Showing papers on "Oyster published in 1996"

Bacterial problems associated with scallop Pecten maximus larval culture.

Abstract: Scallop Pecten maximus larvae have been cultured at the Argenton and Tinduff (Brittany, France) hatcheries with antibiotic treatment (chloramphenicol at 8 ppm) for 15 yr. Without treatment, outbreak of disease has normally occurred between Day 12 and Day 19 or sometimes earlier. A bacteriological study of larvae reared with and without antibiotic was performed over a 4 yr period. Among the collected strains, 2 clusters (C and F) of vibrios were present at high densities only in larvae cultured without treatment. One cluster (C) was routinely isolated over the 4 yr of study, while the other (F) was collected only in the third year. Their virulence with respect to scallop larvae and their lack of infectivity with respect to oyster larvae were demonstrated in an exposure experiment. The vibrio F strain tended to lose its virulence after 5 subcultures, whereas the vibrio C strain retained the ability to kill scallop larvae in experimental infections. Three other vibrios isolated in moribund oyster larvae caused mortality in oyster larvae but not in scallop larvae. Different methods were used to determine the taxonomic position of these virulent bacteria. The phenotypic traits of bacterial isolates were determined with the Biolog GN microplate, the API 20E system and the reference method. Patterns of cytoplasmic proteins were identified by electrophoresis in SDS-PAGE. These different methods consistently confirmed the existence of 2 vibrio species pathogenic to scallop larvae. Affiliation of cluster F with Vibrio splendidus was assessed by Biolog tests and by analysis of 16S rRNA sequences. One pathogenic bacteria of oyster larvae was also very close to this second cluster, whereas the 2 others from moribund oyster larvae and cluster C may constitute 2 different species.

Chemical Induction of Larval Settlement Behavior in Flow.

Abstract: The ability of dissolved chemical cues to induce larval settlement from the water column has long been debated. Through computer-assisted video motion analysis, we quantified the movements of individual oyster (Crassostrea virginica) larvae in a small racetrack flume at free-stream flow speeds of 2.8, 6.2, and 10.4 cm/s. In response to waterborne chemical cues, but not to seawater (control), oyster larvae moved downward in the water column and swam in slow curved paths before attaching to the flume bottom. Effective stimuli were adult-oyster-conditioned seawater (OCW) and a synthetic peptide analog (glycyl-glycyl-L-arginine) for the natural cue. The chemically mediated behavioral responses of oyster larvae in flow were essentially identical to those responses previously reported in still water. Our experimental results therefore demonstrate the capacity of waterborne cues to evoke settlement behavior in oyster pediveligers under varying hydrodynamic conditions.

A virion concentration method for detection of human enteric viruses in oysters by PCR and oligoprobe hybridization.

Abstract: This article reports the development of a method to purify and concentrate intact virions from oyster extracts to volume and quality compatible with viral genomic nucleic acid amplification by reverse transcriptase PCR (RT-PCR) and confirmation by oligonucleotide probe hybridization. Fifty-gram oyster samples were processed by an adsorption-elution -precipitation method and then seeded with 10(1) to 10(5) PFU of poliovirus type 1 (PV1) or hepatitis A virus (HAV). Seeded viruses in oyster extracts were purified by fluorocarbon extraction and concentrated by polyethylene glycol (PEG) precipitation and elution. Virus recovery after elution of PEG precipitates was dependent upon PEG concentration and averaged 60% for PV1 and 40% for HAV. The next processing step used the protein-precipitating agent Pro-Cipitate (Affinity Technology, Inc., Brunswick, N.J.) in an adsorption-elution -precipitation scheme to further concentrate viruses and reduce sample volumes to 100 microliter. Oyster extracts processed by Pro-Cipitate adsorption-elution-precipitation were directly compatible with RT-PCR and yielded virus recoveries of > 80% for both PV1 and HAV. When extracts from 50-g oyster samples were seeded and processed by the combined concentration and purification scheme, direct RT-PCR detection of viral genomic RNA was possible at initial inoculum levels of 10 PFU for both PV1 and HAV and with low levels of Norwalk virus. Virus recoveries based on cell culture infectivity were 25 to 35% for PV1 and 5 to 10% for HAV. When tested on artificially contaminated raw oysters, the combined method successfully detected > or = 10(3) PFU of PV1 and HAV and 10(5) RT-PCR-amplifiable units of Norwalk virus. Virus detection by RT-PCR and cell culture infectivity was consistent and well correlated among replicate samples and at different virus titers. The procedure developed in this study is rapid, sensitive, and effective for the direct detection of enteric viruses in oysters by RT-PCR.

