Mortality in single‐pair mating families of QX disease‐resistant and wild‐type Sydney rock oysters (Saccostrea glomerata)

QX disease causes mass mortalities among Sydney rock oysters (Saccostrea glomerata). To overcome commercial production losses, Industry & Investment NSW has been developing mass selected QX disease‐resistant breeding lines since 1997. This breeding programme has significantly reduced QX‐associated mortality in the Lime Kiln Bar (LKB) breeding line relative to non‐selected, wild‐type (WT) oysters. The current study assessed mortality in families produced by single‐pair mating between LKB and WT oysters. When these families were grown in a QX disease‐prone area, the progeny of LKB × LKB crosses had significantly lower mortality compared with LKB × WT or WT × WT families. Mortality in the different crosses was associated with infection by sporulating Marteilia sydneyi, the parasite responsible for QX disease. Overall, the study identified a strong association between parentage and mortality resulting from QX disease.     

Evaluation of the progeny of third-generation Sydney rock oyster Saccostrea glomerata (Gould, 1850) breeding lines for resistance to QX disease Marteilia sydneyi and winter mortality Bonamia roughleyi

A breeding program for Sydney rock oysters Saccostrea glomerata (Gould, 1850) has been selecting oysters for resistance to QX disease (Marteilia sydneyi) and winter mortality (Bonamia roughleyi) for three generations at three sites in Georges River, New South Wales, Australia. The experimental sites are located at the upper, middle and lower reaches of oyster growing areas in the estuary. QX disease mainly occurs in the middle and upper reaches and is most severe at the latter. Winter mortality on the other hand occurs mainly at the lower and middle reaches and is most severe at the former. Progeny of third‐generation Sydney rock oyster breeding lines were evaluated for resistance to both QX disease and winter mortality against a non‐selected control. Line 1, selected for QX disease resistance at the upper estuary site, had excellent resistance to one season of exposure to disease, but suffered high mortality during the second season of exposure. However, these oysters had already reached market size of 50 g whole weight, with low mortality at 2 years of age, before the second episode of QX disease. Line 2 showed good improvement in resistance to both diseases, whereas Line 3, was the most resistant to winter mortality. Selection for resistance to QX disease did not appear to confer resistance to winter mortality and the converse also applied.     

Evaluation of the progeny of the fourth‐generation Sydney rock oyster Saccostrea glomerata (Gould, 1850) breeding lines for resistance to QX disease (Marteilia sydneyi) and winter mortality (Bonamia roughleyi)

The Sydney rock oyster breeding programme began in 1990 and initially focused on faster growth and resistance to winter mortality disease (WM, Bonamia roughleyi) before including QX disease (QX, Marteilia sydneyi) resistance in 1997. Four generations of oysters have now been exposed to these diseases at three sites in the Georges River, NSW, Australia (Lime Kiln Bar, LKB; Woolooware Bay, WB; and, Quibray Bay, QB). Non‐selected control oysters and lines developed at each site (Line 1 – LKB, Line 2 – WB, Line 3 – QB) were placed at the three sites alongside a new QX‐resistant line (Line 4) bred from QX survivors in other NSW estuaries. Line 1 oysters grew to a marketable size (>50 g) in two years with minimal losses following QX disease outbreaks: 28% mortality compared with 97% in controls. Losses in Line 3 oysters selected for WM resistance at QB were reduced by more than half (23% versus 52%). Line 2 performed best at WB, but this line showed excellent resistance to QX at LKB and WM at QB, indicating that breeding for resistance to both diseases is effective. However, selection of oysters for QX did not confer resistance to WM and vice versa.     

Molecular diagnosis of Marteilia sydneyi (Paramyxea) in Sydney rock oysters, Saccostrea commercialis (Angas)

Abstract. To prepare a diagnostic test, the polymerase chain reaction (PCR) with universal primers was used to amplify the internal transcribed spacer 1 (ITS1) of Marteilia sydneyi rDNA. A radiolabelled probe for M. sydneyi comprising putative ITS1 rDNA gave a strong signal for genomic DNA from M. sydneyi and no signal for host genomic DNA in Southern blots. A PCR to detect M. sydneyi used a forward primer designed from an internal site within the sequenced region and a reverse universal primer. It amplified a 650-bp fragment of M. sydneyi DNA when a combination of host and parasite DNA, extracted from an infected oyster, was used as the template.     

