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Abstract Background The hard clam (Mercenaria mercenaria), a marine bivalve distributed along the U.S. eastern seaboard, supports a significant shellfish industry. Overharvest in the 1970s and 1980s led to a reduction in landings. While the transition of industry from wild harvest to aquaculture since that time has enhanced production, it has also exacerbated challenges such as disease outbreaks. In this study, we developed and validated a 66K SNP array designed to advance genetic studies and improve breeding programs in the hard clam, focusing particularly on the development of markers that could be useful in understanding disease resistance and environmental adaptability. Results Whole-genome resequencing of 84 individual clam samples and 277 pooled clam libraries yielded over 305 million SNPs, which were filtered down to a set of 370,456 SNPs that were used as input for the design of a 66K SNP array. This medium-density array features 66,543 probes targeting coding and non-coding regions, including 70 mitochondrial SNPs, to capture the extensive genetic diversity within the species. The SNPs were distributed evenly throughout the clam genome, with an average interval of 25,641 bp between SNPs. The array incorporates markers for detecting the clam pathogen Mucochytrium quahogii (formerly QPX), enhancing its utility in disease management. Performance evaluation on 1,904 samples demonstrated a 72.7% pass rate with stringent quality control. Concordance testing affirmed the array's repeatability, with an average agreement of allele calls of 99.64% across multiple tissue types, highlighting its reliability. The tissue-specific analysis demonstrated that some tissue types yield better genotyping results than others. Importantly, the array, including its embedded mitochondrial markers, effectively elucidated complex genetic relationships across different clam groups, both wild populations and aquacultured stocks, showcasing its utility for detailed population genetics studies. Conclusions The 66K SNP array is a powerful and robust genotyping tool that offers unprecedented insights into the species’ genomic architecture and population dynamics and that can greatly facilitate hard clam selective breeding. It represents an important resource that has the potential to transform clam aquaculture, thereby promoting industry sustainability and ecological and economic resilience.

Background: The hard clam (Mercenaria mercenaria), a marine bivalve distributed along the U.S. eastern seaboard, supports a significant shellfish industry. Overharvest in the 1970s and 1980s led to a reduction in landings. While the transition of industry from wild harvest to aquaculture since that time has enhanced production, it has also exacerbated challenges such as disease outbreaks. In this study, we developed and validated a 66K SNP array designed to advance genetic studies and improve breeding programs in the hard clam, focusing particularly on the development of markers that could be useful in understanding disease resistance and environmental adaptability. Results: Whole-genome resequencing of 84 individual clam samples and 277 pooled clam libraries yielded over 305 million SNPs, which were filtered down to a set of 370,456 SNPs that were used as input for the design of a 66K SNP array. This medium-density array features 66,543 probes targeting coding and non-coding regions, including 70 mitochondrial SNPs, to capture the extensive genetic diversity within the species. The SNPs were distributed evenly throughout the clam genome, with an average interval of 25,641 bp between SNPs. The array incorporates markers for detecting the clam pathogen Mucochytrium quahogii (formerly QPX), enhancing its utility in disease management. Performance evaluation on 1,904 samples demonstrated a 72.7% pass rate with stringent quality control. Concordance testing affirmed the array's repeatability, with an average agreement of allele calls of 99.64% across multiple tissue types, highlighting its reliability. The tissue-specific analysis demonstrated that some tissue types yield better genotyping results than others. Importantly, the array, including its embedded mitochondrial markers, effectively elucidated complex genetic relationships across different clam groups, both wild populations and aquacultured stocks, showcasing its utility for detailed population genetics studies. Conclusions: The 66K SNP array is a powerful and robust genotyping tool that offers unprecedented insights into the species' genomic architecture and population dynamics and that can greatly facilitate hard clam selective breeding. It represents an important resource that has the potential to transform clam aquaculture, thereby promoting industry sustainability and ecological and economic resilience. [ABSTRACT FROM AUTHOR]

This study investigates the impact of various zinc supplementation methods on anemia in rats induced by phenylhydrazine (PHZ) and in 5/6-nephrectomized anemic rats. We compare oral zinc sulfate (ZnSO4) supplementation, oyster Crassostrea gigas supplementation, and hard clam Meretrix lusoria supplementation on red blood cell (RBC) levels. Oral zinc-rich oyster supplementation (2.70 mg Zn (30 g oyster)/day/rat) effectively corrects anemia in both experimental groups. Rats orally fed oysters for four days exhibit similar effectiveness as those receiving a single ZnSO4 injection (0.95 mg Zn (4.18 mg ZnSO4⋅7H2O)/rat). In contrast, oral ZnSO4 supplementation (2.70 mg Zn (11.88 mg ZnSO4⋅7H2O)/day/rat) does not significantly increase RBC levels, suggesting better zinc absorption from oysters. A placebo group of anemic rats supplemented with hard clams, similar in composition to oysters but much lower in zinc, did not change RBC counts. This supports oysters' high zinc content as the key to correcting anemia. Oysters also contain high iron levels, offering a potential solution for iron-deficiency anemia while supporting bone marrow erythropoiesis. In summary, oral oyster supplementation emerges as an effective strategy to correct anemia in rats with added zinc and iron support for erythropoiesis. [ABSTRACT FROM AUTHOR]

