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Background: The hard clam Mercenaria mercenaria is an important seafood species widely exploited along the eastern coasts of the United States and play a crucial role in coastal ecology and economy. Severe hard clam mortalities have been associated with the protistan parasite QPX (Quahog Parasite Unknown). QPX infection establishes in pallial organs with the lesions typically characterized as nodules, which represent inflammatory masses formed by hemocyte infiltration and encapsulation of parasites. QPX infection is known to induce host changes on both the whole-organism level and at specific lesion areas, which imply systemic and focal defense responses, respectively. However, little is known about the molecular mechanisms underlying these alterations. Results: RNA-seq was performed using Illumina Hiseq 2000 (641 Million 100 bp reads) to characterize M. mercenaria focal and systemic immune responses to QPX. Transcripts were assembled and the expression levels were compared between nodule and healthy tissues from infected clams, and between these and tissues from healthy clams. De novo assembly reconstructed a consensus transcriptome of 62,980 sequences that was functionally-annotated. A total of 3,131 transcripts were identified as differentially expressed in different tissues. Results allowed the identification of host immune factors implicated in the systemic and focal responses against QPX and unraveled the pathways involved in parasite neutralization. Among transcripts significantly modulated upon host-pathogen interactions, those involved in non-self recognition, signal transduction and defense response were over-represented. Alterations in pathways regulating hemocyte focal adhesion, migration and apoptosis were also demonstrated. Conclusions: Our study is the first attempt to thoroughly characterize M. mercenaria transcriptome and identify molecular features associated with QPX infection. It is also one of the first studies contrasting focal and systemic responses to infections in invertebrates using high-throughput sequencing. Results identified the molecular signatures of clam systemic and focal defense responses, to collectively mediate immune processes such as hemocyte recruitment and local inflammation. These investigations improve our understanding of bivalve immunity and provide molecular targets for probing the biological bases of clam resistance towards QPX. [ABSTRACT FROM AUTHOR]

Quahog Parasite Unknown (QPX) is a fatal protistan parasite that causes severe losses in the hard clam ( Mercenaria mercenaria ) fisheries along the northeastern coast of the US. Field and laboratory studies of QPX disease have demonstrated a major role for water temperature and M. mercenaria genetic origin in disease development. Infections are more likely to occur at cold temperatures, with clam stocks originating from southern states being more susceptible than clams from northern origin where disease is enzootic. Even though the influence of temperature on QPX infection have been examined in susceptible and resistant M. mercenaria at physiological and cellular scales, the underlying molecular mechanisms associated with host–pathogen interactions remain largely unknown. This study was carried out to explore the molecular changes in M. mercenaria in response to temperature and QPX infection on the transcriptomic level, and also to compare molecular responses between susceptible and resistant clam stocks. A M. mercenaria oligoarray (15 K Agilent) platform was produced based on our previously generated transcriptomic data and was used to compare gene expression profiles in naive and QPX-infected susceptible (Florida stock) and resistant (Massachusetts) clams maintained at temperatures favoring disease development (13 °C) or clam healing (21 °C). In addition, transcriptomic changes reflecting focal (the site of infection, mantle) and systemic (circulating hemocytes) responses were also assessed using the oligoarray platform. Results revealed significant regulation of multiple biological pathways by temperature and QPX infection, mainly associated with immune recognition, microbial killing, protein synthesis, oxidative protection and metabolism. Alterations were widely systemic with most changes in gene expression revealed in hemocytes, highlighting the role of circulating hemocytes as the first line of defense against pathogenic stress. A large number of complement-related recognition molecules with fibrinogen or C1q domains were shown to be specially induced following QPX challenge, and the expression of these molecules was significantly higher in resistant clams as compared to susceptible ones. These highly variable immune proteins may be potent candidate molecular markers for future study of M. mercenaria resistance against QPX. Beyond the specific case of clam response to QPX, this study also provides insights into the primitive complement-like system in the hard clam. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate the antibacterial properties of oyster, hard clam, and sea urchin shell powders as a result of calcination. After subjection to calcination at 1050 °C for 2 h, and as identified by FTIR and XRD spectra, the structures of oyster, hard clam, and sea urchin shell powders were mainly transformed into calcium oxide, with slight amounts of calcium hydroxide. Metal content testing revealed no detectable harmful heavy metals, and showed rich content of trace elements including Ba, Sr, Mg, and Mn. To evaluate their antibacterial properties, activity against five foodborne microorganisms was assessed using the disk diffusion method, which indicated the presence of antibacterial activity in these products at a concentration of 1 %. These results indicate antibacterial potential for oyster, hard clam, and sea urchin shell powders after subjection to calcination. [ABSTRACT FROM AUTHOR]

