Oyster Crassostrea Angulata Research Articles

Application of metabolomics approach to investigate the flavor substance differences between triploid and diploid oysters (Crassostrea angulata)

Oysters, particularly Portuguese oyster (Crassostrea angulata), are highly valued for their nutritional and flavor qualities, making them important in global aquaculture. Triploid oysters have gained attention for maintaining higher meat quality year-round compared to diploids, but there is limited research on how ploidy affects their biochemical and flavor profiles. This study uses a non-targeted metabolomics approach, including gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS), to investigate flavor substance differences between triploid and diploid C. angulata. A total of 13 volatile compounds were identified in diploid oysters, while 28 were found in triploids. Significant upregulation of inosine, guanosine, L-aspartic acid, and taurine in triploids contributes to their enhanced flavor profile. Additionally, triploids showed higher nicotinamide concentrations, while diploids had increased 25-hydroxycholesterol. These findings highlight the advantages of triploid oysters in aquaculture for improved flavor and nutrition, supporting their potential for year-round production.

Effects of oxidation reduction potential levels on bacterial density in Portuguese oysters (Crassostrea angulata) utilising a sonoelectrochemical depuration system

ABSTRACT The consumption of raw oysters is on the rise and poses a significant health risk because of the presence of bacteria such as Escherichia coli, Salmonella spp., and Vibrio spp. Sonoelectrochemical technology offers a promising solution by creating nanobubbles charged with negative ions, which effectively kill bacteria in oysters without affecting human health, and is also environmentally friendly. This study evaluated the bacterial reduction capability of this technology on Portuguese oysters (Crassostrea angulata) using different oxidation redox potential (ORP) levels of 450, 600 and 750 mV compared with clean seawater (control) after 8, 16 and 24 hours. The results showed that extended exposure time did not significantly decrease E. coli and Salmonella spp. densities, except for the 750 mV treatment. The ORP level of 750 mV for 16 hours was the most effective in reducing bacterial population in oysters with total Vibrio, E. coli and Salmonella spp. reduced by 1.14, 0.95, and 0.85 logCFU/g, respectively. Further research is needed to optimise oyster depuration using sonoelectrochemical technology to enhance its efficiency and practical application.

4D-FastDIA-based quantitative proteomics reveals protein biomarkers linked to flavor traits between triploid and diploid oysters (Crassostrea angulata)

In this study, the 4D-FastDIA-based quantitative proteomics strategy was employed to identify protein biomarkers linked to flavor traits in triploid and diploid oysters (Crassostrea angulata). A comprehensive analysis identified a total of 61,947 peptides and 9,703 protein groups across four sample groups, with 3,679 common proteins shared among all groups. Differentially expressed proteins (DEPs) were found to be significantly associated with flavor-related traits, revealing notable differences in amino acids, lipids, and nucleotides between triploid and diploid oysters. Enrichment analysis further elucidated significant pathways involved in metabolic processes, biosynthesis, and immune responses. Among the DEPs, 864 were correlated with flavor quality traits, highlighting key proteins such as S-adenosylmethionine synthase and pyruvate kinase as potential biomarkers for flavor traits. These findings provide valuable insights into the molecular mechanisms underlying flavor differences in oysters and offer potential biomarkers for evaluating and enhancing oyster quality.

Comparative transcriptome analysis reveals molecular damage associated with cryopreservation in Crassostrea angulata D-larvae rather than to cryoprotectant exposure

BackgroundThe Portuguese oyster Crassostrea angulata, a bivalve of significant economic and ecological importance, has faced a decline in both production and natural populations due to pathologies, climate change, and anthropogenic factors. To safeguard its genetic diversity and improve reproductive management, cryopreservation emerges as a valuable strategy. However, the cryopreservation methodologies lead to some damage in structures and functions of the cells and tissues that can affect post-thaw quality. Transcriptomics may help to understand the molecular consequences related to cryopreservation steps and therefore to identify different freezability biomarkers. This study investigates the molecular damage induced by cryopreservation in C. angulata D-larvae, focusing on two critical steps: exposure to cryoprotectant solution and the freezing/thawing process.ResultsExpression analysis revealed 3 differentially expressed genes between larvae exposed to cryoprotectant solution and fresh larvae and 611 differentially expressed genes in cryopreserved larvae against fresh larvae. The most significantly enriched gene ontology terms were “carbohydrate metabolic process”, “integral component of membrane” and “chitin binding” for biological processes, cellular components and molecular functions, respectively. Kyoto Encyclopedia of Genes and Genomes enrichment analysis identified the “neuroactive ligand receptor interaction”, “endocytosis” and “spliceosome” as the most enriched pathways. RNA sequencing results were validate by quantitative RT-PCR, once both techniques presented the same gene expression tendency and a group of 11 genes were considered important molecular biomarkers to be used in further studies for the evaluation of cryodamage.ConclusionsThe current work provided valuable insights into the molecular repercussions of cryopreservation on D-larvae of Crassostrea angulata, revealing that the freezing process had a more pronounced impact on larval quality compared to any potential cryoprotectant-induced toxicity. Additionally, was identify 11 genes serving as biomarkers of freezability for D-larvae quality assessment. This research contributes to the development of more effective cryopreservation protocols and detection methods for cryodamage in this species.

