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Crassostrea ariakensis (Fujita, 1913) is one of the most important economic and ecological oysters that is naturally distributed along the coast of Asia, separated by the Yangtze River estuary. They are usually compared as different populations, while there is no consensus on whether C. ariakensis in northern and southern areas should be considered as two species or subspecies. Here, we analyzed morphological characteristics, COI, 16s rRNA, mitogenome sequences, and species delimitation analysis (ASAP and PTP) to resolve the intraspecific taxonomic status of the C. ariakensis. Phylogenetic and ASAP analysis highlight that C. ariakensis was divided into N-type and S-type. PTP was unable to differentiate between the two types of C. ariakensis. The divergence time of N-type and S-type C. ariakinsis is estimated to be 1.6 Mya, using the relaxed uncorrelated lognormal clock method. Additionally, significant morphological differences exist between the two groups in terms of the adductor muscle scar color. Despite these differences, the COI (0.6%) and 16S rRNA (0.6%) genetic distance differences between N-type and S-type C. ariakensis has not yet reached the interspecific level. These results suggest that N-type and S-type C. ariakensis should be treated as different subspecies and renamed as C. ariakensis ariakensis subsp. nov and C. ariakensis meridioyangtzensis subsp. nov. [ABSTRACT FROM AUTHOR]

Aminotransferases are enzymes found in living organisms that catalyze transfer reactions between amino acids and keto acids, crucial for amino acid metabolism and synthesis. Aminotransferase classes I and II play a vital role in regulating osmolarity, protecting cells, and improving metabolic homeostasis and cellular fitness. To investigate the characteristics of the aminotransferase class I and II gene family and their roles in osmotic pressure regulation in the Jinjiang oyster (Crassostrea ariakensis), the gene structure, chromosomal localization, and phylogeny were characterized and the genes' expression in the gill under high-salt stress was analyzed. In this study, eighteen Aminotransferase class I and II genes, including SPTLCa and SPTLCb, SPTa and SPTb, ALAT2a and ALAT2b, KAT3a and KAT3b, and ASTa, ASTb and ASTc, were identified. The physicochemical properties of 11 family members were stable, with their instability factors less than 40. Subcellular localization prediction showed that aminotransferase classes I and II were localized in the cytoplasm or mitochondria. Chromosomal localization results showed that the 18 aminotransferase class I and II genes were located on eight chromosomes. All members of this gene family had the Aminotran_1_2 structural domain which is associated with osmotic pressure regulation by adjusting the conversion reaction between amino acids and keto acids. Most gene expressions showed an initial increase followed by a decrease from 0 h to 12 h when the oysters were challenged by acute stress using artificial seawater with a salinity of 40. However, the expression of CarAGT2 and CarKAT3b genes showed an increased trend with increasing stress time. This study systematically investigated the bioinformatics characteristics of the aminotransferase class I and II gene family in C. ariakensis and their role in osmotic pressure regulation, which provides scientific data for understanding the potential functions of these genes in physiological adaptation, thereby expanding the research on osmoregulation in bivalves. [ABSTRACT FROM AUTHOR]

Jinjiang oyster Crassostrea ariakensis, a species with economic and ecological value, is distributed along the estuaries and coasts of East Asia. With the decline in natural resources, the conservation and aquaculture of this species is urgent. However, studies characterizing their shell shape remain scarce. We investigated the morphological differences in the shells of wild Jinjiang oysters from six populations (Qinzhou, Shanghai, Nantong, Qingdao, and Binzhou hard or muddy bottom) along the coast of China. The color of the shell and adductor muscle scar showed associations with temperature gradient along its geographical distribution. Oyster shape was defined by shell height to shell length ratio, and the ratio varies among geographic locations of the populations. They were found nearly round (Qinzhou and Nantong populations), oval (Qingdao and Binzhou populations), or water-droplet-shaped (Shanghai population). Binzhou populations living on muddy substrates are more elongated than those on hard substrate. In addition, we developed a method to measure the cavity volume in oysters. Correlation and path analysis showed that shell height significantly influenced cavity volume. The synergistic effect of the two factors (the height, length, and width of the shell in pairs) on the cavity volume resulted in differences between northern and southern groups: samples from the southern group (Qinzhou and Shanghai) showed correlation between shell height and shell width, while those from the northern group (Nantong, Qingdao, and Binzhou) showed correlation between shell height and shell length. All populations showed significant correlation between shell height and cavity height, and shell length and cavity length, while the correlation between shell width and cavity width was minimal, which may have been resulted from uneven shell thickness. The linear equation for shell height and cavity volume under different ratios of shell height to length was obtained. In this study, we determined that shell height has the most influence on cavity volume, and specific cavity volume fitting linear equations are given for different shell types, which may provide a reference for future oyster breeding for shell shaping. [ABSTRACT FROM AUTHOR]

Comparing the responses of closely related species to environmental changes is an efficient method to explore adaptive divergence, for a better understanding of the adaptive evolution of marine species under rapidly changing climates. Oysters are keystone species thrive in intertidal and estuarine areas where frequent environmental disturbance occurs including fluctuant salinity. The evolutionary divergence of two sister species of sympatric estuarine oysters, Crassostrea hongkongensis and Crassostrea ariakensis, in response to euryhaline habitats on phenotypes and gene expression, and the relative contribution of species effect, environment effect, and their interaction to the divergence were explored. After a 2‐month outplanting at high‐ and low‐salinity locations in the same estuary, the high growth rate, percent survival, and high tolerance indicated by physiological parameters suggested that the fitness of C. ariakensis was higher under high‐salinity conditions and that of C. hongkongensis was higher under low‐salinity conditions. Moreover, a transcriptomic analysis showed the two species exhibited differentiated transcriptional expression in high‐ and low‐salinity habitats, largely caused by the species effect. Several of the important pathways enriched in divergent genes between species were also salinity‐responsive pathways. Specifically, the pyruvate and taurine metabolism pathway and several solute carriers may contribute to the hyperosmotic adaptation of C. ariakensis, and some solute carriers may contribute to the hypoosmotic adaptation of C. hongkongensis. Our findings provide insights into the phenotypic and molecular mechanisms underlying salinity adaptation in marine mollusks, which will facilitate the assessment of the adaptive capacity of marine species in the context of climate change and will also provide practical information for marine resource conservation and aquaculture. [ABSTRACT FROM AUTHOR]

Glycogen, a stored form of glucose, is an important form of energy for aquatic shellfish, contributing to the flavor and quality of the oyster. The glycogen synthase (GYS) and glycogen synthase kinase 3β (GSK3β) are two major enzymes in the glycogenesis. However, the information of the two genes in the Jinjiang oyster Crassostrea ariakensis remains limited. In this study, we identified the genes of GYS and GSK3β and further explored their function in the glycogen synthesis of C. ariakensis. The GYS and GSK3β were distributed in all tested tissues, and high expression of GYS and glycogen content were detected in the gonad, labial palp, hepatopancreas, and mantle, while the high expression of GSK3β was observed in the gill and adductor muscle. The expression of GYS was positively correlated with the glycogen content, while GSK3β was negatively correlated. Additionally, knockdown of GSK3β using RNAi decreased the GYS expression, revealing the negative regulatory effect of GSK3β on GYS. These findings enrich the research data of GSK3β and GYS involved in glycogen synthesis, providing valuable information for further research on the function of GSK3β and GYS in the glycogen synthesis process of oyster. [ABSTRACT FROM AUTHOR]

Peptides from oysters have several bioactive functions. In this study, we identified antioxidant peptides from oysters (Crassostrea rivularis) and investigated their structure–function relationship. We used an 8 kDa molecular‐weight (MW) cut‐off membrane and semiprep reversed‐phase liquid chromatography to collect five peptides (F1–F5) and identified the highest‐abundance ion‐peak sequences AWVDY (F1), MSFRFY(F2), EPLRY(F3), RKPPWPP(F4), and YAKRCFR(F5) having MWs of 652, 850, 676, 877, and 943 Da, respectively, using ultra‐performance liquid chromatography‐quadrupole/time‐of‐flight tandem mass spectrometry. These peptides exhibited high antioxidant activities, similar to butylated hydroxytoluene, reduced glutathione, and ascorbic acid. F5 demonstrated the highest scavenging activity for DPPH radicals (IC50 = 21.75 μg/ml), hydroxyl radicals (IC50 = 18.75 μg/ml), and superoxide radicals (IC50 = 11.00 μg/ml), while F3 demonstrated the highest reducing power. Furthermore, F5 significantly protected Caco‐2 cells from H2O2‐induced oxidative damage. These results suggest that the antioxidant peptide F5 is a promising food additive that protects against oxidative damage. [ABSTRACT FROM AUTHOR]

