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Dissertations / Theses on the topic 'Pacific oyster'

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Published: 4 June 2021
Last updated: 15 June 2025

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1

Davis, Jonathan P. "Studies on the influence of ambient temperature and food supply on growth rate, carbohydrate content and reproductive output in diploid and triploid Pacific oysters, Crassostrea gigas (Thunberg) /." Thesis, Connect to this title online; UW restricted, 1994. http://hdl.handle.net/1773/5347.

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2

Paltiel, Charles J. "An analysis of the 1994-1996 northern Strait of Georgia oyster survey." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/MQ51440.pdf.

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3

Takagi, Masaya. "Studies on the shell formation mechanism of pacific oyster." Kyoto University, 2007. http://hdl.handle.net/2433/136536.

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Kyoto University (京都大学)<br>0048<br>新制・課程博士<br>博士(農学)<br>甲第13117号<br>農博第1622号<br>新制||農||941(附属図書館)<br>学位論文||H19||N4243(農学部図書室)<br>UT51-2007-H390<br>京都大学大学院農学研究科応用生物科学専攻<br>(主査)助教授 豊原 治彦, 教授 田中 克, 教授 永尾 雅哉<br>学位規則第4条第1項該当
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4

Grason, Emily W. Miner Benjamin G. "Alien vs. predator : effects of a native predator on two invasive oyster drills and oysters in Washington State /." Online version, 2010. http://content.wwu.edu/cdm4/item_viewer.php?CISOROOT=/theses&CISOPTR=360&CISOBOX=1&REC=5.

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5

Perera, Percy. "Heavy metal concentrations in the Pacific oyster Crassostrea gigas thesis submitted in partial fulfilment of the degree of Master of Applied Science, Auckland University of Technology, September 2004." Full thesis. Abstract, 2004.

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6

Pieterse, Aldi. "Growth, condition, survival and feeding rate of the Pacific oyster (Crassostrea gigas Thunberg) cultured in three distinct South African environments." Thesis, Stellenbosch : Stellenbosch University, 2013. http://hdl.handle.net/10019.1/79833.

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7

Money, Cathryn. "Trace metal chemical speciation and acute toxicity to Pacific oyster larvae." Thesis, University of Plymouth, 2008. http://hdl.handle.net/10026.1/2252.

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Controlled laboratory studies showed that the toxicity induced by biologically relevant trace metal species of Cu, Cd, Pb and Zn on embryo-larval development occurred at concentrations in excess of those found in the natural environinent, except for Cu in metal perturbed areas. Average free ion concentrations inducing 50% abnormal development( EC50feew) ere determineda s 0.23 nM CU2+8, 8.0 rim Cd2+,1 28 nM Zn2+a nd 3 62 nM Pb 2+ . However, the response to some binary metal combinations indicated enhanced (synergy) toxicity at concentrations relevant for estuarine waters (e. g. EC5of'. for Cu2+i n the presence of C(ý: +, Zn2+a nd Pb2 +w as 0.004,0.02 and 0.04 nM, respectively). A comparison of voltammetric instrumentation (voltammetric in situ profiling (VIP) system versus Hanging Mercury Drop Electrode with potentiostat) highlighted the advantage of high resolution measurements (ca. 20-60 min intervals) for environmental studies and the minimisation of artefacts associated with discrete sampling methodologies. Field-based studies were carried out in two contrasting estuaries in SW England, one heavily impacted with metal contaminants (Fal Estuary) and another subject to greater variety of anthropogenic influences (Tamar Estuary). High resolution in situ trace metal speciationm easurementsc, arried out over tidal cycles, identified important information on the temporal and spatial distributions of biologically relevant dynamic (<4 nm) metal species of Cd, Pb and Cu. Variation in embryo-larval responses to discrete samples from these estuaries, effectively paralleled the metal speciation measurements showing enhanced toxicity when the marine water influence was at its lowest. In both systems, the results indicated that the combined effect of the metals studied was likely to have provided a significant contribution to the bioassay response. However, the difficulty in de-coupling the speciation measurements with biological responses was evident and supports the need for more comprehensive campaigns to study the impact of contaminants on ecosystem functioning. Bioassay and metal speciation analysis techniques were complementary, exhibiting high sensitivity and rapid responses, and would be considered effective screening tools for waters subject to intermittent inputs of metal contaminants and areas with recognised pressures. The integrated approach has extended our knowledge of trace metal speciation in estuarine environments and their effects on the developing embryos of the Pacific oyster. This approach has the potential for wider application.
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8

Evans, Olivia May. "Transmission of Ostreid herpesvirus-1 in the Pacific Oyster (Crassostrea gigas)." Thesis, The University of Sydney, 2016. http://hdl.handle.net/2123/15819.

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Ostreid herpesvirus-1 microvariant (OsHV-1) is a member of the family Malacoherpesviridae within the order Herpesvirales. OsHV-1 microvariants have been responsible for mass mortality events in commercially produced Pacific oysters (Crassostrea gigas) in Australia, New Zealand and Europe, since their first detection in France and Australasia in 2008 and 2010, respectively. OsHV-1 presents a significant threat to the Australian C. gigas industry (worth AU$53 million in 2007/08), with all age and size classes of C. gigas affected by the virus. Oysters <1 year of age are the most susceptible age class, with mortalities of 60% to 100% observed in France and Australia. Of great concern to the industry is the propensity of the virus to persist in a waterway after initial infection, resulting in recurrent, seasonal outbreaks of disease. The commercial production of C. gigas has ceased entirely in two key estuaries in NSW, Australia as a result of the recurrent disease caused by OsHV-1. The need to develop robust farm management strategies that will allow growers to produce C. gigas in the presence of OsHV-1 is apparent. In order to achieve this goal, a thorough understanding of the transmission and spread of OsHV-1, and the factors that lead to transmission and expression of the disease is required. One of the largest knowledge gaps concerns the transmission of the virus in the estuarine environment. This thesis was focused on addressing several of these gaps by assessing the transmission, detection and distribution of OsHV-1 in seawater, the occurrence of OsHV-1 disease outbreaks to identify periods of high and low risk, the persistence of OsHV-1 in farmed and wild oysters and the potential for them to act as sources of virus in subsequent outbreaks, and possible risk factors for OsHV-1 transmission and expression of clinical disease.
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9

Lokmer, Ana [Verfasser]. "Pacific oyster holobiont in the changing environment : a microbial perspective / Ana Lokmer." Kiel : Universitätsbibliothek Kiel, 2018. http://d-nb.info/1169132618/34.

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10

Switzer, Soleil Elana. "Invertebrate fouling community composition associated with Pacific oyster (Crassostrea gigas) suspended tray culture." Thesis, University of British Columbia, 2010. http://hdl.handle.net/2429/21646.

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Fouling organisms associated with suspended oyster aquaculture can significantly increase operational costs for growers and significantly decrease product marketability. Currently, there is little information available on the fouling communities present on deep-water, suspended tray Pacific oysters (Crassostrea gigas). In general, the industry practice in tray production of Pacific oyster is to use plastic trays, but a new polyvinyl-coated metal tray, which accommodates higher oyster densities, has recently become available. The objectives of this thesis were firstly, to assess whether differences exist in the extent of tray fouling between the 2 tray types using abundance, species richness, biomass, and dominance (univariate analyses) and the Bray-Curtis Dissimilarity Coefficient (multivariate, cluster analysis) as measures (Chapter 2) and secondly, to describe variation in the fouling organisms present on the oysters in the 2 tray types using the same univariate and multivariate analyses (Chapter 3). This study took place on a commercial oyster farm between the months of October 2006 and October 2007. Overall, there was little difference in the extent of fouling communities between the tray types, although a few species were present on plastic trays only, but in very low abundance. The fouling communities associated with the trays and oysters were studied in the winter, spring, summer (tray only) and fall to determine seasonal variation in the fouling communities. Abundance, species richness, biomass and dominance in the tray fouling communities were affected by season with the greatest values in July and the lowest values in January. Season also influenced the oyster fouling communities. Abundance, biomass and dominance of the fouling communities on the oysters was higher in October, while species richness was lowest in January compared to April or October. The seasonal changes observed in the fouling communities on both the trays and oysters were driven largely by a few species. High abundances of Caprella mutica and Mytilus sp. on the trays in July could impact oyster growth through the reduction of water flow through the trays or, in the case of Mytilus sp., through direct competition with the oysters for food and/or space.
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11

Cardona, Costa José. "EMBRYOLOGICAL AND MICROMANIPULATION TECHNIQUES IN ZEBRAFISH (Danio rerio) AND PACIFIC OYSTER (Crassostrea gigas)." Doctoral thesis, Universitat Politècnica de València, 2010. http://hdl.handle.net/10251/8326.

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En este trabajo de tesis, se presentan diversos estudios experimentales, desarrollados prin cipalmente en pez cebra pero también en ostra del Pacífico, que persiguen la puesta a punto de técnicas relevantes para la utilización de estas dos especies en el campo de la biomedicina, la toxicogenómica y la acuicultura como modelo experimental. En pez cebra, se han puesto a punto y testado: Técnicas de vitrificación de tejido de aleta caudal, de blastómeras (en microvolúmenes) y de tejido gonadal. Técnica de quimerismo de la línea germinal en estadio MBT, con una penalización previa por radiación ultravioleta de los embriones receptores. Técnica de quimerismo larvario (larvas de 48-72 h) utilizando como donantes células testiculares obtenidas de individuos adultos y previamente criopreservadas. Técnica de transplante nuclear utilizando como donantes núcleos de células somáticas adultas y larvarias. Técnica de electroactivación en medio iónico de oocitos de pez cebra. In ostra del Pacífico, se han puesto a punto y testado: Evaluación de los cambios estacionales en la calidad oocitaria y espermática en ostra del Pacífico. Técnica de electrofusión cigótica de cigotos obtenidos por fecundación in vitro en ostra del Pacífico. Técnicas de vitrificación de tejido de aleta caudal, de blastómeras (en microvolúmenes) y de tejido gonadal. En relación con este grupo de técnicas, señalar el diferente nivel de dificultad de cada una de ellas e incluso de los resultados alcanzados. Así, la vitrificación de tejido de la aleta caudal no ha supuesto problema adicional respecto a la aplicación de dicha técnica en los últimos años a tejidos epiteliales de cinco especies de mamíferos, lo que da idea de la versatilidad en el uso de dicha técnica de vitrificación básica. Por contra, la criopreservación de blastómeras ha supuesto un verdadero reto, ya que los patrones de permeabilidad celular en esta especie acuática es muy diferente a la característica en mamíferos.<br>Cardona Costa, J. (2010). EMBRYOLOGICAL AND MICROMANIPULATION TECHNIQUES IN ZEBRAFISH (Danio rerio) AND PACIFIC OYSTER (Crassostrea gigas) [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/8326<br>Palancia
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12

Bucklin, Katherine Adelaide. "Analysis of the genetic basis of inbreeding depression in the Pacific oyster Crassostrea gigas /." Connect to Digital dissertations. Restricted to UC campuses. Access is free to UC campus dissertations, 2002. http://uclibs.org/PID/11984.

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13

de, Kantzow Maximilian Clarence. "Epidemiological investigations inform Ostreid herpesvirus 1 disease control in Pacific oysters (Crassostrea gigas)." Thesis, University of Sydney, 2020. https://hdl.handle.net/2123/23494.

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The high mortality and economic loss in farmed Pacific oysters (Crassostrea gigas) caused by the virulent microvariant genotypes of Ostreid herpesvirus - 1 (OsHV-1) has spurred research into strategies to mitigate the impact of the disease. The two aims of this thesis are i) to examine the effect of farm management and other risk factors on mortality caused by OsHV-1 during a natural outbreak and ii) to use a laboratory infection model for OsHV-1 that provides control of the environment to examine the specific risk factors and there interactions on mortality due to OsHV-1. Water temperature has a strong effect on OsHV-1 pathogenesis in Pacific oysters that could be leveraged to develop ways to reduce mortality due to OsHV-1 in commercial oyster aquaculture. Exposing oysters to OsHV-1 at a low water temperature (18°C) reduced mortality when oysters were subsequently exposed to OsHV-1 at a higher water temperature (22°C). The different pattern of expression of some immune genes at 18°C compared to at 22°C suggested that the response to OsHV-1 is influenced by different water temperatures and provided an insight into Pacific oyster immune function.
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14

Bagusche, Frauke. "Environmental effects on the physiology of calcification in the Pacific oyster Crassostrea gigas Thunberg, 1793." Thesis, University of Southampton, 2013. https://eprints.soton.ac.uk/355539/.

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15

Cassis, David. "The role of phytoplankton and environmental variables in Pacific oyster (Crassostrea gigas) aquaculture in British Columbia." Thesis, University of British Columbia, 2011. http://hdl.handle.net/2429/39859.

