Ark Shell Research Articles

Effects of a Sudden Drop in Salinity on Scapharca subcrenata Antioxidant Defenses and Metabolism Determined Using LC-MS Non-targeted Metabolomics

In this experiment, the effects of a sudden drop in salinity on the antioxidant defense system and related gene expression of the ark shell Scapharca subcrenata were examined. The sudden drop in seawater salinity after a rainstorm was simulated, and subsequently differentially expressed metabolic markers were identified by LC-MS non-targeted metabolomics. When the salinity dropped to 14‰ (S14), the total anti-oxidant content, activity of Na+/K+-ATPase, superoxide dismutase (SOD), and catalase (CAT), content of malondialdehyde, and expression levels of Mn-SOD, CAT, and C-type lectin of S. subcrenata were significantly higher than in groups with salinity of 22‰ (S22) or 30‰ (S30) (P < 0.05). The activity of glutathione peroxidase (GPx), the content of reduced glutathione, and the expression levels of GPx were not significantly different between S14 and S22, but the values in each group were significantly higher than those in S30 (P < 0.05). Using the metabolomics technique, 361, 271, and 264 metabolites with significant differences were identified from S22 vs. S14, S30 vs. S14, and S30 vs. S22, respectively. The drop in salinity was accompanied by up-regulation of phosphatidylcholine (PC) (20:4 (5Z, 8Z, 11Z, 14Z)/P-18: 1 (11Z)), PC (16:0/22: 6 (4Z, 7Z, 10Z, 13Z, 16Z, 19Z)), phosphatidylethanolamine (PE) (18:4 (6Z, 9Z, 12Z, 15Z)/24:1 (15Z)), phosphatidylinositol (PI) (20:1 (11Z)/0:0), phalluside-1, C16 sphinganine, and LacCer (d18:0/14:0) and by significant down-regulation of PI-Cer (d18:1/14:0) and PE (14:0/16:1(9Z). The results of this study illustrate how these nine metabolites can be used as metabolic markers for the response of S. subcrenata to a sudden drop in salinity. They also provide the theoretical groundwork for selection of bottom areas with salinity that is optimal for release and proliferation of S. subcrenata, which is needed to restore the declining populations of this species.

Microbial community and interspecies interaction during grazing of ark shell bivalve (Scapharca subcrenata) in a full-scale bioremediation system of mariculture effluents

A novel biological approach using ark shell bivalves as potential species for remediation of effluents was studied to determine the microbial community interspecies interaction and nutrient cycling in a restoration system of mariculture effluents. A field study showed that Scapharca subcrenata was the main driver of the microbial community's interspecies-interaction (PERMANOVA, R = 0.0572, P = 0.005) in the treatment zone (TZ). Analysis of co-occurrence networks based on random matrix theory (RMT) indicated that the network's complexity parameters were enhanced in the TZ and disrupted in the control zone (CZ) due to eutrophic disturbances. Concurrently, the TZ was correlated with more profound network modifications (i.e., higher modularity, total nodes (n), cohesion, and proportion of positive links), suggesting that S. subcrenata influenced microbial interspecies interactions in the system. Similarly, the co-occurring networks of generalists Proteobacteria (OTU2037) at genus Anaerospora and Actinobacteria (OTU9660) at genus Candidatus aquiluna for anaerobic ammonia-oxidation (ANAMMOX) were highly significant in the TZ. The top-down and bottom-up forces of S. subcrenata influenced the removal efficiency of nitrogenous compounds by reducing 81.51% of nitrite (NO2−-N), 84.61% of total ammonium nitrogen (TAN) and 72.78% of nitrate (NO3−-N). Generally, the introduction of ark shell bivalve (S. subcrenata) to the system as a biofilter provides a very low-cost bioremediation technology that could be one of the best restorations and remediation tools for mariculture effluents.

Liquid chromatography-electrospray ionization-tandem mass spectrometric assay for d-aspartate N-methyltransferase activity in ark shells.

A liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) method for the separation and quantification of the enantiomers of N-methylaspartate and N-methylglutamate, after derivatization with Nα-(5-fluoro-2,4-dinitrophenyl)-L-leucinamide was established. The time required for the LC-ESI-MS/MS analysis was within 20min and the detection limit was approximately 10fmol per injection, demonstrating that this method can be used for the rapid determination of D-aspartate N-methyltransferase activity in the ark shell clam Scapharca broughtonii.Abbreviations: NMDA: N-methyl-D-aspartate; NMLA: N-methyl-L-aspartate; NMDG: N-methyl-D-glutamate; NMLG: N-methyl-L-glutamate; NMA: N-methylaspartate; NMG: N-methylglutamate; HPLC: high-performance liquid chromatography; SAM: S-adenosyl-L-methionine; OPA: o-phthalaldehyde; LC-ESI-MS/MS: liquid chromatography-electrospray ionization-tandem mass spectrometry; FDLA: Nα-(5-fluoro-2,4-dinitrophenyl)-L-leucinamide; FDAA: Nα-(5-fluoro-2,4-dinitrophenyl)-L-alaninamide; ESI: electrospray ionization; LC-ESI-MS: liquid chromatography-electrospray ionization-mass spectrometry; MS/MS: tandem mass spectrometry.

Trace elements and oxidative stress in the Ark shell Arca noae from a Mediterranean coastal lagoon (Bizerte lagoon, Tunisia): are there health risks associated with their consumption?

The current study examined the concentrations of ten trace elements (TE) (nickel, chromium, cadmium, iron, zinc, manganese, aluminum, copper, selenium and lead) in the edible tissue of the Ark shell Arca noae (L. 1758) from a Mediterranean coastal lagoon, the Bizerte lagoon during 2013-2014. The analysis of several redox status biomarkers, metallothioneins (MTs), malondialdehyde (MDA), glutathione peroxidase (GPx), reduced glutathione (GSH) and acetylcholinesterase (AChE), was monitored as a response to TE bioaccumulation and environmental parameters variability. Significant differences (p < 0.05) were observed between mean seasonal TE concentrations in A. noae soft tissue. The highest TE concentrations in A. noae soft tissues were recorded during summer, which coincided with the increase of body dry weight (BDW) and the gonad index (GI). During this season, biomarker responses were enhanced, revealing significant increases of MTs, MDA and GSH levels as well as GPx activity in A. noae tissues, while a decrease of AChE activity was observed. The levels of TE analyzed in A. noae and several parameters used to assess the potential human risk (estimated weekly intake, target hazard quotient and target hazard risk) were lower than the permissible limits for safe seafood consumption. Consequently, this shellfish can be considered safe for human consumption. This preliminary study presents prospects for the valorization of this seafood product in Tunisia's food sector. It also gives basal information for future environmental assessment studies in which A. noae could be used as early warning tools in the field of biomonitoring programs and confirms the usefulness of biomarkers to monitor the health status of aquatic organisms.

Metabolic response of Scapharca subcrenata to heat stress using GC/MS-based metabolomics.

Marine mollusks are commonly subjected to heat stress. To evaluate the effects of heat stress on the physiological metabolism of the ark shell Scapharca subcrenata, clams were exposed to different high temperatures (24, 28 and 32 °C) for 72 h. The oxygen consumption and ammonia excretion rates were measured at 2, 12, 24, 48 and 72 h. The results indicated that the metabolic rates of the ark shell significantly increased with increasing heat stress, accompanied by mortalities in response to prolonged exposure. A metabolomics approach based on gas chromatography coupled with mass spectrometry was further applied to assess the changes of metabolites in the mantle of the ark shell at 32 °C. Moreover, multivariate and pathway analyses were conducted for the different metabolites. The results showed that the heat stress caused changes in energy metabolism, amino acid metabolism, osmotic regulation, carbohydrate metabolism and lipid metabolism through different metabolic pathways. These results are consistent with the significant changes of oxygen consumption rate and ammonia excretion rate. The present study contributes to the understanding of the impacts of heat stress on intertidal bivalves and elucidates the relationship between individual-level responses and underlying molecular metabolic dynamics.