The Jinjiang oyster Crassostrea ariakensis, naturally distributing in estuarine regions with low salinity, is an important economic and ecological species in China. However, studies on its genomics and population genetics remain lacking. Here, we assembled the chromosome‐level genome of a female C. ariakensis and re‐sequenced 261 individuals from five locations in China representing three typical habitats. The C. ariakensis genome was 662.9 Mb with contig N50 length of 5.9 Mb using PacBio HiFi‐CCS long reads, and 99.83% sequences were anchored onto 10 pseudochromosomes using Hi‐C data. A total of 26,354 protein‐coding genes were predicted. We identified three significantly expanded gene families which are closely associated with osmotic pressure regulation, including CDO, SLC13 and SDR. Population structure analysis revealed that the C. ariakensis from five locations were clustered into three typical groups (northern, southern and Shanghai) (K = 3) and their phylogenetic relationship was consistently correlated to their geographical distribution. Furtherly, the differentiation between northern and southern groups was clearly demonstrated by estimated population differentiation coefficient (FST = 0.1154), and the PSMC distribution showed the two groups of effective population size separated at 0.1 Ma. Meanwhile gene flow from southern to Shanghai was detected. Selective sweep analysis between northern and southern group detected genes associated with heat response and salinity adaptation. This study could provide valuable genomic resources and information for further research on the molecular evolution, genetic breeding, biological function and evolutionary adaptation of C. ariakensis. [ABSTRACT FROM AUTHOR]

Understanding the roles of genetic divergence and phenotypic plasticity in adaptation is central to evolutionary biology and important for assessing adaptive potential of species under climate change. Analysis of a chromosome-level assembly and resequencing of individuals across wide latitude distribution in the estuarine oyster (Crassostrea ariakensis) revealed unexpectedly low genomic diversity and population structures shaped by historical glaciation, geological events and oceanographic forces. Strong selection signals were detected in genes responding to temperature and salinity stress, especially of the expanded solute carrier families, highlighting the importance of gene expansion in environmental adaptation. Genes exhibiting high plasticity showed strong selection in upstream regulatory regions that modulate transcription, indicating selection favoring plasticity. Our findings suggest that genomic variation and population structure in marine bivalves are heavily influenced by climate history and physical forces, and gene expansion and selection may enhance phenotypic plasticity that is critical for the adaptation to rapidly changing environments. Ao Li, He Dai, and Ximing Guo et al. present a high-quality genome from the estuarine oyster, Crassostrea ariakensis. They highlight the climate impact on population divergence, a suite of genes likely important for adaptation to environments of different temperatures and salinities, and provide further insight into the evolution of this species. [ABSTRACT FROM AUTHOR]

The hybridization experiments have been made between Crassostrea ariakensis and C. gigas several times. However, it is difficult to obtain a large number of hybrid offspring, which becomes the bottleneck of subsequent cross‐breeding. To explore whether the production of hybrid larvae is affected by salinity, we investigated the effects of salinity (16, 20, 24, 28 and 32 psu) on the early activities of artificial hybridization between C. ariakensis and C. gigas at 23–24°C. In this study, the results showed that during artificial insemination, the appropriate salinity of high‐quality gametes in C. ariakensis and C. gigas was 20–32 psu and 24–32 psu respectively. Besides, the fertilization rate of AG (C. ariakensis♀ × C. gigas♂) and GA (C. gigas♀ × C. ariakensis♂) at 24–28 psu was significantly (p <.05) higher than that at 16–20 psu. For incubation, the optimal salinity of embryo incubation was 28 psu, under which all embryos of AG and GA can develop rapidly to the D‐larvae and yielded a high hatching rate. During larval rearing, the larval shell height and survival rate of AG were of no significant difference (p >.05) at all salinities, and the optimum salinity for larval growth and survival of GA was 24–28 psu. These findings can contribute to the increase in the hybrid progeny yield, which can serve as the new resource for genetic improvement of oyster germplasm. [ABSTRACT FROM AUTHOR]

To understand the environmental adaptations among sessile bivalves lacking adaptive immunity, a series of analyses were conducted, with special emphasis on the widely distributed C. ariakensis. Employing Pacbio sequencing and Hi-C technologies, whole genome for each of a C. ariakensis (southern China) and C. hongkongensis individual was generated, with the contig N50 reaching 6.2 and 13.0 Mb, respectively. Each genome harbored over 30,000 protein-coding genes, with approximately half of each genome consisting of repeats. Genome alignment suggested possible introgression between C. gigas and C. ariakensis (northern China), and re-sequencing data corroborated this result and indicated significant gene flow between C. gigas and C. ariakensis. These introgressed candidates, well-represented by genes related to immunity and osmotic pressure, may be associated with environmental stresses. Gene family dynamics modeling suggested immune-related genes were well represented among the expanded genes in C. ariakensis. These outcomes could be attributed to the spread of C. ariakensis. [ABSTRACT FROM AUTHOR]

[Display omitted] • Bioavailability of two typical shellfish species were performed using in vitro method. • Bioavailability of Zn and Cd in cooked C. rivularis samples both exceeded 82%. • Bioavailability of Zn and Cd in cooked P. undulata samples both exceeded 83%. • The intake of Cd from both shellfish species is safety. Dynamic extraction of edible tissues of Jinjiang oyster (Crassostrea rivularis) and Flower clam (Paphia undulata) was conducted using a fully biomimetic digestion (in vitro) method. The impact of different cooking methods on the bioavailability of Zn and Cd in the edible shellfish tissues was analyzed, and the human health risk of Zn and Cd was evaluated. The results show that the gastric biomimetic extractions of Zn and Cd in unheated samples of C. rivularis and P. undulata were higher than those in the intestinal biomimetic extraction. The extraction patterns of cooked samples were consistent with those of raw samples. The bioavailability of Zn and Cd in cooked samples of C. rivularis was 94.9% and 82.5%, respectively, indicating increased Zn bioavailability but decreased Cd bioavailability compared to the raw samples. The bioavailability of Zn and Cd in cooked samples of P. undulata was 85.1% and 83.0%, respectively, both of which decreased compared to the raw samples. Consumption of C. rivularis can provide 21.0% to 34.2% of the daily required Zn intake, while consumption of P. undulata can provide 3.8% to 6.4%. The intake of Cd from both shellfish species is below the monthly tolerable intake recommended by FAO/WHO. Consuming cooked C. rivularis can increase the intake of Zn and decrease the intake of Cd. [ABSTRACT FROM AUTHOR]

[Display omitted] • Bioavailability of two typical shellfish species were performed using in vitro method. • Bioavailability of Zn and Cd in cooked C. rivularis samples both exceeded 82%. • Bioavailability of Zn and Cd in cooked P. undulata samples both exceeded 83%. • The intake of Cd from both shellfish species is safety. Dynamic extraction of edible tissues of Jinjiang oyster (Crassostrea rivularis) and Flower clam (Paphia undulata) was conducted using a fully biomimetic digestion (in vitro) method. The impact of different cooking methods on the bioavailability of Zn and Cd in the edible shellfish tissues was analyzed, and the human health risk of Zn and Cd was evaluated. The results show that the gastric biomimetic extractions of Zn and Cd in unheated samples of C. rivularis and P. undulata were higher than those in the intestinal biomimetic extraction. The extraction patterns of cooked samples were consistent with those of raw samples. The bioavailability of Zn and Cd in cooked samples of C. rivularis was 94.9% and 82.5%, respectively, indicating increased Zn bioavailability but decreased Cd bioavailability compared to the raw samples. The bioavailability of Zn and Cd in cooked samples of P. undulata was 85.1% and 83.0%, respectively, both of which decreased compared to the raw samples. Consumption of C. rivularis can provide 21.0% to 34.2% of the daily required Zn intake, while consumption of P. undulata can provide 3.8% to 6.4%. The intake of Cd from both shellfish species is below the monthly tolerable intake recommended by FAO/WHO. Consuming cooked C. rivularis can increase the intake of Zn and decrease the intake of Cd. [ABSTRACT FROM AUTHOR]

Regulatory variants in gene expression serve as bridges linking genetic variation and phenotypic plasticity. Environmental conditions typically influence the effects of regulatory variants on phenotypic plasticity; however, such genotype-by-environment interactions (G × E) are poorly understood. This study aimed to investigate the genetic basis of G × E in estuarine oyster (Crassostrea ariakensis), which is an important model animal for studying environmental adaption owing to its high plasticity and large intraspecific divergence. Genome-wide mapping of expression quantitative trait loci (eQTLs) for 23 environmental adaptive genes was performed for 256 estuarine oysters. We identified 1194 eQTL single nucleotide polymorphisms (eSNPs), including 433 cis -eSNPs in four genes and 722 trans -eSNPs in eight genes. The expression variation explanation of cis -eSNPs (9.95%) was significantly higher than that of trans -eSNPs (9.15%). We specifically showed cis- and trans-eSNPs with high linkage disequilibrium (LD) for Traf7 , Slc6a5 , Ggt , and Dap3. For example, we identified a cis -regulatory LD block containing 68 cis -eSNP and a trans -regulatory LD block, including 20 trans -eSNPs in Traf7. A high proportion (85%) of 40 vital eSNPs exhibited significant G × E effects. We identified crossing and nonparallel interactions of G × E, with the tag cis -eSNPs of Baat and Slc6a5 as representatives. Our results indicated that cis -eQTLs are highly conserved. This study provides insights into the understanding of adaptive evolutionary mechanisms and phenotypic response prediction to variable environments, as well as the genetic improvement for superior adaptive traits for genetic resource conservation and aquaculture. • We identified trans and cis regulatory variants and built potential regulatory networks. • Cis -eSNPs had larger contributions to gene expression plasticity and are conserved in different environments. • Trans -eSNPs are more abundant than cis -eSNPs and usually environment-specific. • A large proportion of eSNPs exhibited significant G × E effects. • Crossing and nonparallel G × E patterns were identified. [ABSTRACT FROM AUTHOR]