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Pacific oyster aquaculture in British Columbia faces serious challenges, such as high cadmium (Cd) concentrations, low growth and high mortalities during summer, and inability to directly gauge stress levels. The goal of this dissertation was to address these challenges by investigating the role of biological, physical and chemical oceanographic parameters in controlling them in various oyster farms in the Strait of Georgia. Three studies were undertaken. The first, from August 2004 to July 2005, investigated the role of phytoplankton in controlling Cd levels in the oysters in a Deep Bay farm. Phytoplankton mediated the transfer of dissolved Cd to the particulate phase, accounting for 90% of the summer reduction in dissolved Cd. This suggests that phytoplankton act as a sink for dissolved Cd, reducing the main source to the oysters. Two descriptive models for annual oyster Cd concentrations were developed based on environmental variables. The second study, from June to October of 2008, investigated how environmental factors, culture depth and seed size controlled oyster mortality and growth in four farms. Farms with less stratified, colder waters rich in diatoms fared better than those with highly stratified, higher temperature waters and persistent blooms of flagellates. Larger oyster seed presented low mortalities, while smaller seed were more susceptible to adverse conditions due to their ineffective particle processing capabilities. The best yield was obtained at a culture depth of 3 m, despite higher mortalities. A depth manipulation technique was investigated as a means to reduce summer mortalities without success. The third study, during the summer and fall of 2007 in Deep Bay, investigated a novel proteomic technique to detect and quantify heat-shock proteins (HSP) 70 and 90 in oysters to assess their stress levels. Mortalities were relatively low during that year (8.5% accumulated). The abundance of HSP 70 sequences was positively directly with non-harmful diatom biomass and negatively with high temperature and reproductive state. In contrast, the levels of HSP 90 were correlated negatively to the biomass of non-harmful diatoms, and positively to that of potentially-harmful algae, indicating that HSP 70s and 90s may have different triggers.
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16

Mizuta, Darien Danielle. "Water quality improvement and the promotion of cultured oyster production by artificial upwelling." Kyoto University, 2014. http://hdl.handle.net/2433/188768.

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Kyoto University (京都大学)<br>0048<br>新制・課程博士<br>博士(農学)<br>甲第18330号<br>農博第2055号<br>新制||農||1022(附属図書館)<br>学位論文||H26||N4837(農学部図書室)<br>31188<br>京都大学大学院農学研究科応用生物科学専攻<br>(主査)教授 荒井 修亮, 教授 山下 洋, 准教授 笠井 亮秀<br>学位規則第4条第1項該当
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17

Jones, Trevor O. "Uptake and depuration of the antibiotics, oxytetracycline and Romet-30 in the Pacific oyster, Crassostrea gigas (Thunberg)." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/28991.

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Use of antibiotics in the aquaculture industry for the control of bacterial infections in salmon has led to public concern regarding antibiotic residues in salmon tissue and the potential health risk this poses to humans. Oxytetracycline and Romet-30 are two common antibacterial agents utilized to control disease in the local finfish aquaculture industry of British Columbia, Canada. Many fish farms in British Columbia are located within close proximity to existing shellfish stocks. The potential for antibiotic bioconcentration and the production of bacterial resistance to the drugs in bivalves is a concern. The development of a solid phase extraction technique for these two drugs from Pacific oysters, Crassostrea gigas was accomplished. Analysis of whole oysters via HPLC revealed detectable levels of oxytetracycline and Romet-30 up to 4 weeks after antibiotic treatment at the salmon farm site. Oysters suspended in the salmon net pens and surrounding waters were sampled over a 5 month period. Concentration of oxytetracycline residues in oyster tissue reached a maximum of 0.11 ppm (n=2). Levels of sulphadimethoxine in oyster tissue reached a maximum concentration of 1.27 ppm (n=2). Maximum detectable concentrations of ormetoprim in oysters were 0.26 ppm (n=2). A controlled study investigating uptake and depuration of oxytetracycline and Romet-30 in the Pacific oyster revealed results similar to those described for the salmon farm. A flow through drug delivery system for the Pacific oyster was utilized over a ten day uptake and thirty day depuration period. Levels of oxytetracycline in whole animal tissue increased in a linear fashion (r²=0.984) over the uptake period. This indicates that the drug was bioaccumulated in the oyster reaching a maximum concentration of 10.72 ± 2.4 s.e. ppm (n= 3) on day 10 of uptake. Depuration of the drug was rapid. After thirteen days a concentration of 0.21 ± 0.04 s.e. ppm (n=7) was detected. The detection of Romet-30 in the uptake and depuration in the oyster was more erratic. Day 7 of uptake revealed a maximum concentration of sulphadimethoxine and ormetoprim of 1.092 ± 0.24 s.e. ppm (n=7) and 0.21 ppm (n=3) respectively. Depuration of Romet-30 was rapid. The concentration decreased to 0.029 ppm (n=3) by day 13. Condition indices of oysters sampled before and after antibiotic treatment indicated a significant increase (p<0.05) in condition index after treatment with medicated feed. A quantitative survey of bacteria associated with the gut of the oyster was performed. Relative numbers of endogenous bacteria were compared to oysters before and after antibiotic treatment. Numbers of bacteria significantly decreased (p< 0.05) following treatment.<br>Land and Food Systems, Faculty of<br>Graduate
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18

Vogeler, Susanne. "Nuclear receptors in the Pacific oyster, Crassostrea gigas, as screening tool for determining response to environmental contaminants." Thesis, University of Exeter, 2016. http://hdl.handle.net/10871/23626.

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Marine environments are under constant pressure from anthropogenic pollution. Chemical pollutants are introduced into the aquatic environment through waste disposal, sewage, land runoff and environmental exploitation (harbours, fisheries, tourism) leading to disastrous effects on the marine wildlife. Developmental malformations, reproduction failure including sex changes and high death rates are commonly observed in aquatic animal populations around the world. Unfortunately, the underlying molecular mechanisms of these pollution effects, in particular for marine invertebrate species, are often unknown. One proposed mechanism through which environmental pollution affects wildlife, is the disruption of nuclear receptors (NRs), ligand-binding transcription factors in animals. Environmental pollutants can directly interact with nuclear receptors, inducing incorrect signals for gene expression and subsequently disrupt developmental and physiological processes. Elucidation of the exact mechanism in invertebrates, however, is sparse due to limited understanding of invertebrate endocrinology and molecular regulatory mechanisms. Here, I have investigated the presence, expression and function of NRs in the Pacific oyster, Crassostrea gigas, and explored their interrelation with known environmental pollutants. Using a suite of molecular techniques and bioinformatics tools I demonstrate that the Pacific oyster possesses a large variety of NR homologs (43 NRs), which display individual expression profiles during embryo/larval development and supposedly fulfil distinct functions in developmental and physiological processes. Functional studies on a small subset of oyster NRs provided evidence for their ability to regulate gene expression, including interactions with DNA, other NRs or small molecules (ligand-binding). Oyster receptors also show a high likeliness to be disrupted by environmental pollutants. Computational docking showed that the retinoid X receptor ortholog, CgRXR, is able to bind and be activated by 9-cis retinoic acid and by the well-known environmental contaminant tributyltin. A potential interaction between tributyltin and the peroxisome proliferator-activated receptor ortholog CgPPAR has also been found. In addition, exposure of oyster embryos to retinoic acids and tributyltin resulted in shell deformations and developmental failure. In contrast, computer modelling of another putative target for pollutants, the retinoic acid receptor ortholog CgRAR, did not indicate interactions with common retinoic acids, supporting a recently developed theory of loss of retinoid binding in molluscan RARs. Sequence analyses revealed six residues in the receptor sequence, which prevent the successful interaction with retinoid ligands. In conclusion, this investigative work aids the understanding of fundamental processes in invertebrates, such as gene expression and endocrinology, as well as further understanding and prediction of effects of environmental pollutants on marine invertebrates.
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19

Nice, Helen Elizabeth. "The effect of endocrine disruptors on the growth and development of the Pacific oyster, Crassostrea gigas (Thunberg)." Thesis, Royal Holloway, University of London, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.271354.

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20

Pathirana, Bhagini Erandi. "Environmental influences on the Pacific oyster (Crassostrea gigas) microbiome and disease associated with Ostreid herpesvirus-1 (OsHV-1)." Thesis, University of Sydney, 2020. https://hdl.handle.net/2123/23241.

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Pacific oyster mortality syndrome (POMS) is a high mortality disease which has negatively impacted oyster farming. Despite the causal relationship between OsHV-1 and oyster mortality, the incidence and severity of disease is determined by complex interactions between the physiology of oysters, the environmental conditions and secondary pathogens. Understanding the multifactorial nature of the disease is required to develop management strategies. Recently, changes in the microbiome of oysters were associated with POMS. It is important to identify if differences in the microbiome are an outcome of the pathogenesis of the disease or whether the features of the microbiome predispose or contribute to the severity of disease. This thesis focused on the influence of important environmental factors on the composition of the Pacific oyster microbiome and determined how this impacted the outcome of OsHV-1 infections in oysters. Research chapter 1 investigated how the microbiome of genetically related Pacific oysters with a common hatchery origin was different when they were grown in different estuaries. Using the 16S rRNA gene diversity, the different estuarine environments were shown to generate unique microbiomes which were also associated with a differential response to the OsHV-1 infection. The quantitative dynamics of total bacteria and Vibrio spp. during an OsHV-1 infection was assessed using qPCR assays. The microbiome changed with the environment and after an OsHV-1 challenge. A strong correlation was observed between the OsHV-1 and Vibrio quantities in OsHV-1 infected oysters. Different microbiomes responded differently with a differential outcome of OsHV-1 challenge. Optimizing the quality and quantity of bacterial DNA from oyster tissues to facilitate accurate identification of the microbiome proved critical for microbiome studies. Research chapter 2 focused on evaluating methods to sample tissues and extract nucleic acids from Pacific oysters to accurately determine the microbiome. These procedures substantially impacted the quantity and diversity of bacteria identified. The controlled environment of a laboratory experimental system has been utilized to understand infectious diseases of oysters including POMS. A period of acclimation to environment before an experimental study can induce changes to the microbiome that may confound findings attributed to the disease being studied. Research chapter 3 focused on assessing changes in the Pacific oyster microbiome during acclimation to a laboratory environment when oysters are maintained in constant immersion in water and in a simulated tide. The oyster microbiome changed during acclimation irrespective of the management strategy (constant immersion vs. simulated tide). Research chapter 4 discusses the impact of the environment on the microbiome of oysters subsequent to challenge with OsHV-1. Although the microbiome composition changed after viral infection, it was the same for constant and partial immersion and did not explain higher mortality in oysters in simulated tidal conditions. Knowledge of the role of environmental factors on disease expression can help direct advice on oyster farm management strategies. Seawater temperature plays a major role in triggering diseases in the marine environment. Research chapter 5 discusses the impact of temperature and temperature fluctuations in water on the oyster microbiome and how it affects the outcome of an OsHV-1 infection. Unlike with temperature fluctuations the microbiome behaved differently at higher temperatures (26 0C) but did not create any distinct impact on the cumulative survival.
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Salinas-Flores, Liliana, and n/a. "Understanding and improving the cryopreservation of pacific oyster (Crassostrea gigas) oocytes via the use of two approaches : modification of an existing cryopreservation protocol and manipulation of the lipis fraction of the oocytes." University of Otago. Department of Food Science, 2008. http://adt.otago.ac.nz./public/adt-NZDU20080305.143446.