Effects of temperature on herpes-like virus detection among hatchery-reared larval Pacific oyster Crassostrea gigas

Abstract: This paper describes effects of temperature on herpes-like virus detection in Pacific oyster Crassostrea gigas larvae held at different temperatures. Intranuclear, intracytoplasmic and extracellular viral particles were observed in velum and mantle connective tissues of oyster larvae reared at 25-26°C. In larvae held at 22-23OC, although nuclear lesions were observed, the presence of viral particles was not detected. Results were obtained for oyster larvae with 4 different parental origins. Herpesvirus infection was found in 3 of the 4 groups of oyster larvae held In the same conditions at the higher temperature.

Modeling Diseased Oyster Populations. II. Triggering Mechanisms for Perkinsus marinus Epizootics

Abstract: Dens1ucs of Crassostrea virgi11 ica remain high enough to suppon substantial fishene, 1hroughout 1he Gulr of !\\1exico despite high n1onah1y ra1es produced by the endoparas1tc Perl.111s11s 111ar11111s The infrequency of cp,zoot1cs 111 these populanons suggests c.hat con1rols exist on the disease mten~ificauon process. The progre~sion or epizootics tn oyster populations. the factors that trigger ep1 zoo11cs. and the factors 1ha1 1em1inate epizoo1ics once sianed were investigaied with a coupled oyster popula11onP. mari1111s model. The tin1e develop1nen1 uf a ,imula1ed epizootrc wa, triggered by environmental conchuons that occurred and disappeared as much as 18 months prior 10 the onset of n1ortality 1n the oyster popula1ion. lnitia1 ion of epi20011c condi1ions was de1ec1ed as an increase in infec1ion iniensily in the submarke1-s ize adu lt and Juvenile pon1ons of chc oysccr population. Infection intensic y of the m:uke1-s ize adults 1s maincained a1 a relati ve ly s1able level by che death of heavily infected individuals and 1he slow rate of P. man1111s d1v1sion a1 high 1nfec11on in1ens11 ies Once starred, mosc of the simula1ed ep1zoo1ics re,ulted in population extinction 1n 2 lo 4 years Scopping an epizootic requi red reducing Lhe mfecuon in1ens11y in the submarkc1-size adults and Juveniles. The 1nfec1ion in1ensi1y of marke1-size aduhs does no1 need to be reduced 10 stop an ep1zoonc nor musl ic be ra1:.ed to sian one. The simulaced oys1er populations show 1ha1 a reduc1ion in ingestion race (by reduced food $Upply or increased turbidi ty) can trigger an epizootic. especially if the reduce ion occurs durrng 1he stunmer. lncreasu1g food supply or dccrcas,ng turbidity m the following year does 1101 necessari ly prcven1 chc occurrence of an epizoocic. Ra1her. 1he onse1 or che event is sin1ply delayed. Add11ional ,imulauons show that the rela1ive co1nbination of variacions in saiini1y and 1emperacure i~ important in de1e rn11ning che occurrence of an ep1zoot1c. A dry (high-sahni1y) sununer followed by a wann winter produce, condicions that favor 1he developmcnc of an epizoouc. Conversely. a warm dry year followed by a cool wc1 year fa1b to produce an epizoo1ic. Sin1uiacions that consider varia1ions in lhe biologrcal characteriscics of oyscer populauons. such as changes in recruitment race or disease resis1ance. show 1hat 1hese are 1mponan1 m regula1ing the occurrence of an epizoo1ic as \" ell a, in terrninacing the evenc In particular. increased recruicment rate diluce, the infected population sufficiently co 1erm1na1e an epizootic One prin1ary conclusion that can be obcained from the,e simula1ion~ i, 1hat epizootics of P. 111ari1111s in oy~cer population, are difficult 10 generate simply with changes in ei1her 1e1nperature or salinity. Rather. che epizoo11cs ,ire criggered by some 01her factor. such as reduced food supply or reduced recru1tmen1 ralC. cha1 occurs prior to or co1ncrden1 w11h high salini1y or cempcraturc condicions. KEY V.10 RDS: Perk111s11s 111ari1111s disease. disease model. oys1er disease. eastern oysters. Crassostreo 1·irgi11 ica

