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This study aimed to evaluate the effect of cultivation conditions in the context of light on the retention of selected vitamins, minerals and polyphenols in the stem and cap of the oyster mushroom (Pleurotus ostreatus L.). Additionally, the effect of the retention of bioactive components on the antioxidant activity of mushroom extracts was evaluated, taking into account the morphological part. Oyster mushrooms grown in the light of 200 lux had higher riboflavin content compared to mushrooms exposed to the light of lower intensity. The thiamine content of the mushrooms dropped with decreasing light intensity during cultivation. The content of biologically active compounds was found to be equal in the stem and the cap. In the case of riboflavin, it was shown that its contents in cap fractions, irrespective of the cultivation method, was statistically significantly higher than in stems. The mineral composition of caps and stems differed from each other. No differences in Zn and Cu content between the morphological parts of the mushroom studied were found. However, it was shown that the stems, regardless of the type of light, contained less iron, magnesium and sodium. Thus, it was observed that limited light exposure caused an increase in the content of total polyphenolic compounds, which did not correlate with antioxidant activity. There was no effect of the light on the antioxidant activity of mushrooms. It was also shown that stem extracts had higher antioxidant activity compared to the extracts obtained from the caps. This findings point to the possibility and potentail of use both fraction of mushrooms in the new food products development.

Purpose of the paper is to determine the expertise practical aspects of bivalve mollusks –oysters.Methodology. Collection and analysis of actual material concerning the investigated problem.Findings. Illustrated in the scientific publications of Ukrainian researchers investigations are significant, but they relate mainly to the mechanisms of marine biological resources development, technical and ecological problems of sea fishing, oyster farming organizing, factors that are involved in the formation of their delicate flavor properties. Oysters are a delicious, high value dietary product and are among the few types of food eaten alive. They are a perishable food product and the cause of rapid spoilage besides pathogenic microorganisms is in the active actionof the mollusk own enzymes. Alive healthy oysters still contain a certain number of microorganisms, the amount of which continuously increases during storage. Oysters are the subject for veterinary and sanitary expertise. The peculiarity of oysters expertise is the mandatory microbiological and bacteriological control to establish their general safety. Organoleptic properties of shellfish are primarily determined during the research. Then researches on the presence of pathogenic microflora are performed, the presence of toxins is determined andbacteriological studies are conducted. In addition to the body of mollusks, the liquid that fills the shell also is examined. Since oysters are benthic animals, their primary microflora corresponds to the microflora ofsea sediment, silt and water. Therefore, simultaneously with the microbiological control of mollusks, seawater from the areas of their cultivation and extraction is controlled. The state standard of Ukraine, which would set the requirements for the quality of oysters, has not been developed, because oysters business in Ukraine is on the initial development stage. Ukraine is a member of the international organization Codex Alimentarius Commission and thestandards of this organization are used as normative documents on the quality and safety of oysters.Originality. The results of the analysis of quality indicators responsible for the safety of eating raw mollusks are described in the article. Research on the extraordinary importance of microbiological criteria of the raw mollusks quality in determining their suitability for consumption and safety for consumers are further developed.The practical value. Aspects of oysters expertise as a biologically valuable food are shown.The need to comply with hygienic rules in the process of natural extraction, cultivation and storage of bivalve mollusks is justified. An urgent need for harmonization of national legislation on food safety with international legislation is stated.

The increasing demand for slipper oyster ( Crassostrea iredalei ) has propelled farmers to expand oyster cultivation areas in the Philippines, chiefly for local consumption and feasibly for export overseas. Being filter feeders, oysters can accumulate pathogens from their surrounding waters, which can cause foodborne diseases once consumed. Monitoring oyster farming areas for microbiological quality and levels of heavy metals is therefore crucial. In the current study, the microbiological quality of oysters and culture waters of the major oyster farming areas in Cogon and Palina rivers and Cabugao bay, located in Roxas City and municipality of Ivisan, Capiz Province, Western Visayas, Philippines, respectively, were examined monthly during the wet (May to October) and dry (November to April) seasons over a period of 12 months. Regardless of the sampling period, high levels of fecal coliforms in the water and Escherichia coli in oysters were noted, clearly illustrating that these oyster growing areas would comply with the lower Class B standard and 'Prohibited' areas under the European Union and United States classification systems, respectively. Moreover, while Salmonella was erratically detected in oysters, V. cholerae and V. parahaemolyticus count were not detected and within acceptable limit, respectively. The levels of heavy metals in oyster's meat were also determined twice, i.e. during the wet (July) and dry (March) seasons. Zn and Cu were the most abundant metals detected while the levels of Pb, Cd, Hg, and Cr were below the regulatory limits set by the European Union and United States Food and Drug Administration, respectively. Taken together, these oyster culture areas studied should be urgently rehabilitated to improve oysters' poor microbiological quality. Additionally, depuration or relaying of oysters harvested from these sites is imperative to ensure quality and safety.

While high levels of siltation are known to be deleterious to eastern oysters (Crassostrea virginica), the collective effect of suspended and bedded sediment is understudied from the perspective of oyster farming and bed restoration. In this study, we used laboratory experiments to explore spat settlement rates on a wild bed proxy substrate (i.e., empty shells on the bottom of experimental tanks) in conditions simulating a siltation event and the presence of suspended spat collectors. Using high-frequency valvometry, we also described the behavioural effects of acute sediment burial on wild adult oysters in situ. The vast majority of larvae settled on bottom substrate as opposed to suspended collectors. Sediment negatively affected overall oyster spat settlement on bottom shell, as spat densities were ≈3 × lower when sediment was present. This negative effect was largely attributed to severely depressed spat densities on the upper side (top) of bottom shells. Settlement on the underside of bottom shell was less affected. Wild adult oyster behaviour was negatively affected by acute burial, which ultimately resulted in death. We suggest that the reduction in settlement in the presence of siltation is likely due to the combined effects of suspended sediment on cue detection and bedded sediment on substrate availability. Given that oysters are ecosystem engineers, the negative effects of siltation on both larval and adult oysters can ultimately result in cascading effects to the surrounding biological community.

Shellfish aquaculture has been proposed to abate eutrophication because it can remove nutrients via shellfish filter-feeding. Using a three-dimensional physical-biogeochemical model, we investigate how effective oyster aquaculture can alleviate eutrophication-driven hypoxia off the Pearl River Estuary. Results show that oysters reduce sediment oxygen consumption and thus hypoxia, by reducing both particulate organic matter directly and regenerated nutrients that support new production of organic matter. The hypoxia reduction is largest when oysters are farmed within the upper water of the low-oxygen zone, and the reduction increases with increasing oyster density although oyster growth becomes slower due to food limitation. When oysters are farmed upstream of the hypoxic zone, the farming-induced hypoxia reduction is small and it declines with increasing oyster density because the nutrients released from the farm can increase downstream organic matter production. An oyster farming area of 10 to 200 km2 yields a hypoxic volume reduction of 10% to 78%, equaling the impact of reducing 10% to 60% of river nutrient input. Our results demonstrate that oyster aquaculture can mitigate eutrophication and hypoxia, but its effectiveness depends on the farming location, areal size, and oyster density, and optimal designs must take into account the circulation and biogeochemical characteristics of the specific ecosystem.

In the last decades the oyster faming stands out as the main mitigating measure to the decline of the fishery, as it presents socio-economic and environmental viability. However, for the success of the activity, it is necessary to understand the stages of cultivation, as well as the growth performance of the species to be cultivated. The present work aims to characterize the growth and survival of Crassostrea tulipa, cultivated on the Amazon coast. For this purpose, oysters were grouped by commercial size class (seed, juvenile, baby, average and masters) and compared the growth rates and their relationships with the abiotic variables. There was no difference in the average growth between the oyster classes, however, when comparing them in the total and percentage growth rates, a higher performance was observed in the oysters classified by juvenile and seed, respectively. The relationship of salinity to oyster growth was evidenced only in the class of juvenile oysters. The cultivation time required to obtain native oysters in the commercial size varied between four and seven months, being inferior to those found in other Brazilian regions.