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Cryopreservation of gametes is a valuable tool for the fast-growing aquaculture industry in New Zealand. In the present study, research was aimed to improve the cryopreservation of Pacific oyster (Crassostrea gigas) oocytes. For this, two main approaches were used: the modification of an existing published (standard) cryopreservation protocol for oyster oocytes and the modification of the oocytes themselves prior to cryopreservation. The objectives in the chapters of this thesis were: (a) determination of the cryobiological characteristics of oyster oocytes; (b) assessment and reduction of intracellular ice formation (IIF) in oocytes; and (c) modification of the lipid fraction (cholesterol and fatty acids) of oocytes prior to cryopreservation. Knowledge of the membrane permeability parameters in response to concentrations of water and ethylene glycol (EG), the influence of temperature upon these parameters, and the osmotic tolerance limits of oyster oocytes were used to develop computer models that simulated the cellular volume changes that oocytes underwent during EG addition and removal. The models predicted that when one part of EG was added in one step to one part of oocyte suspension and equilibrated for 20 min at 20 �C, similar volume changes in oocytes would be obtained, compared to a more complicated multi-step addition method. This method of addition resulted in similar post-thaw fertilization rates to those obtained by using the multi-step addition method, thus reducing oocyte handling. Cryomicroscopy was used to assess the effect of cooling rates and EG concentration on the temperature at which oocytes underwent IIF. It was found that IIF occurred at higher subzero temperatures when fast cooling rates were used (30 and 5 �C min⁻�) and at EG concentrations ranged between 0 and 15%. At a relatively slower cooling rate of 0.3 �C min⁻� and with 10% EG, which are the conditions employed in the standard cryopreservation protocol, no IIF occurred. The steps of the standard protocol that were more likely to cause oocyte damage were identified by evaluating the fertilization rate of oocytes at each step. Results showed that oocytes were most damaged by cooling them to -35 �C and followed by plunging them in liquid nitrogen. Contrary to what had been observed under the cryomicroscope, transmission electron microscopy (TEM) analysis revealed that all oocytes cryopreserved by the standard protocol contained cytoplasmic ice. In addition, it was also observed that oocytes were at two developmental stages when frozen (prophase and metaphase I). These observations prompted the development of alternative cooling programmes aimed to reduce intracellular ice. The effect of cooling rate, plunge temperature and time held at the plunge temperature were thus evaluated, based on post-thaw fertilization rate of oocytes. Overall, neither the cooling rate nor the holding time had an effect on oocyte fertility. However, the plunge temperature had an effect, where oocytes plunged at -60 �C had lower post-thaw fertilization rates than oocytes plunged at -35 �C. Through the slowing of the cooling rate, lengthening of the holding time and lowering of the plunge temperature, it was possible to reduce the amount of ice in the cytoplasm. However, the reduction of intracellular ice did not improve the post-thaw fertilization rate of the oocytes; on the contrary, post-thaw fertilization decreased notoriously. From these results, it can be suggested that oyster oocytes are more likely to be damaged by exposure to high intra and extracellular solute concentration than IIF during cryopreservation. In an effort to modify the lipid content of oyster oocytes prior to cryopreservation and thus, making them more resistant during cryopreservation, oocytes were incubated in solutions that would add or remove cholesterol or in solutions rich in long chain fatty acids (EPA or DHA). Oocytes incubated in cholesterol-rich solutions showed a positive uptake of fluorescently labelled cholesterol and this effect was dose dependent. Nevertheless, this uptake did not improve the post-thaw fertilization rate nor did it increase the total cholesterol content of the oocytes. When oocytes were incubated in non-conjugated or conjugated EPA or DHA, no increase in the proportion of these fatty acids was identified in the fatty acid profiles of whole oocytes and no improvement of the post-thaw fertilization rate was recorded. Given that there was no uptake of fatty acids from the incubation media by the oocytes, a different approach was taken. This involved the supplementation of lipid-rich diets to the oyster broodstock during gametogenesis (cold-conditioning) and vitellogenesis (warm-conditioning). Despite results showing that lipid content and, indeed, fatty acid profile was altered through the diet, the results also showed that fresh oocytes from broodstock fed during cold-conditioning did not show any improvement in their fertilization rates, nor did they benefit from a lipid-rich diet during warm-conditioning. On the other hand, cryopreserved oocytes did have higher post-thaw fertilisation rates when broodstock were fed during cold-conditioning and, although no effect was found from feeding broodstock with either of the lipid-rich diets during warm-conditioning, trends indicated that a diet consisting of fresh microalgae or the commercial supplement Algamac would yield the highest post-thaw fertilization rates. This thesis has furthered the understanding of some of the factors that determine cryosurvival in oyster oocytes and has demonstrated that both physical and biological issues must be taken into consideration for cryopreservation. Specifically, the results in this thesis helped to modify an empirically developed cryopreservation protocol for Pacific oyster oocytes. In addition, the results also showed strong evidence of the survival of oyster oocytes to intracellular ice and highlighted the importance of supplying the broodstock with lipid-rich food during the periods of gamete formation and maturation in order to obtain oocytes that are more amenable to cryopreservation. These benefits could be of significant practical importance and may be extended for the development or refinement of cryopreservation protocols for other shellfish species of commercial importance to the aquaculture industry of New Zealand.
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22

Picard, Manon. "Effects of ocean acidification on early developmental stages of the Pacific oyster (Crassostrea gigas) in an aquaculture setting." Thesis, University of British Columbia, 2014. http://hdl.handle.net/2429/48410.

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Ocean acidification is a great concern worldwide. It has important impacts on the shellfish industry. However, more information is needed to assess the impacts of ocean acidification (OA) on economically important shellfish in a realistic industry setting. The goal of this thesis was to determine the effects of OA on the early developmental stages of the Pacific oyster, Crassostrea gigas. To better represent industrial-scale oyster production than is possible in small-volume, short-term laboratory studies, experiments were conducted at the Island Scallops hatchery facility using large volume containers and appropriate time scales. In Chapter 2, I investigated the effects of acidification on fertilization and larval development to explore the potential links between vulnerability at these life stages and documented mass mortality events in hatcheries in the past. Elevated pCO₂ contributed to increased egg fertilization. However, not all fertilized eggs were viable, and elevated pCO₂ reduced the likelihood of further development to later embryonic stages, resulting in decreased overall fertilization success in C. gigas. Increased pCO₂ levels also negatively affected oyster larvae by reducing growth and reducing the production sufficiently large to be suitable for aquaculture rearing practices. Larval deformity and mortality also showed a trend towards increases in acidified conditions whereas feeding was reduced. In Chapter 3, I assessed early development in benthic juveniles to test for potential for carry-over and/or acclimation effects of prior larval exposure to elevated pCO₂. Settlement did not depend on pCO₂ conditions during the larval phase. However, metamorphosis was reduced when larvae had been exposed to elevated pCO₂ levels. Juvenile growth and condition were both reduced after juvenile’s exposure at higher pCO₂ levels, but shell strength was unaffected. ii Overall, these findings suggest that OA had negative impacts on multiple life history stages in C. gigas. However, the lack of larval exposure effects on juvenile growth or condition suggests an absence of carry-over effects or acclimation for juveniles. These results have important implications for the aquaculture industry and for the development of best practices for combating the effects of ocean acidification.<br>Science, Faculty of<br>Zoology, Department of<br>Graduate
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Pogson, Grant H. "Biochemical studies on the expression of overdominance at the phosphoglucomutase-2 locus in the Pacific oyster, Crassostrea gigas (Thunberg)." Thesis, University of British Columbia, 1988. http://hdl.handle.net/2429/29262.

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Numerous studies have documented significant associations between multiple-locus heterozygosity and fitness-related traits in natural populations, but the explanations for these patterns remain unknown. The objective of the present study was to examine the merits of the overdominance hypothesis as the mechanism responsible for a positive correlation between adult body weight and heterozygosity involving the phosphoglucomutase-2 (Pgm-2) locus in the Pacific oyster, Crassostrea gigas. The kinetic and structural properties of seven Pgm-2 genotypes were examined over physiological ranges of temperature and pH. Significant differences were detected between Pgm-2 genotypes in a variety of enzymic parameters, but these were largely confined to genotypes possessing the Pgm-2-92 allele, and heterozygotes displayed strict intermediacy for all functional and structural properties examined. The expression of marginal overdominance at the Pgm-2 locus was considered unlikely because of the limited scope of the observed variation between allozymes, and its incompatibility with allelic frequencies in natural populations. The three most common heterozygotes at the Pgm-2 locus displayed the extremely unusual property of overdominant enzyme activities. The magnitude of this overdominance was similar in the mantle and adductor muscle tissues, and was consistently observed in population samples from two intertidal positions in three different seasons. A physiological impact of the Pgm-2 polymorphism was demonstrated on the metabolism of glycogen, the biochemical pathway in which PGM functions. Pgm-2 genotypes exhibited different concentrations of glycogen in their mantle, but not their adductor muscle tissues, -which were directly associated with variation in their PGM activity levels. It was suggested that Pgm-2 genotype-dependent enzyme activity variation may affect rates of glycogen synthesis by a partitioning effect at the glucose-6-phosphate branch point. Non-random associations were detected between the PGM activities of Pgm-2 genotypic groups and the activities of adjacent glycogen synthesis pathway enzymes, but none that could clearly account for the differing glycogen concentrations observed between genotypes. The expression of overdominance for PGM activity, and its impact on mantle glycogen levels, provided direct evidence favoring the overdominance explanation as the cause of the larger body weights of heterozygotes at the Pgm-2 locus in Crassostrea gigas.<br>Science, Faculty of<br>Zoology, Department of<br>Graduate
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24

Evans, B. S. "The ecology and reproductive biology of the Pacific oyster (Crassostrea gigas (Thunberg 1795)) in the Daucleddau Estuary, West Wales." Thesis, Swansea University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636917.

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This thesis is concerned with the ecology and mariculture of the Pacific oyster <i>Crassostrea gigas</i> (Thunberg, 1795) in U.K. waters. Oyster culture in the U.K. is reviewed, with detailed assessment of operations in the Daucleddau Estuary, South-West Wales. Growth performance and gametogenesis of <i>C. gigas</i> were monitored over two seasons (1986 and 1987) at two oyster farms in the Daucleddau Estuary (Carew Oysters and Cosheston Fish Farms Ltd.), and at a control site in the Menai Strait (Tal-y-foel). Environmental water quality was regularly monitored over the same period. Environmental requirements for the mariculture of <i>C. gigas</i> are reviewed and environmental suitability of each study site is appraised. Assessment is made of the environmental impact of tributyltin (TBT) pollution on <i>C. gigas</i> fisheries, with specific evaluations for each site. <i>C. gigas</i> did not present any physiological anomalies, either in the Daucleddau estuary or the Menai Strait. Each year, maximum and minimum condition factors were recorded during summer and winter respectfully, with maximum growth rates between April and November. Annual increments in live weight were less than those predicted, partly because of poor nutritive conditions. These may have been associated with natural deficiencies and TBT pollution. Growth performance was better at Tal-y-foel than at both Daucleddau sites; and was better at Carew Oysters than at Cosheston Fish Farms. Numerous intersite differences in water quality may have contributed to these trends, with quantitative and qualitative differences in food, together with TBT impact, being most important. At each site, water temperature, salinity, dissolved oxygen, and suspended particulates were unlikely to have substantially inhibited growth performance during the study period. The timing of gametogenic phases was similar within each population. Gametogenesis was initiated from a resting state in April (> 8<SUP>o</SUP>C), with maximum gametogenic activity during May and June (> 10-15<SUP>o</SUP>C). Each population exhibited a marked synchrony in gonad maturation, with a maximum incidence of morphologically ripe individuals during August. Spawning was partial (incomplete) delayed (until late August, September, October) and was succeeded by substantial gamete resorption. A degree of asynchrony in gonad regression was evident within population, especially in males. The proportion of gonads reduced to a resting state increased with progression into the winter. The inability of <i>C. gigas</i> to propagate in the Daucleddau is not entirely a result of spawning failure, but rather a failure of the shed gametes to reach a settled spat stage.
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Hart, Courtney. "THE EFFECTS OF 4-NONYLPHENOL ON THE IMMUNE RESPONSE OF THE PACIFIC OYSTER, CRASSOSTREA GIGAS, FOLLOWING BACTERIAL INFECTION (VIBRIO CAMPBELLII)." DigitalCommons@CalPoly, 2016. https://digitalcommons.calpoly.edu/theses/1609.

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Endocrine disrupting chemicals (EDCs) are compounds that can interfere with hormone signaling pathways and are now recognized as pervasive in estuarine and marine waters. One prevalent EDC in California’s coastal waters is the xenoestrogen 4-nonylphenol (4-NP), which has been shown to impair reproduction, development, growth, and in some cases immune function of marine invertebrates. To further investigate effects of 4-NP on marine invertebrate immune function we measured total hemocyte counts (THC), relative transcript abundance of immune-relevant genes, and lysozyme activity in Pacific oysters (Crassostrea gigas) following bacterial infection. To quantify these effects we exposed oysters to dissolved phase 4-NP at high (100 μg l-1), low (2 μg l-1), or control (100 μl ethanol) concentrations for 7 days, and then experimentally infected (via injection into the adductor muscle) the oysters with the marine bacterium Vibrio campbellii. 4-NP significantly altered the effects of bacterial infection had on THC. Oysters exposed to both high and low 4-NP did not experience a bacteria-induced increase in THC, as seen in control oysters. We also determined that V. campbellii infection induced differential expression of a subset of immune-related genes tested (Cg-bigdef2, Cg-bpi1, Cg-lys1, Cg-timp) in some, but not all, tissues; 4-NP exposure altered expression patterns in two of these genes (Cg-bpi1 and Cg-tgase). Exposure to 4-NP alone also caused differential expression in some genes (Cg-bpi1, Cg-galectin1, Cg-clec2). Lastly, low levels of 4-NP significantly increased lysozyme activity 24 h post-infection. These results suggest that exposure to 4-NP can alter both cellular and humoral immune responses to bacterial infection in C. gigas.
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Manders, James G. "A current analysis of the status and prospects for the culturing of the Pacific oyster, Crassostrea gigas (Thunberg, 1793) in British Columbia, Canada." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/mq24200.pdf.

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Downing, Sandra Leigh. "Triploid and diploid interspecific and conspecific crosses between the Pacific oyster, Crassostrea gigas (Thunberg), and either Crassostrea virginica (Gmelin) or Crassostrea rivularis (Gould) /." Thesis, Connect to this title online; UW restricted, 1993. http://hdl.handle.net/1773/5283.