Marine bivalves are commonly affected by disseminated neoplasia of presumed hemocytic origin (i.e., hemic neoplasia and hemocytic neoplasia). Histopathology of 520 cultured hard clams (Mercenaria mercenaria) from Florida was performed for health surveillance over a consecutive 13-month period. Disseminated neoplasia was identified in 9 of 520 animals (1.7%). The neoplasia was characterized by the presence of large, round to oval, anaplastic cells within hemolymphatic vessels and sinusoids with variable infiltration into adjacent connective tissues of the visceral mass, mantle, foot, and/or adductor muscles. Frequent involvement and/or infiltration of the gill was also identified (5/9). Disseminated neoplasia in other species of clams, mussels, and cockles is considered a transmissible disease. At this time, it is unknown if these hard clams represent de novo development of the disease or potential transmission; however, this report expands both the geographic and host range for this condition. [ABSTRACT FROM AUTHOR]

Abstract Choice of microalgae diet affects production outcomes in bivalve hatcheries. This study aimed to identify an optimal microalgae diet to improve hard clam, Mercenaria mercenaria, juvenile production. Four microalgae species (Tisochrysis lutea, Pavlova lutheri, Chaetoceros gracilis and Cyclotella nana) in six dietary combinations were fed for 6 weeks; then, growth, survival and fatty acid profiles of juveniles were evaluated. The highest numerical growth and survival of juveniles were attained by feeding a tetra‐species microalgae diet, but no statistical difference was found by feeding bi‐ or tri‐species diets that consisted of a mix of flagellate and diatom microalgae. Significant differences in fatty acid profiles were found among clams fed different microalgae diets. A contrasting polyunsaturated fatty acid (PUFA) profile was found in juveniles fed flagellate‐ or diatom‐only diets. Clams fed flagellate‐only diets contained a higher percentage of docosahexaenoic acid (DHA) but a lower percentage of (n‐6) PUFAs, whereas those fed diatom‐only diets had a higher percentage of arachidonic acid (ARA) and eicosapentaenoic acid (EPA) but a lower percentage of DHA. In contrast, the percentage of EPA, DHA and ARA was neither very high nor very low in juveniles fed the tetra‐species diet. The complementary nutritional profile of the tetra‐species microalgae diet resulted in enhanced production and exhibited a more balanced fatty acid profile in clam tissue. The tetra‐species microalgae diet should be a preferable choice for feeding hard clam juveniles, but the cost of producing multiple microalgae species for hatchery/nursery operations should be taken into consideration as bi‐ and tri‐species diets provided statistically similar growth and survival. Results of this study can be used to improve productivity and profitability in M. mercenaria hatcheries.

Harmful algal blooms (HABs) such as those formed by the ichthyotoxic dinoflagellate, Margalefidinium (aka Cochlodinium) polykrikoides can have adverse effects on bivalves. While M. polykrikoides has caused significant die offs of bivalves and other marine organisms, the Northern quahog or hard clam, Mercenaria mercenaria, is comparatively more resistant to this HAB. This study quantified clearance rates of juvenile hard clams (10-20 mm) exposed to three different North American populations of M. polykrikoides (bloom, strain CP1, strain CPSB-1G) as well as the nonharmful cryptophyte, Rhodomonas salina and the nonharmful dinoflagellate, Gymnodinium aureolum, in single and mixed algal exposures. Multiple biovolume exposures with M. polykrikoides bloom water and R. salina (1,000, 1,500, 3,000 cells mL-1M. polykrikoides biovolume equivalent) were completed to assess the effects of increasing biomass on hard clam clearance rates and selection. Hard clams opened and actively cleared algal mixtures at and below 1,000 M. polykrikoides cells mL-1. During single species exposures, strain CPSB-1G and R. salina were cleared significantly faster than wild M. polykrikoides populations and strain CP1. During mixed exposures, R. salina was cleared significantly faster than CPSB-1G but not other M. polykrikoides populations and there was no difference between hard clam clearance rates of G. aureolum and R. salina. Clearance rates of M. polykrikoides at ≥1,500 cells mL-1M. polykrikoides/R. salina mixtures were not significantly different than zero unlike clearance of those at 1,000 cells mL-1) bloom densities. Given this, and the documented survival of hard clams during blooms, M. mercenaria may be candidate for aquaculture and restoration in regions prone to HABs caused by M. polykrikoides.