Size-frequency distributions of Meretrix lusoria, a commercially important bivalve in Japan, were compared among 6 sites in tidal flats of a small river in Kafuri Bay, northern Kyushu, Japan during 2006-2008. In Kafuri Bay, the hard clam resource is strictly managed and mean biomass of this species on the fishing ground (about 1.5 km) exceeded 1.5 kg m in 2008. Small clams (<5 mm in shell length, SL) were most abundant in the border area between the river and the sea, while large clams (>40 mm SL) were rare there. In contrast, in the lower site of the marine area (site L), most clams were >30 mm SL. These results indicate that small clams move from riverine to marine areas with growth (post-settlement movement). Year-round, very small clams (<1 mm SL) were present and clams that were 2-5 mm SL were very rare, although the spawning season is thought to occur in summer. Probably, the early growth of many new recruits is very slow and most may even be <1 mm SL in the next spring, although some clams grow to >5 mm SL in a short period of time. [ABSTRACT FROM AUTHOR]

Abstract: QPX (Quahog Parasite Unknown) is a protistan parasite affecting hard clams (Mercenaria mercenaria) along the Northeast coast of the United States. The fact that QPX disease epizootics are usually observed in field sites with high salinities led to the general assumption that salinity represents an important factor for disease distribution. This study was designed to investigate the effect of salinity on QPX disease development as well as constitutive and QPX-induced defense factors in M. mercenaria. Naïve and QPX-infected (both experimentally and naturally) clams were submitted to 17 and 30psu for 4months. Standard and QPX-specific cellular and humoral defense parameters were assessed after 2 and 4months. These included total and differential hemocyte counts, reactive oxygen species production, phagocytic activity of hemocytes, lysozyme concentration in plasma, anti-QPX activity in plasma and resistance of hemocytes to cytotoxic QPX extracellular products. Results demonstrated higher QPX-associated mortality in naturally infected clams maintained at high salinity compared to those held at 17psu. Our findings also showed an increase in mortality following experimental challenge with QPX in clams submitted to 30psu but not in those held at 17psu. Constitutive clam defense factors and the response to QPX challenge were also affected by salinity. QPX challenge caused significant but transitory changes in hemolymph parameters that were obvious at 2months but disappeared at 4months. Overall, our results show that salinity modulates clam immunity and the progress of QPX disease although its impact appears secondary as compared to findings we reported earlier for temperature. [Copyright &y& Elsevier]

LPS-induced TNF-α (LITAF) is a novel transcriptional factor that mediates the expression of inflammatory cytokines in LPS-induced processes. In the present study, the full-length cDNA encoding LITAF (designated as Mm-LITAF) was identified from Asiatic hard clam, Meretrix meretrix, by expressed sequence tag and rapid amplification of cDNA ends (RACE) approaches. The full-length cDNA of Mm-LITAF was 1653 bp, consisting of a 5′ untranslated region (UTR) of 91 bp, a 3′UTR of 1166 bp with one cytokine RNA instability motif (ATTTA) and one polyadenylation signal (AATAAA), and an open reading frame (ORF) of 396 bp encoding a polypeptide of 131 amino acids with a theoretical isoelectric point of 7.49, and predicted molecular weight of 14.47 kDa. The deduced amino acid of Mm-LITAF shared 29-63% similarity with the LITAFs from other species, indicating that Mm-LITAF should be a member of the LITAF family. Two highly conserved CXXC motifs forming a compact Zn-binding structure were also identified in Mm-LITAF. A quantitative reverse transcriptase real-time PCR (qRT-PCR) assay was developed to assess the expression of Mm-LITAF mRNA in different tissues, and the temporal expression of Mm-LITAF in clams challenged with Vibrio anguillarum. The mRNA transcript of Mm-LITAF could be detected in all the examined tissues with the highest expression level in the gill. Mm-LITAF expression was up-regulated significantly at 16 h in the gill and at 8 h in haemocytes after bacterial challenge, respectively. These results suggest that the Mm-LITAF is a constitutive and inducible acute-phase protein that perhaps involved in the innate immune response of hard clam. [ABSTRACT FROM AUTHOR]