The antioxidant and aphrodisiac properties of oyster meat (OM) and its hydrolysates by alcalase (OMA) were compared. The results showed that OMA displayed a higher antioxidant activity than OM with or without gastrointestinal digestion. Furthermore, the study reported that oral administration of OM or OMA could induce aphrodisiac activities and consequently enhance the sexual behavior in normal male mice, at a dose of 250 mg/kg. Additionally, OMA also exhibited better antioxidant activity in vivo than OM by improving the activities of the endogenous cellular antioxidant enzymes and decreasing the MDA levels, which may be helpful in improving the sexual function. These results indicated that oysters' could be a potential functional ingredient with antioxidant and aphrodisiac activities, and the activities could be improved by alcalase hydrolysis. Unlabelled Image • OMA displayed higher antioxidant activity both in vitro and in vivo. • OMA could improve the sexual function of normal male mice more efficiently. • The antioxidant activity may contribute to the aphrodisiac property. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Hemocyte parameters of oysters were determined by FC in vitro and in vivo. • Synergistic effects of Cu and low pH on oyster hemocyte were observed. • Cu exerted a stronger influence on hemocyte parameters than low pH. • Carry-over impacts of Cu and low pH were found during the recovery period. Abstract With the development of industry and agriculture, the metal pollutants (e.g., Cu) are inevitably released into the aquatic environment. In addition, ocean acidification (OA) as a major environmental stress is affecting marine organisms. In this study, we investigated the hemocyte responses of the estuarine oyster Crassostrea rivularis exposed to six combinations of two pH levels (8.1 and 7.7) and three Cu concentrations (0, 10 and 50 μg/l) using flow cytometry in vitro and in vivo. In both experiments, Cu and low pH jointly affected the hemocyte parameters of oyster. High Cu exposure resulted in decreased total hemocyte count (THC), esterase activity (EA) and lysosomal content (LC) and increased hemocyte mortality (HM), phagocytosis activity (PA) and reactive oxygen species (ROS) production, especially under low pH conditions. The immune suppression of metal-exposure was more significant than low pH exposure with a 28-d experimental period in oysters. A slight recovery of the immune parameters was observed in THC, HM, PA, ROS and LC. During the depuration period, the modulatory effects of pH were still obvious. In addition, carry-over effects of high Cu and low pH were still observed. Overall, our results showed that copper and low pH weaken immune functions of hemocyte in oysters, with synergistic effects. This work provides new evidence of sublethal negative effects of metals on marine animals under global change scenarios, and copper likely leads to reduced fitness of oysters under low pH conditions. [ABSTRACT FROM AUTHOR]

Abstract: Crude polysaccharide was prepared from Crassostrea rivularis by 30% (w/v) potassium hydroxide solution at 90°C for 120 min. Three fractions (OG1, OG2, and OG3) were purified by DEAE‐52 cellulose and Sepharose 2B gel column chromatography. The chemical structures were determined using gas chromatography (GC), high‐performance gel permeation chromatography (HPGPC), Fourier‐transform infrared (FT‐IR) spectroscopy, and 1H and 13C nuclear magnetic resonance (NMR) spectroscopy. The results indicated that OG1 was composed of rhamnose and little mannose (8.71%), the ratio of Rha: Gal: Xyl: Fuc in OG3 were 14:5.5:3:1. And their average molecular weights (Mw) were about 1.66 × 106 and 2.33 × 106 Da, respectively. OG2 was composed only of glucose (98.23%), which means it was glycogen. OG2 was consisted mainly of →4)‐ α‐D‐Glc‐(1→, with the branch chain every 6.5 glucose residues on average, which is →4,6)‐α‐D‐Glc‐(1→ and trace amount of α‐D‐Glc‐(1→ branched units. The Mw was 2.27 × 106 Da. It provides the bases for the bioactivity research. [ABSTRACT FROM AUTHOR]

This study investigates the nutritional properties of edible oysters cultivated in Hong Kong (i.e. Deep Bay) to determine their nutritional values compared with other foodstuffs (e.g. land and aquatic-based foods). A total of ∼300 edible oysters were harvested and studied from aquaculture areas in Hong Kong. The Hong Kong oyster (Crassostrea hongkongensis) contained the highest concentrations (up to 32%) of polyunsaturated fatty acids (PUFAs), when compared to the Portuguese (Crassostrea angulata) and the Suminoe (Crassostrea ariakensis) oyster species. The C. hongkongensis also exhibited the best meat yield (∼28%) compared to oyster species from other regions (e.g., Crassostrea gigas). The C. ariakensis showed the highest concentrations (µg/g dwt.) of macro-and micro nutrients, e.g. Mg (∼3600), Na (∼22000), Zn (∼5000); compared to C. hongkongensis and C. angulata. Essential amino acids (EEA; mg/100 g wwt.) were highest in C. angulata (3439), followed by C. ariakensis (3330) and leaving C. hongkongensis (2619) as the poorest species in EAA. The comparison of the nutritional profile of oyster species cultivated in Hong Kong with different seafood species and other foodstuffs showed that oysters are nutrient-rich (or superfoods) shellfish species, which contribute with beneficial compounds (e.g. PUFAs, EAAs) and elements (e.g. Cu, Zn) for a human healthy diet. • The C. hongkongensis contained the highest concentration of PUFAs among oysters. • The C. hongkongensis has the best meat yield compared to oysters from other regions. • The C. ariakensis showed the highest concentrations of macro-and micro nutrients. • EEA were highest in C. angulata , following by C. ariakensis and C. hongkongensis. • Consumption of Hong Kong edible oysters can contribute positively for human health. [ABSTRACT FROM AUTHOR]

A polyclonal antibody specific to an egg protein of Suminoe oyster Crassostrea ariakensis was previously developed in our laboratory to assess the reproductive life cycle of the oyster. The present study was undertaken to investigate vitellin of C. ariakensis (CAVt). Vitellin is an essential component of egg proteins in marine invertebrates as it provides energy and nutrients to the embryo and larvae. CAVt was purified from eggs of the oyster using ammonium sulfate precipitation followed by affinity chromatography with Concanavalin A-agarose. Native polyacrylamide gel electrophoresis (PAGE) and sodium dodecyl sulfate PAGE showed that CAVt is a high molecular weight [532 kiloDaltons (kDa)] protein, with multiple subunits. Similar to other vitellin proteins, it is a phospholipoglycoprotein composed of phospholipids (12.06%), carbohydrates (mannose, 10.08% or glucose, 9.84%), and alkali-labile phosphates (4.16%). Affinity chromatography, enzyme-linked immunosorbent aasay (ELISA) and western blot analysis revealed that CAVt is only present in the ovary, and two subunits of CAVt (72 and 35 kDa) are believed to be incorporated from the hemolymph into the oocyte. The antibody specific to CAVt (anti-CAVt), raised in rabbit, strongly cross reacted with the egg proteins of oyster species and scallops, suggesting that the antigenic epitopes are highly conserved among species. Our results suggest that the anti-CAVt antibody can be used to develop a tool similar to ELISA or western blotting for investigation of the effect of microorganisms on reproduction as well as the effect of chemicals on the endocrine system in C. ariakensis. [ABSTRACT FROM AUTHOR]

Oysters are a keystone species in estuaries and intertidal zones and have important economic and ecological significance; however, worldwide, the dominant aquaculture oyster species suffers from mass mortality owing to anthropogenic impacts and rapid climate change. As a possible solution, inter/intraspecies hybridization is a feasible way to breed new germplasms with genetic improvement and high environmental adaptability. Suminoe oysters (Crassostrea ariakensis) are broadly distributed in the estuaries of China and have evolved strong genetic divergence between the northern and southern populations; therefore, they are ideal candidates to explore intraspecies heterosis and the associated molecular mechanisms. In this study, we performed reciprocal hybridization and examined fitness traits in oysters cultured in both northern and southern habitats. Reciprocal hybrids performed better than inbred populations in both environments, indicating heterosis in Suminoe oysters. Hybrids reared in maternal habitats showed faster growth, higher field survival, and greater aerobic metabolism than alternative hybrid oysters under the same conditions. The transcriptional analysis identified modules related to heterosis and maternal effect, while genes responsible for galactose metabolism, glycolysis/gluconeogenesis, and the tricarboxylic acid cycle were enriched and upregulated in hybrids, especially those in maternal environments. Our findings reveal that accelerated aerobic energy metabolism, which may result from mitonuclear coadaptation, underlies the molecular basis of heterosis and maternal effect in the hybridization of Suminoe oysters. Thus, we provide important insights for the aquaculture management of marine species, revealing that selecting appropriate environments (maternal habitats) is critical for heterosis in cross-breeding. • Hybrids from divergent oyster populations showed heterosis in growth and survival. • Hybrids in maternal habitat exhibited better performance indicating maternal effect. • Accelerated aerobic metabolism underlies heterosis and maternal effect in oyster. • Our findings propose better hybridization breeding of hybrids in maternal habitat. [ABSTRACT FROM AUTHOR]