The use of red grape pomace (GP; Vitis vinifera L. var. Shiraz) as a source of beneficial bioactive compounds in ruminant diets is limited by high levels of indigestible compounds in the grape skin matrix. This problem demands innovative, inexpensive, and easy-to-use strategies that improve the digestibility of GP. The bioconversion of GP using edible oyster mushrooms (Pleurotus ostreatus) is one such strategy that has not been previously explored. Therefore, this study evaluated the effect of cultivating oyster mushrooms on GP on chemical composition and in vitro ruminal fermentation parameters of the spent mushroom substrate. The GP was inoculated with oyster mushroom spawns at 0, 200, 300, 400, or 500 g/kg, and incubated for 4 weeks. Organic matter, acid detergent lignin, sodium, manganese, cobalt, and copper linearly declined (P < 0.05) as spawn rates increased. A quadratic trend was observed for crude protein, neutral detergent fibre, acid detergent fibre, magnesium, phosphorus, and calcium content in response to increasing spawn rates. Higher spawning rates (20–50%) had a positive effect (P < 0.05) on gas production from the immediately fermentable fraction (a), rate of gas production from the slowly fermentable fraction (c) and effective gas production. However, gas production from the slowly fermentable fraction (b) and potential gas production linearly declined in response to increasing spawning rates. There was a linear increase (P < 0.05) in the immediately degradable fraction (a), while quadratic effects were observed for partition factors, effective degradability, and in vitro organic matter degradability at 48 h in response to spawning rates. It can be concluded that inoculating GP with oyster mushroom spawn reduced fibre content while increasing crude protein content and in vitro ruminal fermentation efficiency of red grape pomace. Based on the quadratic responses of partition factors at 48 hours post-inoculation, the optimum spawning rate for maximum ruminal fermentation efficiency of GP was determined to be 300 g/kg.

The objective of this study was to assess the effect of environmental factors on the microbiological quality of water and oyster flesh (Crassostrea gasar) farmed in two Amazon estuaries in Para, Brazil. The estuaries were located in the Nova Olinda community in Augusto Correa (site 1) and the Lauro Sodre community in Curuca (site 2). Physicochemical water parameters (the rainfall, salinity, temperature and pH) were evaluated over a one-year period. A total of six liters of water and 720 oyster samples from oyster farms were used to analyze coliforms, Escherichia coli, coagulase-positive staphylococci, molds, yeasts and Salmonella spp. The rainfall and salinity were the environmental factors that most strongly influenced the microbiological quality of the water and oyster flesh. The mean total and thermotolerant coliforms were higher in the farming water from site 2 (Curuca) than from site 1. The oyster flesh from site 1 (Augusto Correa) had higher mean levels of total and thermotolerant coliforms, coagulase-positive staphylococci and molds and yeasts than that from site 2. E. coli was absent from the water and oyster flesh of both sites. Salmonella spp. was found in 38.33 % of oyster flesh with no significant differences across sites and seasonal periods. The water quality was considered good for farming bivalve mollusks. However, the presence of Salmonella spp. in the oyster flesh compromised the sanitary quality and represents a threat to public health. Therefore, depuration facilities and microbiological monitoring are required.

In this work, we identified the bacterial microbiota associated with farmed oystersin estuarine regions of four states in the north eastern region of Brazil. During the drought and rainy seasons, for eight months, twenty oysters were sampled seasonally from seven different marine farms. In the laboratory, DNA extraction, amplification, and sequencing of the 16S rRNA gene were performed to establish the taxonomic units. We identified 106 genera of bacteria belonging to 103 families, 70 orders, 39 classes, and 21 phyla. Out of the total, 40 of the genera represented bacteria potentially pathogenic to humans; of these, nine are known to cause foodborne diseases and six are potentially pathogenic to oysters. The most prevalent genera were Mycoplasma, Propionigenium, Psychrilyobacter, and Arcobacter. The results indicate the need for more systematic monitoring of bacteria of the genus Mycoplasma in oyster farming operations in the Brazilian north eastern region. Currently, Mycoplasma is not one of the microorganisms analysed and monitored by order of Brazilian legislation during the oyster production and/or commercialization process, even though this genus was the most prevalent at all sampling points and presents pathogenic potential both for oysters and for consumers.

Increased levels of norovirus contamination in oysters were reportedly associated with a gastroenteritis epidemic occurring upstream of an oyster farming area. In this study, we monitored the norovirus concentration in oysters weekly between November 2014 and March 2015 and investigated the statistical relationship between norovirus genogroup II (GII) concentrations in oyster and sewage samples and the number of gastroenteritis cases in the area using cross-correlation analysis. A peak correlation coefficient (R = 0.76) at a time lag of +1 week was observed between the number of gastroenteritis cases and norovirus GII concentrations in oysters, indicating that oyster contamination is correlated with the number of gastroenteritis cases with a 1-week delay. Moreover, weekly variations in norovirus GII genotypes in oysters were evaluated using pyrosequencing. Only GII.3 was detected in November and December 2014, whereas GII.17 and GII.4 were present from January to March 2015. GII.17 Kawasaki 2014 strains were detected more frequently than GII.4 Sydney 2012 strains in oyster samples, as previously observed in stool and sewage samples collected during the same study period in Miyagi, Japan. Our observations indicate that there is a time lag between the circulation of norovirus genotypes in the human population and the detection of those genotypes in oysters.

Oyster farming is among the main economic activities in eastern Thailand. The timing of when to harvest and to seed the new mollusk larvae is determined by the salinity of the river, which in turn depends on the influence of the monsoon. The harvest has to be carried out before a mass of fresh water flows down the river in July. The farmers seed the larvae for the next year’s products in December. Global warming potentially extends and intensifies the rainy season, disrupting the harvest cycle and harming oyster products. This research attempts to predict when the rainy season will end by looking at the relationship between the onset of the season in May and the withdrawal in October. Based on statistical analysis, years with an early onset have a late withdrawal, and years with a late onset have an early withdrawal. This knowledge can help farmers decide when to seed the mollusk larvae, and is a useful adaptation tool in dealing with the effects of global warming.

Aquaculture currently provides half of all fish for human consumption, and this proportion is expected to increase to meet the growing global demand for protein. As aquaculture, including oyster farming, expands, it is increasingly important to understand effects on coastal ecosystems. The broad-scale ecological effects of oyster aquaculture are well documented; however, less is known regarding the influence of oyster aquaculture on sediment bacterial communities. To better understand this relationship, we compared three different oyster farming practices that varied in oyster biomass and proximity of oysters to the sediment. We used high-throughput sequencing and quantitative polymerase chain reaction to examine the effect of oyster farming on sediment bacterial communities. We examined the entire bacterial community and looked specifically at bacteria that support essential estuarine ecosystem services (denitrifiers), as well as bacteria that can be detrimental to human health (members of the Vibrio genus). We found that oyster biomass increased Vibrio richness and sediment carbon content, which influenced bacterial community composition. When compared to reference sites, the overall abundance of bacteria was increased by the bottom planting method, but the associated increases in denitrifiers and Vibrio were not significant. We were unable to detect V. parahaemolyticus, V. vulnificus, or V. cholera, the three most common Vibrio pathogens, in any sample, suggesting that oyster farming did not enhance these potential human pathogens in sediments at the time of sampling. These results highlight how differences in oyster farming practice can affect sediment bacterial communities, and the ecosystem services they provide.