Abstract Background The hard clam Mercenaria mercenaria is a major marine resource along the Atlantic coasts of North America and has been introduced to other continents for resource restoration or aquaculture activities. Significant mortality events have been reported in the species throughout its native range as a result of diseases (microbial infections, leukemia) and acute environmental stress. In this context, the characterization of the hard clam genome can provide highly needed resources to enable basic (e.g., oncogenesis and cancer transmission, adaptation biology) and applied (clam stock enhancement, genomic selection) sciences. Results Using a combination of long and short-read sequencing technologies, a 1.86 Gb chromosome-level assembly of the clam genome was generated. The assembly was scaffolded into 19 chromosomes, with an N50 of 83 Mb. Genome annotation yielded 34,728 predicted protein-coding genes, markedly more than the few other members of the Venerida sequenced so far, with coding regions representing only 2% of the assembly. Indeed, more than half of the genome is composed of repeated elements, including transposable elements. Major chromosome rearrangements were detected between this assembly and another recent assembly derived from a genetically segregated clam stock. Comparative analysis of the clam genome allowed the identification of a marked diversification in immune-related proteins, particularly extensive tandem duplications and expansions in tumor necrosis factors (TNFs) and C1q domain-containing proteins, some of which were previously shown to play a role in clam interactions with infectious microbes. The study also generated a comparative repertoire highlighting the diversity and, in some instances, the specificity of LTR-retrotransposons elements, particularly Steamer elements in bivalves. Conclusions The diversity of immune molecules in M. mercenaria may allow this species to cope with varying and complex microbial and environmental landscapes. The repertoire of transposable elements identified in this study, particularly Steamer elements, should be a prime target for the investigation of cancer cell development and transmission among bivalve mollusks.

Microplastics and heavy metals are the two main contaminants that are often found in aquatic environments and can lead to major issues for aquatic organisms. Polystyrene (PS) is a type of microplastic that is commonly found in aquatic environments. Hard clams are one of the organisms that are often used as a bioindicator of water pollution, and they can live in a certain salinity range. The objective of this study is to investigate the potential of PS particles as heavy metal vectors in M. lusoria influenced by differences in salinity. The result showed that the highest increase in concentrations of all heavy metals in hard clams was found in those placed at higher salinities. Hard clams that were placed at higher salinity required more water, allowing more PS particles to enter the clams’ bodies. Hard clams placed at salinity 30‰ always gathered significantly more PS particles (p

Background: The hard clam Mercenaria mercenaria is a major marine resource along the Atlantic coasts of North America and has been introduced to other continents for resource restoration or aquaculture activities. Significant mortality events have been reported in the species throughout its native range as a result of diseases (microbial infections, leukemia) and acute environmental stress. In this context, the characterization of the hard clam genome can provide highly needed resources to enable basic (e.g., oncogenesis and cancer transmission, adaptation biology) and applied (clam stock enhancement, genomic selection) sciences. Results: Using a combination of long and short-read sequencing technologies, a 1.86 Gb chromosome-level assembly of the clam genome was generated. The assembly was scaffolded into 19 chromosomes, with an N50 of 83 Mb. Genome annotation yielded 34,728 predicted protein-coding genes, markedly more than the few other members of the Venerida sequenced so far, with coding regions representing only 2% of the assembly. Indeed, more than half of the genome is composed of repeated elements, including transposable elements. Major chromosome rearrangements were detected between this assembly and another recent assembly derived from a genetically segregated clam stock. Comparative analysis of the clam genome allowed the identification of a marked diversification in immune-related proteins, particularly extensive tandem duplications and expansions in tumor necrosis factors (TNFs) and C1q domain-containing proteins, some of which were previously shown to play a role in clam interactions with infectious microbes. The study also generated a comparative repertoire highlighting the diversity and, in some instances, the specificity of LTR-retrotransposons elements, particularly Steamer elements in bivalves. Conclusions: The diversity of immune molecules in M. mercenaria may allow this species to cope with varying and complex microbial and environmental landscapes. The repertoire of transposable elements identified in this study, particularly Steamer elements, should be a prime target for the investigation of cancer cell development and transmission among bivalve mollusks. [ABSTRACT FROM AUTHOR]

Background: Meretrix petechialis is one of the commercially important marine bivalves. In this study, we selected six highly polymorphic EST-derived microsatellite markers to assess the genetic diversity and population differentiation on nine wild populations of Meretrix petechialis. Results: The number of alleles detected per locus ranged from 4 to 30 (mean NA = 27.5) with a total of 165 alleles. The mean value of observed and expected heterozygosities varied from 0.717 to 0.861 and from 0.797 to 0.856, respectively. Meanwhile, the result of Neighbor-joining and overall FST = 0.214 (P

Vibrio sp. NTOU- M3 is a potential new bacterium isolated from hard clam ( Meretrix taiwanica ) in the estuarine region of Taiwan. The complete sequences obtained using Oxford Nanopore Technologies and Illumina sequencing consist of a 3,272,438-bp large circular chromosome and a 1,584,497-bp small circular chromosome., Competing Interests: The authors declare no conflict of interest.

