 5-hydroxytryptamine.4. The positive inotropic action of SBT and TPD was retained in K-free medium, but it completely disappeared in Na-free or Cafree medium. When more or less Na+ or Ca2+ was present in the medium, the action of SBT and TPD appeared as in the normal medium.5. The positive inotropic action of SBT and TPD, therefore, is believed to be closely related to the transport system of the cellular membrane of the clam heart muscle, in which Na+ and Ca2+ are involved.

Non-heat-coagulable protein was isolated from muscle extracts of Meretrix meretrix, Mactra sulcataria, and Atrina Japonicum, respectively. Content of this proteinous material in muscle as well as contents of nitrogen and reducing substance in the material was estimated (Table 1). The paper-electrophoretic analysis revealed that the material consisted at least of three subfractions with different mobilities. From these three, one having zero mobility was precipitated with acetic acid. It was found furthermore that the heat-coagulable components of muscle extracted with a buffer solution of low ionic strength (μ=0.1, pH 7.8)turned noncoagulable when dialyzed for short time (about 3 hours) against the same buffer solution as the above extractant. Whereas the paper-electrophoretic behaviours remained unchanged after such dialysis, the coagulability of these comppnents changed to a high degree. These non-coagulable matters were found to be of low mobility, while the coagulated porteins showed no mobility as expected. Molecular event leading to the said loss of coagulability is not clear as yet, though the loss seems to be connected mcre or less intimately with pH of the dialysate.

1. 1. An adenosine aminohydrolase was extracted from the mid-gut gland of the clam, Meretrix meretrix lusoria (Gmelin), in a highly purified form which, though heat-labile, could be stored over a month at 0°C without losing the specific activity amounting to 750-fold. 2. 2. The preparation catalysed the reaction of the first order, with the activation energy of 14,600 cal under the experimental conditions, showing the velocity constant of 13·18 × 10 −2 min −1 . 3. 3. A sharp optimum was found at pH 5·0. The Michaelis-Menten constant was 6·9 × 10 −5 M at 26°C at the optimal pH. 4. 4. This enzyme specifically decomposes adenosine and deoxyadenosine. Mercury, either metallic or organic, and fluoride inhibit the enzymatic reaction, though many common agents are not foond effective.

1. 1. A precipitate of water-homogenized midgut gland was suspended in 3 M NaCl, heat-shocked (50°C, 5 min), dialyzed against 0·2 M NaCl and suspended in 3 M NaCl to obtain a preparation with 17·7-fold activity of dephosphorylating 5′-AMP. 2. 2. It decomposed 2′-, 3′- and 5′-AMP, 5′-dAMP, 5′-UMP, 5′-IMP, 5′-GMP, 5′-CMP, 5′-ADP, ATP, β-glycerophosphate and p- nitrophenyl phosphate at pH 8·8, but did not attack l -α-lecithin and sodium creatine phosphate.

1. 1. Phosphohydrolytic activity was studied in the homogenized mid-gut gland tissue, using nucleotides (5′-AMP, 3′-AMP, 5′-IMP and GMP) and β-glycerophosphate as substrates. 2. 2. For nucleotides there were two optima of pH (8·5–9·7, 4·0–4·2). For β-glycerophosphate the activity was restricted to the alkaline region (pH 9·5).

The present study aims to make contributions to our knowledge, now rather scanty, of various effects of chemicals in the medium on pisces and mollusca living in. Cyprinus carpio L., Anguilla japonica and Meretrix meretrix (L.), were kept in water in which various chemical substances were dissolved with varying concentrations, and their responses were observed. According to the degree of the responses, the chemical substances employed may be arranged in discending order as follows: metallic salts (such as cupper sulphate, zinc sulphate and lead nitrate), acids and alkalis (such as sulphuric acid, sulphurous acid, ammonia and sodium carbonate) and the others (neutral salts such as salts of alkali metals and alkali earth metals).

Chemical composition and some physicochemical properties were studied on the body fluid which flow out from the body of Meretrix meretrix, Paphia philippinarum and Mactra sulcataria when the shells were removed. Each the liquid taken from the shells given above containes no taurine but betaine, and three kinds of picrates were isolated from monoaminofraction. The picrate deeived from Paphia is identical with oxyproline picrate. The melting point of picrates from Meretrix and Mactra is 260-262°C, 260°C, and nitrogene content 17.1%, 20.8%, respectively. The melting point of benzoyl deriva ive of the matter taken out from the picrate of Mactra is 172-173°C, and ninhydrine reaction assumed a deep blue violet colour.

1. 1. F-actin was directly isolated from adductor muscle of the clam Meretrix meretrix by the method of Szent-Gyorgyi and his associates (1970). The purity of F-actin was approximately 20 per cent. The preparation contained a number of spherical particles of about 250 A in diameter. 2. 2. Clam F-actin was rather stable in 0·1 M KC1, pH 8·0 or in 0·04 M KC1, pH 6·0. 3. 3. Clam F-actin was very heterogeneous in particle length, the number-average length: 0·24 μ and the weight-average length: 1·07 /gm. 4. 4. Trypsin treatment resulted in an appreciable digestion of F-actin particles. F-actin became short in length by sonication, but the recovery of length after sonication was slow and incomplete.

The ciliary movement of the gills of Meretrix meretrix (LINNE) as studied by the method of NOMURA and TOMITA in sea water, with its density 1•0200 at 15C, is shown in Fig. 1. The maximum value 1.27cm/min was got at a temperature 25.5C. The movement in question was almost null at temperatures 1•5°C and 41°C.