Disease processes and transmission dynamics of Perkinsus marinus in American oysters (Crassostrea virginia)

The once thriving oyster industry in the Chesapeake Bay and east coast of the United States, has been threatened by overfishing, and diseases caused by two protistan parasites, Haplosporidium nelsoni (MSX) and Perkinsus marinus (Dermo). Three lifestages are recognized in the lifecycle of P. marinus, meronts (trophozoites), prezoosporangia, and the biflagellated zoospores. The effects of the diseases caused by the two protists have been well documented (Andrews 1988, Barber et. al. 1988, Ford 1988, Ford and Figueras 1988, Chu et al 1993, Chu and LaPeyre 1993a, 1993b, Paynter and Burreson 1991). Since 1986, P. marinus has reportedly caused greater oyster mortalities in lower Chesapeake Bay than H. nelsoni (Andrews 1988). (...

Humoral Defense Factors in Marine Bivalves

Natural humoral components have been discovered and described in hemolymph from several marine bivalve species including eastern oyster Crassostrea virginica, blue mussel Mitilus edulis, northern quahog Mercenaria mercenaria, softshell Mya arenaria, and Pacific oyster Crassostrea gigas, These hemolymph components are enzymes of lysosomal origin, agglutinins, lectins, hemolysin, and antimicrobial substances, These components are proteins or glycoproteins found in the serum, hemocytes, or both, The exact relationship of these substances to the internal defense of marine bivalves against parasites and pathogenic microorganisms is not known. Lysosomal enzymes seem to have a double role, defense and nutrition. The free- and cell-bound lectins and agglutinins are believed to serve as recognition factors for the attachment of nonself particles to the phagocytes. The nature of bivalve hemolymph components appears to be innate and nonspecific. It has been suggested that the elevation in titer of enzymes of lysosomal origin in bivalve hemocytes and hemolymph after antigenic challenge is the acquired humoral protection produced by the animal. As yet, no experimental evidence has been obtained to support this idea. Whether humoral factors can be acquired in oysters and other marine bivalves needs further investigation. The specificity and the function of humoral factors relating to internal defense remain to be determined. Several mechanisms have been hypothesized for humoral defense in invertebrates. In these hypothesized mechanisms, recognition sites presented on the hemocytes are proposed for the events of phagocytosis, encapsulation, hypersynthesis and release of lysosomal enzymes.https://scholarworks.wm.edu/vimsbooks/1120/thumbnail.jp

A study of nutritional requirements of the larvae of the American oyster (Crassostrea virginica)

The purpose of this study is to obtain information for the formulation of artificial diets for larvae of the American oyster (Crassostrea virginica) and to test procedures related to presenting these diets to the oyster larvae. In order to determine the nutrient components usually provided in larval diets, biochemical analyses of lipids and fatty acids, proteins and amino acids and polysaccharide carbohydrates were performed on five algae species used as a food source for oyster larvae. These algae are Chlorella sp., Pyramimonas virginica, Pseudoisochrysis paradoxa, Pavlova (Monochrysis) lutheri and Isochrysis galbana. The biochemical analyses indicate that the nutritional value of the algal species was not correlated with the total lipid or carbohydrate content, but to the concentration of total protein of the algae. The major fatty acid components of the total lipids of the five species were the C12, C14, C16, and C18 saturated fatty acids and the C16 and C18 mono- and polyunsaturated acids. The total w6 fatty acids were found to be higher in some of the algae. The principal sugar components in the polysaccharide of these five algal species are glucose, mannose, ribose, xylose, rhamnose and fucose. The major constituent was glucose which accounts for 28 to 86% of the total carbohydrate. Mannose was usually the second most abundant carbohydrate component. In addition to the five algae mentioned above, the protein and amino acid composition of four other algal species, Nannochloris oculata, Dunaliella tertiolecta, Phaeodactylum tricornutum and Tetraselmis suecica were also investigated. The major free amino acid components were alanine, arginine, glutamic acid, lysine, proline, serine and taurine. The principal protein amino acids were alanine, aspartic acid, glutamic acid, glycine, leucine, lysine, proline, serine, threonine and valine. Two types of microcapsules, gelatin-acacia and nylon-protein, were tested for acceptability to and digestibility by oyster larvae. Gelatin-acacia and nylon protein capsules were fed to oyster larvae Crassostrea virginica. Larvae were observed to ingest and digest both types of microcapsules. It was found that both types of microcapsules supported growth of larvae. Results also indicated that microcapsule concentration affected growth rate