The on‐site culture of live microalgae represents a major challenge for bivalve hatchery operations due to high cost and labour demands. This study evaluated the efficacy of commercially available microalgae concentrates as a partial or complete replacement diet for live microalgae for culture of the hard clam, Mercenaria mercenaria, larvae. Larvae were fed from D‐larval stage to post‐set, 2–14 days post fertilization (DPF). Larvae fed the complete replacement diets were significantly smaller than those fed partially replaced or live microalgae diets. Foot development was significantly delayed in larvae fed complete replacement diets compared to partially replaced or live microalgae diets. Although early survival (at 5 DPF) was similar among the treatments, final survival (at 14 DPF) varied significantly among treatments. The average final survival was 69%–77% for larvae fed live microalgae, 60%–61% for larvae fed partially replaced diets and 14%–16% for larvae fed complete replacement diets. These results suggest that a live microalgae diet could be partially replaced by a concentrate to feed hard clam larvae. However, complete replacement diet may be used only for a short duration (up to 3 days) without affecting survival. [ABSTRACT FROM AUTHOR]

The dynamic regulation of ions and amino acids in the gills and mantle of the Asian hard clam, Meretrix lusoria, following the exposure to a hyperosmotic environment was hitherto unclear. The present study revealed that the osmolality as well as the Na+ and Cl– concentrations in the hemolymph were significantly increased 3 h after transferring the clams from an environment with the salinity of their natural habitat (brackish water; BW; 20‰) to one with hyperosmotic salinity (seawater; 35‰). In addition, we found that the specific activities of Na+/K+-ATPase, a key enzyme that plays a significant role in cell osmoregulation, in the gills and mantle of clams were significantly increased at 72 and 12 h post-transfer, respectively, during acclimation to hyperosmotic salinity. Similarly, the contents of free amino acids (FAAs) such as taurine, alanine, and glycine were significantly elevated during hyperosmotic salinity acclimation. Previous research indicates that taurine is the most abundant FAA in the gills and mantles of Asian hard clams and that the taurine transporter (TAUT) plays an important role in taurine accumulation. The present study showed that TAUT mRNA and protein expression were significantly and transiently increased in the mantle of Asian hard clams following exposure to seawater; although the expression of TAUT mRNA in the gills of Asian hard clams was also transiently stimulated by exposure to hyperosmotic salinity, the relative TAUT protein abundance decreased only at later stages. Accordingly, the findings of this study improve our understanding of the dynamic processes of ion and amino acid regulation in the peripheral tissues of bivalves under hyperosmotic stress.

Hard clam, Mercenaria mercenaria, aquaculture is heavily dependent on the production of high-quality hatchery seed, yet information on the optimal diet for larval culture is limited and primarily anecdotal. This study aims to determine the optimal microalgae diet for hard clam larvae by comparing various combinations of typically fed microalgae species: Isochrysis galbana(clone T. Iso), Pavlova lutheri, Chaetoceros gracilis and Chaetoceros muelleri. Two separate experiments were conducted, each at 2–14 days post fertilization. In the first experiment, the effects of feeding two species of flagellates - singly or in combination with diatoms was evaluated. In the second experiment, the effects of feeding T. Iso singly or in combination with diatoms - fed in equal proportion initially or gradually added to a T. Iso dominant diet was evaluated. The highest levels of larval growth, development and survival were achieved by feeding T. Iso and C. gracilis in equal proportion for the entire larval duration. The flagellate T. Iso provided higher growth and survival than P. lutheri when clams were fed a mono-species diet (P < 0.05). The diatom C. gracilis provided higher growth and survival than C. muelleri when either of them was combined with T. Iso as a bi-species diet (P < 0.05). An initial diet consisting of T. Iso alone, followed by a gradual step-wise addition of diatoms did not enhance larval performance over the diet consisting of equal proportions of T. Iso and C. gracilis. Based on the results achieved in this study we advocate a feeding strategy that includes an equal proportion of T. Iso and C. gracilis for the entire larval period. Adoption of this feeding strategy is predicted to improve hard clam hatchery productivity, translating into increased economic return.

