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Blooms of Alexandrium catenella threaten to disrupt subsistence, recreational, and commercial shellfish harvest in Alaska, as the paralytic shellfish toxins (PSTs) produced pose a serious public health risk and can lead to costly shutdowns for shellfish farmers. Current methods of PST detection in the region range from monitoring programs utilizing net tows to detect A. catenella to direct shellfish tissue testing via mouse bioassay (MBA) for commercial aquaculture harvest, as well as various optional testing methods for subsistence and recreational harvesters. The efficacy and feasibility of these methods vary, and they have not been directly compared in Southeast Alaska. In this study, we sought to assess and compare A. catenella and PST early detection methods to determine which can provide the most effective and accurate warning of A. catenella blooms or PST events. We found microscope counts to be variable and prone to missing lower numbers of A. catenella, which may be indicative of bloom formation. However, quantitative polymerase chain reaction (qPCR) significantly correlated with microscope counts and was able to effectively detect even low numbers of A. catenella on all sampling days. Paralytic shellfish toxin concentrations measured by enzyme‐linked immunosorbent assay and MBA significantly correlated with each other, qPCR, and some microscope counts. These results show that qPCR is an effective tool for both monitoring A. catenella and serving as a proxy for PSTs. Further work is needed to refine qPCR protocols in this system to provide bloom warnings on an actionable timescale for the aquaculture industry and other shellfish harvesters. Integr Environ Assess Manag 2024;20:2189–2202. © 2024 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC). This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA. Key Points: The species‐specific quantitative polymerase chain reaction (qPCR) assay effectively detects Alexandrium catenella at numbers too low for other methods.A threshold of ~90 000 000 A. catenella qPCR copies per liter may indicate elevated paralytic shellfish toxins in Pacific oysters.Microscope counts of A. catenella cells are variable and miss low quantities.Enzyme‐linked immunosorbent assays detect elevated paralytic shellfish toxins, and correlate with approved testing methods. [ABSTRACT FROM AUTHOR]

In recent years, Pacific oyster growers in British Columbia (BC), Canada have experienced devastating losses due to summer mortality syndrome. While anecdotal evidence suggests that intertidally-grown oysters may fare better during mass mortality events than deep-water counterparts, there remains a lack of research examining how different culture conditions may influence severity. To address this, we compared growth, condition, histopathology, reproductive status, and survival between intertidally- and deep-watercultured oysters over 2 years at three oyster farms in Baynes Sound (BC). A reciprocal transplant was carried out after 1 year to test the use of the intertidal as a mechanism for promotion of physiological resilience prior to deep-water deployment. Field trial results showed significantly higher final survival in oysters transferred from the intertidal to deep water (83.5%) compared to those maintained in deep water (63.6%), but only at one farm, likely as a consequence of varying physical and/or biological characteristics associated with particular farm locations. Histopathology showed little role of disease with regards to varying survival among treatments, though higher occurrence of Viral Gametocytic Hypertrophy was observed in Year 1 oysters under deepwater (62.2%) versus intertidal (37.8%) conditions. Additionally, after 2 years, there was no significant difference in oyster size nor condition index between oysters transplanted from the intertidal to deep water and those solely cultured in deep water. A laboratory-challenge experiment determined significantly different survival curves of Year 1 intertidally- and deep-water-cultured oysters under immersion/emersion and warming conditions, with final survival of 88% and 64%, respectively, under conditions of high temperature (25°C) and immersion. Likewise, Year 2 (i.e. post-transfer) intertidally- and deep-water-cultured oysters showed significantly different survival curves under laboratory-based Vibrio challenge conditions (16°C) with final survival of 63% and 34%, respectively. Results suggest that partial culture in the intertidal at some farms may be an effective method for conferring resilience to summer mortality in Pacific oysters. [ABSTRACT FROM AUTHOR]