The estuarine oyster (Crassostrea ariakensis), a species native to Asia, is widespread throughout the estuarine region along the northern and southern coasts of China and has important ecological and economic values. Owing to runoff dropping and environmental threats caused by climate change and anthropogenic influences, the natural resources of C. ariakensis have persistently declined. Therefore, breeding oysters with high adaptability, which requires efficient and accurate genotyping tools, is beneficial to restore the germplasm resources and aquaculture. However, targeted genotyping tools are poorly developed for this species and even in other aquatic species. Previously, we have detected some selective regions and genes associated with temperature and salinity adaptation using selection signature analysis and found that the upstream regulatory regions of the environment-responsive genes exhibited higher differentiation. In this study, we developed a single nucleotide polymorphism (SNP) targeted genotyping tool for C. ariakensis , which includes 30 K SNPs located in previously identified target regions. The target genomic regions were enriched by hybridization capture using double-stranded DNA (dsDNA) biotin-labeled probes, and sequenced with high depth. A total of 24,541 (81.8%) high-quality SNPs were successfully genotyped in 655 samples. Compared to the genotypes obtained from previous genome-wide resequencing, 74.2% of the SNPs had a consistency rate of 1, with an average consistency rate for each sample of 97.8%. Population structure analysis showed three divergent populations (northern, southern, and middle) on the coast of China, consistent with those constructed using SNPs derived from whole-genome resequencing data. Most of the 30 K SNPs were located in the intergenic and regulatory regions, whereas 7% were located in the coding region. These high-quality SNPs were located in 953 genes, including 100 heat-response and 348 high-salinity-responsive genes. Therefore, this panel can be used to evaluate the adaptive divergence between populations, and causative SNPs related to temperature and salinity adaptation in the linkage and association analysis, providing robust support for the molecular breeding of estuarine oyster. To the best of our knowledge, this study proposes the first high-throughput SNP-targeted genotyping tool for studying the genetic basis of environmental adaptation in oyster, and providing insights into the development of targeted SNP genotyping tools for the adaptation study in other aquatic species under climate changes. • We developed a 30 K targeted genotyping tool for Crassostrea. Ariakensis. • 24,541 high-quality SNPs were successfully genotyped in 655 samples. • These high-quality SNPs were located in environment-responsive genes. • 74.2% of the SNPs had a consistency rate of 1 with resequencing. Population structure analysis showed three divergent populations on the coast of China • This study could be used to dissect the genetic basis of environmental adaptation. [ABSTRACT FROM AUTHOR]

Densoviruses have short ssDNA genomes and mainly infect arthropods. To characterize viral nucleic acid in shellfish, oysters ( Crassostrea ariakensis) were analyzed using viral metagenomics. Two large de novo assembled contigs, CaaDV1 and CaaDV2, consisting of nearly complete densovirus genomes (5860 nucleotides (nt) and 4034 nt) with two major ambisense protein coding regions were identified. Several potential non-structural proteins and capsid proteins were encoded by these genomes, but these were divergent from the existing densoviral species. The NS1 protein of the two CaaDVs shared 43.3%~61.5% amino acid identities with the sea star-associated densovirus and cherax quadricarinatus densovirus, with the four species clustering by phylogenetic analysis. This is the first report of densovirus detection in shellfish, increasing the potential host range of densoviruses and the genetic diversity of the genus Ambidensovirus. [ABSTRACT FROM AUTHOR]

Cyclophilins (CyPs) are a family of proteins that bind the immunosuppressive agent cyclosporin A (CsA) with high-affinity and belong to one of the three superfamilies of peptidyl-prolyl cis-trans isomerases (PPIase). In this report, three cyclophilin genes (Ca-CyPs), including Ca-CyPA, Ca-CyPB and Ca-PPIL3, were identified from oyster, Crassostrea ariakensis Gould in which Ca-CyPA encodes a protein with 165 amino acid sequences, Ca-CyPB encodes a protein with 217 amino acid sequences and Ca-PPIL3 encodes a protein with 162 amino acid sequences. All of the three Ca-CyPs genes contain a typical CyP-PPIase domain with its signature sequences and Ca-CyPB contains an N-signal peptide sequences. Tissue distribution study revealed that Ca-CyPs were ubiquitously expressed in all examined tissues and the highest levels were observed in hemocytes. RLO incubation upregulated the mRNA expression levels of Ca-CyPs, indicating that three Ca-CyPs might be involved in oyster immune response against RLO infection. [ABSTRACT FROM AUTHOR]

A central composite experimental design and response surface method were used to investigate the combined effects of water temperature (18-34°C) and copper ion concentration (0.1-1.5 mg/L) on the catalase (CAT) activity in the digestive gland of Crassostrea ariakensis. The results showed that the linear effects of temperature were significant ( P<0.01), the quadratic effects of temperature were significant ( P<0.05), the linear effects of copper ion concentration were not significant ( P>0.05), and the quadratic effects of copper ion concentration were significant ( P<0.05). Additionally, the synergistic effects of temperature and copper ion concentration were not significant ( P>0.05), and the effect of temperature was greater than that of copper ion concentration. A model equation of CAT enzyme activity in the digestive gland of C. ariakensis toward the two factors of interest was established, with R, Adj. R and Pred. R values as high as 0.943 7, 0.887 3 and 0.838 5, respectively. These findings suggested that the goodness of fit to experimental data and predictive capability of the model were satisfactory, and could be practically applied for prediction under the conditions of the study. Overall, the results suggest that the simultaneous variation of temperature and copper ion concentration alters the activity of the antioxidant enzyme CAT by modulating active oxygen species metabolism, which may be utilized as a biomarker to detect the effects of copper pollution. [ABSTRACT FROM AUTHOR]

• Oysters with 400 or 600 MPa pressure can improve the safety and maintain the delicious taste. • HHP increased the L* values of oysters, while storage temperature did not affect their color. • HHP and storage at −20 °C for 15 d could not affect the fatty acid profiles of oysters. • EUC values decreased with the increase of pressure. The effects of HHP and storage temperature on bacterial counts, color, fatty acids and flavor compounds of oysters Crassostrea ariakensis were investigated. Counts of Vibrio vulnificus and Vibrio parahaemolyticus decreased to undetectable levels in ≥ 400 MPa-treated oysters. Storage at −20 °C significantly restrained microbial growth compared to 4 °C (P < 0.05). L* values of HHP-treated oysters significantly increased compared to raw oysters (P < 0.05). Storage slightly affected the color according to total color difference (ΔE*) values. Fatty acid profiles and betaine contents in 400 and 600 MPa-treated oysters at 0 and 15 d were almost the same as raw samples. Contents of total free amino acids (FAAs), Na+ and Ca2+ were significantly higher in 400 and 600 MPa-treated oysters than those in raw oysters at 0 d (P < 0.05), while the opposite results were observed in 5′-adenosine monophosphate (AMP), 5′-guanosine monophosphate (GMP), citric acid, succinic acid, K+ and PO 4 3− (P < 0.05). At 400 and 600 MPa, FAAs significantly decreased after 15-d storage at 4 °C and −20 °C (P < 0.05), while no significant changes were observed in nucleotides, organic acids and inorganic ions. [ABSTRACT FROM AUTHOR]

Ocean acidification and microplastics pollution are two consequences of anthropogenic activities. In regions such as estuarine areas, ocean acidification (OA) and microplastics (MPs) pollution are occurring simultaneously. The present study tested the combined effects of OA and MPs on the embryonic development and physiological response of the larval oyster Crassostrea rivularis in a short exposure duration. The fertilization process was exposed to six combinations of three MPs levels (0, 10 and 1000 items L−1) × two pH levels (7.3, 8.1) for 9 d after hatching. As a result, the hatching rate was not affected by either pH reduction or MPs exposure, while the deformation rate increased under low pH, MPs exposure and their combination. Larval shell length was reduced under low pH, MPs exposure and the combined exposure of the two factors. Furthermore, swimming speed decreased under low pH throughout the experiment but the MPs' effect was limited. Predictably, MPs in the body increased with the increase of MPs concentration. Compared to low pH, the oyster ingested more MPs under normal pH. But combined OA and MPs didn't affect the MPs intake. Moreover, no significant effects of OA and MPs on total antioxidant capacity and malondialdehyde were observed. However, alkaline phosphatase was significantly affected by low pH and MPs exposure independently. PCA showed that development of C. rivularis larvae changed over time and MPs concentration increase augmented intake of MPs by oysters. Consequently, we speculate that OA and MPs exposure may harm oyster C. rivularis embryonic and larval development, but not induce their antioxidant response in a short duration. Long term study about combined effects of OA and MPs on C. rivularis development is needed in the future. • OA and MPs increased the deformation rate of C. rivularis spawn. • OA and MPs impaired the shell development of the C. rivularis larvae. • The moderate concentration of MPs exposure induced the increase of ALP. • The oyster larva has filter selectivity to reduce the microplastics intake. [ABSTRACT FROM AUTHOR]