In this study, we examined ion and amino acid regulation in the gill and mantle of the hard clam Meretrix lusoria. We found that the osmolality and Na+ and Cl‐ concentrations of hard clam hemolymph were significantly reduced after transferring clams from the salinity of their natural habitat [20‰ saltwater (SW)] to a lower salinity environment (10‰ SW). Specific activities of Na+, K+‐ATPase (NKA), which provides the driving force for the secondary ion transport associated with cell osmoregulation in gills and mantles, were unaffected during the acclimation to lower salinity. In contrast, there was a significant decline in the contents of free amino acids (FAAs) in the gills and mantles of hard clams during lower salinity acclimation. Taurine was established to be the dominant FAA, the content of which is considerably higher than that of other FAAs in the hard clam. Following acclimation to the lower salinity environment, mRNA expression of the taurine transporter (TAUT), which plays a pivotal role in regulating intracellular taurine contents, was significantly upregulated in the gill and downregulated in the mantle of hard clams at different time points. However, the relative abundance of TAUT protein in the gill and mantle was significantly increased after transfer from 20‰ SW to 10‰ SW, which may reflect feedback regulation in response to reduced taurine contents in the gill and mantle of hard clams. Collectively, the findings of this study provide important insights on the dynamic processes of ion and amino acid regulation in the peripheral tissues of bivalves. Highlights: Dynamic processes of ion and amino acid regulation in the gill and mantle of hard clams upon low salinity challenge were evaluated.Na+,K+‐ATPase activity in the gill was not in response to low salinity challenge.Taurine transporter mRNA and protein expression in the gill and mantle were differently regulated after transfer to low salinity. [ABSTRACT FROM AUTHOR]

Hard clam, Meretrix meretrix is the principal bivalve resource collected by artisanal fishermen in the coastal areas of Marudu Bay, Malaysia. Population parameters of the clam in the intertidal zone of Marudu Bay, Sabah were analyzed using FiSAT software, based on monthly length and weight data collected from May 2017 to April 2018. A total of 1,745 clams with shell lengths ranging from 18.3 to 101.7 mm were analyzed. Asymptotic length (L∞) and growth coefficient (K) of the von Bertalanffy growth formula (VBGF) for M. meretrix were estimated at 107.63 mm and 0.47 year-1, respectively. The estimated growth performance index (ϕ) was 3.736. The theoretical age at length zero (t0) was -0.1412. The predicted maximum life span of the clam was 6.38 years. The sampled population of M. meretrix exhibited consistent and moderate fatness (3.88±0.84) throughout the year. The total mortality (Z) was estimated at 2.65 year-1, fishing mortality (F) at 1.87 year-1, and natural mortality (M) at 0.78 year-1. The exploitation level (E) of the M. meretrix population was 0.70, while the maximum allowable limit of exploitation (Emax) was 0.499 for the highest yield. This study clearly indicates that the M. meretrix stock in Marudu Bay experiences over-exploitation that warrants immediate action by the fisheries management authority. [ABSTRACT FROM AUTHOR]

Pea crab is a small crustacean known as kleptoparasite and belongs to the family Pinnotheridae, inhabit bivalves, gastropods, and other species. Nonetheless, pea crab is one of the unfamiliar species to the Malaysia citizen and the information is limited. This study aimed to determine the distribution of pea crab from four bivalves species (mud clam, oyster, hard clam and cockle) in Setiu Wetlands, Terengganu. Sampling was conducted twice, in October 2018 and February 2019, in which mud clam, oyster, cockle and hard clam were collected. In this study, the distribution of pea crab was observed by collecting randomly fifty samples of each bivalve at four sites and checked for any presence of pea crab. The size shell length of mud clams measured was 40 to 75 mm, oysters were 30 to 80 mm, marine clams and cockles were 20 to 40 mm. Pea crab presence was analysed and identified for the genus identification based on the microscopic and macroscopic methods. The result showed that, pea crab only present in the mud clam but none in other bivalves. Fifteen pea crabs were isolated from the first sampling (mean=0.3) with 11 females, whilst 13 pea crabs from the second sampling (mean=0.26) with 10 femalesidentified. The size of the pea crab measured was between 10 mm to 15 mm and belongs to the genus of Arcotheres sp. However, there were other none pea crab species were found in the oyster. On the other hand, the correlation between the carapace width of pea crab and mud clam shell length were analysed using linear regression (r²=0.0699, p=0.341) from first sampling, while (r²=0.2885, p=0.058) from second sampling. The size range of mud clams without pea crab was 35 to 60 mm shell length. [ABSTRACT FROM AUTHOR]

