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Thesis(M.S.)--Auburn University, 2005. / Abstract. Vita. Includes bibliographic references.

Thesis (M.S.)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 53-59). Also available on the World Wide Web.

Thesis (Ph. D.)--Rutgers University, 2008. / "Graduate Program in Geography." Includes bibliographical references (p. 315-324).

Thesis (Ph. D.)--University of New South Wales, 2003. / Title from PDF title page (viewed on July 18, 2005). Includes bibliographical references.

Within the East coast and West Coast oyster market, oysters are generally marketed using product attributes and brand name. However the Gulf oyster market does not involve branding. Using choice experiment method and online survey data, the study estimated the effect of branding Gulf oysters on Gulf and Non-Gulf consumers’ willingness to pay. Alternative-specific conditional logit, Nested logit and Alternative-specific multinomial probit methods of analysis were used to investigate the Independence of Irrelevant Alternative assumption made about consumers. Pooled and scaled models were used to analyze the identified data categories from which consumers were found to share the same oyster preferences. The results found that consumers on the average were willing to pay more for the oysters harvested from their own region relative to those harvested from outside their region. They were willing to pay a less for oysters harvested outside their region.

The ingestion, uptake, and metabolism of liposomes by juvenile Pacific oysters (Crassostrea gigas) were studied by several methods in an effort to assess their potential as encapsulating agents. Liposomes composed of egg phosphatidylcholine-cholesterol-stearylamine (7:1:2) formed readily and appeared stable in 20°/oo seawater. Radiotracer studies with liposomes made with ¹⁴C-labeled cholesterol or phosphatidylcholine showed uptake of up to 40% of the dose in 24 hrs, with the majority of uptake occurring in the visceral mass. Only slight amounts of label were observed in adductor muscle or mantle tissue. Absence of label in free fatty acids in oysters fed liposomes made with di[l-¹⁴C] palmitoyl phosphatidylcholine indicated a lack of significant amounts of fatty acid hydrolysis from phospholipid in the stomach or lumen of the digestive diverticula. However, radioactivity was observed in lipid other than phosphatidylcholine, including triglyceride, phosphatidylethanolamine, and an unidentified polar lipid. Radioactivity in these lipids resided exclusively in the fatty acids, indicating breakdown of the ¹⁴C-phosphatidylcholine via acyl transfer. To examine metabolism of liposome-encapsulated substances, [1-¹⁴C]glucose and [U-¹⁴C]amino acids were entrapped and fed to oysters. Label from glucose appeared largely in a choloroform-methanol-insoluble fraction, with little radioactivity recovered in the lipid or soluble aqueous fractions. Most label from amino acids was recovered in trichloroacetic acid-precipitable protein. Control oysters given the same amounts of non-encapsulated [1-¹⁴C] glucose or [U-¹⁴C]amino acids as in liposome trials showed (1) the same uptake of label from free amino acids in comparison with encapsulated glucose, and (2) increased uptake of free, amino acids in comparison with encapsulated amino acids. Label from free glucose or amino acids entered the same fractions as encapsulated label. Evidence for intracellular uptake of liposomes was obtained with fluorescence microscopy after feeding oysters with liposomes containing bovine serum albumin conjugated with fluorescein isothiocyante (FITC). The appearance of small fluorescent inclusions within the apical portions of many of the ducts and tubules of the digestive diverticula suggest phagocytosis of intact liposomes. Uptake was not observed in other parts of the alimentary canal. The feeding of liposomes in which the stearylamine had been conjugated with FITC resulted in generalized fluorescence in most of the digestive diverticula and stomach epithelium, perhaps due to extracellular hydrolysis of FITC and its subsequent diffusion into epithelial cells. No fluorescence occurred in tissues other than those of the digestive tract. Autoradiography studies with liposomes containing di[l-¹⁴C]palmitoyl phosphatidylcholine showed radioactivity dispersed throughout the epithelial cells of the ducts and tubules of the digestive diverticula. Only slight radioactivity was observed in the intertubular connective tissue or the lumen of the tubules or stomach. This distribution of liposomal materials resembled that of fluorescence from feeding trials with FITC-tagged liposomes, and indicated uptake of intact liposomes followed by intracellular breakdown and dispersal of the liposomal components. To investigate the process of particle selection in oysters, polyacrylamide beads (2 [plus or minus] 1μ) with aminoethyl side groups, and beads with FITC-conjugated side groups were fed to oysters. Large quantities of both types of beads were observed in the stomach and intestine, but not in the digestive diverticula, indicating recognition as non-food particles despite their organic nature. The ingestion of such derivitizable particles suggests their use in studies of acceptance-rejection processes in the stomach of bivalves. The ingestion, intracellular uptake, and breakdown of liposomes and their contents indicates a use for these particles in studies of nutrition or pollutant-food web relationships in bivalve molluscs or other filter-feeding organisms. / Graduation date: 1981