Abstract: Quahog Parasite Unknown (QPX) is a protistan parasite affecting hard clams Mercenaria mercenaria along the Northeastern coast of the United States. The geographic distribution and occurrence of disease epizootics suggests a primary role of temperature in disease development. This study was designed to investigate the effect of temperature on constitutive and QPX-induced defense factors in M. mercenaria. Control and QPX-challenged (both experimentally and naturally) clams were maintained at 13, 21 and 27°C for 4months. Control and experimentally-infected clams originated from a southern broodstock (Florida, no prior reports of disease outbreak) while naturally-infected clams originated from a northern broodstock (Massachusetts, enzootic area). Standard and QPX-specific cellular and humoral defense parameters were assessed after 2 and 4months. Measured parameters included total and differential hemocyte counts, reactive oxygen species production, phagocytic activity of hemocytes, lysozyme concentration in plasma, anti-QPX activity in plasma and resistance of hemocytes to cytotoxic QPX extracellular products. Results demonstrated a strong influence of temperature on constitutive clam defense factors with significant modulation of cellular and humoral parameters of control clams maintained at 13°C compared to 21 and 27°C. Similarly, clam response to QPX challenge was also affected by temperature. Challenged clams exhibited no difference from controls at 27°C whereas different responses were observed at 21°C and 13°C compared to controls. Despite differences in infection mode (experimentally or naturally infected) and clam origin (northern and southern broodstocks), similarities were observed at 13°C and 21°C between QPX infected clams from Florida and Massachusetts. Clam response to temperature and to QPX exhibited interesting relationship with QPX disease development highlighting major influence of temperature on disease development. [Copyright &y& Elsevier]

Abstract: Quahog Parasite Unknown (QPX) causes disease and mortality in hard clams, Mercenaria mercenaria. Seasonality of QPX disease prevalence in the field and changes in QPX growth and survival in vitro suggest a role of temperature in the hard clam-QPX interaction and disease development. This study specifically examined the effect of temperature on QPX disease development and dynamics. Naturally and experimentally infected clams were separately maintained in the laboratory at 13°C, 21°C, or 27°C for 4months. Following this initial treatment, temperature was adjusted to 21°C for 5 additional months to simulate seasonal changes of temperature in the field and to investigate the effect of temperature variations on QPX disease dynamics. Mortality was continuously monitored during the experiment and clams were sampled at 2, 4 and 9months for the assessment of QPX disease prevalence and intensity using our standard histological and quantitative PCR techniques. Results demonstrated significantly higher QPX disease prevalence and intensity, as well as higher mortality, in naturally-infected clams maintained at 13°C as compared to those held at 21°C or 27°C. Similarly, disease development was significantly higher in experimentally infected clams maintained at the colder temperature (70% prevalence after 4months) as compared to those maintained under warmer conditions (<10%). Additionally, our results demonstrated an improvement in the condition of clams initially maintained at 13°C for 4months after transfer to 21°C for 5 additional months, with a significant reduction of QPX prevalence (down to 19%). Interestingly, disease development or healing in clams maintained at different temperatures exhibited a strong relationship with clam defense status () and highlighted the impact of temperature on clam activity and QPX disease dynamics. These findings should be taken into account for the timing of activities involving the monitoring, movement (e.g. relays, transplants) or grow out (e.g. commercial culture, municipal enhancement) of hard clams in enzootic areas. [Copyright &y& Elsevier]