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28

Burioli, Erika Astrid Virginie <1977&gt. "An Integrated Approach to Improve the Knowledge of Ostreid Herpesvirus Type 1 and the Comprehension of Mortality Events in the Pacific Oyster Crassostrea Gigas." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2017. http://amsdottorato.unibo.it/8142/1/Tesi%20dott%20Burioli.pdf.

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In a period of expansion of oysters farming in Italy, the present work aimed to contribute to this challenge approaching several important aspects connected with oyster health management. Firstly, we evidenced the presence of natural populations of C. gigas along the Italian coasts and showed differences in the distribution and density population between Adriatic and Tyrrhenian Sea. The presence of OsHV-1 infecting these wild populations was detected in all the Adriatic beds, demonstrating high diversity of genotypes, and showing that these individuals may play a role as reservoir of infection in farmed stocks allocated in the same sites. No other potential reservoir hosts have been evidenced during the investigation conducted in other mollusc species. The obtainment of the complete sequence of OsHV-1 µVar genome represents a significant goal reached during the present work. In particular, this result will permit the exploration of virulence factor in future, a better use of transcriptomics, and the development of new specific diagnostic tools.The complete comprehension of the mechanisms at the origin of the mortality events, observed during the two-year survey, is arduous but the study allowed to observe and obtain highly useful information on oyster mortalities and associated pathogens, specifically in the Italian context. In particular, the impact of V. aestuarianus seems to be relevant in some areas.A potential new pathogen for adult oysters, a Tenacibaculum strain, has been decribed.
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Mai, Huong. "Evaluation of the deleterious effects of heavy metals and pesticides on early life stages and gametes of the Pacific Oyster, Crassostrea gigas : application to the pollution context of the Arcachon Bay." Phd thesis, Université Sciences et Technologies - Bordeaux I, 2013. http://tel.archives-ouvertes.fr/tel-01053814.

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The coastal areas are subject to multiple anthropogenic pressures including chemical pollution that can pose a real risk to the sustainability of aquatic species. The Arcachon Bay, macrotidal lagoon located on the French Atlantic coast, is the important ecosystem for oyster farming. But for several years, the oyster farms face lower recruitment and high mortality of oyster spat. Chemical contamination of the environment as a factor that may contribute to the observed effects on oysters has so far not been investigated.The present thesis aimed at evaluating through different approaches, of the potential toxicity of heavy metals and pesticides representative of the Arcachon Bay contamination on the early life stages of the Pacific oyster, Crassostrea gigas. Embryotoxicity, genotoxicity and expression levels of eleven targeted genes were studied. Firstly, different pesticides (S-metolachlor, irgarol, and diuron) and metals (copper and cadmium) were separately tested to determine their spectrum of effects. It were shown that exposure of gametes and embryos of oyster to environmental concentrations of pesticides and copper increased developmental abnormalities and DNA damage, and reduced fertilization success and affected offpring quality. Cadmium, meanwhile, showed no embryotoxic and genotoxic effects at the concentrations found in the Arcachon Bay. Metabolites of metolachlor, metolachlor ESA and metolachlor OA, are found in the Arcachon Bay at higher concentrations than their parent compound. The results showed that these metabolites were less embryotoxic and genotoxic on oyster embryos and spermatozoa than metolachor. Significant changes in expression of genes involved in antioxidant defense were observed for oyster larvae exposed to metolachlor and metolachlor ESA. Toxicity of mixtures of pesticides representative of the Arcachon Bay contamination with and without copper was then evaluated. Exposures of oyster embryos to these mixtures lead to development defects, DNA damage and changes in the expression of genes involved mainly in oxidative stress responses. Finally, mapping of toxicity of sediments from the Arcachon Bay was conducted for four seasons of 2011 with the oyster embryo-larvae assay. Sediments collected from Arguin exhibited low toxicity, regardless any season. In contrast, sediments from Le Tès showed higher toxicity in spring and summer seasons compared to winter season.From this work, it can be hypothesized that chemical contamination of the Arcachon Bay represents a threat for oyster reproduction and development.
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30

Picot, Sandy. "Caractérisation de la voie de l’autophagie chez l’huître creuse Crassostrea gigas en réponse à une infection par le virus OsHV-1." Thesis, La Rochelle, 2019. http://www.theses.fr/2019LAROS006.

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Les importantes mortalités observées sur le naissain de l’huître creuse, Crassostrea gigas, ont fortement affecté l’économie aquacole de plusieurs pays dans le monde. Les causes de ces mortalités sont complexes, mais un agent viral appartenant à la famille des herpèsvirus, appelé ostreid herpesvirus 1 (OsHV-1), a été identifié comme étant le principal facteur responsable de ces mortalités. Les moyens disponibles pour lutter contre le virus OsHV-1 restent limités et une meilleure connaissance des interactions entre l’huître creuse et le virus est nécessaire. Récemment, les résultats de plusieurs études et la caractérisation du génome de C. gigas ont démontré l’existence potentielle chez cette espèce de plusieurs voies antivirales connues chez les mammifères. La voie de l’autophagie est impliquée dans de nombreux processus cellulaires dont la défense immunitaire. Cette voie serait fonctionnelle dans le manteau de C. gigas et impliquée dans la réponse de l’huître creuse à différentes pathologies incluant les infections virales. Dans le cadre de la thèse, un travail a été réalisé afin d’approfondir les connaissances sur le mécanisme de l’autophagie chez C. gigas et sur sa régulation au cours d’une infection par le virus OsHV-1. Ces travaux de thèse ont permis de mettre en évidence une forte conservation de la voie de l’autophagie au niveau moléculaire. Pour la première fois chez C. gigas, il a été observé des structures autophagiques chez les hémocytes. Ce résultat a permis de développer de nouvelles approches afin de détecter et suivre la régulation de l’autophagie chez l’huître creuse. Un suivi de l’autophagie au cours d’une infection par le virus OsHV-1 a montré une réplication virale suivie d’une modulation de l’autophagie dans le manteau et dans l’hémolymphe. Enfin, il a été montré une régulation différentielle de l’autophagie au niveau transcriptiomique dans le manteau et dans l’hémolymphe<br>Mortality outbreaks of young Pacific oysters, Crassostrea gigas, have seriously affected the aquaculture economy in several countries around the world. Although the causes for these mortalities outbreaks are complex, a viral agent was identified as the main factor, the ostreid herpesvirus 1 (OsHV-1). The mean to fight against the virus remains limited and Pacific oyster/virus interactions need to be further investigated. Recently, the results of several studies and the C. gigas genome sequencing have demonstrated the potential existence of several known mammals’ antiviral pathways in the Pacific oyster. The autophagy pathway is involved in many cellular processes including immune defense. This pathway seems to be functional in the mantle of C. gigas and involve in the response of the Pacific oyster to several pathologies including viral diseases. As part of this Phd work was to improve knowledge about the autophagy pathway mechanism in C. gigas and to decipher it modulation during the process of an infection by the virus OsHV-1. This work has highlighted a strong conservation of the pathway of autophagy at the molecular level. For the first time in C. gigas, autophagic structures were observed in haemocytes. This result has allowed to development new approaches to detect and monitor the regulation of autophagy in Pacific oyster. A monitoring of autophagy during an infection by the virus OsHV-1 showed that the viral replication is followed by a modulation of autophagy in the mantle and in haemolymph. Finally, a differential regulation of the autophagy pathway at the transcriptomic level in the mantle and haemolymph has been shown
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Moreau, Pierrick. "Étude des interactions entre infection à ostreid herpesvirus 1, immunité, autophagie et pesticides chez l’huître creuse, Crassostrea gigas." Thesis, La Rochelle, 2014. http://www.theses.fr/2014LAROS028/document.

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Le travail de thèse s’inscrit dans la problématique très actuelle des mortalités massives de naissain et de juvéniles d’huîtres creuses, C. gigas, et des questionnements autour de l’implication des pesticides dans ce phénomène. La première partie de la thèse a été consacrée à l’étude des effets de pesticides sur les capacités hémocytaires de l’huître creuse (in vitro et in vivo). L’effet immuno-modulateur des xénobiotiques sélectionnés (seul ou en mélange) a été exploré principalement au travers de la cytométrie en flux. La deuxième partie de la thèse a concerné l’étude des effets d’un mélange de pesticides sélectionnés sur le virus OsHV-1 et l’infection qu’il induit chez l’huître creuse. Les effets des pesticides sur le virus lui-même ont été évalués. Les expériences réalisées n'ont pas permis de mettre en évidence, dans les conditions testées, de dégradation des particules virales en présence des polluants. D’autre part, leurs effets sur les huîtres elles-mêmes ont été explorés après traitement des animaux avec un mélange de pesticides lors d’essais de pathologie expérimentale. Il a ainsi pu être montré que des huîtres préalablement contaminées par un mélange de pesticides à des concentrations retrouvées dans l’environnement semblaient être plus sensibles à l’infection virale. La troisième partie de la thèse a concerné l’étude de l’autophagie chez l’huître creuse, C. gigas. La publication du génome complet de cette espèce en 2012 a ouvert de nouvelles possibilités pour étudier l'immunité innée. L’étude de l’autophagie réalisée pour la première fois chez l’huître creuse a consisté lors d’une première étape en la recherche in silico de gènes impliqués dans cette voie et des protéines correspondantes par western blotting. Puis, le rôle de ce processus important dans l’immunité innée a été exploré au travers d’essais de reproduction d’infections en présence ou non de modulateurs de l’autophagie. Les résultats obtenus semblent montrer que l’autophagie soit un processus important pouvant être impliqué dans les capacités de défense de l’huître creuse vis-à-vis d’infections virales et bactériennes<br>The thesis work is part of the very current issue on mass mortality outbreaks affecting Pacific oyster, C. gigas, spat and juveniles and questions about the involvement of pesticides in this phenomenon. The first part of this thesis was devoted to study the effects of pesticides on hemocyte parameters in the Pacific oyster (in vitro and in vivo). The immunomodulator effect of selected pesticides (alone or in mixture) has been explored principally through flow cytometry. The second part concerned the study of the effects of a pesticides mixture on OsHV-1 itself. No direct effects have been reported on the viral particles in presence of the pollutants. Moreover, pesticide effects on Pacific oysters were also explored through experimental pathology assays after treatment of animals with a polluant mixture. Results showed that pesticide treated oysters appeared more susceptible to the viral infection in experimental conditions. The third part concerned the study of autophagy in the Pacific oyster, C. gigas. The publication of the complete genome in 2012 has opened up new possibilities for the study of innate immunity in this species. The study of autophagy for the first time in oysters consisted in a first step in the in silico search for genes involved in this pathway and the corresponding proteins by Western blotting. Then, the role of this important process in innate immunity has been explored through reproduction infections tests with or without modulators of autophagy. Results showed that autophagy appeared as involved in defence mechanisms against viral and bacterial infection in Pacific oysters
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Segarra, Amélie. "Étude des interactions hôte/virus chez l’huître creuse, Crassostrea gigas, et son virus Ostreid herpesvirus 1." Thesis, Lorient, 2014. http://www.theses.fr/2014LORIS344/document.

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Le virus ostreid herpesvirus type 1 (OsHV-1), peut être considéré comme un des agents infectieux majeur affectant les élevages d’huîtres creuses, Crassostrea gigas, en France. Des différences de sensibilité à l’infection ont également été observées au sein de cette espèce. Des travaux précédents suggèrent un lien entre la base génétique et la survie des animaux face à l’infection. Dans ce contexte, l’objectif principal du travail de thèse était de mieux comprendre les interactions entre l’huître creuse et OsHV-1, et plus particulièrement, les bases moléculaires du cycle viral. Nos résultats montre que le virus est capable de se répliquer chez l’hôte quel que soit son stade de développement, et sa sensibilité. Cependant, la cinétique de multiplication est plus rapide chez des individus sensibles comparés aux moins sensibles. Il apparaît également que chez les individus survivants, le virus ne soit plus détectable après une phase de réplication active. Cette observation laisse suspecter (i) une rémission avec une élimination du virus ou (ii) une persistance du virus sans symptômes détectables. Ces résultats mettent en lumière la possibilité du virus de circuler au sein des individus survivants. Ces individus peuvent excréter des particules virales et intervenir ainsi dans le processus d’infection en milieu naturel. L’ensemble de ces résultats représentent une premier contribution à la compréhension du cycle d’ OsHV-1 chez l’huître creuse, plus particulièrement au niveau moléculaire<br>In France, Ostreid herpesvirus type 1 (OsHV-1), can be considered one of the major infectious agents in Pacific oysters, Crassostrea gigas. Susceptibility differences to infection were observed in this species. Previous work suggested that the genetic basis and the survival animals to infection were related. In this context, the main objective of this thesis was to understand the interactions between oysters and OsHV-1, in particular, the molecular basis of the viral cycle. Our results shows that the virus is able to replicate in the host regardless of its stage of development or its susceptible. However, multiplication kinetic is faster in susceptible individuals compared to less susceptible individuals. After a active replication, it would appear that the virus is no detectable in survival individuals. This observation suggests (i) a remission with elimination of the virus or (ii) a virus persistence without detectable symptoms. These results highlight the ability of the virus circulating in the host without causing mortality. These individuals can excrete viral particles and interfere with the infection process in field. All these results represent a first contribution to the understanding of OsHV-1 cycle in Pacific oysters, particularly at the molecular level
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Lafont, Maxime. "Mécanismes et spécificité du priming immunitaire antiviral chez un Lophotrochozoaire, l'huitre creuse Crassostrea gigas." Thesis, Perpignan, 2017. http://www.theses.fr/2017PERP0041/document.

