Zealand Oyster Research Articles

Vibrio parahaemolyticus: Predicting effects of storage temperature on growth in Crassostrea gigas harvested in New Zealand

The frequency of gastroenteritis outbreaks caused by Vibrio parahaemolyticus has been increasing in many parts of the world including New Zealand. Some outbreaks in New Zealand have occurred at times when V. parahaemolyticus concentrations in shellfish in growing waters are low. V. parahaemolyticus is mesophilic, so is not expected to grow under refrigeration. Therefore, one possible explanation for the outbreaks is that the organism was able to grow to hazardous concentrations (e. g. >10,000/g) because of inadequate post-harvest refrigeration. To model the response of growth rates to temperature, we collected Pacific oysters (Crassostrea gigas) containing natural populations of V. parahaemolyticus over three consecutive summers, stored them for various times at 5, 10, 15, 20, 25 and 30 °C and determined V. parahaemolyticus concentrations. A simple log-linear fit was best to determine the growth rates at each temperature for each season. Applying a square root model (√growth rate (MPN/h) = b x (Temperature (°C) - T0) to all the growth rates gave a good fit (R2 = 0.84, RMSE = 0.0178) with b = 0.0096 and T0 = 8.44 °C. Fitted growth rates were considerably lower than previously reported, but the hypothetical minimal growth temperature was also lower. Thus, concentrations of V. parahaemolyticus are likely to increase more slowly in New Zealand oysters than was previously thought, but the organism may also be able to grow at lower temperatures. Both models suggest that the recommended minimum storage temperature of 7 °C in current New Zealand and US regulatory schemes is adequate. This information will be useful for evaluating food safety risks from storing Pacific oysters at different temperatures for different times. It will also assist in formulating time-temperature recommendations for safe handling of Pacific oysters.

Bonamia ostreae in the New Zealand oyster Ostrea chilensis: a new host and geographic record for this haplosporidian parasite

Previous reports of the haplosporidian parasite Bonamia ostreae have been restricted to the Northern Hemisphere, including Europe, and both eastern and western North America. This species is reported for the first time in New Zealand infecting the flat oyster Ostrea chilensis. Histological examination of 149 adult oysters identified 119 (79.9%) infected with Bonamia microcells. Bonamia generic PCR of several oysters followed by DNA sequencing of a 300 bp portion of the 18S rDNA gene produced a 100% match with that of B. ostreae. All DNA-sequenced products also produced a B. ostreae PCR-restriction fragment length polymorphism (PCR-RFLP) profile. Bonamia species-specific PCRs further detected single infections of B. exitiosa (2.7%), B. ostreae (40.3%), and concurrent infections (53.7%) with these 2 Bonamia species identifying overall a Bonamia prevalence of 96.6%. Detailed histological inspection revealed 2 microcell types. An infection identified by PCR as B. ostreae histologically presented small microcells (mean ± SE diameter = 1.28 ± 0.16 µm, range = 0.9-2 µm, n = 60) commonly with eccentric nuclei. A B. exitiosa infection exhibited larger microcells (mean ± SE diameter = 2.12 ± 0.27 µm, range = 1.5-4 µm, n = 60) with more concentric nuclei. Concurrent infections of both Bonamia species, as identified by PCR, exhibited both types of microcells. DNA barcoding of the B. ostreae-infected oyster host confirmed the identification as O. chilensis. A suite of other parasites that accompany O. chilensis are reported here for the first time in mixed infection with B. ostreae including apicomplexan X (76.5%), Microsporidium rapuae (0.7%) and Bucephalus longicornutus (30.2%).

ChemInform Abstract: Gymnodimine, a New Marine Toxin of Unprecedented Structure Isolated from New Zealand Oysters and the Dinoflagellate, Gymnodinium sp.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Gymnodimine, a new marine toxin of unprecedented structure isolated from New Zealand oysters and the dinoflagellate, Gymnodinium sp.

A new marine toxin, gymnodimine, was isolated from New Zealand oysters, Tiostrea chilensis, and the dinoflagellate Gymnodinium cf. mikimotoi. Its unique structure was elucidated by spectroscopic methods.