Abstract: Strombine dehydrogenase (SDH, EC 1.5.1.22) from the foot of the hard clam Meretrix lusoria was purified over 470-fold to apparent homogeneity. It has a monomeric structure with a relative molecular mass of 46,000. Two isoenzymes were identified with isoelectric points of 6.83 and 6.88. SDH is heat labile, and has pH and temperature optima of 7.4–7.6 and 45–46°C, respectively. l-Alanine, glycine, and pyruvate are the preferred substrates. l-Serine is the third preferred amino acid. Iminodiacetate with the lowest Ki of SDH at both pH 6.5 and 7.5 was the strongest inhibitor among succinate, acetate, iminodiacetate, oxaloacetate, and l-/d-lactate. The inhibitory activities of succinate at pH 6.5, and iminodiacetate and oxaloacetate at pH 7.5 on the SDH were higher. These inhibitors are either competitive or mixed-competitive inhibitors. Half of the enzymatic activity of SDH was inhibited by 0.2mM Fe3+ and 0.6mM Zn2+. [ABSTRACT FROM AUTHOR]

The article discusses a study which determined the size-dependent pH effect on calcification in post-larval hard clam Mercenaria spp. using the alkalinity anomaly method. In the study, experimental water acidity was controlled by bubbling with air-carbon dioxide blends to obtain pH values of 8.02, 7.64 and 7.41, which are typically found in many near-shore terrigenous marine sediments. The study found that calcification rate decreased with lower pH in all 5 classes measured, and also a significant effect of size on calcification rate.

The purpose of this article is to provide a risk-based predictive model to assess the impact of false mussel Mytilopsis sallei invasions on hard clam Meretrix lusoria farms in the southwestern region of Taiwan. The actual spread of invasive false mussel was predicted by using analytical models based on advection-diffusion and gravity models. The proportion of hard clam colonized and infestation by false mussel were used to characterize risk estimates. A mortality model was parameterized to assess hard clam mortality risk characterized by false mussel density and infestation intensity. The published data were reanalyzed to parameterize a predictive threshold model described by a cumulative Weibull distribution function that can be used to estimate the exceeding thresholds of proportion of hard clam colonized and infestation. Results indicated that the infestation thresholds were 2–17 ind clam−1 for adult hard clams, whereas 4 ind clam−1 for nursery hard clams. The average colonization thresholds were estimated to be 81–89% for cultivated and nursery hard clam farms, respectively. Our results indicated that false mussel density and infestation, which caused 50% hard clam mortality, were estimated to be 2,812 ind m−2 and 31 ind clam−1, respectively. This study further indicated that hard clam farms that are close to the coastal area have at least 50% probability for 43% mortality caused by infestation. This study highlighted that a probabilistic risk-based framework characterized by probability distributions and risk curves is an effective representation of scientific assessments for farmed hard clam in response to the nonnative false mussel invasion. [ABSTRACT FROM AUTHOR]

The ability of pathogens to neutralize host defence mechanisms represents a fundamental requisite in the successful establishment of an infection. Host-pathogen interactions between quahog parasite unknown (QPX) and its hard clam host are poorly understood. Our prior in vivo investigations have shown that different QPX isolates display varying levels of pathogenicity toward clams. Similarly, field investigations and laboratory transmission studies revealed some variations in the susceptibility of different hard clam stocks to QPX infection. An in vitro approach was developed in this study to evaluate the toxicity of QPX cells and extracellular products toward haemocytes using a neutral red uptake assay. Results demonstrated that QPX produces virulence factors that are cytotoxic to M. mercenaria haemocytes. This cytotoxicity appears to be induced by clam factors, suggesting that it may play an important role in supporting QPX infection and proliferation within the host. Moreover, application of this technique to different QPX isolates and clam broodstocks indicates variations of QPX cytotoxicity in agreement with previous in vivo experiments, strengthening the existence of different QPX strains. [ABSTRACT FROM AUTHOR]