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Depuis 2008, des épisodes de surmortalité massive d’origine multifactorielle, affectent mondialement les élevages de juvéniles d’huître creuse Crassostrea gigas dont le virus de type herpès, l’OsHV-1, peut être considéré comme un des agents pathogènes majeurs. L’immunité des huîtres, repose sur un système immunitaire inné et a longtemps été considéré comme peu spécifique et dépourvu de mémoire. Cependant, cette vision a été remise en question via des études ayant démontré l’existence d’une réponse immunitaire spécifique et mémoire chez des invertébrés. Dans le cadre de cette thèse, l’objectif était de caractériser le priming immunitaire antiviral ainsi que ses mécanismes chez l’huître face au virus OsHV-1. En stimulant les huîtres avec un agent mimétique viral, le poly(I:C), nos travaux ont montré que cette molécule protégeait spécifiquement contre l’OsHV-1 en milieu contrôlé et en milieu naturel sur le long terme, en améliorant le taux de survie des huîtres de près de 100%, mais pas d’infections bactériennes. Une approche RNA-seq nous a permis d’identifier différentes voies de signalisations immunitaires antivirales régulées suite à la stimulation par le poly(I:C). Les profils de régulation sont majoritairement maintenus dans le temps (au moins 10 jours), ce qui pourrait expliquer la protection observée. L’ensemble de ces résultats montre l’existence d’un phénomène de priming immunitaire antiviral efficace chez un Lophotrochozoaire et apporte une contribution à la compréhension des mécanismes moléculaires sous-jacents à ce phénomène. Ces travaux ont permis d’apporter des pistes de sortie de crise pour la filière ostréicole jusqu’alors inexplorées<br>Since 2008, mass mortality events of multifactorial origin have affected the Pacific oyster Crassostrea gigas farms worldwide, in which a herpesvirus, the OsHV-1, can be considered as one of the major pathogens. The immunity of oysters, as for all invertebrates, is based on an innate immune system that has long been considered to be scarcely specific and to lack memory. However, in recent years this simplistic view has been questioned through studies that have demonstrated the existence of a specific immune response and memory. However, knowledge about the mechanisms underlying these phenomena still remains extremely fragmentary. The aim of this thesis was to characterize the antiviral immune priming and its mechanisms in the oyster against OsHV-1. By stimulating oysters with a viral mimic, poly(I:C), we have shown that this molecule specifically protects against OsHV-1 in controlled environment and in natural environment, protecting oysters from mass mortality events on the long term (min. 5 months) by improving oyster survival by almost 100% but does not protect against bacterial infection. A RNA-seq approach carried out during this thesis allowed us to identify different antiviral immune pathways regulated following the stimulation by poly(I:C). The regulation profiles are mostly maintained over time (at least 10 days), which could explain the observed protection. All these results show the existence of an effective antiviral immune priming phenomenon in a Lophotrochozoan and contribute to the understanding of the molecular mechanisms underlying this phenomenon. This work opens new perspectives hitherto unexplored to support oyster farming against this crisis
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Tallec, Kevin. "Impacts des nanoplastiques et microplastiques sur les premiers stades de vie (gamètes, embryons, larves) de l'huître creuse Crassostrea gigas Surface functionalization determines behavior of nanoplastic solutions in model aquatic environments, in Chemosphere 225, June 2019 Nanoplastics impaired oyster free living stages, gametes and embryos, in Environmental Pollution 242 (Part B), November 2018 Constraints and priorities for conducting experimental exposures of marine organisms to microplastics, in Frontiers in Marine Science 5(252), July 2018 Cellular responses of Pacific oyster (Crassostrea gigas) gametes exposed in vitro to polystyrene nanoparticles, in Chemosphere 208, October 2018." Thesis, Brest, 2019. http://www.theses.fr/2019BRES0103.

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Depuis 70 ans, les débris plastiques dont la fin de vie a été négligée par les sociétés humaines s’accumulent dans les océans. L’évaluation des effets engendrés par cette contamination ubiquitaire est une préoccupation majeure, notamment au regard des micro- et potentiels nanoplastiques (MNP ; &lt; 5 mm) du fait de leur biodisponibilité pour la plupart des organismes marins. L’objectif de cette thèse était de déterminer les effets des MNP sur les jeunes stades de vie d’une espèce ingénieure des habitats côtiers, l’huître creuse Crassostrea gigas. Les impacts des MNP sur ces jeunes stades sont apparus dépendants de la taille des particules. Le rapport surface/volume important des nanosphères de polystyrène (nano-PS ; 50 nm) a favorisé les interactions avec les gamètes et embryons, induisant une inhibition de la fécondation et de l’embryogénèse tandis que les microsphères (0,5 et 2 μm) n’ont causé aucun effet phénotypique visible. La toxicité des nano-PS est apparue dépendante de leurs propriétés de surface (e.g groupements chimiques, charge) qui dirigent leur agrégation dans l’eau de mer et les interactions avec les membranes biologiques. Les nano-PS cationiques, qui restent à l’échelle nanométrique dans l’eau de mer, sont à l’origine des effets toxiques les plus marqués. L’exposition embryonnaire à une dose non létale a notamment diminué les performances larvaires et modulé la réponse de la génération suivante à une réexposition embryonnaire. Toutefois, ces effets néfastes sont observés à des concentrations numéraires supposément non-représentatives de l’environnement actuel (la quantité de NP n’étant pas caractérisée en mer à ce jour), suggérant un risque limité des micro- et nanosphères de polystyrène sur les jeunes stades de C.gigas. Les prochaines études devront tenir compte de la complexité et de la réalité des MNP environnementaux (e.g. polymères, formes, contaminants adsorbés, concentrations) sur plusieurs générations de bivalves dans le but d’appréhender plus précisément le risque pour les écosystèmes côtiers<br>For 70 years, mismanaged plastic waste accumulates in the oceans. Risk assessment of this contamination is a major concern, especially regarding micro- and presumably nanoplastics (MNP; &lt;5 mm) which are bioavailable for most marine species. The objective of this thesis was to assess adverse effects of MNP to early life stages of the oyster Crassostrea gigas, a key engineer species in coastal ecosystems. MNP toxicity on oyster young stages depended on the particle size. The high surface area- to - volume ratio of polystyrene nanobeads (nano- PS; 50 nm) promoted their reactivity and interactions with biological membranes of gametes and embryos, leading to an inhibition of the fertilization and embryogenesis success while 0.5 and 2 μm polystyrene beads had any detectable effects. The nano-PS toxicity depended on the particle surface properties (e.g. surface functionalization and charge) which govern their aggregation in seawater and affinity with biological membranes. Furthermore, cationic nano- PS which remained at nanometric scale in seawater, had the highest toxic potential to oyster gametes and embryos. Embryonic exposure to these particles at a non-lethal dose reduced first generation larval performances and modulated larval growth at the second generation in response to the same embryonic exposure. All adverse effects were observed at supposedly unrealistic environmental concentrations (no in situ data exists on NP), suggesting low risk of polystyrene beads to oyster early life stages. Future studies will have to take into account the complexity and reality of MNP in oceans (e.g. polymer and shape diversity, concentrations, contaminants adsorption) to assess effects on bivalve species across generations in order to establish more accurately the risks for coastal environments
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Tucker, Gene Rhea. "Oysters, macaroni, and beer: the Texas Pacific and Manufacturing Company of Thurber, Texas /." Stephenville, Tex. : Tarleton State University, 2006. http://www.geocities.com/geneheatucker/library-thesis-thurberbibliography.html.

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36

Rozmankova, Eliška. "Currently used pesticides and their mixtures : what are the risks to non-target aquatic organisms? Laboratory and in situ approaches." Thesis, Bordeaux, 2020. http://www.theses.fr/2020BORD0301.

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Les pesticides ont pour rôle de protéger les cultures des espèces nuisibles permettant ainsi d’intensifier le rendement agricole pour nourrir une population toujours en augmentation. Néanmoins, les pesticides se retrouvent souvent dans le réseau aquatique, par exemple via le ruissellement, où ils peuvent nuire aux organismes non-cibles. Les concentrations environnementales des pesticides sont souvent considérées sans risque pour les écosystèmes aquatiques, mais elles peuvent cependant induire des effets sublétaux dans les organismes exposés. De plus, les organismes ne font généralement pas face à un seul pesticide provenant d’un champ voisin, mais à un mélange complexe de différents composés chimiques qui interagissent entre eux pour former un cocktail potentiellement toxique avec des impacts inconnus et difficilement prévisibles. Ces composés, peuvent se dégrader au fil du temps et forment des métabolites plus au moins toxiques et persistants qui aggravent encore la complexité des mélanges.Cette thèse s’intéresse à la toxicité de pesticides seuls, en mélange ou en nanoformulation sur des organismes aquatiques non-cibles. Les stades de vie précoces vulnérables de deux organismes modèles : le poisson zèbre (Danio rerio) d’eau douce et un bivalve euryhalin l’huître creuse (Magallana gigas) ont été utilisés afin d’évaluer les effets sublétauxe de concentrations environnementales (détectées dans les cours d’eau européens) de différents pesticides couramment utilisés dont l’herbicide S-métolachlore avec ses deux métabolites acides oxanilique et sulfonique du métolachlore, l’insecticide imidaclopride et le fongicide propiconazole. En complément, une approche in situ a été développée pour évaluer les effets toxiques sur les stades embryo-larvaires de l’huître creuse associés à la qualité de l’eau du Bassin d’Arcachon, réceptacle final de différentes substances provenant des bassins versants.Les résultats indiquent une grande sensibilité des embryons et larves de poisson zèbre aux concentrations environnementales de propiconazole et à un degré moindre de l’imidaclopride. Au contraire, le S-métolachlore et ses métabolites ne présentent que peu d’effet sur le développement, les fonctions neurocomportementales et l’expression des gènes à l’exception des gènes impliqués dans le système thyroïdien. Ces pesticides en mélange semblent se comporter selon un modèle d’addition des concentrations si l’on considère le développement du poisson zèbre. Ces observations sont en lien avec un risque des pratiques agricoles actuelles.Les résultats obtenus lors de ce travail montrent une faible toxicité du propiconazole et de l’imidaclopride sur le développement et le comportement des embryons et larves de l’huître creuse. Quelques effets causés par ces composés seuls ou en mélange sont observés au niveau moléculaire. La concentration environnementale du mélange a induit les malformations larvaires, néanmoins, les embryons d’huître encagés dans le Bassin d’Arcachon ne présentent pas de malformations quel que soit le site d’exposition, ce qui suggère une qualité suffisante de l’eau du Bassin pour le développement de l’huître creuse. Cependant, des différences au niveau de l’expression des gènes sont observées pour les embryons exposés dans la partie interne du bassin d’Arcachon suggérant des conséquences potentielles sur le long terme.Ces résultats indiquent que les stades embryo-larvaires du poisson zèbre et de l’huître creuse sont des outils pertinents pour l’évaluation des faibles concentrations de pesticides seuls ou en mélange. De plus, la mise en œuvre d’expérimentations in situ en complément des approches de laboratoire s’avère utile dans une démarche d’évaluation des risques environnementaux<br>Pesticides have enabled humankind to protect its crops from pests, intensifying thus the crop yields to sustain the growing population. However, pesticides often end up in aquatic water bodies, e.g. via field runoff, where they may harm non-target organisms. The environmental concentrations of pesticides are often considered safe for aquatic ecosystems although they might induce sublethal changes in exposed organisms. Moreover, the organisms are generally not dealing with only one pesticide issued from a nearby field but with a complex mixture of various chemical compounds, interacting amongst themselves, and creating a toxic cocktail with unknown and hardly predictable impacts. These compounds, each with different environmental fate, eventually degrade and form more or less toxic and persistent metabolites aggravating the complexity of the mixtures.This dissertation thesis summarizes the state-of-the-art in pesticide mixture toxicity research and is composed of five research articles dealing with sublethal effects of selected pesticides on non-target aquatic species. Vulnerable embryo-larval stages of two model organisms: freshwater zebrafish (Danio rerio) and euryhaline bivalve Pacific oyster (Magallana gigas) were used to assess the sublethal toxicity of especially environmental concentrations (detected in selected European water bodies) of commonly used herbicide S metolachlor with its two metabolites metolachlor oxanilic acid and metolachlor ethanesulfonic acid, insecticide imidacloprid, and fungicide propiconazole, alone and in a mixture. A complementary in situ approach was carried out to evaluate a real impact on early-life stages of the Pacific oyster in Arcachon Bay in France, a final recipient of various substances including pesticides from respective watersheds.First, zebrafish embryo-larval stages were observed to be highly sensitive to environmentally relevant concentrations of propiconazole and to a lesser extent also to imidacloprid. In contrast, S-metolachlor and its metabolites had almost no effect on their development, neurobehavioral functions, or gene expression except for altered genes implicated in the thyroid system. A mixture of these compounds exhibited a concentration addition effect on zebrafish development. These observations imply that the development of freshwater fish may be at risk with current agricultural practice.Second, a study with Pacific oyster embryos and larvae revealed very low toxicity of propiconazole and imidacloprid on their development and locomotion patterns. Few effects caused by these compounds were observed at the molecular level, as well as the effects caused by the mixture. The environmental concentration of the mixture induced developmental malformations in oyster larvae, however, those exposed in situ in Arcachon Bay did not show higher proportions of abnormal larvae suggesting that the water quality of Arcachon Bay is sufficient for oyster development. Nevertheless, oyster larvae exposed in the inner part of Arcachon Bay showed different gene expression levels than larvae from the reference site located near the ocean entrance, which may indicate consequences of a potential long term impact.These results documented that embryo-larval stages of zebrafish and Pacific oysters are relevant tools for the assessment of low concentrations of pesticides and pesticides in a mixture, and that laboratory studies complemented with field research are useful for (eco)toxicity assessment and of high ecological relevance
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Flahauw, Emilie. "Caractérisation génétique de l'effort reproducteur de l'huitre creuse, Crassostrea gigas, dans le cadre des mortalités estivales de juvéniles : approche QTL." Thesis, La Rochelle, 2013. http://www.theses.fr/2013LAROS406/document.