Seagrass beds are one of the most important coastal habitats with high productivity and biodiversity, which can provide various ecosystem services for human beings. Therefore, seagrass beds are often considered as a target for ecosystem restoration. This study demonstrated the contribution of oyster farmers’ long-term activities to eelgrass bed restoration in the Hinase area, based on a DNA analysis of the eelgrass population genetic structure using seven microsatellite markers. The Hinase area was famous for the fishing by coastal pound netting to catch the fish and shrimp migrating to eelgrass beds; however, the fishing was gradually replaced with oyster farming because of the massive loss of eelgrass distribution. The fishermen decided to conduct eelgrass bed restoration, which used a seeding method for several decades even after the oyster farming became their major activity, because they already knew eelgrass vegetation can maintain a better coastal environment for oyster farming as well as coastal productivity for fishing. The farmers collected eelgrass seeds from natural sites with better environmental conditions and then sowed those seeds in the sites where eelgrass beds had disappeared. We collected eelgrass shoots as DNA samples from each of the nine sites where they sowed the seeds and from where the farmers collected seeds. The analysis revealed the farmers’ seeding activity did not disturb the genetic structure of natural dispersal but facilitated the recovery of the eelgrass distribution, suggesting that the eelgrass–oyster farmer relationship in Hinase is a good practice as an ideal ecosystem restoration.

The southern coast of Korea comprises many small bays where the Pacific oyster, Crassostrea gigas, has been cultivated intensively employing a long-line hanging culture system. Naturally harvested oyster spats used in the long-line culture system are hardened in mid-intertidal area and transplanted to the center of the bay for grow-out usually in May. The May transferred oyster produced considerably smaller quantity of eggs during spawning in September. To enhance the reproductive effort and growth during grow-out, we transferred the hardened oyster juveniles to grow-out sites in January rather than May to allow them to accumulate energy reserves at the time of spring phytoplankton bloom that normally occurs during April and early May. The January transferred oyster juvenile (JTO) showed fast somatic and shell growth during grow-out, reaching a marketable size in August, while the juvenile oyster transplanted in May (MTO) did not reach a market size until November. JTO spawned from June to September, with a single spawning pulse in July, while most of the MTO spawned in September. Quantity of eggs produced by the JTO was 5.7 times higher than MTO, indicating that early grow-out enhanced egg production. The meat weight and levels of tissue carbohydrate and protein of JTO harvested in November were significantly higher than MTO harvested at the same time, suggesting that the meat quality of JTO is superior to the MTO. Overall, our results suggest that transplanted hardened juveniles to grow-out in January increase natural oyster seed harvest in the bay as well as improve quality of the oyster for marketing. Statement of relevance Oyster farming is one of the leading aquaculture industries in the world, producing over 4 million tons of oysters annually world-wide. In the oyster industry, Crassostrea gigas, the Pacific oyster, has been cultured extensively in Asia, and recently in Europe using different modes of culture. In Asia, the Pacific oysters are raised using subtidal hanging long-line system, while they are cultured in intertidal areas using net bags and rack system in Europe. In Korea and Japan, the oyster seeds are supplied mostly from wild, by harvesting oyster larvae during post-spawning season. The newly harvested oyster spats are stunted in intertidal before they are transplanted to the subtidal hanging long-lines, to maximize survival of the seed oysters. This stunting process is called hardening and the hardening of oyster has been practiced for several decades in Korea and Japan. In Korea, the hardening seed oysters are transplanted in May, and the May transplanted oysters are harvested in December as they grow up to 8 cm in shell length. The May transplanted oysters produce relatively smaller quantity of eggs during their first spawning, although the small reproductive effort may increase their survival during post-spawning season. The natural oyster spats harvested in late summer or early fall for the oyster culture in Korea are mostly originated from the May transplanted oysters. Currently, the natural oyster spat harvest in Korea suffers from insufficient quantity. In part, this insufficiency is associated to the poor reproductive activity of the May transplanted oyster. Low reproductive effort of May transplanted oysters during their first spawning is, in part, associated to too late transplantation to the bay, and earlier transplantation of the stunted oysters from the hardening ground to the grow-out ground in the bay may enhance the reproductive effort, resulting in subsequent successful larval recruitment and settlement of the larvae. Accordingly, we experimentally transplanted the hardened oysters 4 months earlier to the traditional transplanting period (January) and monitored their reproduction and growth. Although the hardening process has been practiced over 50 years, no studies have compared growth and reproduction of differentially transplanted oysters in Korea. As the data demonstrated, January transplanted oyster demonstrated earlier gonad maturation and produced 5 × more eggs during spawning, compared to May transplanted oysters. No severe mortality was observed from the early transplanted oysters during the course of study, although reproductive activity of January transplanted oysters was relatively intensive, compared to May transplanted oysters. The present study first attempted to evaluate effectiveness of transplantation timing of the hardened oysters, in terms of growth and reproduction. Also, quantity of the eggs produced from differentially transplanted female oysters was first measured and compared in this study using ELISA. As the data indicated, January transplanted oyster produced 5 × more eggs, which may enhance the natural oyster spat harvest in the bay, as well as to evaluate the transplantation period and management of oyster farming on the south coast of Korea.

Aquaculture plays an increasingly important role in the growing demand for seafood. Hatchery production of oyster larvae is an integral component of oyster farming, providing single seed for off-bottom farming or larvae for setting on larger substrates for on-bottom farming. Larvae from certain tanks in an established aquaculture enterprise were dying from an unknown etiologic agent. A metagenomic approach was used to examine oyster larvae and water from larval tanks with high and low survival rates to evaluate the epidemiological efficacy of this approach.

The shellfish producers world-wide consider depuration as one of the main options for preserving the viability of their industry. The faster rate of bacterial elimination from polluted shellfish that can be achieved in a recirculating system was confirmed by K. Sangrungruang. The levels of various bacterial species in the depuration water depend on their ability to survive and multiply at different temperatures. The recirculation rate should be such that the rate of kill of bacteria in the depuration water by ultraviolet irradiation exceeds the rate of bacterial multiplication. The recirculation rate of the water in the depuration plant has an important effect on the efficiency of oyster depuration. The etiological agent was a Norwalk virus and the oysters had been harvested from waters that had suffered extreme sewage pollution due to persistent heavy rainfall. The problem is intrinsically linked to the pollution of oyster farming waters with human sewage and associated pathogenic microorganisms.

The presence of Centroceras clavulatum is reported for the first time in the Western Channel, off Bréhat island. We hypothesize and discuss that its presence is linked with the oyster farming activities., Centroceras clavulatum est signalée pour la première fois dans les eaux de l’île de Bréhat. Il s’agit de la première observation de cette espèce en Manche occidentale. L’hypothèse d’une introduction via des transferts d’huîtres est privilégiée.

Oyster farming in estuaries and coastal lagoons frequently overlaps with the distribution of seagrass meadows, yet there are few studies on how this aquaculture practice affects seagrass physiology. We compared in situ nitrogen uptake and the productivity of Zostera marina shoots growing near off-bottom longlines and at a site not affected by oyster farming in San Quintin Bay, a coastal lagoon in Baja California, Mexico. We used benthic chambers to measure leaf NH4 + uptake capacities by pulse labeling with 15NH4 + and plant photosynthesis and respiration. The internal 15N resorption/recycling was measured in shoots 2 weeks after incubations. The natural isotopic composition of eelgrass tissues and vegetative descriptors were also examined. Plants growing at the oyster farming site showed a higher leaf NH4 + uptake rate (33.1 mmol NH4 + m−2 day−1) relative to those not exposed to oyster cultures (25.6 mmol NH4 + m−2 day−1). We calculated that an eelgrass meadow of 15–16 ha (which represents only about 3–4 % of the subtidal eelgrass meadow cover in the western arm of the lagoon) can potentially incorporate the total amount of NH4 + excreted by oysters (∼5.2 × 106 mmol NH4 + day−1). This highlights the potential of eelgrass to act as a natural biofilter for the NH4 + produced by oyster farming. Shoots exposed to oysters were more efficient in re-utilizing the internal 15N into the growth of new leaf tissues or to translocate it to belowground tissues. Photosynthetic rates were greater in shoots exposed to oysters, which is consistent with higher NH4 + uptake and less negative δ13C values. Vegetative production (shoot size, leaf growth) was also higher in these shoots. Aboveground/belowground biomass ratio was lower in eelgrass beds not directly influenced by oyster farms, likely related to the higher investment in belowground biomass to incorporate sedimentary nutrients.