Crassostrea ariakensis is widely distributed in the estuaries of China and has the advantages of wide salinity adaptation and strong resistance, but the artificial aquaculture of C. ariakensis is mainly concentrated in southern China. Long-term geographical isolation resulted in genetic variation between the northern and southern C. ariakensis populations. In this study, the reproductive isolation between two independent population of C. ariakensis was evaluated by hybridization. Results showed that the fertilization rate, cleavage rate and D Larval rate of interpopulation hybrids (NS- northern ♂ × southern ♀ and SN- southern ♂ × northern ♀) were significantly lower than those of intrapopulation inbreed groups (SS and NN). Moreover, southern maternal larvae (SS and NS) have significant survival advantages. The growth trend between the two sites was very different in early stage (from 90th to 210th day), but it was consistent in late stage (from 210th to 480th day), with a significant decreasing trend of SS > NS > SN > NN. The survival rates of SN and NS was significantly higher than that of NN, indicating that the high temperature tolerance and stress resistance of hybrids were improved. The positive maternal effect advantages (MEAs) at most time points of both sites demonstrated that parental origin, especially the maternal origin, had a significant effect on the survival and growth of progeny. Hybrid advantages (HAs) for growth of both sites were opposite, and positive HAs of survival accounted for most of both sites, indicating that environmental conditions and survival could significantly affect the growth, and interpopulation hybrids did not necessarily always show positive HAs. Moreover, the maternal origin would affect the shell shape and shell hardness, resulted in NS similar to SS and SN similar to NN, respectively. Additionally, all interpopulation hybrids could produce mature gametes. These results confirmed that there was no serious reproductive isolation between the two populations. The southern maternal groups, especially SS, had better growth and survival advantages, could be used as good new strains for large-scale breeding in southern China, and also provided basic data for the commercial promotion of C. ariakensis in southern China. • First systematic comparison of the southern and northern populations of Crassostrea ariakensis and hybrids in southern China. • No serious reproductive isolation between two populations, although interpopulation hybrids had significantly low hatching rate. • The maternal origin would affect the shell shape and hardness of offspring, and the hybrids were fully fertile. • The south maternal groups, especially SS, had better performance, could be used as excellent strains for commercial breeding in southern China. [ABSTRACT FROM AUTHOR]

Crossbreeding and polyploid breeding are two important tools for the genetic improvement of oysters, and their cross-application is expected to provide new benefits to oyster breeding. To evaluate the aquaculture traits of allotriploids between Crassostrea gigas and Crassostrea ariakensis , two triploid hybrids (TAG (diploid C. ariakensis ♀ × tetraploid C. gigas ♂) and TGA (tetraploid C. gigas ♀ × diploid C. ariakensis ♂)) were established. Phenotypic traits including growth, survival and reproduction were analyzed in two diploid hybrids (AG (diploid C. ariakensis ♀ × diploid C. gigas ♂) and GA (diploid C. gigas ♂ × diploid C. ariakensis ♀)) as controls. The results showed that TAG presented triploid advantage in fertilization rates and hatching rates, up to 11.34% and 26.50% respectively, while TGA did not. The survival rate of TAG and the shell height of TGA exhibited triploid advantage throughout the larval stage and were significantly higher (P < 0.05) than those of AG and GA at day 25. During the grow-out stage, triploid advantages appeared in the shell height of TAG and TGA, but only TAG showed triploid advantages in the survival rate. The triploid rates of TAG and TGA began to decrease during the grow-out stage, and reached 96.11% ± 4.41% and 90.56% ± 3.47%, respectively, at day 350. It was also found that the reproduction of TAG and TGA on day 350 was poor, manifesting as a high proportion of individuals with no gametes or a low number of gametes. Overall, TAG always presents triploid advantages in terms of growth and survival throughout the grow-out stage and shows potential value as a new resource of oyster farming or genetic improvement. • Yearling triploid hybrids derived from Crassostrea gigas tetraploids and Crassostrea ariakensis diploids were obtained. • Comparisons of the diploid and triploid hybrids in the growth, survival and reproduction were made. • The poor growth and survival of diploid hybrids between C. gigas and C. ariakensis were revealed • Triploid hybrid from 2n female C. ariakensis × 4n male C. gigas showed distinct improvement in growth and survival. [ABSTRACT FROM AUTHOR]

Abstract: The combined effects of temperature and ammonia concentration on the percent fertilization and percent hatching in Crassostrea ariakensis were examined under laboratory conditions using the central composite design and response surface methodology. The results indicated: (1) The linear effects of temperature and ammonia concentration on the percent fertilization were significant (P<0.05), and the quadratic effects were highly significant (P<0.01). The interactive effect between temperature and ammonia concentration on the percent fertilization was not significant (P>0.05). (2) The linear effect of temperature on the percent hatching was highly significant (P<0.01), and that of ammonia concentration was nonsignificant (P>0.05). The quadratic effects of temperature and ammonia concentration on the percent hatching were highly significant (P<0.01). The interaction on the percent hatching was not significant (P>0.05). Temperature was more important than ammonia in influencing the fertilization and hatching in C. ariakensis. (3) The model equations of the percent fertilization and hatching towards temperature and ammonia concentration were established, with the coefficients of determination R 2=99.4% and 99.76%, respectively. Through the lack-of-fit test, these models were of great adequacy. The predictive coefficients of determination for the two model equations were as high as 94.6% and 98.03%, respectively, showing that they could be used for practical projection. (4) Via the statistical simultaneous optimization technique, the optimal factor level combination, i.e., 25°C/0.038mgmL−1, was derived, at which the greatest percent fertilization 95.25% and hatching 83.26% was achieved, with the desirability being 97.81%. Our results may provide advantageous guidelines for the successful reproduction of C. ariakensis. [Copyright &y& Elsevier]

The oyster Crassostrea ariakensis is an economically important bivalve species in China, unfortunately it has suffered severe mortalities in recent years caused by rickettsia-like organism (RLO) infection. Prevention and control of this disease is a priority for the development of oyster aquaculture. Allograft inflammatory factor-1 (AIF-1) was identified as a modulator of the immune response during macrophage activation and a key gene in host immune defense reaction and inflammatory response. Therefore we investigated the functions of C. ariakensis AIF-1 (Ca-AIF1) and its antibody (anti-CaAIF1) in oyster RLO/LPS-induced disease and inflammation. Ca-AIF1 encodes a 149 amino acid protein containing two typical Ca2+ binding EF-hand motifs and shares a 48–95% amino acid sequence identity with other animal AIF-1s. Tissue-specific expression analysis indicates that Ca-AIF1 is highly expressed in hemocytes. Significant and continuous up-regulation of Ca-AIF1 is detected when hemocytes are stimulated with RLO/LPS (RLO or LPS). Treatment with recombinant Ca-AIF1 protein significantly up-regulates the expression levels of LITAF, MyD88 and TGFβ. When anti-CaAIF1 antibody is added to RLO/LPS-challenged hemocyte monolayers, a significant reduction of RLO/LPS-induced LITAF is observed at 1.5–12 h after treatment, suggesting that interference with Ca-AIF1 can suppress the inflammatory response. Furthermore, flow cytometric analysis indicated that anti-CaAIF1 administration reduces RLO/LPS-induced apoptosis and necrosis rates of hemocytes. Collectively these findings suggest that Ca-AIF1 functions as a pro-inflammatory cytokine in the oyster immune response and is a potential target for controlling RLO infection and LPS-induced inflammation. [ABSTRACT FROM AUTHOR]

Abstract: P-glycoprotein (P-gp), as an ATP-binding cassette transporter, can transport a variety of substrates across the cell membrane in human and animals, even in aquatic animals. Multixenobiotic resistance phenomenon (MXR) related to the P-gp has been identified and characterized in several aquatic organisms, however, the nature of this transporter and the structural basis for the resistance are still poorly understood. In this study, to provide an insight into the roles of P-gp in resistance of bivalve against environmental pollution and toxins, complete cDNA of P-gp gene in Crassostrea ariakensis was cloned and analyzed. The accumulation of okadaic acid (OA), a main component of diarrhetic shellfish poisoning (DSP) toxins, and expression of P-gp in gills, digestive glands and mantle of C. ariakensis, were detected upon exposure to Prorocentrum lima, a known producer of DSP toxins. The complete sequence of oyster P-gp showed a high identity to MDR/P-gp/ABCB proteins from other species and contained some classical features of ABCB transport proteins. Upon exposure to P. lima for 72h, the OA level increased 2.5-fold in gills and 6.4-fold in digestive glands of C. ariakensis. Meanwhile, the expression of P-gp mRNA increased 2.4-fold in gills and decreased slightly in digestive glands. No significant difference in P-gp protein expression was found by western blot in all of the tissues analyzed in P. lima-exposed oysters. Taking all of our results into account, we speculate that P-gp likely plays a role in the response to DSP toxins in C. ariakensis. [Copyright &y& Elsevier]

Highlights: [•] We surveyed Marteilioides infection in marine bivalves using histology and PCR. [•] Marteilioides infection was also confirmed in the male oysters and clams. [•] The nested PCR was much more sensitive than histology in the detection of Marteilioides. [•] Marteilioides found in Manila clam is a considered to be a new Marteilioides sp. [Copyright &y& Elsevier]