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L’huître creuse, Crassostrea gigas, est une espèce dont la production aquacole représente un intérêt économique tant au niveau mondial qu’aux niveaux européen et français. Cependant, cette espèce subit des mortalités estivales enregistrées dès le début du 20ème siècle et, depuis 2008, ce phénomène s’est amplifié et menace essentiellement les huîtres juvéniles. La production aquacole d’huître creuse subit les conséquences de ces mortalités massives ; c’est pourquoi ce phénomène est étudié depuis de nombreuses années. En France, la bactérie Vibrio splendidus et le virus Ostreid Herpes Virus 1 (OsHV-1) sont le plus souvent associés aux épisodes de mortalités massives d’huîtres creuses juvéniles et il a été démontré que les individus sélectionnés pour leur résistance aux mortalités estivales étaient capables de ralentir l’augmentation de la charge virale en OsHV-1 dans leurs tissus puis de la faire régresser. Ces mêmes individus présenteraient également un effort reproducteur plus modeste que des individus sélectionnés pour leur sensibilité aux mortalités estivales. Ce travail de thèse s’inscrit dans ce contexte et a donc eu pour principal objectif d’améliorer la connaissance de l’architecture génétique de la reproduction de C. gigas en identifiant des régions du génome ou QTLs (Quantitative Trait Loci) impliquées dans l’effort reproducteur et de mettre en évidence d’éventuelles relations génétiques entre survie et reproduction, des QTLs impliqués dans la survie ayant déjà été détectés. Afin de caractériser l’effort reproducteur, il a été nécessaire de développer un ensemble de nouveaux outils. D’un point de vue biologique, 21 familles F2 ont été produites à partir des lignées sélectionnées pour leur réponse contrastée aux mortalités estivales. D’un point de vue moléculaire, de nouveaux marqueurs SNP (Single Nucleotide Polymorphism) ont été développés afin d’augmenter la densité de la carte génétique déjà disponible pour C. gigas. D’un point de vue technique, l’Imagerie par Résonance Magnétique (IRM) a permis d’observer la gamétogenèse de 300 individus d’une même famille F2 au cours de huit sessions réparties sur deux années alors que les études précédentes étaient limitées à une observation ponctuelle; les méthodes classiques d’observation de la gamétogenèse entrainant nécessairement la mort des animaux. Une forte corrélation a été mise en évidence entre les observations par IRM et par la méthode classique de l’histologie. En plus de l’estimation du rapport gonado-somatique (indice traditionnellement utilisé pour caractériser l’effort reproducteur), l’IRM a également permis d’observer des variations individuelles de la cinétique de la gamétogenèse ainsi que des différences entre les mâles et les femelles; le sexe étant identifiable sur les images obtenues par IRM. Parallèlement, 300 individus de deux autres familles F2 ont été sacrifiés pour estimer le rapport gonado-somatique par histologie. Cette approche a ainsi permis de détecter des QTLs impliqués dans de nombreux traits concernant la gamétogenèse. Des individus provenant des trois familles F2 caractérisés pour l’effort reproducteur ont été caractérisés pour la survie à un épisode de mortalités estivales. Cette étude a permis de détecter des QTLs impliqués dans le caractère « survie ». Ces QTLs correspondent, pour certains, à ceux détectés au cours d’une étude précédente. De plus, ces QTLs sont parfois colocalisés avec des QTLs impliqués dans l’effort reproducteur. Bien que la reproduction de l’huître creuse soit un caractère complexe à suivre, les nouveaux outils utilisés au cours de ce travail de thèse ont permis d’acquérir de nouvelles connaissances. Le séquençage du génome complet de Crassostrea gigas ainsi que les nouvelles méthodes de séquençage pourront peut-être permettre d’affiner les régions QTLs détectées<br>The Pacific oyster, Crassostrea gigas, is a major aquacultured species whose production represents an economic interest at worldwide, european and french levels. However, this species undergoes summer mortalities recorded from the beginning of the 20th century and, since 2008, this phenomenon increased and threatens mainly juvenile oysters. Aquaculture production of oysters suffers consequences of mass mortalities, that’s why this phenomenon has been studied for many years. In France, the bacterium Vibrio splendidus and the Ostreid virus Herpes Virus 1 (OsHV-1) are often associated with mass mortality outbreaks of juveniles oysters and it was demonstrated that selected individuals for resistance to summer mortality were able to slow the increasing in viral load OsHV-1 in their tissues and then to decline it. These same individuals also present a lighter reproductive effort than individuals selected for their sensitivity to summer mortality. In this context, this study aimed to improve the knowledge of genetic architecture of reproduction of C. gigas by identifying some regions of the genome called QTLs (Quantitative Trait Loci) involved in reproductive effort and highlighting possible genetic relationships between reproduction and survival; QTLs involved in survival being already detected. To characterize the reproductive effort, it was necessary to develop a set of new tools. From a biological point of view, 21 F2 families were produced from lines selected for their contrasting response to summer mortality. From a molecular point of view, new SNPs (Single NucleotidePolymorphism) were developed to increase density of the genetic map already available for C. gigas. On a technical point of view, Magnetic Resonance Imaging (MRI) allowed to observe the gametogenesis of 300 individuals of the same family F2 during eight sessions over two years while previous studies were limited to a one-time observation because of the conventional methods of observation of gametogenesis leading necessarily to the death of the animals. A strong correlation was found between observations by MRI and observations by the conventional method of histology. In addition to the estimation of gonadic index (index traditionally used to characterize there productive effort), MRI also revealed individual variations in kinetics of gametogenesis and differences between males and females, the sex being identifiable on MRI images. In parallel, 300 individuals from two F2 families were sacrificed to estimate the gonadic index by histology. This approach enabled the detection of QTLs involved in many gametogenesis traits. Individuals from the three families characterized for F2 reproductive effort were characterized for survival during a summer mortality outbreak. This study was able to detect QTLs involved in the trait "survival". These QTLs correspond to some of those detected in a previous study. In addition, these QTLs are often collocated with QTLs involved in reproductive effort. Although there production of the Pacific oyster is a complex trait to follow, the new tools used in this thesis allowed acquiring new knowledges. The sequencing of genome of Crassostrea gigas and Next-Generation Sequencing technologies may be able to help to refine the detected QTL regions
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38

Diederich, Susanne. "Invasion of Pacific oysters (Crassostrea gigas) in the Wadden Sea competitive advantage over native mussels = Eingeführte Pazifische Austern (Crassostrea gigas) im Wattenmeer : Konkurrenzvorteil gegenüber heimischen Miesmuscheln /." [S.l.] : [s.n.], 2005. http://e-diss.uni-kiel.de/diss_1690/d1690.pdf.

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Delisle, Lizenn. "Rôle de la température dans l'interaction huître creuse / Ostreid Herpesvirus de type 1 : réponses transcriptomiques et métaboliques." Thesis, Brest, 2018. http://www.theses.fr/2018BRES0090/document.

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Crassostrea gigas est la principale espèce d’huître cultivée dans le monde. Depuis 2008, de sévères épisodes de mortalités affectent les huîtres âgées de moins d’un an en Europe et en Océanie et sont associées à l’émergence de l’Ostreid herpèsvirus μVar (OsHV-1 μVar). En Europe, ces mortalités sont saisonnières et surviennent lorsque la température de l’eau de mer est comprise entre 16°C et 24°C. Dans le cadre de ce travail, l’effet des hautes températures (21°C, 26°C et 29°C) est évalué sur la sensibilité des huîtres à OsHV-1 mais aussi sur la persistance et la virulence du virus. La survie des huîtres infectées maintenues à 29°C (86%) est supérieure à la survie des huîtres placées à 21°C (52%) et à 26°C (43%).Les températures élevées (29°C) diminuent la sensibilité des huîtres à OsHV-1 sans altérer l'infectivité du virus et sa virulence. L’exposition des huîtres infectées à 29°C pourrait réduire l’expression des gènes viraux et la synthèse de virions par la réduction de l’expression de gènes hôtes codant pour des protéines impliquées dans la transcription et la traduction, la réduction de l’expression de gènes impliqués dans le catabolisme, le transport des métabolites, et synthèse de macromolécules.Finalement, l’induction conjointe de l’apoptose, des processus d’ubiquitinylation et de la réponse immunitaire, pourrait permettre l’élimination d’OsHV-1<br>Crassostrea gigas is the main species of oyster cultivated in the world. Since 2008, mass mortality events have been affecting oysters aged less than one year old in Europe and Oceania and have been associated with the emergence of the Ostreid herpes virus μVar (OsHV-1 μVar). In Europe, these events are seasonal and occur when the seawater temperature is between 16°C and 24°C. In this work, the effect of high temperatures (21°C, 26°C and 29°C) was evaluated on the susceptibility of oysters to OsHV- 1 but also on the virulence of virus.High temperatures (29°C) reduce the susceptibility of oysters to OsHV-1 without altering the infectivity of the virus and its virulence. High temperature could reduce viral infection and virus synthesis by reducing the expression of host genes that encode proteins involved in transcription and translation, catabolism, metabolites transport, and macromolecules biosynthesis. Finally, the induction of apoptosis, ubiquitinylation processes and immune response could lead to the elimination of OsHV-1
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40

Kent, GN. "Gynogen induction and diploid restoration in the Pacific oyster Crassostrea gigas." Thesis, 2010. https://eprints.utas.edu.au/20761/1/whole_KentGregNeil2010_thesis.pdf.