Salmonella enterica is a leading cause of food-borne gastrointestinal disease worldwide. A survey conducted in 2002-2003 showed that oysters may contain Salmonella and thus may also be a source of salmonellosis. Since oysters are commonly consumed raw, no amount of food safety education will prevent consumers from ingesting a possibly infectious dose from Salmonella contaminated oysters. The research in this dissertation employed a combination of traditional culture techniques as well as genomics-based molecular applications to explore Salmonella infection in oysters and the subsequent risk to consumers of raw oysters. A year-long survey of oysters served on the half-shell in local restaurants determined that overall 1.2% of oysters were contaminated with Salmonella. Oysters containing Salmonella were found in 7 of the 8 months surveyed and 7 of the 8 restaurants served contaminated oysters. Six different serovars were isolated, but one strain of S. Newport, as determined by matching pulsed field gel electrophoresis patterns, represented 43% of the positive samples. Interestingly, this is the same strain that was predominantly isolated in the earlier survey of oysters and was also resistant to at least 7 different antimicrobials. The remainder of this dissertation work was an exploration of why this particular strain is seen so often in oyster infections. A custom microarray was used to perform a transposon site hybridization (TraSH) assay to identify genes that are necessary for S. Newport survival in the oyster. In this way, a negative selection was able to determine the genes that were necessary for S. Newport to survive in oysters. A subset of the genes identified by TraSH was selected and site-directed mutagenesis was performed to knock those genes out of LAJ160311. Oysters were infected with those mutant strains to test for their ability to survive in oysters and thereby determine the role of those individual genes in pathogenesis. The conclusions of the TraSH assay were that virulence factors that are essential for survival of Salmonella in mammalian models, particularly the type three secretion systems, may not be important in the oyster model. Motility provided by flagella was identified as a major virulence factor in oyster colonization by S. Newport.

Thesis (Ph.D.)--Boston University

This study investigates the concentrations and characteristics of PCB congeners in aquaculture oysters (Crassostrea gigas) along the western coast of Taiwan. Oyster samples were collected from 5 aquacultural areas, Hsinchu, Changhua, Yunlin, Chiayi and Tainan, during May 2003 and March 2004. The results showed that the total PCB concentrations in the oysters were between 3.43 and 93.3 ng/g dry weight, and the median concentration was 20.3 ng/g dry weight. The highest concentrations were found in the oysters collected from Luermen (Tainan) (74.7~93.3 ng/g). Samples from other two stations of Tainan aquacultural area, Cigu and Anping, were also found relative high total PCB concentrations (46.5~72.0 ng/g) than the rest area. This indicates a local pollution source should be blamed on. Except the above areas, the total PCB concentrations were found evenly distributed throughout the coast (3.43~41.2 ng/g with a median concentration of 14.9 ng/g). The PCB concentrations were not significantly correlated with lipid contents and shell lengths. Therefore, the variation of PCB concentrations in all stations might be dependent on the presence of localized sources of contamination rather than on the lipid content and shell length variation of oysters. In some observed stations, the PCB concentrations of oysters in autumn are significantly higher than in summer. That is because the adoptive tide in winter will lead to the tendency to reduce PCB concentrations of oysters.