French oyster farming has been experiencing severe mortalities since 2008 in Crassostrea gigas spat and juveniles mainly during the summer months. This recent phenomenon can be explained by the involvement of many factors including pathogenic agents such as the Ostreid Herpesvirus 1 (OsHV-1). From July 2008 to September 2010, 424 oyster samples received from French oyster farmers were tested to follow the concentration of OsHV-1 by quantitative real-time PCR. Comparisons of OsHV-1 loads were also made according to oyster age, ploidy, origin (hatchery-bred or wild-collected) and sample status (healthy or dying). The survey revealed that high viral loads detected in spat and juvenile oyster tissues were associated with summer mortality occurrence. No significant differences were observed in pathogen detection in relation to oyster ploidy and origin. Finally, this study allowed us to define a viral load threshold of 8.8 × 103 of OsHV-1 DNA per mg of tissue, which can be useful to oyster farmers in evaluating mortality risk during the different stages of oyster handling.

Ostreid oysters (the 'true oysters') represent a large and commercially important family of bivalve molluscs. Several species, such as the Pacific oyster (Magallana gigas), the American oyster (Crassostrea virginica), the European oyster (Ostrea edulis) and the Sydney rock oyster (Saccostrea glomerata), are currently farmed at a large scale. However a number of other species may also be suitable for commercial-scale aquaculture. One such species is the 'black-lip oyster', a large Saccostrea species of uncertain taxonomic affinity found in northern Australia. Here, phylogenetic analysis of the COI gene places this oyster within a clade identified in a previous study of Japanese Saccostrea species, 'Saccostrea lineage J'. To facilitate comparisons between this oyster and the better-studied S. glomerata, de novo transcriptomes were generated from larval stages and adult tissues of both species. Patterns of orthology indicated an expansion of repetitive elements within Saccostrea genomes when compared to M. gigas and C. virginica, which may be reflected in increased evolutionary rates and/or genome sizes. The generation of high-quality transcriptomes for these two commercially relevant oysters provides a valuable resource for gene identification and comparison of molecular processes in these and other mollusc species.

Mass die-offs of Pacific oysters have become a widespread concern in northwestern Mexico. Cultivation of the species occurs in shallow inland waters (lagoons, estuaries, and reservoirs) at high stocking densities and under elevated seasonal temperatures; all conditions that are potential causes for high die-offs. Cultivation outside inland waters may be an alternative to reduce the impact of possible stressors. This study compares growth, condition, and survival of oysters ( Crassostrea gigas ) cultivated at different densities within a subtropical lagoon and on the gulf side of Laguna La Cruz in the State of Sonora. Three densities were tested at each site using cultivation trays. Temperature, salinity, oxygen, pH, seston content, and chlorophyll a content were measured at sampling stations inside and outside the lagoon. Results showed that cumulated mortality was significantly lower for oysters cultivated outside the lagoon. Peak mortality occurred in November–December 2006 and March–May 2007, which coincided with mass die-offs in the region and with abrupt changes in temperature. High variations in temperature were related to water masses from the open ocean. Lagoon oysters were influenced by slightly higher mean daily temperatures and showed continuous shell growth and were significantly larger than oysters on the gulf side. However, lagoon oysters showed similar dry weights as gulf side oysters, indicating retarded somatic growth, probably from a relatively low food supply. Gulfside oysters had a higher condition index than oysters in the lagoon throughout the period of study. Results showed that oysters were sensitive to overstocking, since growth at high densities was less than at low densities at both sites. This suggested an advantage for cultivation at intermediate and low densities. Although C. gigas responded in a similar way to overstocking at both sites, they responded differently in relation to culture site. Diminished somatic growth, condition, and survival suggest that oysters in the lagoon experienced more stress than oysters at the gulfside site, probably from differences in water quality. Cultivation of these oysters outside of protected waters is an alternative that producers may try to obtain a better product and reduce mortality.

Oyster farming in estuaries is a globally important industry based primarily around the Pacific oyster Crassostrea gigas , for which a common technique is elevated culture on racks, trestles and other structures. We review literature on cultivation impacts, revealing a research focus and state of knowledge that largely parallels that for other aquaculture species and cultivation methods. Ecological studies of elevated culture effects have focused on changes to the benthos from biodeposition, and largely show that impacts are localized and minor by comparison with many other forms of aquaculture. The broader ecological issues associated with elevated oyster culture include the effects of pests (fouling pests, toxic/noxious microalgae, disease), creation of novel habitat (e.g. by fouling of farm structures and accumulation of shell), alteration to nutrient cycling, depletion of suspended particulate matter by oyster crops, and related effects on higher trophic level animals including fish, seabirds and marine mammals. These issues are less well understood for elevated culture systems, but ecological effects can be inferred from the few studies that have been conducted, from other forms of bivalve aquaculture (e.g. mussels), and to some extent from fundamental knowledge of the role of oysters as ‘ecosystem engineers’. We use a risk ranking method to evaluate ecological risks (and associated uncertainty intervals) for each of the issues associated with estuarine oyster culture, based on subjective assessment of the likelihood and consequences (severity, spatial extent and duration) of adverse effects. Our assessment reveals that the introduction and spread of pest species are potentially important but often overlooked consequences of oyster cultivation. By comparison with most other sources of impact, the spread of pests by aquaculture activities can occur at regional scales, potentially leading to ecologically significant and irreversible changes to coastal ecosystems. We suggest that future studies of cultivation effects redress the balance of effort by focusing more on these significant issues and less on the effects of biodeposition in isolation. Furthermore, the acceptability of aquaculture operations or new developments should recognize the full range of effects, since adverse impacts may be compensated to some extent by the nominally ‘positive’ effects of cultivation (e.g. habitat creation), or may be reduced by appropriate planning and management. Even more broadly, aquaculture developments should be considered in relation to other sources of environmental risk and cumulative impacts to estuarine systems at bay-wide or regional scales, so that the effects of cultivation are placed in context.

An experiment was carried out to compare the performance of various cohorts of oysters Ostrea edulis from each of four different geographic origins that were born and cultured in the same environment. This paper reports the variation of gonad condition of the oysters through on growing and analyses of the relationship between gametogenesis and infection by Bonamia ostreae. Nineteen cohorts of spat were produced in a hatchery from four oyster populations: Irish, Greek, and two Galician: Ortigueira and Coroso; the spat were transferred to a raft in the Ria de Arousa, an area affected by bonamiosis, for grow-out for two years. Significant differences were observed in the temporal pattern of gonad condition between oysters from different geographic origins. Irish oysters showed a short period of gonad activity and a long gonad resting phase. By contrast, Greek oysters had the longest period of gonad activity and the shortest gonad resting phase, as well as the highest percentage of male oysters compared to oysters from other origins. Galician oysters, from both origins, showed a pattern of gonad development intermediate between Irish and Greek, with a higher percentage of females during the second reproductive period. Significant differences were also observed between cohorts within Greek, Coroso and Irish origin, but not from Ortigueira, whose cohorts showed a similar temporal pattern of gonad condition. The differences between oysters from different origins would indicate adaptation to different environments; nevertheless the significant differences that were found between cohorts within origins would indicate that there is variability that eventually could allow adaptation to new environments. Considering sex categories, heavy infections by B. ostreae were significantly more frequent in oysters with a predominant female component; considering gonad stage, heavy infections were significantly more frequent in ripe and partially spawned oysters. The results suggest a hypothetical enhancement of progression of infection by B. ostreae associated with female maturation.