Characterization Studies on the Cadmium-Binding Proteins from Two Species of New Zealand Oysters

Two different types of New Zealand oysters--Ostrea lutaria (OL) and Crassostrea glomerata (CG)--contained different concentrations of zinc, copper, and cadmium. OL oysters had 5.3 micrograms Cd/g, 3.4 micrograms Cu/g, 100 micrograms Zn/g; CG oysters had 1.4 micrograms Cd/g and 936 micrograms Zn/g. Both kinds of oysters were shown by gel filtration (G-75) to contain cadmium and zinc in fractions corresponding to a high molecular weight protein (corresponding to the size of albumin or larger) which was heat labile. OL oysters contained cadmium in fractions corresponding to a molecular weight of approximately 6500. The cadmium-binding protein in these fractions was heat-stable. This protein contained no detectable amounts of zinc and was not present in the CG oysters. Further purification by gel filtration (G-50) was performed to obtain a purer protein fraction. Isoelectric focusing of the protein obtained by G-50 filtration showed one main fraction of protein with a pI approximately 5.9 at approximately 13 degrees C. CG oysters contained cadmium and zinc in a polypeptide with low molecular weight (MW 1000). The cadmium-binding oyster proteins are minimally reactive in a competitive binding radioimmunoassay in comparison to the reactivity of a typical vertebrate metallothionein; the proteins may be metallothioneins, but, if so, they do not exhibit the principal determinants characteristic of vertebrate metallothioneins.

Characterization studies on the cadmium-binding proteins from two species of New Zealand oysters.

Two different types of New Zealand oysters--Ostrea lutaria (OL) and Crassostrea glomerata (CG)--contained different concentrations of zinc, copper, and cadmium. OL oysters had 5.3 micrograms Cd/g, 3.4 micrograms Cu/g, 100 micrograms Zn/g; CG oysters had 1.4 micrograms Cd/g and 936 micrograms Zn/g. Both kinds of oysters were shown by gel filtration (G-75) to contain cadmium and zinc in fractions corresponding to a high molecular weight protein (corresponding to the size of albumin or larger) which was heat labile. OL oysters contained cadmium in fractions corresponding to a molecular weight of approximately 6500. The cadmium-binding protein in these fractions was heat-stable. This protein contained no detectable amounts of zinc and was not present in the CG oysters. Further purification by gel filtration (G-50) was performed to obtain a purer protein fraction. Isoelectric focusing of the protein obtained by G-50 filtration showed one main fraction of protein with a pI approximately 5.9 at approximately 13 degrees C. CG oysters contained cadmium and zinc in a polypeptide with low molecular weight (MW 1000). The cadmium-binding oyster proteins are minimally reactive in a competitive binding radioimmunoassay in comparison to the reactivity of a typical vertebrate metallothionein; the proteins may be metallothioneins, but, if so, they do not exhibit the principal determinants characteristic of vertebrate metallothioneins.

The potential food poisoning hazard ofVibrio parahaemolyticusin New Zealand Pacific oysters

Abstract The level of Vibrio parahaemolyticus was generally very low in Pacific oysters sampled from 4 New Zealand oyster farms between November 1982 and May 1983. Of the 149 samples collected, only one was found to contain greater than the 1000 organisms g‐1regarded as the maximum allowable by international standards (International Commission on Microbiological Specifications for Foods 1982: Micro‐organisms in Foods, Vol. 2. Academic Press, New York). V. parahaemolyticus was detected in 57% of the oyster samples, but 95% of these contained less than 10 organisms g‐1. Maximum levels appeared to coincide with high water temperatures at the farm sites. Chilling, freezing, and depuration reduced V. parahaemolyticus numbers in oysters after harvest. However, holding at ambient temperatures (19–25°C) resulted in up to a 35‐fold increase in organism numbers with a maximum after one day. The food poisoning hazard from V. parahaemolyticus in New Zealand‐grown Pacific oysters thus appears to be minimal. Recommenda...

Ligands binding cadmium, zinc, and copper in a species of New Zealand oyster (Ostrea lutaria).