The article focuses on the variation in hard clam Mercenaria mercenaria reproduction relative to changes in the species composition of the phytoplankton abundance in the U.S. It tests the hypothesis that the fall in the population of hard clam in south shore bays in Long Island, New York was attributed to the alterations in reproduction brought by variations in phytoplankton availability as food resource. It notes that changes in the number, species composition, or timing of phytoplankton blooms can change the quantity and quality of the food available to the suspension-feeding hard clams. It adds that such alterations in food supply can decrease the energy available to adult hard clams.

During the last several decades, the waters of mid Narragansett Bay, Rhode Island have increased in temperature and decreased in chlorophyll concentration, and it is possible that these changes affected the growth and success of a common benthic filter feeder, the hard clam, Mercenaria mercenaria. We determined recent hard clam growth rates through a sclerochronological analysis and compared them to the rich historical record of Narragansett Bay growth rates in order to understand how these opposing changes influenced hard clam growth. We found no significant differences in short-term growth between 1985 and 2000. Long-term juvenile growth showed a significant decrease between the 1960s and 1990s, while long-term adult (mature) growth showed a significant increase over this same time period. While it is not clear why the changes in juvenile and adult growth rates differ, it appears as though the decrease in chlorophyll concentration, together with a change in phytoplankton community composition, increasing water temperature, and an increase in predator abundance, may all have influenced hard clam growth between the 1960s and the 1990s. [ABSTRACT FROM AUTHOR]

Abstract: The meat of hard clam was extracted using hot water. The residual meat was freeze-dried then hydrolyzed at 50°C for 5h by Protamex (PX). The inhibitory effects of hot water extract and hydrolysate against angiotensin I converting enzyme (ACE) were investigated. The IC50 value of hot water extract and hydrolysate on ACE were 1.090 and 0.036mg/ml, respectively. The PX hydrolysate was separated into five fractions by size exclusion chromatography on a Sephadex G-25 column. The fifth fraction of the hydrolysate having molecular weight ranged 350–300Da showed the highest inhibitory efficiency ratio (IER) being 5831%/(mgml). The amino acid sequence of the inhibitory peptide was Tyr-Asn (IC50 =51μM). The hydrolysate showed mixed-type inhibition kinetics while Captopril, the positive control, showed competitive inhibition on ACE. Their K i values were 0.027mg/ml and 0.0067μg/ml, respectively. [Copyright &y& Elsevier]

Abstract: The Lt50 (median lethal time) of hard clam Meretrix lusoria exposed to anoxia was 15.7, 9.7, 3.8, 2.8, and 2.5 days at 15, 20, 25, 30, and 34 °C, respectively. The concentration of alanine and succinate was 5.6 and 0.6 μmol/g in the foot, and the concentration of succinate was 1.6 μmol/ml in the body fluid for the clams following 5 days exposure to normoxia at 30 °C. However, the concentration of alanine, succinate, and propionate was 15.6, 9.7, and 1.4 μmol/g in the foot, and 0.58, 35.3, and 3.66 μmol/ml in the body fluid, respectively for the clams following 5 days anoxic exposure at 30 °C. Clams secreted 97.9 nmol/g of succinate, and 76.7 nmol/g of propionate during the anoxic exposure at 30 °C. Similarly, the concentration of alanine, succinate, and propionate was 14.2, 8.9, and 1.3 μmol/g in the foot, and 0.27, 37.9, and 6.1 μmol/ml in the body fluid for the clams following 8 days exposure to anoxia at 15 °C. Clams secreted 18.9 nmol/g of succinate and 103 nmol/g of propionate during anoxic exposure at 15 °C. Clams that were visible at the surface of the sediment (half-buried or fully exposed) showed significantly higher concentration of alanine in the foot, and concentration of succinate in the body fluid than those completely buried in the sediment. It is suggested that the concentration of alanine in the foot greater than 11 μmol/g and the concentration of succinate in the body fluid greater than 4 μmol/ml are considered indicators of hypoxia in hard clams. [Copyright &y& Elsevier]