Accumulation of metal-based nanoparticles in marine bivalve mollusks from offshore aquaculture as detected by single particle ICP-MS

The exposure risk of metal-based nanoparticles (NPs) to marine organisms and related food safety have attracted increasing attention, but the actual concentrations of these NPs in seawater and marine organisms are unknown. In this work, single particle inductively coupled plasma-mass spectrometry (spICP-MS) was used to quantify the concentrations and size distributions of NPs in different marine mollusks (oysters, mussels, scallops, clams, and ark shells) from an offshore aquaculture farm. Results showed that Ti, Cu, Zn, and Ag bearing NPs were detected in all the five mollusks with the mean sizes at 65.4–70.9, 72.2–89.6, 97.8–108.3, and 42.9–51.0 nm, respectively. The particle concentrations of Ti, Cu, Zn, and Ag bearing NPs in all mollusks (0.88–3.26 × 107 particles/g fresh weight) were much higher than that in the seawater (0.46–0.79 × 107 particles/mL), suggesting bio-accumulation of NPs. For all the five mollusks, Ag bearing NPs had the highest number-based bioconcentration factors (NBCFs) in all the tested NPs due to the smallest mean size of Ag bearing NPs in seawater (30.5 nm). In addition, the clams exhibited the lowest NBCFs of the four NPs than other mollusks. All four NPs were mainly accumulated in the gill and digestive gland, and could transfer to adductor muscle of all mollusks. Although all the four metals (Ti, Cu, Zn, Ag) in mollusks were safe for human consumption by the estimated daily intake (EDI) analysis, the risk of NPs remaining in the mollusks should be further considered when evaluating the toxicity of metals for human health. The findings could improve our understanding on the distribution and health risk of NPs in marine mollusks under offshore aquaculture.

The Effect of Bioturbation Activity of the Ark Clam Scapharca subcrenata on the Fluxes of Nutrient Exchange at the Sediment-Water Interface

Filter-feeding shellfish are common benthos and significantly affect the biogeochemical cycle in the shallow coastal ecosystems. Ark clam Scapharca subcrenata is one of the widely cultured bivalve species in many coastal areas owing to its tremendous economic value. However, there is little information regarding the effects of the bioturbation of S. subcrenata on the fluxes of nutrient exchange in the sediment-water interface (SWI). In this regard, S. subcrenata was sampled during October 2016 to determine the effects of its bioturbation activity on the nutrient exchange flux of the SWI. The results showed that the biological activity of S. subcrenata could increase the diffusion depth and the rate of the nutrients exchange in the sediments. The bioturbation of S. subcrenata could allow the nutrients to permeate into the surface sediments at 6–10 cm and increase the release rate of nutrients at the SWI. The releasing fluxes of DIN and PO 4 3− -P in the culture area were found to be around three times higher than that in the non-cultured region. The culture of S. subcrenata has been proved to be an important contributor to nutrient exchange across the SWI in the farming area of Haizhou Bay. Nutrients exchange in the SWI contributes a part of 86% DIN, 71% PO 4 3− -P and 18% SiO 3 2− -Si for the aquaculture farm.

Enzymatic and Low-Molecular Weight Parts of Antioxidant Complex in Two Species of Black Sea Mollusks with Different Resistance to Oxidative Stress: Mytilus galloprovincialis Lam. and Anadara kagoshimensis (Tokunaga, 1906)