The role of Zip1 and Zip3 in cadmium accumulation in Fujian oyster (Crassostrea angulata)

Oysters are notably susceptible to accumulating substantial amounts of cadmium (Cd), leading to food safety concerns, yet the molecular mechanisms are not fully understood. Previous study identified a significant correlation between polymorphisms in the Zip1 and Zip3 of Fujian oyster (Crassostrea angulata) and the levels of Cd accumulation. Zip1 and Zip3, belonging to the Zip family, are primarily responsible for the cellular transport of zinc and other metal ions. To delve deeper into their roles in Cd transport within oysters, this research cloned and analyzed the sequences of Fujian oyster Zip1 and Zip3. The open reading frames for Zip1 and Zip3 were 960 and 978 bp, respectively, encoding proteins of 319 and 325 amino acids. Following Cd exposure, the expression levels of these genes in the mantle, gills, and other tissues initially increased significantly before decreasing, demonstrating a dose-dependent response. The lowest expression levels were observed in the adductor muscle, with Zip1 reaching its highest expression in the mantle and Zip3 in the visceral mass. In vitro RNAi experiments revealed that silencing Zip1 led to a 1.26-fold decrease in new 113Cd accumulation in the mantle, whereas silencing Zip3 resulted in a 1.29-fold increase. Immunohistochemistry showed weak expression of Zip1 and Zip3 proteins in the connective tissue of the mantle. In summary, Zip1 and Zip3 in Fujian oyster can transport Cd as a substrate, and played different roles in the absorption and efflux of Cd.

First feeding of a marine ornamental fish, the White‐barred Goby Amblygobius phalaena: Investigating the optimal initial live feed organisms and optimal feeding density

AbstractObjectiveThe White‐barred Goby Amblygobius phalaena is a popular ornamental fish in the marine aquarium market. To achieve successful commercial production, efficient larval rearing techniques are crucial. Previous studies have achieved successful cultivation of White‐barred Goby larvae by using a combination of three live feed organisms—the ciliate Euplotes sp., the rotifer Brachionus rotundiformis, and the copepod Apocyclops royi nauplii—during the first feeding stage. However, the specific contributions of these live feed organisms to larval survival and growth remain unclear. Moreover, the optimal feeding density for the critical initial live feed organism has not been determined experimentally. In this study, we aimed to enhance the larviculture protocol for White‐barred Goby by introducing Portuguese oyster Crassostrea angulata trochophores and by addressing these knowledge gaps.MethodsLarvae were initially cultured through individual and combined feeding with four live feed organisms: Euplotes sp., Portuguese oyster trochophores, B. rotundiformis, and A. royi nauplii. The objective was to identify the optimal initial live feed organism during the first feeding stage by assessing the survival and growth performance of larvae. Subsequently, using this optimal live feed organism, larvae were cultured at four feeding densities (2, 5, 10, and 20 individuals/mL). Through evaluating feeding incidence, feeding intensity, survival, and growth performance, the aim was to determine the optimal feeding density for the selected live prey.ResultOur experiments revealed that White‐barred Goby larvae could consume both oyster trochophores and Euplotes sp. during the first feeding stage. However, larvae exhibited superior survival and growth performance when fed oyster trochophores. The optimal feeding density of oyster trochophores was determined to be 10 individuals/mL, while a feeding density as high as 20 individuals/mL resulted in decreased larval feeding incidence.ConclusionThese findings have significant implications for enhancing larval production programs for marine ornamental gobies and promoting their sustainable commercialization.