Predator–prey interaction in aquatic ecosystem is one of the simplest drivers affecting the species population dynamics. Predation controls are recognized as important aspects of ecosystem husbandry and management. In this paper we investigated how predation control cause an increase in host growth in the abundance of hard clam (Meretrix lusoria) populations subject to mercury (Hg)-stressed birnavirus. Here we linked predator–prey relationships with a bioenergetic matrix population model (MPM) associated with a susceptible–infectious–mortality (SIM) model based on a host–pathogen–predator framework to quantify the predator effects on population dynamics of disease in hard clam populations. Our results indicated that relative high predation rates could promote the hard clam abundances in relation to predators that selectively captured the infected hard clam, by which the disease transmission was suppressed. The results also demonstrated that predator-induced modifications in host behavior could have potential negative or positive effects on host growth depending on relative species density and resource dynamics. The most immediate implication of this study for the management of aquatic ecosystem is that, beyond the potential for causing a growth in abundance, predation might provoke greater predictability in aquatic ecosystem species populations and thereby increase the safety of ecosystem production from stochastic environmental events. [Copyright &y& Elsevier]

Abstract: The clam industry is very important for fishermen in the southwestern part of Taiwan. However, massive die-offs of hard clams unexpectedly and frequently occur during the hot season. This greatly impacts the economic status of these fishermen. Hard clams are benthic organisms, but they usually emerge from the bottom mud after becoming stressed and before dying. Therefore, the digging behavior of hard clams can be used as an indicator of their vitality. In a previous 2-h digging experiment, we found that the concentration of Mg+2 in seawater affected the digging behavior of hard clams. This led us to question whether the salt composition of the seawater had changed and how such changes affected the digging behavior of clams. The percentages of divalent cations in refined salt, crude salt, and saline water from a salt farm and groundwater were much lower than those in artificial seawater (ASW). The salt composition of seawater can be changed by adding those salts or saline water. Hard clams in Mg+2-free ASW and K+-free ASW remained in the sediments at 15 °C, while they emerged at 34 °C. After the inclusion of Mg+2 into the Mg+2-free ASW, hard clams returned to the sediments. All of the hard clams died after being exposed to K+-free ASW for 5 days at 34 °C. Anaerobic end products in the foot (alanine and succinate) and hemolymph (succinate and propionate) of hard clams accumulated after they were exposed to Mg+2-free ASW. This indicates that Mg+2-free ASW induced cellular hypoxia as well as affecting the digging behavior. A possible mechanism of why Mg+2-free ASW causes hard clams to emerge is discussed. Finally, it was concluded that the concentrations of Mg+2 and K+ in ASW are especially important for the vitality of hard clams at high temperatures. [Copyright &y& Elsevier]

Abstract: We conducted a two-year study to assess how plankton composition and water quality impacts the distribution, densities, condition, growth, biochemical composition and reproductive success of juvenile and adult Mercenaria mercenaria (L.) in Long Island''s south shore estuaries (LISSE). Juvenile and adult hard clams were placed in suspended cages at 10 locations ranging from the ocean inlets to locations furthest from inlets in Shinnecock Bay (SB), the eastern-most barrier island estuary of LISSE, and Great South Bay (GSB), the western-most barrier island estuary of LISSE. Phytoplankton community composition, temperature, salinity, dissolved oxygen, and clam growth and condition were monitored bi-weekly. A benthic survey of M. mercenaria densities in both estuaries was also conducted. In both 2004 and 2005, juveniles in central bay locations had significantly faster growth rates, lower mortality rates, and higher lipid content relative to sites closest to the inlets. Adult hard clams closest to the Fire Island inlet also had significantly lower condition indexes compared to mid-bay stations and densities of wild M. mercenaria populations in both estuaries were lower near inlets compared to locations further from inlets. In addition to substantial spatial differences within each estuary, differences were also observed between the embayments as juvenile clams in SB grew approximately twice as fast as those in GSB and adults in SB had significantly greater condition indexes than clams in GSB. Instantaneous juvenile growth rates were highly correlated to temperatures below 24 °C (p <0.0001) and were also significantly correlated with several indicators of suspended food quantity and food quality (centric diatoms, phytoplankton cells >5 μm, and dinoflagellates (inverse correlation)) which co-varied independently of temperature. In sum, these results suggest tidal exchange in LISSE promotes a water quality regime (cold water, with low food concentration) which would reduce the growth of juvenile clams and the overall reproductive success of adult hard clams located near newly-formed ocean inlets. However, increased exchange for regions furthest from inlets could enhance juvenile clam growth rates by reducing summer peak temperatures (>24 °C) and densities of poor food sources (dinoflagellates). [Copyright &y& Elsevier]

