Sarah C. Culloty

Season-, age-, and sex-related variation in the prevalence of bonamiasis in flat oysters (Ostrea edulis L.) on the south coast of Ireland

Abstract Monitoring of two age groups of native flat oysters Ostrea edulis L. was undertaken in Cork harbour on the south coast of Ireland over 24 months to determine prevalence and intensity of infection of Bonamia ostreae (Pichot et al., 1980) and levels of mortalities occurring on the beds. Seasonal occurrence, as well as age- and sex-related variation were investigated. Two years appears to be a critical age in relation to disease development; bonamiasis was not detected in oysters younger than this, but once the infection appeared in this group, the disease quickly spread, and prevalence and intensity of infection and mortalities rose rapidly in the following months. Gonad smears indicated that males and females in both age groups were equally affected by the parasite.

Toxicity of copper oxide nanoparticles in the blue mussel, Mytilus edulis: a redox proteomic investigation

Relatively little is known about the fate and effects of nanomaterials even in relatively simple organisms such as Mytilus edulis. Here, copper oxide nanoparticles (CuO NP) are shown to induce dose-dependent toxic effects at the biochemical, physiological and tissue levels in the blue mussel. Stable CuO NP suspensions were sized by differential light scattering and nanoparticle tracking analysis to yield average particle diameters of approximately 100 nm. These were administered to M. edulis, at doses of 400, 700 and 1000 ppb. Ingested copper was predominantly located in the gill tissue with small amounts in digestive gland. Fifteen coomassie-stained spots were excised from two dimensional gel electrophoresis separations of gill tissue extacts and identified by peptide mass fingerprinting. These contained six unique proteins (alpha- and beta-tubulin, actin, tropomyosin, triosephosphate isomerase and Cu-Zn superoxide dismutase). Of these, two spots (actin and triosephosphate isomerase) showed decreased protein thiols while three (alpha-tubulin, tropomyosin and Cu-Zn superoxide dismutase) showed increased carbonylation which is indicative of protein oxidation of cytoskeleton and enzymes in response to CuO NP. The neutral red retention time (NRRT) assay revealed toxicity due to the CuO NPs which was comparable with toxic metal oxide nanoparticles such as chromium and cobalt. In contrast, non-toxic titanium and gold metal oxide nanoparticles gave no NRRT effects at similar NP concentrations. Histology revealed deposition of pigmented brown cells in response to CuO NP, located predominantly along the mantle and gill margin but also lining digestive tubules and some of the sinuses and distributed throughout the connective tissue and in the adductor muscle.

A previously undescribed ostreid herpes virus 1 (OsHV-1) genotype detected in the pacific oyster, Crassostrea gigas, in Ireland.

Significant mortalities of the Pacific oyster, Crassostrea gigas, have been reported worldwide since the 1950s. The impact these re-occurring mortality events have had on the C. gigas industry has highlighted the necessity to determine the factors that may be causing these mortalities. This study investigated the possible role of ostreid herpes virus (OsHV-1) in C. gigas mortalities over 2 successive summers at 2 study areas in Ireland. A single sample of adult C. gigas, which had been experiencing mortalities at one of the sites was screened. Successive cohorts of C. gigas spat obtained from a hatchery outside Ireland was relayed to both sites in 2003 and in 2004. Spat were screened each year prior to relaying. Samples were collected every 2 weeks and mortality counts were recorded and observed at both sites. Polymerase chain reaction (PCR) analysis and subsequent sequencing indicated that a previously undocumented variant genotype of OsHV-1 was present in the single cohort of adult C. gigas and in seed and juveniles at both sites, in both years. Analysis suggests that the Irish OsHV-1 μvar variant genotype is closely related to OsHV-1 μvar, first described in France in 2008.

An evaluation of anaesthetics for Ostrea edulis (L.)

Abstract An effective anaesthetic for oysters was sought, in order to allow for experimental manipulation of live oysters with minimal stress. A range of anaesthetics commonly used with gastropods and cephalopods, as well as a fish anaesthetic, were tested. Most of the chemicals tested were found to be unsuitable for oysters. Magnesium chloride was the most successful agent, inducing anaesthesia quickly, allowing rapid recovery with minimal stress and mortality.

Future Oceanic Warming and Acidification Alter Immune Response and Disease Status in a Commercial Shellfish Species, Mytilus edulis L.