Non-destructive prediction of the total viable count (TVC) in Fujian oysters (Crassostrea angulata) based on the colorimetric sensor array

The total viable count (TVC) is a traditional method for evaluating seafood freshness. This study aimed to predict the TVC of Fujian oysters stored at 4℃ by using the colorimetric sensing array (CSA) technique combined with imaging and visible near-infrared (Vis-NIR) information channels. An optimal quantitative prediction model based on partial least squares (PLS) was established by combining feature variable selection with a data fusion strategy. All three data-fusion strategies showed better predictive performance than the individual datasets. The high-level fusion strategy performed the best, with a root mean square error of prediction (RMSEP) of 0.17, mean absolute error of prediction (MAEP) of 0.14, coefficient of determination of prediction (Rp2) of 0.9822, and residual prediction deviation (RPD) of 7.37. The experimental results showed that CSA combined with multiple detection channels could be effectively used to predict the TVC of Fujian oysters. In this study, a reliable and comprehensive evaluation model was established to achieve a rapid and accurate prediction of oyster freshness.

HIỆN TRẠNG CÔNG NGHỆ SẢN XUẤT GIỐNG VÀ NUÔI THƯƠNG PHẨM HÀU BỒ ĐÀO NHA (CRASSOSTREA ANGULATA) TẠI VIỆT NAM

Portuguese oyster (Crassostrea angulata) is a commercial cultured mollusc which has high economic value due to high growth rate and survival rate. The rapid development of Portuguese oyster aquaculture industry results in some challenges such as shortages of high-quality spat. Spat were imported or reproduced from well-uncontrolled broodstock; leading to disease risk and genetic diversity loss. In addition, spat spawning cycle of Portuguese oysters also has some limitations. Therefore, to close seed production process is one essential step to design culturing areas for sustainable development of oyster industry in Vietnam. This study collected data from Northern, Central and Southern provinces of Vietnam supplied by Department of Agriculture and Rural Development of coastal provinces and Ministry of Agriculture and Rural Development, Vietnam. This article also presents limitations, challenges, and solutions to improve and develop the close seed production cycle of Portuguese oysters in Vietnam.

Adaptive response of triploid Fujian oyster (Crassostrea angulata) to nanoplastic stress: Insights from physiological, metabolomic, and microbial community analyses

Triploid Fujian oyster (Crassostrea angulata) is crucial to aquaculture and coastal ecosystems because of its accelerated growth and heightened resilience against environmental stressors. In light of the increasing prevalence of nanoplastic pollution in the ocean, understanding its potential impact on this organism, particularly its adaptive responses, is of paramount importance. Despite this, the effects of nanoplastic pollution on the physiology of C. angulata remain largely unexplored. In this study, we explored the responses of triploid Fujian oysters to nanoplastic stress during a 14-day exposure period, employing an integrative methodology that included physiological, metabolomic, and 16S rRNA sequencing analyses. Our results demonstrate that the oysters exhibit a strong adaptive response to nanoplastic exposure, characterized by alterations in enzyme activity, metabolic pathways, and microbial community composition, indicative of an adaptive recovery state as opposed to a disordered state. Oysters subjected to elevated nanoplastic levels exhibited adaptive responses primarily by boosting the activity of the antioxidant enzyme catalase and elevating the levels of antioxidants such as adenosine, 3-(4-hydroxyphenyl)pyruvate, D-sorbitol, d-mannose, and unsaturated fatty acids, as well as the functional amino acids l-proline and l-lysine. Nanoplastic treatment also resulted in increased activity of succinate dehydrogenase, a key component of energy metabolism, and increased contents of intermediate metabolites or products of energy metabolism, such as adenosine monophosphate, adenosine, guanosine, creatine, and thiamine. Nanoplastic treatment led to an increase in the abundance of certain advantageous genera of gut bacteria, specifically Phaeobacter and Nautella. The observed adaptive response of triploid Fujian oysters to nanoplastic stress provides valuable insights into the mechanisms underpinning resilience in marine bivalves.

Microplastics in coastal farmed oyster (Crassostrea angulata) shells: Abundance, characteristics, and diversity