Background Pacific oysters along the North American coast from Washington to Alaska contain concentrations of cadmium (Cd) that are high by comparison with Atlantic oysters, frequently exceeding 2 μg/g wet weight, but it is unclear whether this Cd is absorbed by consumers. Objectives To determine the effect of oyster consumption on Cd in blood and urine among a group with high oyster consumption. Methods Sixty-one non-smoking oyster growers and family members with a mean age of 47.3±7.6 years (range 33–64) were interviewed by telephone to assess their oyster consumption and other sources of Cd exposure at present and 5 years prior to the start of oyster farming. Their blood and urine Cd concentrations were measured. Results The geometric mean Cd concentration in blood was 0.83 μg/L and in urine was 0.76 μg/g creatinine. Thirty-six percent of participants had urinary Cd levels above 1 μg/g creatinine and 5% were above 2 μg/g creatinine. Recent (last 12 months) and long-term oyster consumptions were positive predictors of blood Cd but did not directly predict urinary Cd. The optimal model for predicting the variance in blood Cd included recent intake of oyster-derived Cd, serum iron concentration and recent ketchup consumption (R2=0.34, p=0.00004), with the latter two variables showing a protective effect. The factors found to predict urinary Cd were blood Cd concentration and duration of oyster farming. A rise in blood Cd was observed after 12 years of farming oysters, likely caused by higher consumption of oysters during this period. Conclusions Oyster-derived Cd is bioavailable and affects body stores of the metal.

Parue en abstract dans Frontiers in Veterinary Science; Animal movements are one of the main ways to introduce and spread pathogens. In French oyster farming, many stakeholders and premises are heterogeneously divided over the country and a highly dynamic flow of oysters exists among them. In the context of animal disease surveillance and control, analysis of the animal movement’ network can provide useful information to build adapted surveillance strategies or to develop risk management. Movement network analysis has been widely used in terrestrial production, to evaluate the vulnerability of animal movement network to the spread of a specific disease.In France, since 2008, Pacific oyster spat (Crassostrea gigas) has been affected by massive mortality outbreaks associated with the detection of a newly reported variant of ostreid herpesvirus type 1 (OsHV-1). These mortality events have a direct economic impact causing considerable concern to oyster farmers. A previous epidemiological study has highlighted the potential role of oyster transfers in the spread of these outbreaks. However, neither mandatory database nor reliable data is publicly available concerning oyster transfers in France.In this context, a field study was carried out in the main oyster production area in France, Charente-Maritime bay, to map oyster movements and to characterize the corresponding network structure related to potential disease spread. Seventy-five oyster farmers were randomly selected in Charente-Maritime bay between July and September 2010, according to a stratified sampling design based on farm category regarding production type and location (i.e. spat producers, local farmers, beyond farmers, local farmer-senders, beyond farmer-senders). Data related to the farm characteristics and activities, routine rearing scheme and potential changes in husbandry practices were collected during a face-to-face interview of the oyster farmer, using a standardized questionnaire and a land register. Movement data were spatialized and analyzed using social network analysis.A 85.3% participation rate to the study was obtained. Results showed a seasonal variation of oyster transfers in all the sampling strata, with peaks of transfers in spring and autumn, and different geographical patterns of oyster transfers between strata. Growing sites were shared by farms belonging to different farm category which have different behaviour related to oyster movements in time. These results show heterogeneity of contacts between strata both in time and space. Network measures allowed identifying the growing sites having a high risk of becoming infected, of transmitting diseases to other sites or controlling the flow of oysters from one part of the network to another part. The growing sites at high risk of becoming infected could be targeted for surveillance activities (Figure 1). The growing sites at high risk of transmitting diseases to other sites could be the first ones where implementation of early or enhanced control measures (e.g. quarantine, depopulation) could be focused. The growing sites controlling the flow of oysters could be considered as key players in the initial spread of a disease. If these sites would be removed from the network by early movement restriction, this may contribute to contain the disease spread in a smaller part of the area, providing that the propagation by the marine currents and the effect of environmental factors are considered all together.As a conclusion, movement network analysis may provide valuable information to policy makers in preparedness (surveillance) and response (control) to an epidemic.

The Pacific oyster Crassostrea gigas was introduced from Japan to many countries in the world for oyster farming, resulting in the establishment of wild populations in intertidal zones and resource competition with local faunas. This study examined physiological responses of wild oysters and farmed oysters to thermal (15 °C, 25 °C, 37 °C and 44 °C) and salinity stress (39, 50 and 60 ppt). The wild oysters produced more 72 kDa heat shock proteins when the temperature increased from 15 °C to 25 °C and 37 °C and the salinity increased from 39 to 50 and 60 ppt. However, the amount of 69 kDa heat shock protein was similar between farmed and wild oysters when the temperature increased from 15 °C to the sublethal temperature 37 °C, but it was lower in wild oysters than in farmed oysters when the temperature increased from 15 °C to the lethal temperature 44 °C. In the tissues, wild oysters used more glycogen to promote metabolic activities by increasing the level of AEC (adenylate energy charge). The results suggest that farmed oysters might have limited ability to cope with heat stress due to low energy reserve and glycolysis activity for HSP synthesis. This study provides experimental evidence on differential responses between wild and farmed oysters to temperature and salinity changes, leading to a better understanding on the pattern of distribution for invading oyster species in the marine environment and the adaptation of marine invertebrates to the threat of climate change.

Oysters Crassostrea virginica are 'keystone' estuarine species in the southeastern USA, providing essential fish habitat, food for human consumption, filtration of water bodies, and protection against shoreline erosion. Relatively few oyster pathology studies have been conducted in Georgia. The parasitic protozoan Perkinsus marinus was first observed here in the 1960s, but has not been investigated since the late 1990s, when increasing oyster infection levels were apparent. In the late 1990s and early 2000s, the region suffered a prolonged drought, resulting in elevated salinities and the proliferation of various diseases in the marine environment. By 2003, salinities had returned to normal levels, but the effect of the drought on oysters was unknown. In June 2003, oyster reefs throughout Chatham County were sampled to evaluate the prevalence and intensity of P. marinus. The disease appears to have remained prevalent in the coastal waters of Georgia (100% prevalence at some sites), but the intensity was low, ranging from 0 to 1.83 on a scale where heavy infections rated a score of 5. While the disease did not occur at levels high enough to cause oyster mortalities, further monitoring, particularly on a temporal scale, is warranted.

Shellfish aquaculture is an expanding industry in coastal British Columbia, Canada, and occurs in important wintering areas for surf scoters (Melanitta perspicillata) and white-winged scoters (M. fusca). We quantified habitat use by scoters in relation to natural environmental attributes and habitat modifications associated with shellfish aquaculture. We found that, despite the extensive clam and oyster farming in our study area, densities of wintering surf scoters and white-winged scoters were related primarily to natural environmental attributes, particularly intertidal area, clam density, and sediment type; shellfish aquaculture variables were generally poor predictors of bird densities. We conclude that current levels and forms of shellfish aquaculture in our study site were not an important determinant of scoter distribution and abundance, suggesting that winter scoter populations and the shellfish aquaculture industry may be mutually sustainable. We caution that intensification or further industrialization of shellfish aquaculture in British Columbia could eventually lead to detrimental effects if some threshold level of habitat modification is exceeded.

Seed losses of Pacific oysters Crassostrea gigas have been associated with an ostreid herpesvirus-1 (OsHV-1) in Europe, and in 2002, a similar OsHV was detected in Tomales Bay, California, USA. In May of 2003, 5 stocks of seed Pacific oysters were planted at 2 sites (Inner Bay and Outer Bay) in Tomales Bay and monitored for mortality, presence/prevalence of OsHV (using polymerase chain reaction [PCR] and histology), and growth. Temperature (degrees C) and salinity data were collected every half an hour at each site. OsHV was detected at both the Inner and Outer Bay sites on the same sample date and mean temperature predicted OsHV presence (p0.005). High levels of mortality occurred 2 wk (Inner Bay site) and 4 wk (Outer Bay site) after OsHV detection. OsHV presence predicted mortality (p = 0.01). Temperature maximums and overall temperature exposure were greater at the Inner Bay site and may explain why mortality affected these oysters sooner than oysters planted at the Outer Bay site. Differences in cumulative mortality were significant among stocks (p0.0001), but not between sites (p0.05). OsHV prevalence was similar among stocks (p0.05) and between sites (p0.05). No evidence of herpesvirus-induced Cowdry type A nuclear inclusions or other pathogens were observed. Changes in tissue and cellular architecture including dilation of the digestive tubules and nuclear chromatin margination and pycnosis were observed in OsHV-infected oysters, consistent with previously observed OsHV infections. Stocks with smaller oysters had higher mortality rates than those with larger oysters; growth rate did not correlate with mortalities (p0.05). Taken together, these data suggest that the OsHV may cause or act in synergy with temperature to kill Pacific oyster seed in Tomales Bay, but further investigation of OsHV etiology in seed oysters is needed.