A multistep invasive species methodology was used to evaluate the probability that the deployment of sterile non-native oysters (Crassostrea ariakensis,called Asian oyster) in field-based aquaculture could give rise to a reproductive population in Chesapeake Bay. Several pathways that could potentially lead to the unintentional release of reproductiveC. ariakensisfrom aquaculture were identified. For the four quantifiable pathways, a probability was estimated for each step based on knowledge of ecological rates. A conservative estimate for the number of reproductiveC. ariakensisthat could arise over one spawning season at a hypothetical aquaculture site was estimated. A statistical expansion of this probability estimated that it is highly likely that the cultivation of putatively sterileC. ariakensiswould initiate a reproductive population in Chesapeake Bay over a 10-year time span. The potential benefits of restoration actions involving non-native species in estuarine ecosystems must be weighed against potential ecological risks. A probabilistic approach can provide a useful method for summarizing the risk of an unintended introduction that may occur despite a reasonable and presumably “safe” approach for realizing benefits of a non-native species in aquaculture. The results presented here have important implications for future proposals involving the commercial use of non-native species in natural ecosystems. [ABSTRACT FROM AUTHOR]

Background: Crassostrea ariakensis Gould is a representative bivalve species and an economically important oyster in China, but suffers severe mortalities in recent years that are caused by rickettsia-like organism (RLO). Prevention and control of this disease is a priority for the development of oyster aquaculture. It has been proven that mammalian HMGB (high mobility group box) can be released extracellularly and acts as an important pro-inflammatory cytokine and late mediator of inflammatory reactions. In vertebrates, HMGB's antibody (anti-HMGB) has been shown to confer significant protection against certain local and systemic inflammatory diseases. Therefore, we investigated the functions of Ca-HMGB (oyster HMGB) and anti-CaHMGB (Ca-HMGB's antibody) in oyster RLO/LPS (RLO or LPS)-induced disease or inflammation. Methodology/Principal Findings: Sequencing analysis revealed Ca-HMGB shares conserved structures with mammalians. Tissue-specific expression indicates that Ca-HMGB has higher relative expression in hemocytes. Significant continuous upregulation of Ca-HMGB was detected when the hemocytes were stimulated with RLO/LPS. Recombinant Ca-HMGB protein significantly up-regulated the expression levels of some cytokines. Indirect immunofluorescence study revealed that Ca-HMGB localized both in the hemocyte nucleus and cytoplasm before RLO challenge, but mainly in the cytoplasm 12 h after challenge. Western blot analysis demonstrated Ca-HMGB was released extracellularly 4-12 h after RLO challenge. Anti- CaHMGB was added to the RLO/LPS-challenged hemocyte monolayer and real-time RT-PCR showed that administration of anti-CaHMGB dramatically reduced the rate of RLO/LPS-induced up-regulation of LITAF at 4-12 h after treatment. Flow cytometry analysis indicated that administration of anti-CaHMGB reduced RLO/LPS-induced hemocyte apoptosis and necrosis rates. Conclusions/Significance: Ca-HMGB can be released extracellularly and its subcellular localization varies when stimulated with RLO. Ca-HMGB is involved in oyster immune reactions and functions as a pro-inflammatory cytokine. Anti-CaHMGB can significantly suppress RLO/LPS-induced inflammatory responses and hemocyte necrosis and apoptosis, suggesting that Ca-HMGB is a potential target to prevent and control RLO/LPS-induced disease or inflammation. [ABSTRACT FROM AUTHOR]

Abstract: We identified a tetraspanin family member gene, named Ca-TSP, in the oyster Crassostrea ariakensis and found that the transcription profiles of Ca-TSP were variable in the oyster hemocytes. Three distinct patterns of variation of Ca-TSP were observed. Using immunofluorescence and immunoelectron microscopy, we show that Ca-TSP was present in granules and in vesicular structures of the oyster hemocyte. Sequence analysis, structural features and immunogold electron microscopy showed that Ca-TSP is an integral membrane glycoprotein of granules of hemocyte and may be a novel CD63-like gene of the tetraspanin family of molluscs. The gene expression analysis of Ca-TSP using isolated oyster hemocytes, was done following challenge of the oysters with LPS and Poly I:C. The Ca-TSP mRNA levels increased in hemocytes in the first 12 h after LPS and Poly I:C stimulation, and decreased after the addition of H2O2. Western blot analysis using anti-Ca-TSP antibody indicated that gene expression and protein levels were similar. The recombinant Ca-TSP was found to significantly inhibit hemocytes aggregation. Our results suggested that Ca-TSP participates in the innate immunity of the oyster. [Copyright &y& Elsevier]

Abstract: A SMARTer™ cDNA library of hemocyte from Rickettsia-like organism (RLO) challenged oyster, Crassostrea ariakensis Gould was constructed. Random clones (400) were selected and single-pass sequenced, resulted in 200 unique sequences containing 96 known genes and 104 unknown genes. The 96 known genes were categorized into 11 groups based on their biological process. Furthermore, we identified and characterized three complement-related fragments (CaC1q1, CaC1q2 and CaC3). Tissue distribution analysis revealed that all of three fragments were ubiquitously expressed in all tissues studied including hemocyte, gills, mantle, digestive glands, gonads and adductor muscle, while the highest level was seen in the hemocyte. Temporal expression profile in the hemocyte monolayers reveled that the mRNA expression levels of three fragments presented huge increase after the RLO incubation at 3 h and 6 h in post-challenge, respectively. And the maximal expression levels at 3 h in post-challenge are about 256, 104 and 64 times higher than the values detected in the control of CaC1q1, CaC1q2 and CaC3, respectively. [Copyright &y& Elsevier]

Crassostrea sikamea and C. ariakensis are two oysters from Asia that are sympatric and differ slightly in their environmental preference. They can hybridize in one direction, although the fertilization level and survival of hybrid larvae to spat are low. To understand the possible effects of salinity on cross-fertilization and the survival of hybrid larvae, we conducted hybridization experiments at four salinities (20, 25, 30 and 35 ppt). At all salinities, about 10% of C. sikamea eggs were fertilized by C. ariakensis sperm, while the reciprocal cross completely failed to fertilize. Survival of fertilized eggs to D-stage in the hybrid cross (C. sikamea female×C. ariakensis male, SA) was significantly (P<0.05) higher at 35 ppt than at lower salinities, while the effect of salinity was not significant in two pure-species crosses. High salinity negatively affected larval survival to day 7 in C. ariakensis and the hybrid cross. Larval growth in all groups was negatively correlated with salinity (P<0.01). Larval shell height at day 7 as well as daily increment was significantly smaller for hybrid than for purebred larvae (P<0.05). These results indicate that hybrid larvae prefer high salinity during the early stages of development but low salinity at later stages. The low and one-directional fertilization represents a pre-zygote barrier to hybridization, which may play a role in sympatric speciation. [ABSTRACT FROM AUTHOR]

Introducing non-native species can create serious environmental risks, such as changing the attributes of ecosystem, displacing the native species, clogging the natural waterways and channels. Careful examination of the possible consequences before implementation can prevent the adverse consequences of invasive species. However, policy analysis for such an action is often difficult, due to the complexity of the marine environment, and the interactions among the species therein. This paper presents a spatial-explicit agent-based simulation model for analyzing the environmental risks of introducing non-native species, Suminoe oyster ( Crassostrea ariakensis). It is considered to be introduced into the Chesapeake Bay, USA, where there is a native Oyster species (Eastern oyster, Crassostrea virginica) with declining population. The simulation result indicates that the non-native species will likely displace the native species, but this can be controlled by setting up a different harvest plan, and the location and the number of initial spat introduced. [ABSTRACT FROM AUTHOR]

Triploid oyster induction has been very successful. However, during field culture, a certain proportion of triploids apparently loses one set of chromosomes, 'reverting' to diploid-triploid mosaics. The revertants will lose their aquaculture advantages due to the recovery of reproductive ability. Mitotic chromosomes were observed in mosaics of Crassostrea gigas and Crassostrea Ariakensis to elucidate the cytogenetic mechanism of reversion. Most individuals showed a modal number of 30 in triploid cells and varying numbers of chromosomes in other cells. From all 15 mosaics of C. gigas and 16 mosaics of C. ariakensis individuals, high proportions of aneuploid cells with various numbers of chromosomes were observed. Most of the aneuploid cells were hypotriploid cells with 26-29 chromosomes. Notably, in 10 out of 15 C. gigas and 9 out of 16 C. ariakensis, some cells consisted of 20-26 well-spread chromosomes and 3-10 chromosome 'clumps'. Individuals with more chromosome clumps tended to have higher percentages of hypotriploid cells. The correlation between these two categories of cells was significant ( P<0.05) in C. gigas and highly significant ( P<0.01) in C. ariakensis. Thus, we conclude that some chromosomes are eliminated during mitotic divisions because they clump together and are thus unable to undergo normal segregation. [ABSTRACT FROM AUTHOR]