One of the most concerning emerging pollutants is microplastics (MPs), which can infiltrate soft tissues of organisms by ingestion, adhesion, and fusing and may even become embedded in biominerals. However, very little evidence is available about MPs in biominerals found in the wild. This study detected the abundance and characteristics of MPs in the shells of farmed oysters (Crassostrea angulata) off the coast of Taiwan and discussed the distribution, accumulation, and diversity in the oyster shells. The results showed that MPs were ubiquitous in oyster shells, with an average abundance of 0.70 ± 0.40 MPs/g. MPs abundance was significantly (p < 0.01) higher in small oyster shells (shell length < 6.5 cm, weight 5–10 g) and inorganic (CaCO3) fraction (HCl digestion) than in large oyster shells (>6.5 cm, 10–25 g) and an organic fraction (H2O2 digestion), respectively. However, there was no significant difference in MPs abundance between the top and bottom shells (p > 0.05). MPs with a size <2 mm accounted for 78.5 %, fibrous MPs for 93.7 %, and rayon for 89.5 %. The MPs diversity integrated index (MPDII) in oyster shells was low (0.27), and the small and fibrous MPs seemed more easily embedded in biominerals. The findings confirm the presence of MPs in oyster shells in coastal environments. In addition, oyster shells may contain higher amounts of MPs than soft tissues 4–5 times, which needs to be confirmed. Further revealing the distribution and accumulation of MPs in water/terrestrial biominerals will help to understand the fate of MPs in the environment.

Comparative study on tetraploid induction of the Fujian oyster Crassostrea angulata utilizing three typical methods

Comparative study on tetraploid induction of the Fujian oyster Crassostrea angulata utilizing three typical methods

Construction and analysis of the chromosome-level haplotype-resolved genomes of two Crassostrea oyster congeners: Crassostrea angulata and Crassostrea gigas.

The Portuguese oyster Crassostrea angulata and the Pacific oyster C. gigas are two major Crassostrea species that are naturally distributed along the Northwest Pacific coast and possess great ecological and economic value. Here, we report the construction and comparative analysis of the chromosome-level haplotype-resolved genomes of the two oyster congeners. Based on a trio-binning strategy, the PacBio high-fidelity and Illumina Hi-C reads of the offspring of the hybrid cross C. angulata (♂) × C. gigas (♀) were partitioned and independently assembled to construct two chromosome-level fully phased genomes. The assembly size (contig N50 size, BUSCO completeness) of the two genomes were 582.4M (12.8M, 99.1%) and 606.4M (5.46M, 98.9%) for C. angulata and C. gigas, respectively, ranking at the top of mollusk genomes with high contiguity and integrity. The general features of the two genomes were highly similar, and 15,475 highly conserved ortholog gene pairs shared identical gene structures and similar genomic locations. Highly similar sequences can be primarily identified in the coding regions, whereas most noncoding regions and introns of genes in the same ortholog group contain substantial small genomic and/or structural variations. Based on population resequencing analysis, a total of 2,756 species-specific single-nucleotide polymorphisms and 1,088 genes possibly under selection were identified. This is the first report of trio-binned fully phased chromosome-level genomes in marine invertebrates. The study provides fundamental resources for the research on mollusk genetics, comparative genomics, and molecular evolution.

Effects of culture conditions (stocking density, water depth and aquaculture gear) on the aquaculture performance of a new Crassostrea angulata variety “Golden oyster#1”

Bivalve molluscs are a high quality animal protein source for humans, and the demand for farmed bivalves is increasing. Among the bivalve molluscs, the Portuguese oyster Crassostrea angulata, is one of the most popular species and is intensively farmed in warm water. In order to further increase the aquaculture yield of C. angulata through cost-effective farming practices, this study was conducted to evaluate the effects of stocking density, water depth and aquaculture gear on the aquaculture performance of C. angulata in the nursery and grow-out phases. The results of this study revealed that both stocking density and water depth affected the survival rate and growth rate of C. angulata in the nursery and grow-out phases. In the nursery phase, high stocking density reduced the survival rate, but was beneficial to the growth of C. angulata spats, while 1.5 m and 3 m were optimum for the survival and growth of C. angulata spats. In the grow-out phase, the use of lantern net/ rope culture, low stocking density with narrow substrate spacing and shallow water (1.5 m) were beneficial to the survival, growth and yeild of C. angulata. The results of this study can be used as a guide to further improve C. angulata aquaculture practices, and fill the knowledge gap on the effects of stocking density, water depth and aquaculture gear on C. angulata aquaculture.