Abstract: Hard clams (HC), Meretrix lusoria are a popular seafood and traditionally used as a Chinese remedy for liver disease and chronic hepatitis. The goal of this study was to identify compounds from hard clam, which are responsible for inducing apoptosis using bioassay-directed isolation. The effects of ethyl acetate extract of HC (HC-EA) on cell viability in human cancer cells were investigated. The ethyl acetate fraction was then subjected to separation and purification using silica gel column chromatography. The compounds showing strong apoptosis inducing activity were identified by spectral methods as epidioxysterols (EDS). The molecular mechanisms of epidioxysterolds-induced apoptosis as determined by annexin V apoptosis assay, DNA condensation, and sub-G1 DNA were investigated. The results suggest that induction of apoptosis by epidioxysterols may provide a pivotal mechanism for its cancer chemoprevention. [Copyright &y& Elsevier]

Abstract: The purpose of this study was to assess the effects of mercury (Hg) on birnavirus infection in the farmed hard clam (Meretrix lusoria) populations. A stage-structured matrix population model was linked with a nonlinear epidemiological dynamics of host–pathogen model to quantify the effects of increased Hg-stressed birnavirus on population dynamics of disease in hard clam populations. Bioenergetics was incorporated into population stage-structured model to enhance life cycle toxicity assessment on constraining reproduction and growth in life stages of hard clams. We delineated three qualitatively distinct scenarios of virus only, Hg+virus, and virus+Hg. Within a range of disease transmissibility drawn from analysis of Hg-stressed birnavirus in hard clams, different transmissibility led to simulated outbreaks characterized by basic reproductive number (R 0) depicting the allowance population numbers to contain disease spread for all three scenarios. This study suggested that recognizing which of the scenarios best describing a situation in the field could aid in planning disease management and in choosing the most efficient and feasible strategy. The present simple model captured the essential dynamics and its flexible enough to integrate effects occurring at varying temporal scales based on biologically plausible and empirically grounded dynamical models. We were confident that the model could be easily adapted for other aquaculture species and encourage researchers to use the model to diagnose the population-level risk of toxic chemical-stressed pathogen on these species. [Copyright &y& Elsevier]

Abstract: The objective of this study was to determine whether metallothionein (MT) expression was related to Cd accumulation in hard clams (Meretrix lusoria). We cloned clam MT. Then a specific primer for the hard clam was designed for MT mRNA measurements using real-time PCR. The hard clams were exposed to 50, 200, and 1000 μg/L cadmium (Cd) for 1, 3, 5, and 7 days, to determine the relationship between MT mRNA relative quantity (RQ) levels and Cd accumulation. The following results were obtained: (1) the cloned MT, consisting of 228 bp encoding a protein of 76 amino acids showed higher than 55% identity with the deduced amino acid sequence previously published for another bivalve. (2) Both MT mRNA expression and Cd accumulation appeared to be dose-responsive following cadmium treatment for 1, 3 and 5 days, respectively; however, no time-dependent responses were found. According to these results, MT mRNA expression levels can be used as an indicator to monitor the concentrations of Cd in aquaculture farms. [Copyright &y& Elsevier]