Reversion from triploids to diploids or heteroploid mosaics may make the revertants recover reproductive ability and lose their aquacultural advantages. Meiotic chromosomes in triploids and mosaics of Crassostrea gigas and Crassostrea ariakensis were studied. Pachytene spermatocytes showed incomplete trivalent formation, varying 64-72% in C. gigas and 62-69% in C. ariakensis. At metaphase I, trivalents, bivalents and univalents occurred in various combinations. Trivalents occurred in all spermatocytes, ranged 6-10 per spermatocyte and averaged 8.53-8.97 in C. gigas and 8.49-8.95 in C. ariakensis. Univalents and bivalents appeared in 59.2-72.1% of the spermatocytes in C. gigas, and ranged 0.77-1.39 and 1.01-1.51 per spermatocyte respectively. In C. ariakensis, they occurred in 57.5-81% of the spermatocytes, and ranged 0.9-1.32 and 1.03-1.35 respectively. The most common trivalent was formed by a bivalent with the third chromosome attaching to its side to form 'long-tail-cross' or 't' or 'frying-pan'-shaped configurations that constituted 65.7% and 59.9% of the trivalents in C. gigas and C. ariakensis respectively. Other kinds of trivalent associations included tandem chains (14.7%, 16.5%), closed circles or triangles (5.3%, 9.8%), convergent 'T' or 'Y' (5.8%, 7.4%) and unclassified configurations (8.5%, 6.4%). Diploid spermatocytes were not observed from mosaics, although they showed considerable proportions of 'diploid' cells in their gills. [ABSTRACT FROM AUTHOR]

Crassostrea ariakensis is an important aquacultured oyster species in Asia, its native region. During the past decade, consideration was given to introducing C. ariakensis into Chesapeake Bay, in the United States, to help revive the declining native oyster industry and bolster the local ecosystem. Little is known about the ecology and biology of this species in Asia due to confusion with nomenclature and difficulty in accurately identifying the species of wild populations in their natural environment. Even less research has been done on the population genetics of native populations of C. ariakensis in Asia. We examined the magnitude and pattern of genetic differentiation among 10 wild populations of C. ariakensis from its confirmed distribution range using eight polymorphic microsatellite markers. Results showed a small but significant global θST (0.018), indicating genetic heterogeneity among populations. Eight genetically distinct populations were further distinguished based on population pairwise θST comparisons, including one in Japan, four in China, and three populations along the coast of South Korea. A significant positive association was detected between genetic and geographic distances among populations, suggesting a genetic pattern of isolation by distance. This research represents a novel observation on wild genetic population structuring in a coastal bivalve species along the coast of the northwest Pacific. [ABSTRACT FROM AUTHOR]

Abstract: Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL/Apo2L) is one of the tumor necrosis factor (TNF) superfamily members, participating in many biological processes including apoptosis and immune responses. In present study, a novel human soluble TRAIL (sTRAIL) homolog, CasTRAIL was identified from the oyster, Crassostrea ariakensis. CasTRAIL has a 99% and 98% similarity to human sTRAIL over the cDNA sequence and the amino acid sequence, respectively. It mostly distributes in tissues of the oyster defense system and was mainly localized at cell membrane, and has no cytotoxicity to normal hemocytes of oyster. The phosphorylation state of MAP kinases revealed that CasTRAIL induced a rapid increase in the phospho-ERK and phospho-p38 levels, which indicated that the MAPK pathway was involved in CasTRAIL-mediated signaling. In addition, CasTRAIL also showed an ability of anti-RLO infection which might be through the p38-MAPK activation pathway. Present studies provide an understanding and insight of the biological functions of CasTRAIL. [Copyright &y& Elsevier]

This investigation was undertaken to understand the temporal trend, the spatial distribution and the residue level of dichloro-diphenyl-trichloroethanes (DDTs) and hexachlorobenzenes(HCHs) in bivalves from the coast of the South China in recent years. Jinjiang oysters (Crassostrea rivularis) were sampled from 15 bays along the coast of Guangdong province, China between 2003 and 2007. Gas chromatography with electron capture detector was used to quantify the contents of HCH isomers (α-, β-, γ-, δ-HCH), DDT isomers (p,p'-, o,p'-DDT), p,p'-DDD and p,p'-DDE in the oyster tissues. The results demonstrate that annual level of DDTs in the tissue increase throughout the study, particularly between 2004 and 2006. The DDTs content in the tissue varied significantly among sampling regions and some sampling sites (p < 0.05). On the other hand, the HCHs content was significantly lower than DDTs content in the tissue (p < 0.01), and remain constant among sampling years, sampling regions and sampling sites (p > 0.10). Predominance of isomer form of DDTs and higher ratio of γ-HCH/HCHs at some sites indicated that recent input of DDT and lindane in the coastal waters of Guangdong, which might be caused by dicofol spraying in crop planting and lacquer painting on fisher boat. In the soft tissues of the oysters, the highest content of HCHs was 1.21 ng/g (wet weight), and DDTs levels ranged from 0.11 ng/g to 76.3 ng/g (wet weight), far below the Maximum Residual Limits in China and many developed nations. [ABSTRACT FROM AUTHOR]

Abstract: An intertidal oyster reef (∼260ha) was created by planting hatchery-reared seed oysters (Crassostrea rivularis) on an artificial concrete modular reef in the Deepwater Navigation Channel Regulation Project of the Yangtze River estuary. We examined the development of reef communities (oyster, barnacle and motile epibenthic macrofauna), characterized nekton use and assessed the habitat value of the constructed reef. The C. rivularis oyster population showed a rapid exponential increase with time and reached maximum density (3410±241ind./m2) and biomass (3175±532g/m2) after one year of restoration. The barnacle Balanus albicostatus was the most abundant sessile macrofauna and had a significantly greater density in the high intertidal zone than in the low intertidal zone (P <0.05). The reef also supported diverse motile epibenthic macrofauna (11 mollusks, 11 crustaceans, 4 annelids and 2 fishes), and the reef-associated communities were numerically dominated by Neanthes japonica, Perinereis aibuhitensis, Nerita yoldi and Littorinopsis intermedia. A total of 50 nekton species (31 fishes, 9 shrimps and 10 crabs) utilized the constructed intertidal oyster reef, and grass shrimp Palaemon spp. dominated the nekton communities in term of abundance. Since the constructed intertidal oyster reef supports a variety of reef communities and abundant nektons, it should be recognized as an important and protective fish habitat in the Yangtze River estuary. [Copyright &y& Elsevier]

Abstract: The Suminoe oyster Crassostrea ariakensis has been attempted to be introduced in the Chesapeake Bay, USA, as an alternative to the eastern oyster Crassostrea virginica. Commercial production of Suminoe oysters is currently restricted due to the incomplete understanding of their biological, physiological and immunological nature. Accordingly, understanding immune system of C. ariakensis is crucial to prevent disease associated mortality and subsequent management of the Suminoe oyster. We investigated immunological activities and morphology of hemocytes of the Suminoe oyster using flow cytometry and light microscopy. Three types of hemocytes were identified in the hemolymph including hyalinocyte, granulocyte and blast-like cells. Hyalinocytes were the largest cells and the most abundant, while granulocytes were intermediate-size cell containing numerous granules in the cytoplasm. Blast-like cells were the smallest and least numerous. Flow cytometry revealed that the granulocytes are most active in the cell phagocytosis and spontaneous reactive oxygen species (ROS) production. The hyalinocytes also showed a certain level of the phagocytosis and oxidative activity but in a lesser extent than the granulocytes. In contrast, the blast-like cells did not show any phagocytosis or oxidative activity. The flow cytometry used in this study confirmed that as observed from other marine bivalves, the granulocytes are the main hemocytes involved in the cellular defence in the Suminoe oyster. [Copyright &y& Elsevier]

Abstract: The BMP1/TLD-like proteinases are pleiotropic, astacin-like metalloproteinases. They play central roles in regulating the formation of the extracellular matrix (ECM) and signaling through various TGFβ-like proteins in morphogenetic and homeostatic events. Here we describe the cloning, structural characterization and expression of Tolloid-like gene in the oyster, Crassostrea ariakensis (CaTLL). The full-length cDNA of CaTLL spans 3492 nucleotides including an open reading frame of 2811 nucleotides which encodes a hypothetical protein of 936 amino acids, with a molecular mass of approximately 103 kDa. The CaTLL molecule possessed structural features of several motifs including an N-terminal signal peptide sequence, a prodomain with an RTRR motif, an astacin-like domain that contains a conserved zinc-binding motif HELGHVIGFWHEH, five CUBs and two EGF domains with the arrangement CUB-CUB-EGF-CUB-EGF-CUB-CUB. The proteolytic domain of Ca-Tolloid shares more than 30% identity with other astacins of various animals from squail to mammals, indicating its conserved catalytic ability. RT-PCR and quantitative real-time PCR analyses revealed that CaTLL showed the lowest expression level in hemocytes of normal groups, but was affected significantly by the challenge of an obligate intracellular Gram-negative bacterium, Rickettsia-like organisms, suggesting that Ca-Tolloid might be involved in the molluscan immune response, and its function is more diverse than previously assumed. [Copyright &y& Elsevier]