The effect of low salinity on phenoloxidase activity in the Sydney rock oyster,Saccostrea glomerata

This study tested the effects of low salinity on phenoloxidase activity in Sydney rock oysters (Saccostrea glomerata). Phenoloxidase is a key component of the immune system in S. glomerata. Previously, we have shown that decreased phenoloxidase activity is associated with susceptibility to fatal QX disease. In the current study, laboratory-based experiments were used to identify factors that contribute to decreased phenoloxidase activity. We found that exposing oysters to water collected from a QX-prone oyster growing area after heavy rain significantly inhibited their phenoloxidase activities. Similar inhibition was evident when oysters were held in oceanic water with artificially lowered salinities. These results suggest that exposure to low salinity decreases phenoloxidase activity. Field trials that exploited a natural salinity gradient in the Georges River, Sydney, supported this conclusion. The phenoloxidase activities of oysters transplanted to up-river sites that had low salinities were significantly lower than those of oysters held at seaward sites with higher salinities. All of these data implicate low salinity as a key environmental stressor that is associated with inhibition of the S. glomerata immune system.     

Parasites, pathological conditions and mortality in QX-resistant and wild-caught Sydney rock oysters, Saccostrea glomerata

Differences in the survival of QX-resistant fifth generation (QXR₅) and wild-caught (Wild-Caught) Sydney rock oysters were assessed over the QX-disease risk period in the Pimpama River, SE Queensland. Cumulative mortality of Wild-Caught oysters (31.7%) was significantly greater than QXR₅ oysters (0.0%) over the 118 days of the experiment. PCR and histological results showed that Wild-Caught oyster did not die from QX disease. Histology revealed oysters were infected with disseminating hemocytic neoplasia, a Steinhausia-like infection, a Rickettsia-like organism infecting epithelial cells of the gill, digenean flukes encysted in the gonadal tissue and a gill response to an unknown toxin. The cause of mortality is attributed to disseminating hemocytic neoplasia.     

The Sydney rock oyster Saccostrea glomerata (Gould 1850) breeding programme: progress and goals

In 1990, NSW Fisheries initiated a mass selection programme in Port Stephens, NSW, with the aim of breeding faster growing Sydney rock oysters Saccostrea glomerata (Gould 1850). After two generations of selection, an average weight for age advantage of 18% (range 14–23% per breeding line) was achieved. This equates to a reduction of 3 months in the time taken to reach market size. Experiments are planned to determine how much of this 3 months advantage is additive to the 6 months advantage this laboratory has already obtained using triploid S. glomerata. A parallel set of S. glomerata breeding lines was established on the Georges River, NSW, to include selection for resistance to the protistan parasite Mikrocytos roughleyi, the causal agent of winter mortality. The programme was disrupted by the outbreak of QX disease Marteilia sydneyi, another protistan parasite, in 1994. In 1997, the breeding programme was reorganized and expanded. New lines were bred from oysters that had survived both QX and winter mortality. After one generation, a small improvement in resistance to QX has been recorded; however, the exposure of further generations to M. sydneyi will be required to confirm an increase in resistance.     

Polymorphisms in the sequences of Marteilia internal transcribed spacer region of the ribosomal RNA genes (ITS-1) in Spain: genetic types are not related with bivalve hosts

Marteilia refringens is a protozoan parasite causing a disease notifiable to the Office International des Epizooties (OIE) and its distribution has implications for the transfer of live animals. The internal transcribed spacer-1 (ITS-1) from Marteilia clones contains polymorphism. Digestion with HhaI reveals two different restriction profiles, previously referred as 'O' (Marteilia from oyster or Marteilia refringens) and 'M' (Marteilia from mussels or Marteilia maurini). The aim of the present work was to determine whether the two previously described Marteilia molecular types (O and M) exist in the Iberian Peninsula and the strictness of the association with their bivalve host species. The sequence variability in the ITS-1 of Marteilia species was studied in mussels, Mytilus galloprovincialis, and flat oysters, Ostrea edulis, from different geographical locations in Spain, to establish the existence and the distribution of different species or molecular types. Although there were two distinct evolutionary lineages that corresponded more or less strictly with the 'M' and 'O' types, it was evident from the estimated phylogeny that some 'O' types have switched to 'M' type, and vice versa. Moreover, 'O' types were found in mussels and 'M' types were found in oysters, which suggests that there have been several cross-species transmissions of Marteilia between mussels and oysters.     