Severe losses in aquacultured and wild hard clam (Mercenaria mercenaria) stocks have been previously reported in the northeastern United States due to a protistan parasite called QPX (Quahog Parasite Unknown). Previous work demonstrated that clam resistance to QPX is under genetic control. This study identifies single nucleotide polymorphism (SNP) associated with clam survivorship from two geographically segregated populations, both deployed in an enzootic site. The analysis contrasted samples collected before and after undergoing QPX-related mortalities and relied on a robust draft clam genome assembly. ~200 genes displayed significant variant enrichment at each sampling point in both populations, including 18 genes shared between both populations. Markers from both populations were identified in genes related to apoptosis pathways, protein-protein interaction, receptors, and signaling. This research begins to identify genetic markers associated with clam resistance to QPX disease, leading the way for the development of resistant clam stocks through marker-assisted selection. • Hard clam resistance to QPX disease is under genetic control. • A draft genome of the hard clam has been generated. • ddRADSeq allowed the identification of SNPs associated with clam resistance. • Identified SNPs are promising markers for selective breeding. [ABSTRACT FROM AUTHOR]

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The aim of this study was to determine the abundance and distribution of microplastics in a mangrove ecosystem, while investigating its uptake by Meretrix lyrata. Microplastics were extracted from 10 L of mangrove sediment using a floatation method. Soft tissues of M. lyrata were digested and the microplastics were filtered and observed under a light microscope. Microplastics ranging from 21 µm to 100 µm were the most abundant in the mangrove layers at 936 ± 34 particles/kg (dry sediment) to 1,227 ± 55 particles/kg (dry sediment) (27.19% to 31.16% of the total quantity of recovered microplastics). The most abundant microplastics, with size from 5 µm to 1000 µm, were found in the deepest layer. M. lyrata accumulation of microplastics averaged at 0.35 ± 0.08 particles/g tissue and 0.23 ± 0.07 particles/g tissue (wet weight) before and after three-day depuration, respectively. Microplastics with size from 5 to 20 µm were the most commonly uptaken by the clams, averaging at 58% to 72% for predepuration and post-depuration, respectively. This study revealed that the most predominant size of microplastics in the sediment was 5 µm to 20 µm, which concurs with the results of the microplastics most commonly accumulated by M. lyrata. It is believed that microplastics accumulation in mangrove areas increases over time. On the other hand, the uptake rate of microplastics by Meretrix lyrata decreases over time, flushing microplastics from its system more frequently. [ABSTRACT FROM AUTHOR]

• The DEB model for Mercenaria mercenaria accurately replicated its growth dynamics. • Bioremediation potential of shrimp farm waste by M. mercenaria was estimated. • CO 2 fixation potential of hard clams in shrimp aquaculture pond was estimated. • DEB model appears to be a promising tool in polyculture condidate selection. Polyculture practices are important for achieving sustainable aquaculture development. Recently, hard clams polyculture in intensive shrimp ponds has been encouraged because bivalves can consume excess nutrients in aquaculture systems and sequester carbon. To evaluate the bioremediation potential of hard clams polyculture in intensive shrimp ponds, this study built an assessment model based on individual growth models and estimated the potential for nitrogen and phosphorus removal as well as CO 2 fixation by hard clams. Firstly, key parameters required for model construction were obtained through field surveys and physiological experiments. Subsequently, an individual growth model for the hard clam Mercenaria mercenaria was developed based on the Dynamic Energy Budget (DEB) theory. Fitting of the growth data indicated that the model accurately replicated the growth patterns of hard clams, with relative root mean square errors of 9.87 % for shell length and 5.02 % for dry tissue weight. Finally, the assessment model for the bioremediation potential of hard clams demonstrated that, over 110 days in the intensive shrimp mariculture pond, the net removal of nitrogen and phosphorus by hard clams were 3.68 kg ha−1 and 0.81 kg ha−1, respectively, and CO 2 fixation was 507.00 kg ha−1. These findings suggested that the DEB model is an effective tool for evaluating bivalve ecological remediation potential and can aid in selecting species for sustainable polyculture. [Display omitted] [ABSTRACT FROM AUTHOR]

People in South East Asia region have consumed hard clam for a long time. This clam also actively collected and traded by local people around beaches and estuaries in Indonesia. The purposes of this research were to analyze protein and content of hard clam (Meretrix sp.) collected from Bancaran Estuary, Indonesia and to evaluate the content of lead (Pb) and cadmium (Cd). The sample of clams was collected by hand picking during low tide. Fresh samples of clams were kept in a cool box. Fresh samples of the flesh were taken for analysis of nutrient and heavy metal content as well. The content of fat was analyzed using soxhlet method; meanwhile the protein content was analyzed using Kjeldahl method. In addition, the content of cadmium (Cd) and lead (Pb) in the flesh of hard clam were tested using atomic adsorption spectroscopy. The results indicated of the flesh of hard clam contained fat and protein, namely 3.25±0.42% and 10.26±0.46% respectively. Meanwhile, the content of Cadmium (Cd) and Lead (Pb) were 0.0306±0.0053 ppm and 0.0458±0.0035 ppm respectively. The level of Cd and Pb were lower than the level of maximum acceptable limit. Therefore, it can be concluded that the flesh of hard clam was safe for consumption.