We studied the specific features of the joint activity of the enzyme and low-molecular weight parts of the antioxidant (AO) complex in the tissues of two species of the Black Sea bivalve mollusks with different resistance to oxidative stress: a native species, the Mediterranean mussel Mytilus galloprovincialis Lam., and an invader, the ark clam Anadara kagoshimensis (Tokunaga, 1906). In the hepatopancreas and the gills and foot of mollusks, the activity of glutathione peroxidase (GP), glutathione reductase (GR), superoxide dismutase (SOD), catalase, and the level of reduced glutathione (GSH), as well as the contents of glucose, amino acids, and products that react with thiobarbituric acid (TBA-reactive products), have been analyzed. The enzyme part had a leading role in AO defense in the tissues of the Mediterranean mussel. This is indicated by higher activities of GP (hepatopancreas, gills) and SOD (hepatopancreas, foot) but a smaller content of GSH (gills, foot) as compared with ark clam. In ark clam tissues, the role of low-molecular weight part is significant, which is confirmed by the higher GSH level (gills, foot) in combination with the higher activity of GP (foot) and SOD and catalase (gills) than that observed in the Mediterranean mussel. Unlike the mussel, ark clam tissues showed a more effective joint activity of SOD, catalase, and glutathione system, which resulted in a significantly lower content of LPO products than that found in all of the studied Mediterraneanmussel tissues. These features of the joint activity of the enzyme and low-molecular weight parts of the AO complex of the Mediterranean mussel and ark clam largely determine the difference in the resistance to oxidative stress in the mollusks of these species. The results confirm the prevailing idea of the ark clam as one of the most competitive invaders as compared with native species; it has successfully mastered new biotopes in the Azov-Black Sea basin and has become an important component of benthic communities.

Development and practice of teaching material for the hemocyte observation using erythrocyte from the Ark shell, Scapharca broughtonii

Development and practice of teaching material for the hemocyte observation using erythrocyte from the Ark shell, <i>Scapharca broughtonii</i>

Single and double electron capture associated with characteristic K-shell X-ray emission for F9+,8+,7++Ar

SynopsisCross sections for target Ar K-shell ionization associated with single and double electron capture, as well as the corresponding cross sections for total electron capture and the projectile F K x rays, were determined for 1.8-2.2 MeV/u F9+,8+,7+ projectiles. The Ar K x-ray coincidence cross section ratios for double to single capture are found to vary strongly with the incident charge state, with the ratios for F9+ well exceeding unity.

Identification and Expression of Heat Shock Protein 60 (HSP60) from the Ark Shell Scapharca broughtonii

Heat shock protein 60 (HSP60) is evolutionarily highly conserved, and it assists with protein folding in the mitochondria and serves as a molecular chaperone, increasing cell survival under various conditions. Studies of HSP60 in molluscs under stress conditions remain limited. Here, this study first characterize a full-length HSP60 cDNA from the ark shell Scapharca broughtonii (termed SbHSP60) containing a 1,725-bp open reading frame corresponding to a deduced protein of 574 amino acid residues with a predicted molecular mass of approximately 61.4 kDa. The deduced protein has 72.3%–80.3% amino acid identity with homologs from invertebrates and vertebrates. Phylogenetic analysis showed that SbHSP60 grouped with proteins from other molluscs, forming a sister cluster to the HSP60 proteins from vertebrates. The expression pattern of SbHSP60 as examined by quantitative real-time PCR suggested that these mRNA transcripts were distributed across all examined tissues. The highest levels of expression were found in the hepatopancreas and gill, with decreasing levels of expression in the mantle, foot, hemocytes, and adductor muscle. Expression of SbHSP60 after challenge with Vibrio anguillarum showed similar upregulation profiles in the hepatopancreas and gill, indicating that SbHSP60 is involved in the bacterial defense process as an acute-phase protein. Levels of SbHSP60 in the hepatopancreas and gill were higher in cadmium-exposed individuals than in controls. SbHSP60 was significantly upregulated by Cd stress in the gill, but expression was less affected in the hepatopancreas, implying different roles in cellular Cd stress protection. The effects of heat stress on SbHSP60 mRNA expression were duration- and tissue-specific. The induction of SbHSP60 in the heat-stressed group occurred predominantly in the hepatopancreas, suggesting that protein damage and the consequent requirement for the HSP60 protein are increased during the heat shock process.