Increases in atmospheric carbon dioxide are leading to physical changes in marine environments including parallel decreases in ocean pH and increases in seawater temperature. This study examined the impacts of a six month exposure to combined decreased pH and increased temperature on the immune response and disease status in the blue mussel, Mytilus edulis L. Results provide the first confirmation that exposure to future acidification and warming conditions via aquarium-based simulation may have parallel implications for bivalve health. Collectively, the data suggests that temperature more than pH may be the key driver affecting immune response in M. edulis. Data also suggests that both increases in temperature and/or lowered pH conditions may lead to changes in parasite abundance and diversity, pathological conditions, and bacterial incidence in M. edulis. These results have implications for future management of shellfish under a predicted climate change scenario and future sustainability of shellfisheries. Examination of the combined effects of two stressors over an extended exposure period provides key preliminary data and thus, this work represents a unique and vital contribution to current research efforts towards a collective understanding of expected near-future impacts of climate change on marine environments.

Observations raise the question if the Pacific oyster, Crassostrea gigas, can act as either a carrier or a reservoir for Bonamia ostreae or Bonamia exitiosa

This study investigated the ability of the Pacific oyster, Crassostrea gigas, to act as a carrier or reservoir of the protistan Bonamia ostreae. Studies were carried out independently in Ireland and in Spain. Naïve C. gigas were exposed to B. ostreae both in the field and in the laboratory via natural exposure or experimental injection. Naïve flat oysters, Ostrea edulis, were placed in tanks with previously exposed C. gigas. Oysters were screened for B. ostreae by examination of ventricular heart smears and by polymerase chain reaction (PCR) screening of tissue samples (gill and/or heart) and shell cavity fluid. PCR-positive oysters were further screened using histology and in situ hybridization (ISH). B. ostreae DNA was detected in the tissues and/or shell cavity fluid of a small number of C. gigas in the field and in the laboratory. B. ostreae-like cells were visualized in the haemocytes of 1 C. gigas and B. ostreae-like cells were observed extracellularly in the connective tissues of 1 other C. gigas. When C. gigas naturally exposed to B. ostreae were held with naïve O. edulis, B. ostreae DNA was detected in O. edulis; however, B. ostreae cells were not visualized. In Spain, B. exitiosa DNA was also detected in Pacific oyster tissues. The results of this study have important implications for C. gigas transfers from B. ostreae-endemic areas to uninfected areas and highlight B. ostreae and B. exitiosas ability to survive extracellularly and in other non-typical hosts.

An investigation into the relative resistance of Irish flat oysters Ostrea edulis L. to the parasite Bonamia ostreae

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

THE SUSCEPTIBILITY OF YOUNG PRESPAWNING OYSTERS, OSTREA EDULIS, TO BONAMIA OSTREAE

Abstract Young prespawning oysters, Ostrea edulis, were held over 6 mo at two different Bonamia ostreae-endemic sites in Ireland, to determine to what extent they could become infected with this protozoan parasite. Prevalence and intensity of infection were monitored, using the traditional method of ventricular heart smears and polymerase chain reaction (PCR). Results showed that 0+ and 1+ oysters were susceptible to infection. Infection was observed in the naïve and previously exposed oysters 2 months post relaying. Of ventricular heart smears and PCR, PCR was the more sensitive diagnostic technique in detecting B. ostreae in most of the oysters. Current methods recommended by the Office International Epizooties (OIE) and the European Union (EU), histology and screening of heart smears for B. ostreae, may be inadequate because certain low levels of infection may go undetected.

Bonamia parasites: a rapidly changing perspective on a genus of important mollusc pathogens

Organisms of the genus Bonamia are intracellular protistan parasites of oysters. To date, 4 species have been described (B. ostreae, B. exitiosa, B. perspora and B. roughleyi), although the status of B. roughleyi is controversial. Introduction especially of B. ostreae and B. exitiosa to naïve host populations has been shown to cause mass mortalities in the past and has had a dramatic impact on oyster production. Both B. ostreae and B. exitiosa are pathogens notifiable to the World Organisation for Animal Health (OIE) and the European Union. Effective management of the disease caused by these pathogens is complicated by the extensive nature of the oyster production process and limited options for disease control of the cultured stocks in open water. This review focuses on the recent advances in research on genetic relationships between Bonamia isolates, geographical distribution, susceptible host species, diagnostics, epizootiology, host-parasite interactions, and disease resistance and control of this globally important genus of oyster pathogens.

The detection of Bonamia ostreae (Pichot et al. 1980) in frozen oysters (Ostrea edulis L.) and the effect of the parasite on condition

Two year classes of frozen flat oysters, Ostrea edulis L., from four different beds in Cork Harbour (southern Ireland) were analysed. Bonamia ostreae, a parasitic protozoan, was detected from frozen heart tissue. Freezing did not appear to affect the ability to diagnose the infection. The detection of Bonamia from oysters frozen in 1986 pre-dates by nine months the initial diagnosis of the disease from fresh oysters in Ireland. The effect of the endoparasite on condition was also examined. Overall, oysters with heavy Bonamia infections were in poorer condition than uninfected oysters.