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A large proportion of stock improvement in agriculture and more recently aquaculture has come through breeding strategies that work to isolate and fix favourable characters and eliminate undesirable genetic qualities in the target species. The development of homozygous breeding lines, which allow fixing of desirable traits need to be progressed to enhance the effectiveness of breeding strategies. Such lines would also be a valuable research tool for examining genetic versus environmental influence on reproductive biology and stock performance. One potentially rapid and effective method that may produce 100% homozygous individuals is to create what are known as "double-haploids", by suppressing the 1st cell cleavage in haploid zygotes. This project investigated the efficacy of haploid production in the Pacific oyster, Crassostrea gigas, by examining UV irradiation of the paternal DNA, and restoration to the diploid state using the chemicals 6-dimethylaminopurine (6-DMAP) or Cytochalasin B (CB) to suppress either polar body I, polar body II or 1st Cleavage of activated eggs. Additionally, the use of a recessive colour phenotype was examined as a marker to identify parentage of putative gynogen offspring. Sperm Viability via a membrane integrity test ranged between 78-80% viable for controls (no UV exposure) and was significantly greater than all treatment exposures except 60 second low energy exposure (601±22μWcm⁻²s⁻¹), with 300 second high energy exposure (1063±15μWcm⁻²s⁻¹) causing the greatest reduction in sperm viability, ranging between 32-52%. There was no significant difference in egg activation between controls and treatments. In contrast, there was a significant reduction in development of embryos to D larvae with controls averaging approximately 40% development to D stage and the lowest energy treatment (60 seconds @ 601±22μWcm⁻²s⁻¹) averaging a little over 1%. UV radiation of sperm had a significant effect on embryo ploidy levels, with all treatments 180 seconds or longer resulting in less than 20% of cells being diploid or some level of aneuploidy between haploid and diploid. However other published work indicated that, sperm densities and treatment depths are likely to be as important as energy levels when developing irradiation protocols. Survival of putative diploid gynogens was extremely low in all experiments, with the best results yielding 3.9% recovery to D stage larvae and 0.04% recovery to settled spat assessed at 34 days post spawning. Suppression of PB II or 1st Cleavage with CB resulted in the greatest proportion of diploid cells (37.3% and 28.9% respectively) compared with CB suppression of PB I which resulted in the majority of cells produced being tetraploid (35.7%). Microsatellite (mSAT) analysis of these putative gynogen spat revealed a greater level of homozygosity in their genome relative to normal diploid controls; however the presence of null alleles and a lack of genetic variability at some mSAT loci reduced the power of these tools to fully distinguish parentage and validate the production of meiotic or mitotic gynogens. In a direct comparison of 6-DMAP and CB to restore the diploid state by suppression of 1st Cleavage, CB provided a greater percentage of diploid cells (28.4%) compared with 6-DMAP (23.7%) and significantly lower subsequent mortality of larvae. However using 6-DMAP to suppress PB I and II, survival and percentage of diploid cells produced was comparable to that obtained for similar trials using CB. The use of eggs obtained from recessive gold phenotype females crossed with inactivated sperm from homozygous wild type males was investigated to help elucidate the parentage of putative meiotic and mitotic gynogens. Survival of these putative gynogens was lower than for wild type female progeny however gold offspring were produced in both forms of gynogen induction and were not found in corresponding diploid controls. In summary, effective sperm deactivation for subsequent haploid gynogen production can be achieved by exposure to UV radiation for 5 minutes at energy levels ranging between 600 and 1000 μWcm⁻²s⁻¹. Restoring the diploid state of zygotes for meiotic gynogen production can be achieved through the addition of Cytochalasin B or 6-dimethylaminopurine targeting Polar body II suppression, however Cytochalasin B is recommended over 6-dimethylaminopurine for the production of putative mitotic gynogens through 1st cleavage suppression. Mitotic gynogens may be particular useful in the production of genetically identical lines, as they have the potential to be homozygous at every locus.
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41

Robinson, Anja M. "The effects of dietary algal and lipid supplements on the gonadal and larval development of Crassostrea gigas kumamoto (Thunberg) /." 1991. http://hdl.handle.net/1957/7296.

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42

Aagesen, Alisha M. "Investigating Vibrio parahaemolyticus interactions with the Pacific oyster, Crassostrea gigas." Thesis, 2012. http://hdl.handle.net/1957/35769.

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Vibrio parahaemolyticus is a Gram-negative, halophilic, human pathogenic bacterium ubiquitous in the marine environment. Like many Vibrio species, V. parahaemolyticus commonly associates with shellfish, particularly oysters. Ingestion of a raw or under cooked oysters contaminated with V. parahaemolyticus can cause gastroenteritis, which is typically self-limiting and rarely causes death. Globally, oyster production is highly lucrative, especially on the West Coast of the United States where approximately 60% of oyster production occurs each year. Outbreaks of V. parahaemolyticus can result in a significant public health problem as well as an economic burden for the oyster farms implicated in the outbreak. With the increase in overall V. parahaemolyticus outbreaks, improved post-harvest processing strategies have been developed to reduce this natural contaminant. Depuration was developed to allow shellfish to purge contaminants from their tissues into the clean, flowing seawater where they are held. This post-harvest processing technique can typically reduce fecal contaminants from the oyster tissues but is relatively ineffective at eliminating V. parahaemolyticus and other Vibrio species.. Thus, improved methods for reducing this and other human pathogenic Vibrio are needed to effectively produce safer oysters for the consumer. To develop more effective and novel V. parahaemolyticus intervention strategies, first we must identify the factors that are involved in V. parahaemolyticus colonization of the oyster, allowing them toresist depuration. This study sought to investigate specific factors utilized by V. parahaemolyticus and, in the process, determined that various strains of V. parahaemolyticus have different alleles of the Type IV pili, mannose-sensitive hemagglutinin (MSHA)and chitin-regulated pilus (PilA). In addition, we expanded our investigations into the allelic diversity of MSHA and PilA from Vibrio cholerae and Vibrio vulnificus and found that V. cholerae strains that possess the Type IV toxin co-regulated pilus (TCP) maintained highly conserved MSHA and PilA sequences while strains of V. cholerae without TCP, and all of the V. vulnificus and V. parahaemolyticus strains examined, had highly divergent sequences with no discernable connection to isolation source or observed phenotype. Following that discovery, we determined that Type I, and Type IV pili, as well as polar and lateral flagellar systems contribute to V. parahaemolyticus persistence in the Pacific oyster during depuration, while Type III secretion systems and phase variation do not. Overall, we have identified factors involved in colonization of the Pacific oyster by V. parahaemolyticus. Future studies investigating conditions that affect pili and flagella production in V. parahaemolyticus may provide novel depuration conditions that could easily and effectively increase the efficiency of oyster depuration, ultimately reducing the risk of seafood-borne illness by V. parahaemolyticus associated with oysters.<br>Graduation date: 2013
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43

Stick, David A. "Identification of optimal broodstock for Pacific Northwest oysters." Thesis, 2011. http://hdl.handle.net/1957/26654.

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The United States Pacific Northwest is well known for its shellfish farming. Historically, commercial harvests were dominated by the native Olympia oyster, Ostrea lurida, but over-exploitation, habitat degradation, and competition and predation by non-native species has drastically depleted their densities and extirpated many local populations. As a result, shellfish aquaculture production has shifted to the introduced Pacific oyster, Crassostrea gigas. An underlying objective of this dissertation is the use of molecular genetics to improve our ability to accurately identifying optimal oyster broodstock for either restoration of Olympia oysters or farming of Pacific oysters. The ecological benefits provided by oysters as well as the Olympia oyster's historical significance, has motivated numerous restoration/supplementation efforts but these efforts are proceeding without a clear understanding of the genetic structure among extant populations, which could be substantial as a consequence of limited dispersal, local adaptation and/or anthropogenic impacts. To facilitate this understanding, we isolated and characterized 19 polymorphic microsatellites and used 8 of these to study the genetic structure of 2,712 individuals collected from 25 remnant Olympia oyster populations between the northern tip of Vancouver Island BC and Elkhorn Slough CA. Gene flow among geographically separated extant Olympia oyster populations is surprisingly limited for a marine invertebrate species whose free-swimming larvae are capable of planktonic dispersal as long as favorable water conditions exist. We found a significant correlation between geographic and genetic distances supporting the premise that coastal populations are isolated by distance. Genetic structure among remnant populations was not limited to broad geographic regions but was also present at sub-regional scales in both Puget Sound WA and San Francisco Bay CA. Until it can be determined whether genetically differentiated O. lurida populations are locally adapted, restoration projects and resource managers should be cautious of random mixing or transplantation of stocks where gene flow is restricted. As we transition from our Olympia oyster population analysis to our Pacific oyster quantitative analysis, we recognize that traditional quantitative trait locus (QTL) mapping strategies use crosses among inbred lines to create segregating populations. Unfortunately, even low levels of inbreeding in the Pacific oyster (Crassostrea gigas) can substantially depress economically important quantitative traits such as yield and survival, potentially complicating subsequent QTL analyses. To circumvent this problem, we constructed an integrated linkage map for Pacific oysters, consisting of 65 microsatellite (18 of which were previously unmapped) and 212 AFLP markers using a full-sib cross between phenotypically differentiated outbred families. We identified 10 linkage groups (LG1-LG10) spanning 710.48 cM, with an average genomic coverage of 91.39% and an average distance between markers of 2.62 cM. Average marker saturation was 27.7 per linkage group, ranging between 19 (LG9) and 36 markers (LG3). Using this map we identified 12 quantitative trait loci (QTLs) and 5 potential QTLs in the F1 outcross population of 236 full-sib Pacific oysters for four growth-related morphometric measures, including individual wet live weight, shell length, shell width and shell depth measured at four post-fertilization time points: plant-out (average age of 140 days), first year interim (average age of 358 days), second year interim (average age of 644 days) and harvest (average age of 950 days). Mapped QTLs and potential QTLs accounted for an average of 11.2% of the total phenotypic variation and ranged between 2.1 and 33.1%. Although QTL or potential QTL were mapped to all Pacific oyster linkage groups with the exception of LG2, LG8 and LG9, three groups (LG4, LG10 and LG5) were associated with three or more QTL or potential QTL. We conclude that alleles accounting for a significant proportion of the total phenotypic variation for morphometric measures that influence harvest yield remain segregating within the broodstock of West Coast Pacific oyster selective breeding programs.<br>Graduation date: 2012
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44

Bell, Andrew Harwood. "The retention of picoplankton by the pacific oyster, Crassostrea gigas, and implications for oyster culture." 2006. http://hdl.handle.net/2292/504.

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Pacific oyster (Crassostrea gigas) farming in New Zealand has reached a point where the pressures on resources appear likely to constrain current, and future, development. To maintain industry growth, security of juvenile oyster (spat) supply and productivity gains within the existing farm leases, are becoming industry imperatives. The use of hatchery technology could achieve both of these requirements, but it is expensive to establish and maintain. The additional expense of a hatchery could be offset by the establishment of, for example, a selective breeding program to enhance oyster productivity and/or marketability. Consequently a pilot-scale oyster hatchery facility was constructed to investigate the potential for establishing hatchery production of Pacific oysters in New Zealand. This study showed that in the pilot-scale hatchery, oysters could be successfully spawned from in-season broodstock, the eggs fertilised and the resultant larvae reared through to settlement for on-growing to adult size. This process was successful for both oysters selected for morphological characteristics and those which were not. On-growing of the resultant stock indicated growth rate could be normal relative to wild caught oysters spat, although data was limited by the small scale of the experiment. However, an investigation of broodstock conditioning, to achieve out-of-season spawning, was less successful. Disease occurred and condition was lost in some broodstock, suggesting they were enduring stress within the conditioning system. The microalgal food supply was examined but the clearance rate of the microalgal species suggested they were an acceptable feed supply which agreed with previous reports of successful conditioning techniques. Comparing the pilot-scale facility in this study with descriptions of facilities which reported successful broodstock conditioning suggested that the use of a microfiltered recirculating water supply, as opposed to the more common flow-through, natural seawater systems containing a range of small size particles, limited necessary nutrient and/or maturation factors and may have had a significant impact on conditioning. The nanoplanktonic (< 10 μm), food resource, which includes key microalgal species such as Chaetoceros spp. and Isochrysis spp., is generally considered the primary food resource for suspension feeding bivalves, including C. gigas. However, the picoplanktonic fraction (< 3 μm) can provide the largest proportion of this food resource in the water column in terms of abundance and biomass. Consequently, an investigation of the in situ retention of picoplankton populations (picoeukaryotes, Synechococcus-type cyanobacteria and heterotrophic bacteria) by oysters was undertaken. Flow cytometry was used to quantify the picoplankton populations in water samples taken from the inhalant and exhalant feeding currents of individual oysters, allowing retention efficiency of the particles to be calculated. Five picoplankton populations were identifiable by flow cytometry (picoeukaryotes, heterotrophic bacteria and 3 populations tentatively identified as cyanobacteria) and accounted for a large proportion (up to 97 %) of the estimated available carbon (picoplankton + microalgae) in Kerikeri Inlet water. Generally the heterotrophic bacteria accounted for the largest proportion of the biomass with up to 564 ± 51 ng C ml-1. Retention of each picoplankton population was found to be variable and not directly related to particle concentration. Cyanobacteria (Cy2 population) were retained with the greatest efficiency (up to 42 ± 4.4 %), followed by heterotrophic bacteria (up to 38 ± 4.5 %) and picoeukaryotes (up to 12 ± 3.8 %). Overall more picoplankton biomass was retained during the summer months, of which the heterotrophic bacteria made the largest contribution in either cell number or estimated carbon retained. Tracking of the condition and constituent fractions (glycogen, lipid and protein) of the subject oysters showed that in the summer months, post-spawn, these levels were lowest, indicting a period of nutritional stress. This appeared to suggest that C. gigas was able to alter its retention efficiency to expand the range of particles captured, and consequently the available nutrient pool. The retention of greater quantities of heterotrophic bacteria may allow for the acquisition of essential nutrients required for growth and later gametogenesis (such as B vitamins). However, it is also possible that the heterotrophic bacteria mediate access to otherwise inaccessible, or inefficiently accessed, nutrient resources through their degradation of, for example, crystalline cellulose. Consequently, the microbial flora associated with the oyster gut was investigated. An initial investigation, cultivating bacteria from gut contents, showed considerable variability in the numbers of colonies present within and between samples, but was inconclusive for identifying differences in species diversity. Using culture independent histological and 16S rDNA PCR/RFLP techniques to investigate the oyster gut microflora a spirochaete flora, commonly associated with bivalve crystalline styles, was clearly present. Molecular analyses provided evidence of other bacterial in the gut. A signature RFLP band pattern was found in oysters at low tide and this generally reoccurred in oysters that had been immersed for varying lengths of time up to high tide. However, the signature RFLP pattern became more dilute as immersion time/potential feeding time extended. The isolation of culturable bacteria from the oyster gut allowed characterisation and identification of a subset of the oyster gut microflora. 16S rDNA sequence analysis from selected isolates showed a predominance of Vibrio spp. These bacteria had previously been associated with marine molluscs, including as symbionts. Characterisation of these and other isolates from oyster gut showed a diversity of attributes including the ability to degrade cellulose. This suggests the bacterial production of enzymes, such as cellulases, which have been reported by other researchers as being present in ineffectual or low native levels in oysters. Consequently the bacterial presence in the oyster gut may be essential to efficient nutrient acquisition. The results of these investigations have highlighted the potential importance of the heterotrophic bacteria to C. gigas. To date, bacteria have received relatively little attention in terms of their potential nutritive contribution to oysters, primarily due to observations that they are retained with low efficiency. However, even at low retention efficiencies the potential nutritive contribution is large due to the available abundances of heterotrophic bacteria. While the mechanisms and controls of bivalve suspension feeding have yet to be fully elucidated, the published literature indicates that selective mechanisms are available to bivalves including C. gigas and this current research suggests that even pico-sized particles, retained with apparently low efficiency, can be subject to selection. The importance of the heterotrophic bacteria to C. gigas requires further investigation as it will have implications for not only hatchery production, but also farm management, public health and environmental impact monitoring.
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45