The impact of Eastern oyster culture (Crassostrea virginica) on the benthic environment at a shellfish farm in New Brunswick, Canada, was assessed using recommended methods for routine environmental monitoring, specifically measurements of sediment redox and sulfide levels. Maximum culture density was equivalent to 4000 oyster bags per hectare, or a final oyster biomass of 8 kg m− 2. Two culture sites, one with floating bags and one with oyster tables, as well as two reference sites were monitored over 17 months (June 2002–October 2003). Seasonal variations in sediment redox and sulfide levels were observed, but no significant differences were detected between the culture and the reference sites. Biodeposition associated with the oyster biomass contributed to increased sedimentation rates of organic matter at the oyster table site, but there was no indication of organic enrichment in the sediment. Macrofauna biomass, abundance and number of species were higher at the oyster table site than at the other sites in September 2002, but values were similar for all sites in September 2003. In this region of eastern Canada, the bays are typically shallow and the upper layers of the sediment are frequently subjected to re-suspension by wave activity and physical erosion by winter ice. Given these highly dynamic conditions and the relatively low stocking densities per hectare, we would argue that the potential impact of oyster culture on the environment should be assessed on the basis of parameters other than sediment redox and sulfide levels.

Infection by Bonamia ostreae has caused extensive mortalities of oysters Ostrea edulis through European and United States coasts for at least 25 years. The development of a bonamiosis-resistant strain seems a promising strategy to fight against the disease. As a first step, evaluation of variability in productive traits and disease susceptibility of European populations was performed to identify favourable oyster populations with which to start selective breeding in Galicia (NW Spain). Oysters taken from Greece, Ireland, Ortigueira (Galicia) and Coroso (Galicia) were used as brood stock, and 19 seed families were produced (4–5 families from each origin). The oyster families were used to assess variability through on-growing in an area of the Ria de Arousa heavily affected by bonamiosis. Results showed significant differences in growth, mortality and susceptibility to bonamiosis and other diseases, both between origins and between families under origins. Bonamiosis was associated with mortality in the late stage of oyster on-growing. Indications of natural selection of bonamiosis less-susceptible oysters due to the long exposure of the Ortigueira population to bonamiosis were found. Other symbionts and pathological conditions were detected, of which herpes-like viral infections and disseminated neoplasia could also cause mortality. An index of the overall incidence of pathological conditions (OIPC) was estimated for each family. A significant correlation between the OIPC and the cumulative mortality of the families was noted. On average, oysters from autochthonous origins showed better performance. The results obtained with the best-performing families suggest that the profitability of oyster farming in Galicia would improve, even under bonamiosis pressure, by using appropriate oyster spat.

The protistan parasite Mikrocytos mackini, causative agent of Denman Island disease (mikrocytosis), induces mortality and reduces marketability in the Pacific oyster, Crassostrea gigas, in British Columbia, Canada. This parasite is a pathogen of international concern because it infects a range of oyster species, and because its life cycle and mode of transmission are unknown. A digoxigenin-labelled DNA probe in situ hybridisation technique (DIG–ISH) was developed, and its detection sensitivity was compared to standard histological sections stained with haematoxylin and eosin stain (H&E-histo). In H&E-histo preparations, the detection of M. mackini was certain only when the parasite occurred within the vesicular connective tissue of adult oysters. However, the DIG–ISH technique clearly demonstrated the presence of infection in all other host tissues as well as in juvenile oysters with poorly developed vesicular connective tissue. The probe hybridised strongly to M. mackini, did not hybridise to oyster tissues or with the other shellfish parasites tested, and was more sensitive for detecting infections when compared to H&E-histo.

We have developed a PCR-assay for the diagnosis of juvenile oyster disease (JOD) based on the detection of Roseovarius crassostreae directly from affected oysters. Species-specific primers are used to amplify the 16S-23S rDNA internal transcribed spacer (ITS) of R. crassostreae, and confirmation of product identity is accomplished by restriction enzyme analysis. No false positives were obtained with either closely related bacterial species or from other DNAs present in oyster samples. The assay has the potential to detect as few as 10 cells of R. crassostreae per oyster when samples are taken from the inner valve surfaces of the animal. Inclusion of material from soft body surfaces is not necessary, and may reduce sensitivity approximately 10-fold. In a JOD-affected population, a positive PCR result was obtained from all oysters from which these bacteria were subsequently cultured. The assay also detected the presence of R. crassostreae in 2 oysters from which no R. crassostreae isolates were recovered. No R. crassostreae was detected by either PCR or bacteriology in oysters from a population that was not exhibiting JOD-signs. This assay is expected to advance regional disease management efforts and provide valuable insights into the disease process and epizootiology of JOD.

Among the increasing number of species introduced to coastal regions by man, only a few are able to establish themselves and spread in their new environments. We will show that the Pacific oyster (Crassostrea gigas) took 17 years before a large population of several million oysters became established on natural mussel beds in the vicinity of an oyster farm near the island of Sylt (northern Wadden Sea, eastern North Sea). The first oyster, which had dispersed as a larva and settled on a mussel bed, was discovered 5 years after oyster farming had commenced. Data on abundance and size-frequency distribution of oysters on intertidal mussel beds around the island indicate that recruitment was patchy and occurred only in 6 out of 18 years. Significant proportions of these cohorts survived for at least 5 years. The population slowly expanded its range from intertidal to subtidal locations as well as from Sylt north- and southwards along the coastline. Abundances of more than 300 oysters m−2 on mussel beds were observed in 2003, only after two consecutive spatfalls in 2001 and 2002. Analyses of mean monthly water temperatures indicate that recruitment coincided with above-average temperatures in July and August when spawning and planktonic dispersal occurs. We conclude that the further invasion of C. gigas in the northern Wadden Sea will depend on high late-summer water temperatures.

Oyster shells are a waste product from mariculture that presents a major disposal problem in coastal regions such as southeast Korea. It was found in the present study that pyrolysis of waste oyster shells under defined conditions (750 °C for 1 h under a nitrogen atmosphere) transforms this material into a sustainable reagent for efficient (up to 98%) removal of phosphates from wastewater. In comparison, raw oyster shells removed almost no phosphate from water, whereas oyster shells heated to 750 °C under an air atmosphere removed a moderate proportion (up to 68%) of phosphates from water. X-ray diffraction (XRD) analysis of pyrolyzed oyster shells showed peaks that were characteristic of calcium oxide, whereas analysis of raw oyster shells showed peaks that were characteristic of calcium carbonate. Surface morphology of pyrolyzed oyster shells also differed from that of raw oyster shells. Preliminary economic feasibility analysis indicates that cost of activated oyster shell is competitive with other wastewater treatment chemicals.

Cultured pearl production requires grafting of a pearl nucleus, together with a piece of mantle tissue (‘saibo’) from a donor oyster, into a recipient oyster. The donor mantle tissue is an important factor in determining pearl quality. It is desirable that donor oysters resulting in high quality pearls be used as the basis for future hatchery production to ensure high quality pearl production; however, donor oysters are killed as part of the grafting process. This study was conducted to assess the feasibility of keeping donor pearl oysters alive as potential broodstock. To determine whether mantle tissue could be removed from oysters without mortality, Akoya pearl oysters (Pinctada fucata) were anaesthetised with 500 mg l−1 of benzocaine and had the ventral margin of either their left, right or both left and right mantle lobes removed. Survival after 4 weeks was 100% for all treatments and oysters showed regeneration of excised mantle tissue. After 3 months, histological analyses showed complete regeneration of the mantle and its structures. These findings show that donor pearl oysters recover from removal of mantle tissue and could be used as future broodstock for pearl culture operations.