Commercial assessment of growth and mortality of fifth-generation Sydney rock oysters Saccostrea glomerata (Gould, 1850) selectively bred for faster growth

The Sydney rock oyster Saccostrea glomerata (Gould, 1850) industry acquired hatchery-produced spat selected for faster growth for the first time in January 2004. Selectively bred and non-selected (Control) spat produced concurrently were used to compare performance when grown under commercial conditions. Spat were distributed to farmers in seven estuaries in New South Wales. Individual farmers cultivated these oysters using their own techniques and growth and mortality were recorded quarterly. At each site, the two oyster types were cultivated using the same culture method, location and density. Growth was compared when oysters were 27 months of age. At this time, selectively bred oysters were significantly larger and heavier than Control oysters. The same result was obtained when oysters were compared at the point in time when selectively bred oysters had reached 50 g at each site. No significant difference was found for cumulative mortality between the selectively bred oysters and Control oysters across all sites. However, the seven sites had significantly different levels of cumulative mortality. Overall, the performance of selectively bred oysters was superior to the Control oysters and selectively bred oysters reached the 50 g bench mark within 29.3 months when averaged across all sites.     

Comparative experimental infection of the copepod Paracartia grani with Marteilia refringens and Marteilia maurini

Paracartia grani (Copepoda) has been identified as a potential intermediate host in the life cycle of Marteilia   refringens , a paramyxean parasite infecting flat oysters. However, no intermediate host has yet been identified for Marteilia maurini that infects mussels. A better understanding of the life cycle of these two Marteilia types would clarify their taxonomic relationship and hypothesized co-specificity. For this purpose, experimental infections of copepods, P. grani , were performed using naturally infected flat oysters and mussels. Infection patterns were different depending whether copepods were infected from oysters or mussels. M. maurini did not proliferate in copepods while M. refringens rapidly proliferated in infected copepods. Previously unrecognized developmental stages of M. refringens were found during this study.     

IMPACTS OF INTRODUCED AQUACULTURE SPECIES ON MARKETS FOR NATIVE MARINE AQUACULTURE PRODUCTS: THE CASE OF EDIBLE OYSTERS IN AUSTRALIA

Economic competition between introduced and native aquaculture species is of interest for industry stakeholders since increased production can affect price formation if both aquaculture species are part of the same market or even substitutes. In this study, we focus on the Australian edible oyster industry, which is dominated by two major species—the native Sydney rock oyster (grown mainly in Queensland and New South Wales) and the non-native Pacific oyster (grown mainly in South Australia and Tasmania). We examine the integration of the Australian oyster market to determine if there exists a single or several markets. Short- and long-run own, cross-price and income flexibilities of demand are estimated for both species using an inverse demand system of equations. The results suggest that the markets for the two species are integrated. We found evidence that the development of the Pacific oyster industry has had an adverse impact on Sydney rock oyster prices. However, our results show that both species are not perfect substitutes. Demand for Sydney rock oysters is relatively inelastic in the long run, yet no long-run relationships can be identified for Pacific oysters, reflecting the developing nature of this sector.     

Experimental deepwater culture of the Sydney rock oyster (Crassostrea commercialis): III. Raft cultivation of trayed oysters

Sydney rock oysters, normally intertidal, were submerged below rafts in vertical stacks of 15 oyster trays extending 2 m deep. Growth rates and mortality were not good or economically encouraging. The best growth was from small culled spat (43 whole oysters/kg) to large seconds (28/kg), an increase of 59% in 9 months. The minimum mortality was 52%. Fouling growths of barnacles, tunicates, sponges and hydroids were restricted by placing experimental trays on top of the raft for several days to dry out. Compared with controls, this resulted in increased oyster growth in experimental trays during the next 6 months. Oyster mortality and incidence of mudworm blisters (resulting from the polychaete Polydora websteri) were similar in both control and experimental trays during this period. For improved growth of trayed submerged oysters the optimum vertical distance between trays and the optimum density of oysters on trays need to be determined.     

Experimental deepwater culture of the Sydney rock oyster (Crassostrea commercialis = Saccostrea cucullata): II. Pontoon tray cultivation

Pontoons made from plastic pipe were tested as an alternative to racks for deepwater culture of the Sydney rock oyster. The growth and mortality of oysters permanently suspended in water on trays beneath floating pontoons were compared with oysters on trays in an intertidal zone. For both culled spat (30–31 g whole oyster weight) and seconds oysters (37–39 g) beneath pontoons the growth rate, measured by weight increases, was three times that of oysters on intertidal racks over a 5-month period. Mortality (from unknown causes) was higher beneath the pontoons. The mean mortality of spat oysters was 40% compared with 24% on the intertidal trays, and for seconds oysters was 51% compared with 34%.     