Evans, Sanford 1968. "Improving Pacific oyster (Crassostrea gigas) production through selective breeding." Thesis, 2004. http://hdl.handle.net/1957/29975.

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46

Ma, Lei. "Commercial application of high pressure processing for inactivating Vibrio parahaemolyticus in Pacific oysters (Crassostrea gigas)." Thesis, 2012. http://hdl.handle.net/1957/28654.

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Vibrio parahaemolyticus is a Gram-negative, halophilic pathogen that occurs naturally in coastal and estuarine environments. This human pathogen is frequently isolated from a variety of seafood, particular oysters, and is the leading cause of gastroenteritis associated with seafood consumption. Several outbreaks of V. parahaemolyticus infections linked to consumption of raw oysters have been documented. Contamination of oysters with V. parahaemolyticus is a concern for public health. This study investigated the efficacy of high pressure processing (HPP) in inactivating V. parahaemolyticus in raw Pacific oysters (Crassostrea gigas) and identified a process condition capable of achieving greater than 3.52-log reductions of V. parahaemolyticus in raw oysters for commercial application. Raw Pacific oysters were inoculated with a clinical strain of V. parahaemolyticus 10293 (O1:K56) to levels of 10⁴⁻⁵ cells per gram and processed at 293 MPa (43K PSI) for 90, 120, 150, 180 and 210 s. Populations of V. parahaemolyticus in oysters after processes were analyzed with the 5-tube most probable number (MPN) method. A minimum HPP of 293 MPa for 120 s at groundwater temperature (8±1 °C) was identified capable of achieving greater than 3.52-log reductions of V. parahaemolyticus in Pacific oysters. The HPP (293 MPa for 120 s at 8±1 °C) was validated at a commercial scale according to the FDA's National Shellfish Sanitation Program Post Harvest Processing (PHP) Validation/Verification Interim Guidance for Vibrio vulnificus and Vibrio parahaemolyticus. Negative results obtained by the MPN method were confirmed with a multiplex PCR detecting genes encoding thermolabile hemolysin (tl), thermostable direct hemolysin (tdh) and TDH-related hemolysin (trh). Oysters processed at 293 MPa for 120 sec had a shelf life of 6-8 days when stored at 5 °C or 16-18 days when stored in ice. This validated HPP was accepted by the FDA as a post harvest process to eliminate V. parahaemolyticus in raw oysters.<br>Graduation date: 2012
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47

Cowan, Malcolm. "Exploring the mechanisms of Pacific oyster summer mortality in Baynes Sound aquaculture." Thesis, 2020. http://hdl.handle.net/1828/12114.

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In recent years, mortalities of unknown aetiology have occurred in Pacific oyster aquaculture in Baynes Sound, BC during the summer. Field studies were conducted to examine environmental, reproductive and microbial factors that could be contributing to these mortalities. In 2017, oysters were observed at three sites from July 5 to September 15. Each intertidal site had three modules containing seven stacked trays with 80 oysters per tray. Final mortalities ranged from 9.3 ± 1.9 to 38.8 ± 4.9% per module. The mortality per module correlated significantly with gonad length and the proportion of oysters that were female in a multiple linear regression model (R2=0.824, p=0.002). Vibrio aestuarianus, a well-documented pathogen of farmed Pacific oysters in France, was well represented in bacterial cultures from intertidal oysters in 2017 based on recA gene sequencing of 158 bacterial isolates. In 2018, juvenile Pacific oysters were monitored to characterize the onset of a summer mortality event in suspended culture. From May 11 to September 17, data on shell size, reproductive development, environmental conditions, and the microbial community of gill tissue was tracked at culture densities of 150, 300, 450, and 600 oysters tray-1. The onset of mortality was associated with a period of rapid growth, reproductive development, and elevated temperatures. Cumulative mortality per tray ranged from 34 to 75%, with the highest density trays having significantly lower mortality (p=0.023), smaller shell width (p=0.001), smaller shell length (p=0.002) and smaller gonad length (p=0.049) than the lowest density trays in a linear mixed-effects regression. Histology of oysters from August 12, during the mortality event, showed a mixed microbial infection in peripheral gill tissue. High-throughput sequencing of the 16S rRNA gene and qPCR of V. aestuarianus using species-specific recA primers suggest V. aestuarianus is temporally associated with summer mortality. Mortalities observed in 2017 and 2018 occurred in different age classes and with different oyster culture techniques, but all were associated with elevated water temperature, increased reproductive effort, and the presence of V. aestuarianus.<br>Graduate<br>2021-08-06
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48

Holliday, J. E. "Nursery culture of Sydney rock oysters, Saccostrea commercialis (Iredale & Roughley, 1933) and Pacific oysters, Crassostrea gigas (Thunberg 1793)." Thesis, 1995. https://eprints.utas.edu.au/20333/1/whole_HollidayJE1995_thesis.pdf.

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This study of settlement, nursery and growing techniques for Sydney rock oysters, Saccostrea commercialis, and Pacific oysters, Crassostrea gigas, was aimed at developing and evaluating production systems for juvenile oysters (spat). Settlement, retention (spat retained within nursery units from settlement or stocking to harvest), survival and growth of juvenile wild and hatchery produced oysters were assessed in relation to systems design and management at sites in New South Wales (NSVV), Australia.
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49

Krassoi, Frederick Rudolf. "Population ecology of the Sydney rock oyster saccostrea commercialis and the pacific oyster crassostrea gigas in a New South Wales estuary." 2001. http://hdl.handle.net/2100/1107.

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University of Technology, Sydney, 2001.<br>The study of place was often divided between the spatial interests of geographers and local historians intent on constructing heroic lineages. In the period of accelerated globalization however, discrete discourses on time and space are no longer tenable. Histories of place engage the transdisciplinary approach of recent scholarship in understanding the complexities and fluidity of the world in which we live. Places are constructed out of the enmeshing of the material, social and cultural. The reasons why people migrate both within and to particular places are also critical to the ongoing perceptions of that place, and the dynamics by which local communities operate within global networks. This thesis is an historical study of a recent sewage ocean outfall dispute between residents and the local council at Emerald Beach, in the Coffs Harbour region of New South Wales' Mid-North Coast. Alongside documentary sources, it uses oral testimony to examine the factors that contributed to people's understanding of their place, and the processes that resulted in the public contestation over that place. It argues that the positions taken in the sewage dispute cannot simply be perceived as a function of individual residents' responses within a bounded local context, but were a result of the complex processes of internal migration to the region since colonisation, and especially since the 1970s, that brought competing visions for the same place. In exploring the historical traces of the dispute, the thesis examines the first wave of non-Aboriginal migration to the coastal hinterland before turning attention to the second intensive wave of migration in the postwar period. Attention shifted away from the hinterland to the coast, and the chapters examine competing uses for the coast as local born residents, tourists and the influx of new settlers from the 1970s brought diverse dreams for the warm North Coast. In particular, the sewage conflict that grew into the direct-action protests at Emerald Beach provides clear insights into the flows of migration and settlement that led to the particular mix of people who fought for their divergent conceptions of place as critical to their lifestyle and residency. Without examining historical representations of places and events, conflict situations such as the sewage dispute at Emerald Beach cannot be fully illuminated. By demonstrating the force of internal migration on perceptions of, and contestation within place, this thesis provides one framework from which other places might be investigated.
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50

Mitchell, Iona Margaret. "Relationship between water quality parameters (nutrients, seston, chlorophyll a), hydrodynamics and oyster growth in three major Pacific oyster (Crassostrea gigas) growing areas in southern Tasmania (Australia)." Thesis, 2001. https://eprints.utas.edu.au/20928/1/whole_MitchellIonaMargaret2001_thesis.pdf.

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An assessment was made of three Pacific oyster ( Crassostrea gig as) growing areas in southern Tasmania (Pitt Water, Pipeclay Lagoon and Little Swanport) with respect to water quality parameters, oyster growth and hydrodynamic characteristics. This was done in an order to explain differences in reported oyster growth rates and hence address the issue of shellfish productivity in each area. Water samples were collected monthly for 13 months from several sites along the length of each area from a marine site to the. upper reaches of the estuary, or coastal embayment. These were analysed for chlorophyll a, nutrients (NOX, P04-P and Si04-Si), and seston quality and quantity (i.e. total particulate matter (TPM) and particulate organic and inorganic matter (POM & PIM)). Temperature, salinity and secchi disk depths were also recorded. Oyster growth and condition were assessed from studies conducted over three consecutive periods at two sites within each area. Hydrodynamic characteristics were calculated from tide gauge data obtained. Additionally, a biodeposition study was conducted at one area during two seasons to determine rates of deposition and composition of biodeposits. Seston quantity was similar among areas, but seston quality, as expressed as %POM, showed variation attributed to the characteristics of each area. Chlorophyll a concentrations were generally low in each area, ranging from 0.2 to 4.0 μg L-1 . Interestingly, chlorophyll a levels measured were high in winter to early spring months within each area. Higher levels of chlorophyll a were measured following periods of flooding and freshwater inflows, particularly in two of the study areas. Considerable variation among areas was shown in oyster growth, with respect to shell length, width, depth and live weight of oysters. Differences in growth are largely attributed to the water quality and hydrodynamic characteristics noted within each of the areas. Mean biodeposition rates varied from 39.6 g DW m-2 d-1 in winter to 180.5 g DW m-2 d-1 in summer. The average organic content of biodeposits (approximately 19.2% POM) was similar in summer and winter. The organic matter content of sediments under oyster baskets was low(< 2.6 %), and it was concluded that biodeposits were being transported and deposited elsewhere. The overall findings from the study indicated that growth rates and productivity of each area were largely influenced by the supply and availability of food. It appeared that stocking density and spatial arrangement of leases provided the greater limitation on growth rate in Pitt Water and Pipeclay Lagoon. Little Swanport was characterised as having the better growth rates and conditions for growth. Food quality, as measured by chlorophyll a and %POM in particular, was higher than the other two sites, and flow rates indicated that a greater quantity of food was reaching a larger proportion of the cultured population. The marine nature of Pipeclay Lagoon suggested that the main source of food supply to the cultured oyster population is of marine origin. However, flow rates and transport of this material over the culture area is insufficient to provide faster growth rates. Stocking density of oysters, and spatial arrangement of the culture area, is most likely responsible for limitation on available food supply to the majority of the population. Sufficient food is available for maintaining metabolic processes, but is insufficient to enable greater storage and hence growth rates. Similar processes appeared to be occurring in Upper Pitt Water, though it seems the greater fraction of food is sourced from within the estuary, rather than being of marine origin. Sampling during this study was fortunate to coincide with infrequent events of heavy and prolonged rainfalls in the latter part of the year, resulting in flooding of this estuary. The beneficial effects of this were elevated nutrient, chlorophyll a, seston levels and greater increase in oyster dry meat weights, confirming the concerns raised by the oyster farmers with respect to the negative effects of the Craigboume Dam. Shellfish production estimates as used overseas were found to be not applicable to Tasmanian conditions. Differences in culture environments between overseas oyster growing areas and those found within Tasmania are discussed.
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