Silver nanoparticle toxicity to the larvae of oyster Crassostrea angulata: Contribution of in vivo dissolution

Understanding the toxic mechanism of silver nanoparticles (AgNPs) is crucial for it risk assessment in marine environment, but the role of Ag+ release in the AgNP toxicity to marine biota is not yet well addressed. This study investigated the toxicity of AgNPs to the veliger larvae of oyster Crassostrea angulata, with a specific focus on the possibility of the involvement of in vivo dissolution of AgNPs in the toxicity via an aggregation-induced emission luminogen (AIEgen)-based imaging technique. AgNO3 exhibited significantly greater toxicity than AgNPs based on the total Ag, as indicated by lower 50 % growth inhibition concentration (EC50). The average concentration of soluble Ag in seawater at the EC50 of AgNPs was far lower than the EC50 of AgNO3, indicating that the AgNP toxicity could not be fully explained by the dissolved Ag in the medium. Despite the comparable soluble Ag concentration in seawater for both treatments, more Ag was accumulated in the larvae exposed to AgNPs, suggesting their ability to directly ingest particulate Ag, which was further confirmed by the presence of AgNPs aggregates in the esophagus and stomach. With the application of AIEgen-based imaging technique, in vivo dissolution of AgNPs in oyster larvae was thoroughly verified by an increase in Ag(I) content in the larvae exposed to AgNPs after depuration. The results collectively implied that apart from the Ag released in the medium, the Ag dissolved from the ingested AgNPs may also greatly contribute to the toxicity of AgNPs toward the oyster larvae. The findings of this work shed new light on the bioavailability and toxicity of AgNPs in marine environment.

Influence of seasonality on the quality of oysters from the Sado and Mira rivers

There is a lack of knowledge about the influence of seasonality on the microbial and physicochemical quality of oysters in Sado and Mira rivers. Water, sediment, and oysters (Crassostrea angulata and Crassostrea gigas) were collected for microbiological, nutritional, and sensory analyses. The microbiological water quality and the oyster shell contamination were better during the warmer months. No seasonal effect was observed on sediments and on oyster meat. A good physicochemical and nutritional quality was also observed, with high content of polyunsaturated fatty acids, including omega-3 fatty acids, resulting in good lipid quality indices. From the sensory evaluation, both oysters’ species were well scored and presented the highest scores (4) in parameters such as cream-ivory colour, sea smell, firmness and juiciness. These attributes denote the freshness degree at the time of the tasting, reflecting the quality of the bivalve.

Applying Dialysis Bags to Grow Microalgae and Measure Grazing Rates by Secondary Producers

Traditional methods using sealed bottles to determine the grazing rates by secondary producers neglect chemical changes induced by biological activities during the incubation, giving rise to instable levels of nutrients, pH, pCO2, pO2 and other chemicals along with changing microalgal cell concentrations and grazers’ metabolism. Here, we used dialysis bags, which allows exchanges of nutrients and gases, to grow microalgae and to determine grazing rates of secondary producers. The specific growth rate of diatom within the dialysis bags increased with increasing water velocities, indicating its suitability to grow microalgae under dynamic water conditions. Then, we compared the grazing rates by the heterotrophic dinoflagellate Noctiluca scintillans measured with the traditional method using polycarbonate (PC) bottles and the approach with the dialysis bags, and found that these two methods gave rise to comparable grazing rates. Nevertheless, the concentrations of inorganic nitrogen and phosphate in the closed PC bottles were about 89–94% lower than those in the dialysis bags due to the microalga’s assimilation. Subsequently, we applied it to determine the grazing rates by a copepod and an oyster (in the presence of other grazers). Consistent results were obtained using the dialysis bags to determine grazing rates by copepods. During the mesocosm (3000 L) experiment in the presence of primary and secondary producers, the grazing rates by the oyster Crassostrea angulata were determined based on the difference of phytoplankton biomass within and outside of the dialysis bags that held all organisms in the mesocosm except the oyster. Since the dialysis bags are permeable to gases, the grazing rates by the oyster under 410 (AC) and 1,000 (HC) μatm CO2 were successfully measured, with a promising result that HC significantly increased the oyster’s grazing. We concluded that using dialysis bags to grow microalgae and to determine grazing rates is a reliable approach, especially under different levels of CO2 and O2.

Assessment of larval quality of two bivalve species, Crassostrea angulata and Chamelea gallina, exposed and cryopreserved with different cryoprotectant solutions