Experimental deepwater culture of the Sydney rock oyster (Crassostrea commercialis=Saccostrea cucullata): I. Growth of vertical clumps of oysters (‘ren’)

Japanese style ren, consisting of scallop shells encrusted with small Sydney rock oysters and strung on vertical wires, were grown at 23 estuarine stations along the New South Wales coast for up to 21 months. Weight increments of ren were used to evaluate growth rates of oysters in non-cumulative (3–4 months immersion) and cumulative (6–21 months immersion) series. Oyster weight increased at a rate of approximately 10% per month, which was considered suitable for commercial production, but estimated labour costs to make up the ren were high. Mortality rate was 6.3% per 3–4 months immersion. Gaping oysters, through natural mortality, winter mortality, the haplosporidian parasite Marteilia sydneyi, and other causes, accounted for 4.5%. Broken oysters, resulting from fish and crab predation, accounted for 1.8%. Mortality caused by the polychaete mudworm Polydora websteri was negligible; only 1.7% of the 4.5% gapers showed the characteristic blisters.     

养殖牡蛎的选择育种研究与实践

在人类利用自然和改造自然的同时,与人类生活密切相关的动植物也经历着自然进化、人工驯化和人工选育的过程,后者使得这些动植物在生长速度、产量和抗病、抗逆性等方面获得明显的改良.     

Farming triploid oysters

Although the commercial benefits of triploidy have been evaluated in the Pacific oyster Crassostrea gigas (Thunberg, 1793), eastern oyster C. virginica (Gmelin, 1791), Sydney rock oyster Saccostrea glomerata (Gould, 1850) and European flat oyster Ostrea edulis (Linnaeus, 1750), so far this technique has only been commercialised for Pacific oysters.

Commercial production of triploids on the West Coast of North America began in 1985. Since then production of triploids has greatly increased and the use of tetraploid males to fertilise eggs from diploids to produce batches of 100% triploids has been developed. In 1999/2000, triploid Pacific oysters made up 30% of all Pacific oysters farmed on the West Coast of North America. Some hatcheries now use tetraploid males instead of chemical or physical stress to produce triploids. The rapid uptake of triploid and tetraploidy techniques has been facilitated by the almost total dependence that these oyster industries have on hatcheries for the supply of seed. This industry in the Pacific Northwest of the US and in British Columbia, Canada, would not have developed to its current size without hatchery seed supplies. Triploids are preferred over diploids in summer because diploids are less marketable when in spawning condition.

There was only limited interest in triploidy production in France until 1999, when IFREMER began to make sperm from tetraploids available to commercial hatcheries. In 1999/2000, only 10% to 20% of all the hatchery-supplied Pacific oyster spat were triploids, but with the use of sperm from tetraploid oysters, this could increase sharply.

Elsewhere around the world, the commercial uptake of triploid oysters has been slow to develop. However, in countries where the production of Pacific oysters is based on hatchery supply of seed, it is likely that with the use of tetraploid oysters, the farming of triploid oysters will increase in the near future.     

Quantitative measurement of reproductive output in the American oyster, Crassostrea virginica (Gmelin), using an enzyme-linked immunosorbent assay (ELISA)

Abstract. A quantitative gonadal index was developed for oysters, Crassostrea virginica (Gmelin. 1791), using polyclonal antibodies from eggs and sperm. Percoll used in the purification of oyster eggs and sperm greatly improved the purity of antigens compared to filtering the egg or sperm through a fine mesh only. The antigen-antibody reaction was tested with indirect sandwich ELISA using alkaline phosphatase-conjugated goat anti-rabbit igG as a secondary antibody. Rabbit anti-oyster egg IgG and anti-oyster sperm IgG initially exhibited a weak cross-reactivity over somatic tissue. Absoring with acetone-dried oyster tissue powder removed this cross-reactivity. Both antisera exhibited strong specific immunological reactions to oyster eggs or sperm respectively. The quantity of eggs or sperm was measured using ELISA and a quantitative gonadosomatic index (dry wt of egg or sperm/dry wt oyster) (GSI) calculated. GSI from ELISA correlated with gonadal stage measured histologically. Monthly mean GSI of female oysters was highest during late spring to early summer (0·157–0·201) and lowest during early winter to early spring (0·002-0·000). Maximum GSI observed during the study was 0·422 for female oysters and 0·446 for male oysters. Female oysters produce 3·7–65·4 million eggs, with an average of 21·1 million during each spawning. A positive correlation was observed between the number of eggs produced and oyster size; the number of eggs in the gonad increased as oyster size (i.e. total dry wt) increased (r= 0·67); however, the relationship was non-linear. Large oysters contained proportionally fewer eggs. Prevalence of Perkinsus marinus parasitism was high, 90–100%, during the study, as was weighted incidence, 1·33 to 2·67, No statistically significant correlation was observed between infection intensity and the per cent weight of oyster eggs or egg number.     