A population dynamics model was used to simulate variations in the standing stock of the Pacific oyster, Crassostrea gigas, to assess the marketable production in Thau Lagoon (France) and to evaluate the sensitivity of this production to environmental conditions. The model is based on a continuous equation of the oyster abundance as a function of individual growth rate, inter-individual growth variability and mortality rate. The growth model depends on water temperature, particulate organic matter concentration and total individual mass. Inter-individual growth variability was introduced into the general population dynamics equation by a diffusion coefficient K that was set to 0.05. The population dynamics model took into account the two culture methods (i.e. "collees" and "pignes" oysters) and rearing strategies of oyster farmers by using timetables of seeding and harvesting obtained through interviews of oyster farmers. Distributions of standing stocks were obtained through assessments conducted in the lagoon in March 2000, October 2000 and March 2001 and were used to calibrate the model. The model estimated the total marketable production at ca. 17,900 t between March 2000 and March 2001. The major part of the production (ca. 70%) was in spring. Seventy percent of the annual production came from "collees" oysters. Sensitivity analyses showed that the key parameters are those related to harvesting. The model was used to evaluate the effects of different environmental conditions (e.g. a decrease in the oyster growth rate, a harvesting closure due a toxic algae bloom, a massive summer mortality due to an anoxic crisis) on short- and long-term variations in the standing stock and the production for both culture methods. A decrease in the growth rate of ca. 20% resulted in losses of 18% in the first year of production for both culture methods. Long-term simulations showed that the production of "pignes" oysters was more affected than that of the "collees" oysters (reductions of 26% and 4%, respectively). Simulated scenarios included a 2-month long harvesting closure (i.e. November and December) or a massive summer mortality (i.e. 45% and 20% for "collees" and "pignes" oysters, respectively). No long-term effect was predicted for either event, although losses of ca. 10% were estimated in the first year of production for both culture techniques. The model can be a useful tool for predicting marketable production of oysters as a function of rearing strategy and environmental conditions.

Bivalve molluscs are filter feeders, with pearl oysters able to filter water at rates up to 25 l h −1 g −1 of dry wt. tissue. Since this process leads to rapid bioaccumulation of recalcitrant pollutants such as heavy metals, organochlorine pesticides and hydrocarbons from impacted sites, it has prompted the widespread use of molluscs as biomonitors to quantify levels of marine pollution. This paper proposes pearl oyster deployment as a novel bioremediation technology for impacted sites to remove toxic contaminants, reduce nutrient loads and lower concentrations of microbial pathogens. Estimates extrapolated from the literature suggest that a modest pearl oyster farm of 100 t oyster material per year could remove 300 kg heavy metals plus 24 kg of organic contaminants via deposition into the tissue and shell. Furthermore, it was estimated that up to 19 kg of nitrogen may be removed from the coastal ecosystem per tonne of pearl oyster harvested. Pearl oysters are also likely to filter substantial amounts of sewage associated microbial pathogens from the water column. Method of cultivation and site selection are the key to minimising negative environmental impacts of bivalve cultivation. Deployment of oysters at sites with high nutrient and contaminant loadings would be advantageous, as these compounds would be removed from the ecosystem whilst generating a value-added product. Future potential may exist for harvesting bio-concentrated elements for commercial production.

Populations of eastern oysters Crassostrea virginica along the east coast of North America have repeatedly experienced epizootic mass mortality due to infections by protozoan parasites, and molecular diagnostic methodologies are fast becoming more widely available for the diagnosis of protozoan diseases of oysters. In this study we applied a modified version of an existing multiplex polymerase chain reaction (PCR) for detection of the eastern oyster parasites Haplosporidium nelsoni, H. costale and Perkinsus marinus from field-collected samples. We incorporated primers for DNA quality control based on the large subunit ribosomal RNA (LSU rRNA) gene of C. virginica. The multiplex PCR (MPCR) simultaneously amplified genomic DNA of C. virginica, and cloned DNA of H. nelsoni, P. marinus and H. costale. In field trial applications, we compared the performance of the MPCR to that of the conventional diagnostic techniques of histopathological tissue examination and the Ray/Mackin fluid thioglycollate medium (RMFT) assay. A total of 530 oysters were sampled from 18 sites at 12 locations along the east coast of the United States from the Gulf of Mexico to southern New England. The modified MPCR detected 21% oysters with H. nelsoni, 2% oysters with H. costale, and 40% oysters with P. marinus infections. In comparison, histopathological examination detected H. nelsoni and H. costale infections in 6 and 0.8% oysters, respectively, and the RMFT assay detected P. marinus infection in 31% oysters. The MPCR is a more sensitive diagnostic assay for detection of H. nelsoni, H. costale, and P. marinus, and incorporation of an oyster quality control product limits false negative results.

The dinoflagellate Alexandrium minutum strain AM89BM was studied to investigate its capacity to adapt to different salinities and the influence of salinity on cellular content of paralytic shellfish toxins (PST), in batch culture in enriched offshore seawater media. The strain shows optimal growth (average rate � 0.5 div day � 1 ) at salinities between 20 and 37 p.s.u., peaking at 25 p.s.u. (0.63 � 0.07 div day � 1 ). Under a high NO3 ‐ :PO4 3‐ mole ratio (76), cell PST content increased during growth phase, peaking toward the end of growth phase or in the early stationary phase. The PST content was low (� 10 fmol PST cell � 1 ) from 30 to 37 p.s.u., but it increased at lower salinities, with the maximum value (� 50 fmol PST cell � 1 ) recorded at 15 p.s.u. We then compared growth rate and toxin content of A. minutum cells grown in 3- and 0.2-m filtered estuarine water (27 p.s.u.), and a similarly filtered seawater collected from an oyster farming area (36 p.s.u.), with a N- and P-enriched offshore seawater (37 p.s.u.). In both estuarine water treatments, growth was fast (� 0.8 div day � 1 ) and the cell PST content increased only in the early growth phase, peaking in mid-growth phase at 9.56 � 1.06 and 7.63 � 0.44 fmol PST cell � 1 in the 3- and 0.2-m filtered waters, respectively. In the 3-m filtered oyster farm water, although inorganic nutrient concentrations were very low, A. minutum grew well (0.68 � 0.06 div day � 1 ), suggesting mixotrophic nutrition; as PST production was nearly zero, the cell toxin content decreasing to 1.11 fmol PST cell � 1 , we hypothesize that toxin biosynthesis was greatly weakened due to the lack of amino acid precursors in prey material. In the offshore seawater, A. minutum grew slowly (0.18 � 0.04 div day � 1 ) and cells lost toxins down to 1.08 fmol PST cell � 1 , suggesting that growth was limited and PST production stopped due to the lack of some vitamins, and/or trace metals.

The paramyxean protozoan, Marteilia sydneyi , is the etiological agent of QX disease in Sydney rock oysters ( Saccostrea glomerata ). QX disease affects the farming of oysters in Queensland and on five rivers in New South Wales (NSW), Australia. Disease outbreaks occur during summer months (January to April) and are associated with high mortality rates (up to 98%), which limit the growing out period for oyster production. This study investigated the relationship between oyster host defense systems and QX disease. Oysters from the same brood stock were harvested from QX prone and QX free growing areas over the course of the 2000–2001 outbreak. A variety of parameters—infection intensity in the digestive diverticulum, total hemolymph protein content, condition index and phenoloxidase (PO) activity—were measured in these oysters. Phenoloxidase activity, which is often associated with host defense, was significantly suppressed in oysters from the QX prone area when compared to those from the QX free river. There was also a strict negative correlation between phenoloxidase activity and the intensity of parasitic infection ( p =0.0038). In contrast, neither total protein content nor condition indexes differed between oysters from the QX prone and QX free rivers. These data suggest that inhibition of prophenoloxidase cascade may facilitate lethal infection by M. sydneyi .