Influence of temperature on the pathogenicity of Ostreid herpesvirus-1 in ark clam, Scapharca broughtonii

OsHV-1 is an epidemic pathogen of molluscs, and temperature has been recognized as a decisive environmental factor in its pathogenicity. In recent years, ark clam, Scapharca broughtonii, emerged as a host for OsHV-1. In the north of China, massive summer mortalities of ark clams infected with OsHV-1 have been continuously reported since 2012. However, the interaction between temperature and the pathogenicity of OsHV-1 was unknown in ark clams. In this study, the effect of temperature (10 °C to 18 °C stepped by 2 °C) on the occurrence of OsHV-1 disease in ark clams was analyzed. OsHV-1 infection led to gill erosion but not below the critical low temperature (between 12 °C and 14 °C). However, OsHV-1 persisted for more than 2 weeks at 12 °C post inoculation and replication was reactivated when the temperature was elevated to 18 °C. No significant reduction of OsHV-1 DNA load was found when the temperature descended to 12 °C from 18 °C, while the gill erosion remained unchanged. Ark clams failed to show the capability of effective clearance of OsHV-1 below the critical low temperature. Our results demonstrated that the pathogenicity of OsHV-1 was influenced significantly by temperature. Moreover, high temperature favored infection, which could provide more information to understand summer mortality of ark clams.

Morphologic, cytometric and functional characterisation of Anadara kagoshimensis hemocytes

Circulating hemocytes of ark clam, Anadara kagoshimensis, were investigated using light microscopy and flow cytometry. Hemolymph contained 3 morphotype of cells, amebocytes, erythrocytes and intermediate type cells, which formed two distinct subpopulations on flow cytometric dot plots. Large cells (intermediate morphotype and erythrocytes) amounted 85.6 ± 2.8% total cells in hemolymph. Erythrocytes were hemoglobin-containing cells with up to 40 granules presented in the cytoplasm. All hemocyte types, observed in the ark clam hemolymph demonstrated equal capacity to spontaneous production of reactive oxygen species.

Effects of Acute Low-Salinity Stress on the Activities of Catalase (CAT), Superoxide Dismutase (SOD) and Glutathiones-Transferase (GST) in Scapharca broughtonii

Salinity is an important environmental factor of osmotic pressure which is closely related to growth and development of aquatic organisms. Some physiological studies regarding to challenge of salinity have been reported in marine shellfish. However, information about the effects of acute low-salinity stress on the enzyme activities in ark shell, Scapharca broughtonii, is still limited now. In this study, the enzyme activities of catalase (CAT), superoxide dismutase (SOD) and glutathiones-transferase (GST) in five tested tissues of S. broughtonii under different salinity (10, 15, 20, 25 and 30&amp;permil;) for different challenged time (24, 48, 72 and 96h) were investigated. The dynamic change of the three enzyme activities after challenged were further analyzed according to the detected data. Results revealed that low-salinity stress generated great change of CAT, SOD and GST activities in organism, but the change peculiarity in different tissues was different in some degree. Especially, two of the five tissues, hepatopancreas and foot, showed special characteristics responding to the low-salinity stress. It also showed that the variations of the three enzymes activities have tissue specificity and time sequentiality in S. broughtonii.

Two novel peptides from ark shell protein stimulate osteoblast differentiation and rescue ovariectomy-induced bone loss