Comparison Of Infectivity And Pathogenicity Of Meront (Trophozoite) And Prezoosporangiae Stages Of The Oyster Pathogen Perkinsus-Marinus In Eastern Oysters, Crassostrea-Virginica (Gmelin, 1791)

Two experiments were conducted to compare the infectivity and pathogenicity of two life stages of the parasite Perkinsus marinus, meronts (trophozoites) and prezoosporangia (hypnospores), in eastern oysters, Crassostrea virginica. Oysters were inoculated with 5 X 10(4) meronts or prezoosporangia per oyster by injection into the shell cavity. Prevalence and intensity of P. marinus infections, condition index, serum protein concentrations, and lysozyme activities were measured in oysters after 15, 25, 40, and 65 days in experiment 1 and after 20, 40, 50, 65, and 75 days postchallenge by P. marinus cells in experiment 2. Controls were injected with filtered York River water. In the first experiment, P. marinus infections were initially detected in oysters exposed to prezoosporangia after 15 days postchallenge. In the second experiment, infection was not detected in oysters until 40 days postchallenge with either meronts or prezoosporangia. Intensity and prevalence of P. marinus infection were significantly higher (p \u3c 0.002) in oysters challenged by meronts compared with prezoosporangia-challenged oysters at the end of both experiments. In experiment 1, a significant decrease (p \u3c 0.05) was observed in serum protein in infected oysters challenged by prezoosporangia compared with uninfected oysters. Condition index was higher in uninfected oysters compared with infected oysters challenged by prezoosporangia. The differences in condition index and protein were insignificant between oysters infected by meronts or prezoosporangia. Lysozyme activities were significantly lower (p \u3c 0.05) in infected oysters than in uninfected oysters challenged with meronts. No significant differences were observed in condition index, protein concentrations, and lysozyme activities between oysters challenged by meronts and prezoosporangia in experiment 2. Lower condition index and protein concentrations in the groups of oysters infected with prezoosporangia compared with the groups infected by meronts and nonchallenged at the end of experiment 1 suggest a higher energetic demand on these oysters

Perkinsus marinus susceptibility and defense-related activities in eastern oysters Crassostrea virginica: temperature effects

he relationship of potential defense-related cellular and humoral activities and the sus- ceptibility of eastern oysters Crassostrea virginica to the parasite Perkinsus marinus were examined at 10, 15, 20 and 25 C. Oysters were acclimated at experimental temperatures for 20 d and then chal- lenged with R marinus. Total hemocyte counts (TC) and percentage of granulocytes (PG) 20 d after temperature acclimation were higher in oysters at high than at low acclimation temperature. Higher protein (P) and lysozyme (L) concentrations were found in oysters at 10 and 15 C. No significant differ- ences in hemagglutination (H) titers due to temperature acclimation were observed. Infection preva- lence 46 d after challenge by R marinus was 100, 91, 46 and 23 % respectively, for oysters at 25, 20, 15 and 10 C. Disease intensity increased with temperature. Oysters at higher temperatures had greater PG and TC and hemocyte phagocytic activity. No difference was found in TC and PG between control and challenged oysters within each temperature treatment. Bleeding may to some extent reduce TC and PG in oysters. P did not vary much among temperatures. No reduction of P in oysters was found due to P. marinuschallenge and infection. L tended to be higher in oysters at lower than at higher treat- ment temperatures. The oysters at 10 C had the highest L concentration and lowest P marinus infec- tion. But, it is not known whether the high extracellular L in oysters at 10 DC is attributable to the low R marinus susceptibility in these oysters. There was no significant difference in condition index (Cl) between control and challenged oysters and between infected and uninfected oysters. However, C1 de- creased with increasing temperatures. The H titers were not associated with any measured variables. The greater TC, PG, and phagocytic capability in oysters at higher temperatures did not result in fewer or less intense P marinus infections

Effects Of Triclosan On The Oyster Parasite, Perkinsus Marinus And Its Host, The Eastern Oyster, Crassostrea Virginica