Offshore suspension relaying to reduce levels of Vibrio vulnificus in oysters (Crassostrea virginica).

Abstract: Oysters naturally contaminated with 10(3) to 10(4) most probable numbers (MPN) of Vibrio vulnificus per g were relayed to offshore waters (salinity, 30 to 34 ppt), where they were suspended in racks at a depth of 7.6 m. V. vulnificus counts in oysters were reduced to < 10 MPN/g within 7 to 17 days in five of the six studies. At the end of the studies (17 to 49 days), V. vulnificus levels were reduced further and ranged from a mean of 0.23 to 2.6 MPN/g. Oyster mortalities during relaying were < 6%. The reduction of V. vulnificus in relayed oysters is associated with exposure to high-salinity environments essentially devoid of V. vulnificus. Offshore suspension relaying may be a method that industry can employ to reduce V. vulnificus levels in raw Gulf Coast oysters.

History of Oystering in the United States and Canada, Featuring the Eight Greatest Oyster Estuaries

Abstract: Oyster landings in the United States and Canada have been based mainly on three species, the native eastern oyster, Crassostrea virginica, native Olympia oyster, Ostreola conchaphila, and introduced Pacific oyster, C. gigas. Landings reached their peak of around 27 million bushels/year in the late 1800's and early 1900's when eastern oysters were a common food throughout the east coast and Midwest. Thousands of people were involved in harvesting them with tongs and dredges and in shucking, canning, packing, and transporting them. Since about 1906, when the United States passed some pure food laws, production has declined. The causes have been lack of demand, siltation of beds, removal of cultch for oyster larvae while harvesting oysters, pollution of market beds, and oyster diseases. Production currently is about 5.6 million bushels/year.

Suspension feeding: Basic mechanisms controlling recognition and ingestion of larvae

Abstract: Oysters (Crassostrea virginica) are valuable subjects for investigations of basic mechanisms regulating suspension feeding on invertebrate larvae. In separate laboratory experiments, we introduced inert particles or larvae to the oyster mantle cavity. Small inert particles ( 100~pm diam) equal to larvae in size were rejected. Neither particle specific gravity nor phytoplankton in the seawater medium affected ingestion of inert particles or larvae. Oysters consumed a wide range of invertebrate larval forms, including conspecific veligers. Nearly all larvae (> 75%) delivered to the oyster mantle cavity, except those of Bug&a neritina, were eaten and digested. Feeding stimulants in the larvae were a mixture of polar and nonpolar compounds that were insoluble in seawater. Although contrasting mechanisms regulated fteding on different-sized particles, ingestion of larvae was strictly controlled by particle surface chemistry (=flavor).

Detection of human enteric viruses in oysters by in vivo and in vitro amplification of nucleic acids.