Dichloro-Diphenyl-Trichloroethane (DDTs) are potent organic toxins widely used in agriculture and malaria prevention. The extensive use of DDTs has raised concerns about their adverse impacts. This study aimed to evaluate the toxicity of DDTs on Pacific oyster (Crassostrea gigas) larvae and embryos in the lower Sai Gon-Dong Nai River. We exposed oyster larvae and embryos to sediment samples containing DDT concentrations of 0.01, 0.05, 0.1, 0.5, and 1 mg·k·g-1, as well as artificial seawater samples with DDT levels of 0, 0.1, 1, 10, and 100 µg·L-1. The analysis results revealed a significant adverse impact of DDTs on the survival ratio of larvae and the cell division of embryos in both water and sediment samples compared to control samples. The Effective Concentrations in embryo cell division capacity (EC50) after 2 and 24 h of exposure were 66.88 and 4.62 µg·L-1 in artificial seawater and 1.1 and 0.3 mg·kg-1 in sediment, respectively. Lethal Concentrations (LC50) were 4.62 µg·L-1 and 0.3 mg·kg-1, respectively. Transmission Electron Microscopy (TEM) and Scanning Electron Microscope (SEM) images further confirmed the significant morphological disruptions caused by DDTs after 24 h of exposure. These findings indicate that DDT toxicity poses a threat to oyster farming in coastal areas, where chronic pesticide exposure is likely. [ABSTRACT FROM AUTHOR]

Repeated freeze-thaw cycles are among the main causes of quality deterioration in frozen oysters. Here, we focused on changes in texture, pH, moisture distribution, salt-soluble protein content, secondary structure, sulfhydryl (-SH), malondialdehyde (MDA), and Ca2+-ATPase activity of Pacific oysters (Crassostrea gigas) after each freeze-thaw cycle for five cycles. The protein and fat content of C. gigas deteriorated, and the content of salt-soluble protein decreased significantly in the first three freeze-thaw cycles. MDA and -SH levels decreased significantly in the first two freeze-thaw cycles (P < 0.05), and Ca2+-ATPase decreased significantly in the first three cycles (P < 0.05). Therefore, the number of freeze-thaw cycles of C. gigas should be reduced to the greatest possible extent during freezing and storage, and it would be better to limit the cycle to one time to preserve the quality of C. gigas. [ABSTRACT FROM AUTHOR]

Summary: Globally, Pacific oysters (Crassostrea gigas) have a high market demand owing to their increased nutritional value. Crassostrea gigas can be a dietary source to meet the daily nutritional needs. Several studies have evaluated the nutritional value and bioactivity of C. gigas. However, a review of studies examining the nutritional value and bioactivity of C. gigas has not been previously performed. This study aimed to review the studies evaluating the nutritional value and bioactivities of C. gigas components using the Preferred Reporting Items for Systematic Reviews and Meta‐Analyses guidelines. The online databases Web of Science, ScienceDirect, MEDLINE and PubMed were searched to retrieve published studies on the nutritional value and bioactivity of C. gigas. Among the 37 studies obtained after filtering, the highest number of studies evaluated other bioactivities of C. gigas, followed by studies evaluating the antioxidant activity. This review examined the C. gigas components, including protein, moisture, glycogen, minerals, essential amino acids and fatty acids, which exerted beneficial effects on human health. Environmental conditions and cultivation techniques influenced the nutritional contents of C. gigas. The bioactive components of C. gigas exhibited antimicrobial, antioxidant, anti‐inflammatory, antitumor and anticancer, hepatoprotective, antihypertensive, hypoglycaemic, skin whitening, skin immunomodulatory, antiwrinkle, cholesterol‐lowering, antiaudiogenic seizure and probiotic activities. In conclusion, C. gigas has a high nutritional value and comprises various bioactive components. Thus, C. gigas can be a source of bioactive components and a functional food. However, most studies evaluating the bioactivity of C. gigas were performed in vitro. [ABSTRACT FROM AUTHOR]