The microwave-assisted induction heating (MAIH) method—an emerging thermal technique—was studied to heat the prepackaged raw hard clam (Meretrix lusoria). The cooking effects on microbial and physiochemical qualities of clam were investigated. After the heating of the clam meat samples, the aerobic plate count (APC), psychrotrophic bacteria count (PBC), and total volatile basic nitrogen (TVBN) levels decreased with increasing heating time, but the shucking ratio, area shrinkage, and texture (hardness, cohesiveness, and chewiness) increased. In addition, the L* (lightness) and W (whiteness) of the clam meat samples increased significantly at the beginning of the heating period, whereas they decreased significantly with extended heating time. However, a* (redness) had the opposite trend. This study found that when clams were heated for more than 120 s at 130 °C or 150 s at 90 °C, they displayed obvious shrinking and a yellow-brown appearance, indicating that they are overcooked. After heating by MAIH for at least 110 s at 130 °C or 130 s at 90 °C, the samples were cooked well and gains a completely shucking, along with no microbial count detected. Therefore, the results indicated that the optimum heating conditions for prepackaged hard clams subjected to an MAIH machine were 130 °C for 110 s or 90 °C for 130 s.

Motivated by experimental findings, a computational fluid dynamics (CFD) model was used to investigate whether the clam Mercenaria mercenaria may alter its cue downstream variability by an exhalant random pumping behavior. This behavior was hypothesized to occur in the presence of predator chemical signals in order to prevent successful tracking by the predator. Simulated downstream flow and mixing conditions derived from the random nature of the clam exhalant jet in a crossflow were analyzed by computing an intermittency factor, determining the field of finite-time Lyapunov exponents (FTLEs) and identifying the resulting Lagrangian coherent structures (LCSs). Numerical simulations illustrate that the effectiveness of a fluctuating exhalant jet to prevent downstream tracking by a crab, depends on the ratio of the exhalant jet to the crossflow. Specifically, the clam could effectively enhance the downstream dispersion to prevent tracking, but only in the range of parameters where LCSs are generated (jet-to-crossflow ratio ≥ 1). Then, the probability of detection is reduced with respect to the case of a less fluctuating exhalant jet. [ABSTRACT FROM AUTHOR]

Many marine organisms have a well-known adult sessile stage. Unfortunately, our lack of knowledge regarding their larval transient stage hinders our understanding of their basic ecology and connectivity. Larvae can have swimming behavior that influences their transport within the marine environment. Understanding the larval stage provides insight into population connectivity that can help strategically identify areas for restoration. Current techniques for understanding the larval stage include modeling that combines particle attributes (e.g., larval behavior) with physical processes of water movement to contribute to our understanding of connectivity trends. This study builds on those methods by using a previously developed retention clock matrix (RCM) to illustrate time dependent connectivity of two species of shellfish between areas and over a range of larval durations. The RCM was previously used on physical parameters but we expand the concept by applying it to biology. A new metric, difference RCM (DRCM), is introduced to quantify changes in connectivity under different scenarios. Broad spatial trends were similar for all behavior types with a general south to north progression of particles. The DRCMs illustrate differences between neutral particles and those with behavior in northern regions where stratification was higher, indicating that larval behavior influenced transport. Based on these findings, particle behavior led to small differences (north to south movement) in transport patterns in areas with higher salinity gradients (the northern part of the system) compared to neutral particles. Overall, the dominant direction for particle movement was from south to north, which at times was enhanced by winds from the south. Clam and oyster restoration in the southern portion of Barnegat Bay could serve as a larval supply for populations in the north. These model results show that coupled hydrodynamic and particle tracking models have implications for fisheries management and restoration activities.

Hard clams (HCs) are a nutritionally high-quality and popular seafood, and are established to be a potent antitumor food. The aim of the present study was to determine whether HC extracts induce apoptosis in the human gastric cancer cell line, AGS. In contrast with previously reported methods of extraction, crude extracts of HC were obtained by freezing and thawing and by a method free of hot water or organic solvents. The composition, quality and properties of the HC extracts were demonstrated to be stable since the extracts that were evaluated by capillary electrophoresis and HPLC analysis at different timepoints were similar. HC extracts also have an inhibitory effect against the survival of AGS cells. Treatment with HC extracts induced a marked sub-G1 DNA peak and reduced the expression of the anti-apoptotic genes BIRC5 and KPNA2. However, hallmarks of classical apoptosis such as DNA fragmentation and apoptotic body formation were not observed, indicating atypical apoptosis. Furthermore, it was revealed that HC extracts interrupted cell cycle progression in AGS cells through altered expression of six cell cycle-associated genes: CDC20, KPNA2, BIRC5, ANAPC2, CDKN1A and RB1. The present findings suggest that HC may contribute to a novel future anticancer agent. [ABSTRACT FROM AUTHOR]