The Effects of Tidal and Bottom Placement on the Growth, Survival and Fouling of the Eastern Oyster Crassostrea virginica

Oysters Crassostrea virginica in Georgia are naturally small and grow in clusters; however, it is more profitable to harvest large, single oysters. This study attempts to identify favorable tidal and bottom placements for the grow-out of large, single oysters in Georgia. Three bags, each containing 50 single oysters, were placed in four different tidal positions (subtidal on-bottom, subtidal off-bottom, intertidal on-bottom and intertidal off-bottom) at five sites in House Creek, Georgia. Measurements of oyster growth, survival and degree of oyster spat fouling were taken seasonally (every 3 mo). Oysters from on-bottom treatments exhibited significantly lower growth ( P = 0.0364 intertidal only), survival ( P = 0.0044) and degree of fouling ( P = 0.0154) than oysters from the intertidal off-bottom treatment. However, the oysters placed intertidally off-bottom were heavily fouled during the recruitment period. It may be necessary to sacrifice some growth and survival by culturing oysters intertidally on-bottom during the recruitment period in order to reduce the degree of fouling. During the non-recruitment period, placing oyster culture bags intertidally off-bottom maximizes growth and survival.     

长牡蛎MITF基因表达及与壳色的关联

为了解长牡蛎MITF基因的表达及其与壳色的关联,验证了长牡蛎中的4个MITF基因,对长牡蛎MITF氨基酸序列进行了序列分析和多序列比对,分析了长牡蛎幼体发育各时期的转录组,采用荧光定量PCR的方法研究长牡蛎各组织及黑壳、白壳牡蛎特定部位mRNA表达情况。4个MITF基因中有3个基因可能为假基因,有表达的长牡蛎MITF基因共编码448个氨基酸,为亲水性不稳定蛋白,含有N端结构域(MITFTFEBC3N superfamily)和高度保守的功能性结构域HLH结构域。转录组分析发现MITF在长牡蛎个体发育的各个时期均有表达,在稚贝期达到最高。组织表达结果显示MITF在外套膜中的表达水平显著高于其他组织。MITF在黑壳牡蛎闭壳肌中的表达量显著低于白壳牡蛎,而在黑壳牡蛎外套膜中的表达量高于白壳牡蛎,但不显著。在黑壳、白壳牡蛎外套膜边缘的表达量都显著高于内侧。研究表明,长牡蛎MITF基因可能在牡蛎壳形成早期就参与了黑色素的生成调控和个体的生长发育,可调控牡蛎酪氨酸酶Tyr2基因,参与外套膜和贝壳中黑色素的形成。本研究为进一步研究牡蛎壳色形成机制奠定了基础。     

Development of a diagnostic test for Mikrocytos roughleyi, the aetiological agent of Australian winter mortality of the commercial rock oyster, Saccostrea commercialis (Iredale & Roughley)

Abstract. Diagnosis and epidemiology of Mikrocytos roughleyi , the aetiological agent of Australian winter mortality of the rock oyster, Saccostrea commercialis (lredale & Roughley ), has been hampered by the small size of the pathogen and the low intensity of natural infections. Inoculation of experimental oysters with filtered, unpurified tissue homogenate from oysters infected naturally produced experimental infections after 22 weeks but hyperinfection was not successful. DNA was extracted from naturally infected, experimentally infected and uninfected oysters, then oligonucleotide primers were used in polymerase chain reactions to provide the basis for a molecular bioassay. One pair of primers produced an amplicon of 680 base pairs in length that was correlated directly to the presence of M. roughleyi in oyster tissues. The assay was able to detect a single organism of M. roughleyi in 400 host cells.