A new tool, designed to measure the adductor muscle strength in juvenile oysters, is described. This instrument has been applied for the evaluation of muscle strength (F) in relation to dry weight of shell-free oysters, longitudinal (d1) and transversal (d2) diameters, and to sizes of the opaque (O) and translucent (t) portions of the adductor. Our results have established a link between summer mortality and correlation coefficient computed between (F) and dry weight values in juvenile oysters. The regression between (F) and dry weight values was linear in healthy oyster samples. It was not linear, or correlation coefficient was less significant, in samples presenting high mortality. During a 3-year survey in the Bay of Morlaix, France, >40 different stocks of oysters were tested with this tool, used for the diagnosis of healthy, resistant juveniles and recognition of weak specimens.

Apoptosis, or programmed cell death, has been reported as being pivotal in infectious diseases of different organisms. The effects of apoptosis on the progression and transmission of the protistan parasites Perkinsus marinus and Haplosporidium nelsoni in the eastern oyster Crassostrea virginica were studied. Oysters were diagnosed for their respective infections by standard methods, and apoptosis was detected using in situ hybridization to detect DNA fragments by end labeling on paraffin sections. A digoxigenin nucleotide probe was used to label the 200 bp fragment produced by apoptosis and detected immunohistochemically using an antidigoxigenin peroxidase conjugate. The probe/DNA fragment complex was stained with a peroxidase substrate and tissues were counterstained with methyl green. Uninfected oysters had large numbers of apoptotic hemocytes present in the connective tissue underlying the stomach, gill, and mantle epithelia, whereas oysters infected with P. marinus had a reduced number of apoptotic hemocytes. The parasite may prevent hemocyte apoptosis in order to yield a greater number of hemocytes in which to house itself. Large numbers of P. marinus cells in some infected oysters were eliminated via apoptosis in the stomach epithelia, disabling the spread of infectious particles through seawater. The oysters infected with H. nelsoni also had reduced numbers of apoptotic hemocytes, while part of the vesicular connective tissue cells were apoptotic. H. nelsoni plasmodia were eliminated via apoptosis in some oysters. Apoptosis may enhance progression and prevent transmission of infectious oyster diseases.

In the 1960s, oyster culture in France was greatly perturbated by a mass mortality of cupped oyster caused by infection by the protozoan Marteilia sp. But oyster culture could be resumed by the timely help of export of spat from the port of Sanriku, northern Japan. After examination and identification of the pathogens, a large number of single-seed oysters were exported to France in the 1970s (Koganezawa 1984; Goto 2012).

Light-sensitivity is an important aspect of mollusk survival as it plays a vital role in reproduction and predator avoidance. In the Pacific oyster Crassostrea gigas light sensitivity has been demonstrated in the larval stage but has not yet been conclusively demonstrated in adult oysters. In this paper we describe an experiment which was undertaken to determine if adult Pacific oysters were sensitive to light. One LED flashlight was used to shine light onto adult oysters while they were filtering seawater through their shell openings. We found that the degree of opening increased gradually during the light period but rapidly decreased when the flashlight was turned off in the treated group but not in the control group. These results suggest that adult Pacific oyster may be sensitive to light.

The parasite Bonamia ostreae has caused significant mortalities in the flat oyster Ostrea edulis. To date, methods of control and eradication have proved largely unsuccessful. Research is now concentrating on development of a population of oysters that has increased resistance to bonamiasis. This study evaluated the relative resistance of three Irish strains of flat oysters to this disease: two naive strains that had not previously been exposed to the parasite, and one that has been exposed to B. ostreae since the 1980s and has been selectively bred from survivors. In both field and laboratory trials, oysters from the selected strain showed lower prevalence of infection, intensity of infection and mortalities compared to the two naive strains. Development of a strain showing some resistance to B. ostreae would allow oysters to be grown to market size before significant mortalities occurred, and would also allow restocking of areas that have been decimated by the disease.

A population dynamics model, originally derived for the Eastern oyster Crassostrea virginica and later modified for the Pacific oyster C. gigas in Japan, is applied to investigate the effect of food composition on the growth rate of C. gigas, which is in aquaculture in Kamakman Bay, Korea. Annual environmental cycles of temperature, salinity and particle concentration as well as various measures of food are used in the model. The model reproduces the general features of observed oyster growth in the different regions of the bay. Simulations show that chlorophyll-a is an inadequate measure of food for oysters. Using labile lipid+protein+carbohydrate as a food source results in higher growth rates than observed, suggesting that a surplus of potential food is available in the water column, but that much of it is not utilized by oysters and that little of it is present as chlorophyll containing cells. Assuming that most of the food is available as small particles, which are filtered at low retention efficiency by oysters, results in simulated growth rates that are similar to observed field growth rates. The oyster model used in this research is shown to be generally applicable to the Pacific oyster, C. gigas.

Thiamin and riboflavin (vitamins B1 and B2) were measured in different organs of the Pacific oyster Crassostrea gigas over an annual cycle in Marennes Oleron (France), to study the natural accumulation and their possible transfer to gonads and eggs. We observed an annual cycle of vitamin concentration with low levels in winter and high levels in spring. The first increase was observed in the digestive gland (DG) in March with no change in the mantle plus gonad tissue or muscle, suggesting no immediate transfer to gonad tissue or a strong utilisation of these vitamins in the gonad in winter. A second peak was observed in the DG in spring, coinciding with an increase in the gonad plus mantle and muscle, suggesting that vitamin transfer was immediate in spring. The DG could be an intermediate compartment in vitamin transfer. Riboflavin was mainly concentrated in eggs and disappeared from the gonad during spawning. Thiamin was also concentrated in eggs but also in the gonad–mantle tissue. By artificial conditioning, it was possible to increase the thiamin concentration 2.5-fold in eggs in spring, but riboflavin concentrations remained similar to those in nature. No difference was evident in D-larval production from natural or hatchery spawnings, nor in larval growth rate in spring. Vitamins B1 and B2 in eggs were probably above D-larval requirements in spring (9 and 20 fg/egg (dry weight) for thiamin and riboflavin, respectively). Low vitamin concentrations observed in winter coinciding with gonadal mitoses and glycogen metabolism, could be explained by a high vitamin utilisation for these biological processes. These results may explain low levels of vitamins observed in eggs from winter conditioning of oysters as natural vitamin concentration in this period is low, and transfer to gonads seems limited.

Infections of a population of Crassostrea gigas by the copepod Mytilicola orientalis were examined at an oyster growing site at Dungarvan, County Waterford, Ireland. Twenty-one samples, each consisting of 20 to 30 oysters have been examined over 2 yr. Condition, sex, reproductive stage, length, weight, glycogen content and other parasite burdens of the oysters were examined in relation to the degree of infection of M. orientalis; 14.38% of oysters were infested. Mean abundance was 0.6 oyster -1 . The maximum number of copepods in an oyster was 20. M. orientalis had no effect on condition, growth, sex, stage or glycogen content of the oyster but correlated with shell burrowing by Polydora sp.

Mass mortalities of the Japanese pearl oyster Pinctada fucata martensii have widely occurred in western Japan since 1994. The causes of these mass mortalities are at present not thoroughly understood. In this study, we investigated oyster survival in relation to some environmental factors such as water temperature, concentration of chlorophyll a and density or composition of phytoplankton. The examined mass mortality occurred from September to December 1998, and the color on the adductor muscle of the oysters was red-brown, suggesting an infectious disease. Oysters that became moribund during the experiment lost weight, while the weight of unaffected oysters increased. The cell density of Nitzschia spp., an inedible algae for the oyster, in Uchiumi Bay increased before and during the mass mortality event. From the results of our study, we hypothesize that P. fucata martensii was weakened by starvation because of the dominance of inedible food and then contracted an infectious disease that resulted in mortality.