Most marine mollusks are osmoconformers, in that, their body fluid osmolality changes in the direction of the change in environmental salinity. Marine mollusks exhibit a number of osmoregulatory mechanisms to cope with either hypo- or hyperosmotic stress. The effects of changes in salinity on the osmoregulatory mechanisms of the hard clam (Meretrix lusoria, an economically important species of marine bivalve for Taiwan) have not been determined. In this study, we examined the effect of exposure to hypo (10‰)- and hyper (35‰)-osmotic salinity on hard clams raised at their natural salinity (20‰). The osmolality, [Na+], and [Cl-] of the hard clam hemolymph were changed in the same direction as the surrounding salinity. Further, the contents of total free amino acids including taurine in the gills and mantles were significantly upregulated in hard clam with increasing salinity. The gill Na+,K+-ATPase (NKA) activity, the important enzyme regulating cellular inorganic ions, was not affected by the changed salinity. Mantle NKA activity, however, was stimulated in the 35‰ SW treatment. The taurine transporter (TAUT) is related to the regulation of intracellular contents of taurine, the dominant osmolyte. Herein, a TAUT gene of hard clam was cloned and a TAUT antibody was derived for the immunoblotting. The TAUT mRNA expression of the mantle in hard clam was significantly stimulated in 35‰ SW, but protein expression was not modulated by the changed salinity. In gills of the hard clam with 10‰ SW, both TAUT mRNA and protein expressions were significantly stimulated, and it may reflect a feedback regulation from the decreased gills taurine content under long-term hypoosmotic acclimation. These findings suggest that TAUT expression is regulated differently in gills and mantles following exposure to alterations in environmental salinity. Taken together, this study used the physiological, biochemical and molecular approaches to simultaneously explore the osmoregulation in tissues of hard clam and may further help to understand the osmoregulation in bivalves.

Microplastic (MP) contamination in bivalve mollusks has become a significant concern over the last few years. These ecologically and economically valuable species are popular seafood items for human consumption. As filter feeders, bivalves may ingest MPs in their bodies, possibly impacting their physiology and fitness. Additionally, a considerable amount of the seafood that humans consume comes from coastal areas where MP concentrations tend to be the highest. This research provides the first examination of MPs in eastern oysters (Crassostrea virginica) and hard clams (Mercenaria mercenaria) that were grown locally in coastal areas of New York, contributing to a baseline for the northeast and mid-Atlantic regions of the U.S. A total of 48 eastern oysters (n = 12 per site, at four sites) and hard clams (n = 24 per site, at two sites) were sampled in summer 2021. While MP fibers and fragments (i.e. polyethylene terephthalate, polystyrene, and polypropylene) were found in some oysters, other contaminants (e.g. indigo dye, phthalocyanine, dye 823, etc.) were found in both bivalve species. Particle composition was verified using Raman microspectroscopy. Although mean MP concentrations were low in eastern oysters (i.e. 0.008 MPs g−1 of soft tissue wet weight; 0.125 MPs ind−1) and not found in hard clams, more research is needed to assess the magnitude of contamination in these edible bivalves. • First study of microplastics in two commercial bivalve species in Northeast USA • Oysters (Crassostrea virginica) and clams (Mercenaria mercenaria) were assessed. • Microplastic concentrations in oysters were low (0.008 microplastics g−1). • No microplastics were found in clams. • Microplastic concentrations in these bivalves are lower than those in other regions. [ABSTRACT FROM AUTHOR]

The hard clam, Mercenaria mercenaria , is one of the most valuable commercial mollusk species along the eastern coast of the United States. Throughout the past 2 decades, the hard clam industry in the Northeast was significantly impacted by disease outbreaks caused by a lethal protistan parasite known as Quahog Parasite Unknown (QPX). QPX is an opportunistic pathogen and the infection has been shown to be a cold water disease, where warmer conditions (above 21 °C) lead to disease reduction and clam healing. In vitro studies also showed a sharp reduction in parasite growth and survivorship at temperatures exceeding 27 °C. In this study, we evaluated the effect of short-term exposures to high temperatures on QPX disease dynamic and clam recovery. Infected clams were collected from an enzootic site and subsequently submitted to one of ten “heat shock” treatments involving a gradient of temperatures and exposure times. QPX prevalence was compared before and 10 weeks after heat shock to assess the effect of each treatment on disease progress. Expression of several stress-related genes was measured 1 and 7 days after heat shock using qPCR to evaluate the effect of each treatment on clam physiology. Anti-QPX activity in clam plasma was also measured in an attempt to link changes in defense factors to thermal stress and disease progress. Our results suggest that brief exposures to moderate high temperatures promote the greatest remission while imposing the mildest stress to clams. These results are discussed with the aim of providing the industry with possible strategies to mitigate QPX disease. [ABSTRACT FROM AUTHOR]