Abstract: This study describes the detection of enteroviruses and hepatitis A virus in 31 naturally contaminated oyster specimens by nucleic acid amplification and oligonucleotide probing. Viruses were extracted by adsorption-elution-precipitation from 50-g oyster samples harvested from an area receiving sewage effluent discharge. Ninety percent of each extract was inoculated into primate kidney cell cultures for virus isolation and infectivity assay. Viruses in the remaining 10% of oyster extract that was not inoculated into cell cultures were further purified and concentrated by a procedure involving Freon extraction, polyethylene glycol precipitation, and Pro-Cipitate precipitation. After 3 to 4 weeks of incubation, RNA was extracted from inoculated cultures that were negative for cytopathic effects (CPE). These RNA extracts and the RNA from virions purified and concentrated directly from oyster extracts were subjected to reverse transcriptase PCR (RT-PCR) with primer pairs for human enteroviruses and hepatitis A virus. The resulting amplicons were confirmed by internal oligonucleotide probe hybridization. For the portions of oyster sample extracts inoculated into cell cultures, 12 (39%) were positive for human enteroviruses by CPE and 6 (19%) were positive by RT-PCR and oligoprobing of RNA extracts from CPE-negative cell cultures. For the remaining sample portions tested by direct RT-PCR and oligoprobing after further concentration, five (about 16%) were confirmed to be positive for human enteroviruses. Hepatitis A virus was also detected in RNA extracts of two CPE-positive samples by RT-PCR and oligoprobing. Combining the data from all three methods, enteric viruses were detected in 18 of 31 (58%) samples. Detection by nucleic acid methods increased the number of positive samples by 50% over detection by CPE in cell culture. Hence, nucleic acid amplification methods increase the detection of noncytopathic human enteric viruses in oysters.

Benthic community changes associated with intertidal oyster cultivation

Abstract: A study of the environmental effects associated with the trestle cultivation of Pacific oysters, Crassostrea gigas Thunberg, was conducted at a commercial cultivation site in the River Exe estuary, Devon, England. Small, but significant, changes were detected in the macrofaunal community sampled beneath oyster trestles compared with that found in adjacent uncultivated areas. These changes were associated with an increase in organic and silt composition and a reduction in the depth of the oxygenated layer of the sediment beneath the trestles. Water velocity was decreased by the presence of the trestles which probably led to the increase in sedimentation rate observed beneath them. Although biological and physical changes were observed, they were relatively minor compared with the extreme environmental changes associated with the suspended culture techniques used for other bivalve species and fishes. However, other studies suggest that the environmental effects associated with oyster cultivation become more severe in areas of large-scale (hectares) cultivation.

Acid-Base Status of the Oyster Crassostrea virginica in Response to Air Exposure and to Infections by Perkinsus marinus

Abstract: Hemolymph acid-base variables were investigated in the Eastern oyster, Crassostrea virginica, to determine its responses to air exposure and to infections by the parasite Perkinsus marinus. Infected and uninfected oysters were subjected to two treatments of temperature (21° and 30°C) and air exposure (5 and 24 h). Upon exposure to air, oysters underwent a respiratory acidosis that remained uncompensated in uninfected oysters but was partially compensated in highly infected oysters at both 21° and 30°C. The acidosis was significantly greater in oysters with high infections. Hemolymph in uninfected oysters had a greater buffering capacity (-6.80 +/- 0.76 SEM slykes) than hemolymph in highly infected oysters (-3.30 +/- 0.50 SEM slykes). Calcium ion concentrations in hemolymph increase when the hemolymph becomes acidic, suggesting that shell decalcification plays a role in buffering the acid. During air exposure, although oysters do not visibly gape, they access air and are apparently not completely anaerobic.