Mortality outbreaks of young Pacific oysters, Crassostrea gigas , have seriously affected the oyster-farming economy in several countries around the world. Although the causes of these mortality outbreaks appear complex, a viral agent has been identified as the main factor: a herpesvirus called ostreid herpesvirus 1 (OsHV-1). Autophagy is an important degradation pathway involved in the response to several pathologies including viral diseases. In C. gigas , recent studies indicate that this pathway is conserved and functional in at least haemocytes and the mantle. Furthermore, an experimental infection in combination with compounds known to inhibit or induce autophagy in mammals revealed that autophagy is involved in the response to OsHV-1 infection. In light of these results, the aim of this study was to determine the role of autophagy in the response of the Pacific oyster to infection by virus OsHV-1. For this purpose, an experimental infection in combination with a modulator of autophagy was performed on Pacific oysters known to have intermediate susceptibility to OsHV-1 infection. In haemolymph and the mantle, the autophagy response was monitored by flow cytometry, western blotting, and real-time PCR. At the same time, viral infection was evaluated by quantifying viral DNA and RNA amounts by real-time PCR. Although the results showed activation of autophagy in haemolymph and the mantle 14 hours post infection (after viral replication was initiated), they were also indicative of different regulatory mechanisms of autophagy in the two tissues, thus supporting an important function of autophagy in the response to virus OsHV-1. [ABSTRACT FROM AUTHOR]

• The effects of depuration salinity and duration on preservation were evaluated. • The mortality increased with 72 h depuration and 20% salinity fluctuation. • The SWATH-MS-based proteomic was developed to analysis protein changes. • 381 different expression proteins (DEPs) in total uncovered by proteomics analysis. • Most DEPs were relevant to amino acid metabolism. Depuration and anhydrous living-preservation are two important and consecutive steps during the circulation of Pacific oyster (Crassostrea gigas), and two main factors in depuration, salinity and duration, are pivotal to posterior anhydrous living-preservation of C. gigas. In this work, the comprehensive effects of depuration salinity (26–38 g/L) and duration (0–72 h) on anhydrous living-preservation at 4 °C for 7 days were investigated in regard of mortality, biochemical indexes (fatty acids profile analysis, glycogen) and proteome changes as well. The results showed that the mortality of C. gigas increased obviously with 72 h depuration and especially with 20 % salinity fluctuation, concomitantly accompanying metabolism disorder. Furthermore, alterations in salinity and duration resulted in 381 different expression proteins (DEPs), which were gotten more involved in the pathways related to amino acid metabolism. Taken together, it was suggested that duration < 48 h and salinity fluctuations lower than 10 % were the preferred conditions for anhydrous living-preservation. [ABSTRACT FROM AUTHOR]

• The changes of flavor in C. gigas during depuration were characterized. • The flavor of C. gigas improved after 48 h depuration. • Significant alterations in the metabolite level across various depuration periods. • The content of aldehydes, ketones, and alcohols was the lowest at 48 h depuration. The flavor of Pacific oyster (Crassostrea gigas) significantly changed during the depuration process. This work aimed to explore the mechanism of flavor changes during the 72 h depuration by metabolomics combined with gas chromatography-ion mobility spectrometry (GC-IMS). The metabolomics analysis indicated that carbohydrate metabolism was more affected in the early stage of depuration, including the citrate cycle, glyoxylae and dicarboxylate metabolism, etc. After 72 h depuration, it affected mainly the metabolism of global and overview maps and nucleoside metabolism, etc. The equivalent umami concentration (EUC) value was calculated and exhibited a gradual increase following a 48 h depuration. The GC–MS results revealed that the content of furans was the highest, and the content of aldehydes, ketones, and alcohols was the lowest after 48 h depuration, while the content of aldehydes, ketones, and alcohols increased after 72 h depuration. All these results suggested the depuration period was recommended to be controlled within 48 h. [ABSTRACT FROM AUTHOR]