Because temperature plays an important role on progression and transmission of disease caused by Perkinsus marinus in the field. the effects of triclosan on the viability of P. marinus meronts (trophozoites) and oyster hemocytes were tested at a range of environmental relevant temperatures. Additionally, we examined the triclosan effect on reactive oxidative intermediate production (ROI) by oyster hemocytes and tested the efficacy of treating infected oysters with triclosan in eliminating/ reducing P. marinus infection in a pilot experiment. When P. marinus cultivated at 13 degrees C, 20 degrees C, and 28 degrees C was exposed to triclosan at corresponding temperatures, 2-10 mu m triclosan killed 10-30% at 20 degrees C and \u3e= 40% at 28 degrees C, but \u3c= 10% at 13 degrees C. When exposure of P. marimus cultivated at 28 degrees C to triclosan at 26 degrees C similar mortality was noted as those recorded at 28 degrees C. Treating hemocytes from oysters maintained at 13 degrees C, 20 degrees C, or 26 degrees C with 2, 5, 10 mu M triclosan at corresponding temperatures. killed 2% to 13% at 13 degrees C and 6 to 16% at 20 degrees C. No mortality occurred in hemocytes exposed to 2-10 mu M triclosan at 26 degrees C. However, at the highest temperature and triclosan concentration tested (28 degrees C, 10 mu M triclosan), hemocyte mortality exceed 30%. Exposure of hemocytes to triclosan concentrations of 2-10 mu M for 4h at 4 degrees C significantly reduced the ROI production in hemocytes in a dose-dependent response. Treating P. marimus infected oysters with 300 and 600 mu g triclosan/oyster daily for 8 wk, significantly slowed the disease progression

HSP70 levels in oyster Crassostrea virginica exposed to cadmium sorbed to algal food and suspended clay particles

https://scholarworks.wm.edu/vimsbooks/1197/thumbnail.jp

Growth, Reproductive Condition, And Digestive Tubule Atrophy Of Pacific Oyster Crassostrea Gigas In Gamakman Bay Off The Southern Coast Of Korea

Spat of Pacific oysters (Crassostrea gigas) were collected from Gamakman Bay, Korea, and raised in a spat hardening facility located in the low intertidal zone of the bay for a hardening/stunting period of 10 mo. Seasonal changes in growth, reproductive condition, and digestive tubule atrophy (DTA) of these hardened/stunted oysters were monitored for more than a year after transplanting to a suspended longline system in a grow-out area in the bay. After transplantation, the hardened/stunted oysters showed a logarithmic increase in shell size for the first 4 mo, from June to October, and growth remained stable from late fall to early spring. During the 12 mo of the grow-out, the shell size of the hardened/stunted oysters increased from 15.4-74.2 mm, and tissue weight increased from 0.49-12.85 g. Histological analysis revealed that gametogenesis of hardened/stunted oysters commenced as early as February when water temperature remained at 10 degrees C, and spawning occurred from July to September when water temperature reached 25-27 degrees C. DTA assessed from histological analysis was higher from September to February, when the chlorophyll a level in the bay was lower. These data suggest that seasonal fluctuations in water temperature and food availability in the water column are the 2 main environmental parameters governing reproduction and growth of oyster in Gamakman Bay, and DTA could be a useful biomarker for monitoring the nutritional condition of oysters

Correlation dynamics between electrons and ions in the fragmentation of D2_2 molecules by short laser pulses

We studied the recollision dynamics between the electrons and D$_2^+$ ions following the tunneling ionization of D$_2$ molecules in an intense short pulse laser field. The returning electron collisionally excites the D$_2^+$ ion to excited electronic states from there D$_2^+$ can dissociate or be further ionized by the laser field, resulting in D$^+$ + D or D$^+$ + D$^+$, respectively. We modeled the fragmentation dynamics and calculated the resulting kinetic energy spectrum of D$^+$ to compare with recent experiments. Since the recollision time is locked to the tunneling ionization time which occurs only within fraction of an optical cycle, the peaks in the D$^+$ kinetic energy spectra provides a measure of the time when the recollision occurs. This collision dynamics forms the basis of the molecular clock where the clock can be read with attosecond precision, as first proposed by Corkum and coworkers. By analyzing each of the elementary processes leading to the fragmentation quantitatively, we identified how the molecular clock is to be read from the measured kinetic energy spectra of D$^+$ and what laser parameters be used in order to measure the clock more accurately.Comment: 13 pages with 14 figure

Prediction of Anisotropic Single-Dirac-Cones in Bi1−x{}_{1-x}Sbx{}_{x} Thin Films

The electronic band structures of Bi${}_{1-x}$Sb${}_{x}$ thin films can be varied as a function of temperature, pressure, stoichiometry, film thickness and growth orientation. We here show how different anisotropic single-Dirac-cones can be constructed in a Bi${}_{1-x}$Sb${}_{x}$ thin film for different applications or research purposes. For predicting anisotropic single-Dirac-cones, we have developed an iterative-two-dimensional-two-band model to get a consistent inverse-effective-mass-tensor and band-gap, which can be used in a general two-dimensional system that has a non-parabolic dispersion relation as in a Bi${}_{1-x}$Sb${}_{x}$ thin film system