Chemistry and Toxicity of Sediments from San Diego Bay, Including a Biomarker (P450 RGS) Response

Abstract: Thirty sediment samples were collected from the vicinity of the Naval Docking Facility in San Diego Bay and used to conduct bioassays with amphipods, oyster larvae, Microtox, and a new rapid screening test called the cytochrome P450 Reporter Gene System (RGS). This RGS cell line, from a human liver cancer cell, has been engineered to produce luciferase, when the CYP1A1 gene on the chromosome is induced by toxic and carcinogenic organics (dioxin, coplanar PCBs, PAHs). Elutriates were tested with both Microtox and oyster larvae, and organic extracts of sediments were tested with Microtox and the P450 RGS assay. Chemical analyses included total organic carbon (TOC), and acid volatile sulfides (AVS) along with a wide range of metals and organic chemicals. The simultaneously extracted metals (SEM) to AVS ratio was compared to the toxic response of oyster larvae and amphipods. Along each of the piers sampled, contaminant concentrations decreased with distance from shore. A correlation matrix analysis of all biological and chemical data was conducted. The strongest correlation between a chemical measurement and a biological response was that of total PAH versus the P450 RGS response. The use of P450 RGS as a screening tool to assess the relative risk ofmore » contaminants on sediments is biologically meaningful, and is a rapid and inexpensive means of determining which samples require complete chemical characterization.« less

Oysters and the Chesapeake Bay ecosystem: A case for exotic species introduction to improve environmental quality?

Abstract: Restoration of the Chesapeake Bay ecosystem has been a priority for residents and governments of the bay watershed for the past decade. One obstacle in the efforts to “save the bay” has been continuing nutrient enrichment from agricultural and sewer runoff. The attainability of a mandated 40% nutrient reduction goal has yet to be seen. Furthermore, disappearance of certain organisms may have had an adverse effect on the resilience of the ecosystem. The Eastern oyster (Crassostrea virginica), once abundant in Chesapeake Bay, was a vital part of the food web, processing excess phytoplankton and depositing materials on the bottom. Over harvesting and disease have decimated the native oyster population. The introduction of an exotic species, the Japanese oyster (Crassostrea gigas), may be a way to reestablish a robust oyster community in the bay. The literature on the role of bivalve molluscs in estuarine ecosystems shows that they are an essential part of healthy estuaries around the world. A comparison ofC. virginica andC. gigas in terms of temperature and salinity tolerance and resistance to disease shows thatC. virginica is ideally adapted to conditions in Chesapeake Bay, but it is unable to stave off the endemic diseases, whereasC. gigas is adapted to conditions in the lower bay only but is much less susceptible to the same diseases. We conclude that the potential introduction ofC. gigas to Chesapeake Bay would be limited by the Japanese species’ physiological requirements but that the revitalization of a bivalve population is imperative to the restoration of ecosystem function.

Evaluation of First‐Feeding Regimens for Larval Nassau Grouper Epinephelus straitus and Preliminary, Pilot‐Scale Culture through Metamorphosis

Abstract: Two 10-day hatchery experiments were conducted to evaluate s-type (Hawaiian strain) and ss-type (Thailand strain) rotifers Brachionus plicatilis and cryogenically preserved oyster Crassostrea gigas trochophores as first feeds for larval Nassau grouper Epinephelus striatus. Newly hatched grouper larvae were reared at densities of 11.2–20.8/L in 500-L tanks at 36–38 ppt salinity, 25–26 C, and under a 11-h light: 13-h dark photoperiod. Beginning on day 2 posthatching (d2ph), prey were maintained at a density of 20 individuals/mL, while phytoplankton (Nanochloropsis oculata) was maintained at 500 × 103 cells/mL. In experiment 1, survival and growth were higher (P < 0.05) for fish fed small s-type rotifers (mean lorica length = 117 μm; fish survival = 7.96%) selected by sieving than for fish fed non-selected rotifers (mean lorica length = 161 μm; fish survival = 2.13%). These results demonstrated the advantage of small prey size and suggested that super-small (ss-type) rotifer strains would be beneficial. In experiment 2, three feeding regimens were compared: 1) ss-type rotifers (mean lorica length = 147 μm); 2) oyster trochophores (mean diameter = 50 μm) gradually replaced by ss-type rotifers from d5ph; and 3) a mixed-prey teatment of 50% oyster trochophores and 50% ss-type rotifers. Survival was higher (P < 0.05) for larvae fed mixed prey (15.6%) than for those fed rotifers (9.73%) or trochophores and rotifers in sequence (2.55%), which also showed the slowest growth. Oyster trochophores, although inadequate when used exclusively, enhanced survival when used in combination with rotifers, possibly by improving size selectivity and dietary quality. In a pilot-scale trial, larvae were cultured through metamorphosis in two 33.8-m3 outdoor tanks. Fertilized eggs were stocked at a density of 10 eggs/L and larvae were fed ss-type rotifers from d2ph-d20ph, newly hatched Artemia from d15ph-d18ph, 1-d-old Artemia nauplii from d18ph-d62ph. Survival on d62ph was 1.17%, with a total of 5,651 post-metamorphic juveniles produced.