Crassostrea ariakensis oysters are under review for introduction into the Chesapeake Bay. However, the human health implications of the introduction have not been fully addressed. This study evaluated rates of bioaccumulation, retention, and depuration of viruses by Crassostrea virginica and C. ariakensis when the two oyster species were maintained in separate tanks containing synthetic seawater of various salinities (8, 12, or 20 ppt). Oyster bioaccumulation tanks were seeded with 103 PFU/ml of hepatitis A virus (HAV), poliovirus, male-specific bacteriophage (MS2), and murine norovirus 1 (MNV-1) and 103 PCR units/mI of human norovirus (NoV). After 24 h, depuration commenced as oysters (n = 255) were placed in pathogen-free seawater under continuous filtration. Oysters (n = 6) were sampled weekly for 1 month from each tank. Viral RNA was recovered using a modified proteinase K, guanidine, and glassmilk method and analyzed by quantitative reverse transcription-PCR. The odds of C. ariakensis oysters harboring NoV, MNV-1, or HAV were statistically greater than the odds of C. virginica oysters harboring the same viruses (MNV-1 odds ratio [OR], 4.5; P = 0.01; NoV OR, 8.4; P < 0.001; HAV OR, 11.4; P < 0.001). Unlike C. virginica, C. ariakensis bioaccumulated and retained NoV, MNV-1, and HAY for 1 month at all salinities. Additionally, the odds of an oyster testing positive for NoV was 25.5 times greater (P < 0.001) when the oyster also tested positive for MNV-1. This research helps assess the threat of C. ariakensis as a vehicle for viral pathogens due to the consumption of raw oysters and validates the role for MNV-1 as a surrogate for NoV. [ABSTRACT FROM AUTHOR]

In previous studies, we showed that F 1 hybrids of Crassostrea ariakensis and C. hongkongensis had faster growth and higher survival rates than the parent species. Further intraspecific crossing of F 1 hybrids allowed us to further understand the law of trait segregation and indicated a potential direction for breeding of a new strain with high salinity tolerance and fast growth. In this study, we systematically analyzed the growth, survival, fertility and trait segregation of F 2 hybrids and their grandparent species (C. ariakensis and C. hongkongensis) at two sites. Our results confirmed that there were no significant differences in fertilization, cleavage, D larval and survival rates among the three groups of larvae, but the shell heights of F 2 hybrids and C. ariakensis were significantly higher than those of C. hongkongensis on the 12th and 16th days. At the high salinity site (Zhulin Pond), the shell heights and survival rates of the F 2 hybrids were significantly higher than those of C. hongkongensis from the 90th to the 360th day. However, at the low salinity site (Dafeng River), the F 2 hybrids consistently had higher shell heights than C. ariakensis , but there was no significant difference in the survival rates among the three groups. F 2 hybrids were classified into three types based on size and number of holes on the gill water tubes, and only F 2 -A (like C. ariakensis) and F 2 -H/A (intermediate form) were confirmed to survive at the high salinity site. Moreover, three number of ITS-2 gene fragment were identified in the F 2 hybrids, and only A (like C. ariakensis) and HA (like F 1 hybrids) existed at the high salinity site. Paraffin sections of gonad tissue confirmed that all three types of F 2 hybrids were fertile and could produce mature gametes. In summary, through this comprehensive comparative analysis, we confirmed that F 2 -A and F 2 -H/A hybrids had clear advantages in terms of high salinity tolerance and fast growth over their grandparent species, and had potential to be used as the foundations of a new strain. • The first systematic comparative study of F 2 hybrid and their grandparent species (C. hongkongensis and C. ariakensis). • F 2 hybrids had higher salinity tolerance and faster growth than C. hongkongensis at the high salinity site. • F 2 was separated into three types based on phenotypic and genetic traits, and only two types could survive at high salinity. • F 2 -A and F 2 -H/A have potential for use as the foundations of a new highly salinity-tolerant strain. [ABSTRACT FROM AUTHOR]

Management agencies are considering introducing the Suminoe oyster Crassostrea ariakensis into Chesapeake Bay, USA. It is unknown if the growth of feral populations of this non-native oyster would be regulated by the same predators that once controlled the abundance of the native eastern oyster C. virginica. In laboratory studies, we compared the relative susceptibility of juvenile diploids (shell height < 25 mm) of both oyster species to invertebrate predators of eastern oyster juveniles. Predators included four species of mud crabs [ Rhithropanopeus harrisii (carapace width 7–11 mm), Eurypanopeus depressus (6–21 mm), Dyspanopeus sayi (8–20 mm), and Panopeus herbstii (9–29 mm)], the blue crab Callinectes sapidus (35–65 mm), and two sizes of polyclad flatworms ( Stylochus ellipticus and possibly Euplana gracilis; planar area ≲5 mm2 and ∼14 to 88 mm2). All four species of mud crab and the blue crab preyed significantly (ANOVA, P ≤ 0.05) more on C. ariakensis than on C. virginica, but predation by flatworms of both sizes did not differ significantly between oyster species. The greater susceptibility of C. ariakensis to crab predation was likely due to its shell compression strength being 64% lower than that of C. virginica ( P = 0.005). To test for predator-induced enhancement of shell strength, we held oysters of both species for 54 days in the presence of, but protected from, C. sapidus and R. harrisii. Crabs were fed congeneric oysters twice weekly within each aquarium. Compared to controls, shell strength of C. virginica exposed to R. harrisii increased significantly ( P < 0.043), as did shell strength of both oyster species exposed to C. sapidus ( P < 0.01). Despite the changes in shell strength by both oyster species in the presence of C. sapidus, the shell of C. ariakensis remained 57% weaker than C. virginica. We conclude that, because C. ariakensis exposed to predators continued to have a weaker shell relative to C. virginica, the natural suite of crab and flatworm predators in Chesapeake Bay will likely serve to control the abundance of feral C. ariakensis. We caution that the situation in the natural environment may be sufficiently different in some locations that C. ariakensis may be able to compensate for its greater vulnerability to crab predation and hence become a nuisance species. [ABSTRACT FROM AUTHOR]

The introduction of nonnative oysters (i.e., Crassostrea ariakensis) into the Chesapeake Bay has been proposed as necessary for the restoration of the oyster industry; however, nothing is known about the public health risks related to contamination of these oysters with human pathogens. Commercial market-size C. ariakensis triploids were maintained in large marine tanks with water of low (8-ppt), medium (12-ppt), and high (20-ppt) salinities spiked with 1.0 × 105 transmissive stages of the following human pathogens: Cryptosporidium parvum oocysts, Giardia lamblia cysts, and microsporidian spores (i.e., Encephalitozoon intestinalis, Encephalitozoon hellem, and Enterocytozoon bieneusi). Viable oocysts and spores were still detected in oysters on day 33 post-water inoculation (pwi), and cysts were detected on day 14 pwi. The recovery, bioaccumulation, depuration, and inactivation rates of human waterborne pathogens by C. ariakensis triploids were driven by salinity and were optimal in medium- and high-salinity water. The concentration of human pathogens from ambient water by C. ariakensis and the retention of these pathogens without (or with minimal) inactivation and a very low depuration rate provide evidence that these oysters may present a public health threat upon entering the human food chain, if harvested from polluted water. This conclusion is reinforced by the concentration of waterborne pathogens used in the present study, which was representative of levels of infectious agents in surface waters, including the Chesapeake Bay. Aquacultures of nonnative oysters in the Chesapeake Bay will provide excellent ecological services in regard to efficient cleaning of human-infectious agents from the estuarine waters. [ABSTRACT FROM AUTHOR]

Abstract: Triploid Suminoe oysters, Crassostrea ariakensis, are currently being considered for culture on the mid Atlantic coast of the USA. Despite studies comparing the performance of C. ariakensis with the native oyster, Crassostrea virginica, at the grow-out stage, growth and mortality of C. ariakensis and C. virginica have not been compared during nursery rearing in upwellers. If, as in grow-out bags, triploid C. ariakensis in upwellers grow at significantly faster rates than diploid C. virginica, they may suffer food limitation in intensive nursery systems at flows and densities where diploid C. virginica do not. If a consequence of the rapid growth of C. ariakensis is a thinner shell with greater susceptibility to boring worms, it may require potentially stressful treatment against Polydora spp. These hypotheses were tested in an orthogonal experiment, done in fall 2003, in which triploid C. ariakensis and diploid C. virginica were grown in upwellers with high (11.34×10−3 m3 s−1) or low flow (3.56×10−3 m3 s−1), that were treated or untreated against Polydora spp. (by hypersaline dip and drying) and stocked at high or low densities. In the first 2 weeks of the experiment, during which both species grew rapidly, growth of C. ariakensis was up to seven times greater than C. virginica. This difference was reduced in subsequent weeks, when water temperature began to decrease and rates of growth of each species slowed. Contrary to expectation, neither species displayed sizeable reductions in growth at high as compared to low density. Mortality of C. ariakensis was, however, 1–2% greater at high than low density. C. virginica appeared more susceptible to decreased growth at low flow, although the effect of flow in this experiment was small. Both species suffered greatest mortality when previously treated against Polydora spp. The treatment was, however, effective in reducing infestation, to which C. virginica, contrary to expectation, appeared most susceptible. Thus, it appears that similar conditions are suitable for the culture of triploid C. ariakensis in upwellers as for diploid C. virginica. [Copyright &y& Elsevier]