Marine bivalves are valuable resources, however, some shellfish populations are endangered due to factors such as anthropogenic pressure, pathologies or lack of reproduction synchrony. Portuguese oyster (Crassostrea angulata) and striped venus clam (Chamelea gallina) have high socio-economic value and their endangered natural populations require rehabilitation. Cryopreservation is a valuable method for the preservation and management of genetic resources for aquaculture and restocking. Larvae cryopreservation is particularly valuable since diploid organisms are obtained upon thawing. The objective of this work was the establishment of C. angulata and C. gallina D-larvae cryopreservation through the selection of permeant cryoprotectant in the freezing solution, namely ethylene glycol (EG) and dimethyl sulfoxide (Me2SO). Cryoprotectants exposure showed that, in C. angulata, Me2SO promoted significantly higher incidence of abnormalities and enhanced glutathione reductase activity when compared to control (larvae without cryoprotectant exposure) or even to EG treatment. However, for both species, EG significantly reduced D-larvae average path velocity (VAP). In C. angulata post-thaw D-larvae, EG treatment promoted significantly lower motility and velocity when compared to control and Me2SO treatment. Superoxide dismutase (SOD) activity showed a reduction in C. angulata post-thaw D-larvae when compared to control, which was compensated by the enhancement of glutathione peroxidase (GPX) activity. In C. gallina post-thaw D-larvae, only motility, velocity and SOD activity were significantly lower than control. Therefore, the best treatment to cryopreserve C. angulata D-larvae was EG while for C. gallina Me2SO produced better results. This work established for the first time D-larvae cryopreservation protocols for C. angulata and C. gallina.

Histopathologic Lesions in Bivalve Mollusks Found in Portugal: Etiology and Risk Factors

Bivalve mollusks are an important resource due to their socioeconomic value and to the historical and genetic value of some species. Two nationally important oyster species-Portuguese oyster (Crassostrea angulata) and Japanese oyster (Crassostrea gigas) from distinctive areas in Portugal were studied to evaluate their sanitary status. Oysters were sampled from four different sites in Portugal. Oysters collected from Japanese oyster populations were cultivated in a strong ocean-influenced environment and Portuguese oyster populations were cultivated in wild-beds. The histopathological examination of both oyster species revealed the presence of parasites in gills, mantle epithelium, digestive gland tubules and connective tissue, with a moderate prevalence. In both populations was observed hemocytosis in the connective tissue, edema and metaplasia in the digestive gland and tissues necrosis. In wild populations from Sado and Mira estuaries the prevalence of mud blisters and gill lesions were higher than from populations produced on 0.50 m tables from mudflats. Biosecurity measures and diagnostic techniques are fundamental to control pathogenic agents, including the identification of pathogens at an early stage in their life cycles. This will prevent diseases and improve pathogen reduction on transport of animals from different countries and regions to new production areas to avoid the transmission of diseases.

Dioxins Contamination in Sediment and their Effect on Accumulation in the Portuguese Oyster (Crassostrea angulata) and White Shrimp (Litopenaeus Vannamei)

This research aims to realize whether the dioxin accumulation in the oyster and white shrimp which were cultured in the dioxin pollutant sediment. This presented evidence indicated that dioxin was detected in all experimental groups with high concentration accumulated in experiment animals. Observation of the concentration, the PCDD/F, 2,3,7,8-T4CDD was with high concentration in the sediment and declined with the time elapsed. Detection of the dioxin accumulated in the animal, the accumulative maximum amounts was in the oyster as 3746.16 (pg-TEQ/g d.w.) and in the shrimp as 705.44 (pg-TEQ/g d.w.). The detected amount of dioxin in the supernatant was quite low, and less to release into the water. The filter habit animal of oyster and demersal habit of white shrimp were both detected the dioxin accumulated in the organs. As our findings, the dioxin in the sediment is transferred into the oyster and shrimp, the accumulated amount was increased by the bio-magnification with the elapsed time.

One in a Million: Genetic Diversity and Conservation of the Reference Crassostrea angulata Population in Europe from the Sado Estuary (Portugal).

The production of cupped oysters is an important component of European aquaculture. Most of the production relies on the cultivation of the Pacific oyster Crassostrea gigas, although the Portuguese oyster Crassostrea angulata represents a valuable product with both cultural and economic relevance, especially in Portugal. The authors of the present study investigated the genetic diversity of Portuguese oyster populations of the Sado estuary, both from natural oyster beds and aquaculture facilities, through cox1 gene fragment sequencing. Then, a comparison with a wide dataset of cupped oyster sequences obtained from GenBank (up to now the widest available dataset in literature for the Portuguese oyster) was performed. Genetic data obtained from this work confirmed that the Pacific oyster does not occur in the natural oyster beds of the Sado estuary but showed that the species occasionally occurs in the oyster hatcheries. Moreover, the results showed that despite the founder effect and the bottleneck events that the Sado populations have experienced, they still exhibit high haplotype diversity. Risks are arising for the conservation of the Portuguese oyster reference populations of the Sado estuary due to the occurrence of the Pacific oyster in the local hatcheries. Therefore, researchers, local authorities, and oyster producers should work together to avoid the loss of this valuable resource.