Osteoporosis is a common bone disease resulting from imbalance between bone formation and bone resorption. Currently, anti-resorptive agents that inhibit bone resorption are the most available drugs on the market. Biosphosphonates, anti-resorptive drugs most commonly used to treat osteoporosis, are limited by their side effects for long-term continuous treatment. It is important to develop appropriate therapeutic stragegies capable of promoting bone formation to counteract osteoporotic bone loss. Thus, anabolic agents that stimulate bone formation are undoubtedly of interest. Here, we purified and identified two novel osteogenic peptides AWLNH and PHDL from ark shell protein hydrolysates. AWLNH and PHDL stimulated osteoblast differentiation via mitogen-activated protein kinase (MAPK) and bone morphogenetic protein-2 (BMP-2) pathways. The activation of BMP-2 pathway stimulated by AWLNH and PHDL was abolished by treating noggin, BMP antagonist, in bone marrow-derived mesenchymal stem cells (BMMSCs), but not the phosphorylation of JNK1/2, ERK1/2, and p38 MAPK. However, treatment with MAPK inhibitors in BMMSCs downregulated the expression of BMP-2 and p-Smad1/5 and inhibited alkaline phosphatase activity. The dominant inhibitory effects by JNK inhibitor and ERK inhibitor are observed. In ovariectomized (OVX) mice, a reduction of femoral bone mineral density (BMD) was significantly observed, however, AWLNH and PHDL (0.2 mg/kg/per day) injection restored BMD as well as the osteoporotic conditions in OVX mice. Moreover, the increased serum osteocalcin and alkaline phosphatase activity in OVX mice were significantly reduced in AWLNH and PHDL injected-OVX mice. These results suggest that two novel osteogenic peptides AWLNH and PHDL could be attractive therapeutic agents for osteoporosis treatment.

The utility of micro-computed tomography for the non-destructive study of eye microstructure in snails

Molluscan eyes exhibit an enormous range of morphological variation, ranging from tiny pigment-cup eyes in limpets, compound eyes in ark clams and pinhole eyes in Nautilus, through to concave mirror eyes in scallops and the large camera-type eyes of the more derived cephalopods. Here we assess the potential of non-destructive micro-computed tomography (µ-CT) for investigating the anatomy of molluscan eyes in three species of the family Solariellidae, a group of small, deep-sea gastropods. We compare our results directly with those from traditional histological methods applied to the same specimens, and show not only that eye microstructure can be visualised in sufficient detail for meaningful comparison even in very small animals, but also that μ-CT can provide additional insight into gross neuroanatomy without damaging rare and precious specimens. Data from μ-CT scans also show that neurological innervation of eyes is reduced in dark-adapted snails when compared with the innervation of cephalic tentacles, which are involved in mechanoreception and possibly chemoreception. Molecular tests also show that the use of µ-CT and phosphotungstic acid stain do not prevent successful downstream DNA extraction, PCR amplification or sequencing. The use of µ-CT methods is therefore highly recommended for the investigation of difficult-to-collect or unique specimens.

Effects of a Sudden Drop in Salinity on Immune Response Mechanisms of Anadara kagoshimensis.

In this experiment, the effects of a sudden drop of salinity on the immune response mechanisms of the ark shell Anadara kagoshimensis were examined by simulating the sudden drop of salinity that occurs in seawater after a rainstorm. Additionally, the differentially expressed genes (DEGs) were identified using transcriptome sequencing. When the salinity dropped from 30‰ (S30) to 14‰ (S14), the phagocytic activity of blood lymphocytes, the O2− levels produced from respiratory burst, the content of reactive oxygen species, and the activities of lysozymes and acid phosphatases increased significantly, whereas the total count of blood lymphocytes did not increase. Total count of blood lymphocytes in 22‰ salinity (S22) was significantly higher than that in any other group. The raw data obtained from sequencing were processed with Trimmomatic (Version 0.36). The expression levels of unigenes were calculated using transcripts per million (TPM) based on the effects of sequencing depth, gene length, and sample on reads. Differential expression analysis was performed using DESeq (Version 1.12.4). Transcriptome sequencing revealed 269 (101 up-regulated, 168 down-regulated), 326 (246 up-regulated, 80 down-regulated), and 185 (132 up-regulated, 53 down-regulated) significant DEGs from comparison of the S14 vs. S22, S22 vs. S30, and S14 vs. S30 groups, respectively. Gene Ontology enrichment analysis of the DEGs in these salinity comparison groups revealed that the cellular amino acid metabolic process, the regulation of protein processing, the regulation of response to stress, and other terms were significantly enriched. Kyoto Encyclopedia of Genes and Genomes enrichment analysis showed that nucleotide-binding, oligomerization domain (NOD)-like receptor signaling pathway (ko04621), apoptosis-multiple species (ko04215), Toll and Imd signaling pathway (ko04624), NF-κB signaling pathway (ko04064), apoptosis (ko04210), and focal adhesion (ko04510) were significantly enriched in all salinity comparison groups. qRT-PCR verification of 12 DEGs in the above six pathways was conducted, and the results were consistent with the transcriptome sequencing results in terms of up-regulation and down-regulation, which illustrates that the transcriptome sequencing data are credible. These results were used to preliminarily explore the effects of a sudden drop of salinity on blood physiological and biochemical indexes and immunoregulatory mechanisms of A. kagoshimensis. They also provide a theoretical basis for the selection of bottom areas optimal for release and proliferation of A. kagoshimensis required to restore the declining populations of this species.