Wood preservative leachates from docks in an estuarine environment.

Abstract: Environmental concentrations and biological effects of certain metals and organic compounds found in wood preservatives were examined. The study focused on leachates from private residential docks in South Carolina tidal creeks. Copper, chromium, arsenic, and polynuclear aromatic hydrocarbons (PAHs) were measured in composite samples of surficial sediments and naturally occurring oyster populations (Crassostrea virginica) from creeks with high densities of docks, and from nearby reference creeks with no docks. In some cases, metal concentrations in sediments and oysters were higher immediately adjacent to dock pilings than they were elsewhere in the same creek. Sediments from most sites had concentrations of metals and total PAHs which were below levels reported to cause biological effects, however. Solid-phase Microtox® bioassays using whole sediments and rotifer bioassays using sediment pore water showed no significant differences in acute toxicity between creeks with and without docks. Oysters growing directly on dock pilings had significantly higher concentrations of copper than oysters growing at least 10 m away; however, there was no significant difference in the physiological condition of these oysters. Four-day field bioassays measuring percent survival of mummichogs (Fundulus heteroclitus), mud snails (Ilyanassa obsoleta), juvenile red drum (Sciaenops ocellatus), and juvenile white shrimp (Penaeus setiferus) showed no significant differences between sites near to and distant from newly constructed docks. Hatchery-reared oysters showed no significant differences between dock and reference sites in percent survival, growth, or bioaccumulation of metals after six weeks of exposure. The results suggest that, in estuarine environments with a moderate tidal range (1.5–2.0 m), wood preservative leachates from dock pilings have no acutely toxic effects on four common estuarine species, nor do they affect the short-term survival or growth of juvenile oysters.

Effect of oyster mushroom (Pleurotus Ostreatus) and its ethanolic extract in diet on absorption and turnover of cholesterol in hypercholesterolemic rat.

Abstract: The effect of the diet containing 5% of powdered oyster mushroom (Pleurotus ostreatus) or an equivalent amount of mushroom ethanolic extract on cholesterol content in serum and liver, on its distribution in lipoproteins, absorption and turnover was studied in male Wistar rats (initial body weight about 70 g) fed a diet with 0.3% cholesterol. 12 weeks of feeding with whole oyster mushroom or mushroom extract reduced cholesterol level in serum by 52 and 33%, respectively. However, cholesterol content in liver was reduced only by whole oyster mushroom (by 20%). Diminished serum cholesterol level was mediated in 60% by reduction of cholesterol in very-low-density lipoproteins. Both whole oyster mushroom and mushroom extract increased the concentration of cholesterol in high-density lipoproteins. Consuming whole oyster mushroom decreased cholesterol absorption (estimated by dual-isotope plasma ratio method) by nearly 16% while no significant effect of mushroom extract could be demonstrated. Feeding the diet containing whole oyster mushroom or its extract reduced the half-times of decay curve of cholesterol-4-14C by 29 and 35%, respectively and reciprocally increased the fractional catabolic rate of plasma cholesterol.