Analysis of Cd, Zn and Cu in the New Zealand oyster, Ostrea lutaria, showed that on an average it contained 5.8 ..mu..g Cd, 67 ..mu..g Zn and 14.1 ..mu..g Cu per g wet weight. Within the oyster tissue, the amount of Cd was equally distributed between the particulate and soluable (cytosol) fractions. The distribution of Zn and Cu was different, about 70% and 80% respectively being present in the cytosol. Separation of the Cd-binding ligands in the oyster cytosol on Sephadex G-75 column showed that about 60% of the cytosolic Cd was bound to high molecular weight (HMW) proteins eluted near the void volume. Similarly about 40% of Zn and Cu was also present in the HMW proteins.A significant proportion (32%) of the cytosolic Cd was present in low molecular weight (LMW) protein fractions. The protein was estimated to have a molecular weight in the range 6000 to 12,000 daltons and the protein fraction was defined as the metallothionein fraction. Only a very small amount (<1%) of Zn was associated with the MT fraction to the high concentration of Cu (2.23 ..mu..g Cu/g wet tissue). The LMW fraction of the oyster tissue cytosol had less than 1% of cytosolic Cd,more » but it contained a large proportion of Zn (about 60%) and Cu (about 32%).« less

Comparative descriptions of some oyster larvae from New Zealand and Chile, and a description of a new genus of oyster,Tiostrea

Detailed comparisons of the larvae of four species of New Zealand oyster (Saccostrea glomer‐ata, Crassostrea gigas, Ostrea lutaria, and a new species of Ostrea) and one Chilean oyster (Ostrea chilensis) showed that larvae of species other than O. lutaria and O. chilensis share certain features. One conspicuous feature is a distinct tract, termed here the posterior dorsal sulcus, which runs from the posterior margin of prodissoconch I to the valve margin of prodissoconch II; other characteristic features are an umbonate, inequivalve shell and a provinculum bearing distinct teeth. The larvae of O. lutaria and O. chilensis, in contrast, lack the posterior dorsal sulcus, are nonumbonate, and have nearly equal valves with an edentulous provinculum. These distinctive features, together with other adult features, suggest that the two species are more appropriately included in a separate genus. The name Tiostrea is proposed for the new genus. Certain supraspecific groupings within the Ostreinae need to be re‐exam...

Population genetics of the family ostreidae. I. Intraspecific studies of Crassostrea gigas and Saccostrea commercialis

The levels of genetic variation and estimates of genetic similarity and distance were determined for populations of Crassostrea gigas (Thunberg) and Saccostrea commercialis (Iredale and Roughley). The proportion of polymorphic loci in Japanese populations of C. gigas ranged from 0.58 to 0.63, while the individual heterozygosities ranged from 0.20 to 0.22. The proportion of polymorphic loci in Australian populations of S. commercialis ranged from 0.43 to 0.46, the individual heterozygosities from 0.17 to 0.19. The genetic similarity between different geographical populations of both species was approximately 99%. The genetic distance and similarity data derived from this investigation has resulted in some provisional reclassifications. The Portuguese oyster C. angulata (Lamarck) appears to be more appropriately regarded as a recent colonized isolate of C. gigas. The New Zealand oyster S. glomerata (Gould) is considered a subspecies of the eastern Australian rock oyster S. commercialis. The Japanese Kumamoto population of C. gigas warrants reclassification as the non-sibling species C. sikamea.

Abbreviated Pelagic Life of Chilean and New Zealand Oysters

OYSTERS of the genus Ostrea incubate their larvae In O. edulis, for example, veligers are released from the female when 0.15–0.17 mm long, and afterwards undergo pelagic development, usually of 6–14 days, according to water temperature and food supply, before settling and metamorphosing1–3. In O. chilensis Philippi from Chile, however, larvae from incubating females collected by the Lund University Chile Expedition 1948–49 were examined by one of us (R. H. M.), through the courtesy of Dr. T. Soot-Ryen and Prof. H. Brattstrom, and were found to be 0.45–0.49 mm long and to possess the eye spots and foot which other species develop only at the end of their pelagic life. The other (P. J. H.), who is publishing elsewhere a fuller account of the life-history of the New Zealand mud oyster, O. lutaria Hutton, has observed similar larvae in that species. These larvae, when released by the female in laboratory experiments, settled almost immediately. In both species this probably also happens in Nature.