Effect of hypoxic water mass in summer on the distribution of ark shells, &lt;i&gt;Anadara kagoshimensis,&lt;/i&gt; in Lake Nakaumi, Japan

Effect of hypoxic water mass in summer on the distribution of ark shells, &lt;i&gt;Anadara kagoshimensis,&lt;/i&gt; in Lake Nakaumi, Japan

Histochemical Distribution of Three Types of Enzymes and Mucous Cells in the Gill, Mantle and Hepatopancreas of the Ark Shell Scapharca subcrenata

The present study was aimed at evaluating the histochemical distribution of alkaline phosphatase (ALP), nonspecific esterase (NSE), peroxidase (POD) and various types of mucous cells in the gill, mantle and hepatopancreas of the ark shell Scapharca subcrenata. The ALP activity was found in the epithelial cells (EP) of the gill filament and the mantle as well as in the basal lamina of the glandular duct in the hepatopancreas. The staining intensity of ALP in the mantle and hepatopancreas was stronger than that in the gill. The NSE activity was detected in the EP in the gill filament, mantle and hepatopancreas, with the hepatopancreas showing a stronger intensity than the gill. The POD activity was located in the EP of the mantle and glandular duct of the hepatopancreas as well as in the connective tissue of the gill. The mantle showed stronger staining intensity of POD than the hepatopancreas. The Alcian blue (pH 2.5) periodic acid Schiff (AB-PAS) histochemical results revealed four types of mucous cells in the gill, mantle and hepatopancreas. Type III cells (nPAS+AB+) and type IV cells (aPAS+AB+) were observed in the gill, mantle and hepatopancreas. Type I cells (PAS+AB–) were not detected in the hepatopancreas but were distributed ubiquitously throughout the gill filament and mantle. Type II cells (PAS–AB+) were not detected in the gill but were distributed ubiquitously in the digestive ducts of the hepatopancreas.

Chromosomal-level assembly of the blood clam, Scapharca (Anadara) broughtonii, using long sequence reads and Hi-C.

BackgroundThe blood clam, Scapharca (Anadara) broughtonii, is an economically and ecologically important marine bivalve of the family Arcidae. Efforts to study their population genetics, breeding, cultivation, and stock enrichment have been somewhat hindered by the lack of a reference genome. Herein, we report the complete genome sequence of S. broughtonii, a first reference genome of the family Arcidae.FindingsA total of 75.79 Gb clean data were generated with the Pacific Biosciences and Oxford Nanopore platforms, which represented approximately 86× coverage of the S. broughtonii genome. De novo assembly of these long reads resulted in an 884.5-Mb genome, with a contig N50 of 1.80 Mb and scaffold N50 of 45.00 Mb. Genome Hi-C scaffolding resulted in 19 chromosomes containing 99.35% of bases in the assembled genome. Genome annotation revealed that nearly half of the genome (46.1%) is composed of repeated sequences, while 24,045 protein-coding genes were predicted and 84.7% of them were annotated.ConclusionsWe report here a chromosomal-level assembly of the S. broughtonii genome based on long-read sequencing and Hi-C scaffolding. The genomic data can serve as a reference for the family Arcidae and will provide a valuable resource for the scientific community and aquaculture sector.