• The quality and flavor of C. gigas were investigated at different LNF temperatures. • −80 °C LNF maintained the hardness and muscle fiber structure of C. gigas. • −80 °C LNF preserved flavor properties of C. gigas , such as 1-Octen-3-ol. • LNF at −100 °C resulted in freeze-crack and reduced the quality of C. gigas. • Recommended to use −80 °C LNF for liquid nitrogen flash freezing. This study aimed to evaluate the effects of different liquid nitrogen freezing (LNF) temperatures (-20, −40, −60, −80, and −100 °C) on the water holding capacity, texture, microstructure, and flavor of Crassostrea gigas (C. gigas). The results showed that −40 °C LNF, −60 °C LNF, and −80 °C LNF improved the water holding capacity of C. gigas (P < 0.05); −60 °C LNF and −80 °C LNF could effectively maintain the hardness of the body trunk and adductor muscles. Compared with −20 °C refrigerator freezing (RF), the LNF group could form smaller ice crystals and thus reduce the damage to the muscle cell structure damage, especially LNF at −80 °C. Gas chromatography-ion mobility spectrometry (GC-IMS) and e-nose results indicated that −80 °C LNF maintained the flavor profile of few aldehydes and alcohols compared to other freezing groups. Therefore, −80 °C LNF effectively improved the quality and maintain the flavor characteristics of frozen C. gigas. [ABSTRACT FROM AUTHOR]

Depuration is a vital stage to ensure the safety of oyster consumption, and salinity had a great impact on the environmental adaptability of oysters, but the underlying molecular mechanism was poorly understood during depuration stage. Here, Crassostrea gigas was depurated for 72 h at different salinity (26, 29, 32, 35, 38 g/L, corresponding to ±20%, ±10% salinity fluctuation away from oyster's production area) and then analyzed by using transcriptome, proteome, and metabolome combined with bioinformatics techniques. The transcriptome showed that the salinity stress led to 3185 differentially expressed genes and mainly enriched in amino acid metabolism, carbohydrate metabolism, lipid metabolism, etc. A total of 464 differentially expressed proteins were screened by the proteome, and the number of up-regulated expression proteins was less than the down-regulated, indicating that the salinity stress would affect the regulation of metabolism and immunity in oysters. 248 metabolites significantly changed in response to depuration salinity stress in oysters, including phosphate organic acids and their derivatives, lipids, etc. The results of integrated omics analysis indicated that the depuration salinity stress induced abnormal metabolism of the citrate cycle (TCA cycle), lipid metabolism, glycolysis, nucleotide metabolism, ribosome, ATP-binding cassette (ABC) transport pathway, etc. By contrast with Pro-depuration, more radical responses were observed in the S38 group. Based on the results, we suggested that the 10% salinity fluctuation was suitable for oyster depuration and the combination of multi-omics analysis could provide a new perspective for the analysis of the mechanism changes. • Multi-omics was applied to study depuration salinity effect on C. gigas. • 248 metabolites, 464 proteins, and 3185 genes were significantly altered. • More radical responses were observed in the S38 group. • 10% salinity fluctuation was suitable for oyster depuration. [ABSTRACT FROM AUTHOR]

• Proteomic analysis revealed differentiating proteins (DPs) in C. gigas. • Levels of DPs associated with glycolysis increased with salinity stress. • Levels of DPs associated with ECM-receptor interaction pathway increased. • Depuration in 38 g/L salinity was detrimental to oyster quality. • Depuration salinity fluctuation should be controlled within ± 10% of production area. Salinity stress during depuration of Pacific oysters (Crassostrea gigas) leads to degradation in quality; therefore, an understanding of the molecular mechanisms regulating dynamic changes during depuration is needed. Here, C. gigas was depurated for 72 h at salinities ranging from 26 to 38 g/L, a ± 10–20% fluctuation from that in the production area, and the gill proteomes were analyzed by sequential window acquisition of all theoretical fragment ion mass spectra (SWATH-MS). Of the 1218 proteins analyzed, 241 were differentiating proteins (DPs). Salinity stress led to increased levels of DPs associated with glycolysis and the extracellular matrix–receptor interaction pathway, and decreased levels of DPs associated with the citric acid cycle, lipid metabolism, genetic information processing, and cell transformation, especially in oysters exposed to 38 g/L salinity (+20%). Controlling salinity fluctuation within ± 10% of the production area during depuration was conducive to maintaining quality in C. gigas. [ABSTRACT FROM AUTHOR]

Hepatic fibrosis may contribute to liver carcinoma and the mortality of patients with hepatic fibrosis is gradually increasing. However, no definitive treatment has been established for hepatic fibrosis. The hepatic fibrotic process is reversible and can be controlled; therefore, the creation of novel and effective therapeutic methods to prevent or reverse the disease is required. The aim of the present study was to identify whether protein extracts from Pacific oysters (PEPO) could alleviate the hepatic fibrosis induced by CCl4 and to examine the mechanisms involved. A total of sixty rats were randomly divided into the following experimental groups: The normal control group; the hepatic fibrosis model group; the high-dose; medium-dose; and low-dose PEPO groups; and the colchicine group. The results indicated that compared with those of the model group, PEPO treatment significantly decreased the serum levels of alanine aminotransferase, aspartate aminotransferase, γ-glutamyltransferase, alkaline phosphatase, hyaluronic acid, laminin, collagen type IV and procollagen III in rats with hepatic fibrosis. The hematoxylin and eosin staining demonstrated that PEPO markedly alleviated hepatic fibrosis. The experiments using immunohistochemistry, western blotting and quantitative PCR indicated that protein and mRNA expression levels of connective tissue growth factor (CTGF), transforming growth factor β1 (TGFβ-1) and nuclear factor κB (NF-κB) in the liver tissues were significantly reduced by PEPO treatment. Therefore, it was concluded that PEPO successfully alleviated hepatic fibrosis induced by CCl4 and reversed the effects of hepatotoxicity by regulating the serum levels of enzymes and decreasing the expression levels of CTGF, TGF-β1 and NF-κB in liver tissues. These findings may provide a novel treatment option for patients with hepatic fibrosis in the future. [ABSTRACT FROM AUTHOR]

Abstract: An antimicrobial polypeptide was purified from an acidified gill extract of Pacific oyster (Crassostrea gigas) by C18 reversed-phase HPLC. The purified polypeptide had a molecular weight of 8471Da containing 74 amino acid residues. Comparison of the obtained N-terminal sequences with those of others revealed that it was identical to ubiquitin reported from other species and named cgUbiquitin. cgUbiquitin showed broad potent antimicrobial activity against Gram-positive and -negative bacteria including Streptococcus iniae and Vibrio parahemolyticus (minimal effective concentrations, 7.8 and 9.8μg/mL), respectively, without hemolytic activity. The cgUbiquitin cDNA was identified from an expressed sequence tag (EST) library of oyster gill as a precursor form, encoding ubiquitin consisting of 76 amino acids fused to ribosomal protein of S27. Although the cgUbiquitin precursor mRNA was expressed at the intermediate level in the gill, the mRNA was significantly up-regulated at 48h post injection with Vibrio sp. Analysis of the cgUbiquitin C-terminus by carboxypeptidase B treatment and comparison of the retention times revealed that cgUbiquitin lacks the terminal Gly–Gly doublet and ends in an C-terminal Arg residue which might be related to antimicrobial activity. Study of the kinetics of killing and membrane permeabilization showed that this peptide was not membrane permeable and acted through a bacteriostatic process. According to the homology modeling, this peptide is composed of three secondary structural motifs including three α-helices and four β-strands separated by 7 loops regions. Our results indicate that cgUbiquitin might be related to the innate immune defenses in the Pacific oyster and this is the first report for antimicrobial function of ubiquitin isolated from any oyster species. [Copyright &y& Elsevier]

Abstract: In order to understand the strategies of physiological adaptation, Pacific oysters were exposed to different concentrations of polycyclic aromatic hydrocarbons (PAHs). In 50 μg l−1, oysters, at first, maintain their metabolism similar to the rate of control. And then, if exposure is prolonged, oysters tend to decrease their energy intake while increasing catabolic cost due to satisfying the energy demand. In 200 μg l−1, the oyster suppresses metabolic energy intake and facilitates excretive metabolism to eliminate intrusive toxins from the body from the beginning of the exposure. Due to the suppressed feeding activities, oysters accelerate lipid or/and carbohydrate catabolism to satisfy the energy demand. A significant decrease of SFG was attributed to decreased energy intake (decreased CR and Abs. eff.) and increased energy expenditure (increased E and R). [Copyright &y& Elsevier]