The effect of intertidal exposure on the growth and survival of hatchery-reared Pacific oysters (Crassostrea gigas Thunberg) kept in trays during their first ongrowing season

In a number of trials during 1971 and 1972 small populations of hatchery-reared Pacific oyster spat (Crassostrea gigas Thunberg) 0.07–4.1 g mean live weight, were grown intertidally in trays to measure the effect of exposure to air on growth and survival. In the Menai Straits, N. Wales, and at Paglesham Pool, R. Roach, Essex, several stations were selected above low water of spring tides (LWST) to cover the range of 0–30% exposure to air. Live weight, dry meat weight and dry shell weight were reduced with increased exposure to air, but the ratio of dry meat weight to dry shell weight (shell condition index), the gross biochemical composition, and survival were not affected. By extrapolation the point of no growth was found to be at 36 and 47% exposure to air at the sites in the Menai Straits and R. Roach, respectively.     

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.     

Effects of copper- and tin-based anti-fouling compounds on the growth of scallops (Pecten maximus) and oysters (Crassostrea gigas)

Fouling is an important problem in shellfish cultivation. This paper gives the results of growth trials of adult and juvenile scallops, and adult Pacific oysters in enclosures treated with various anti-fouling compounds: copper(I) oxide-based paint, bis-(tri-n-butyltin) oxide (TBT)-based paint, and copper-nickel alloy mesh trays.With the copper oxide treatment there was some increase in the growth of scallop spat, but no effect was observed on the growth of adult scallops or Pacific oysters. The copper-nickel trays, however, caused high mortalities and inhibited growth in adult scallops, but had no effect on oysters. The TBT paint was detrimental to the growth and survival of juvenile scallops, and caused high mortalities, poor growth and thickened shells in oysters. It had no effect on adult scallops.     

Experimental deepwater culture of the Sydney rock oyster (Crassostrea commercialis): IV. Pilot production of faft oysters

Rafts carrying five permanently submerged oyster trays were moored in nine New South Wales estuaries during 1976–1977 to determine how rapidly culled spat oysters (25–29 g whole weight) or seconds (29–40 g) could be grown into first grade (plate) oysters (40–67 g).In the first series of trials results were obtained from seven localities after 3 months summer growth. The average weight increase was 51%; mortality averaged 17%. A further series of trials were conducted for 3 months in autumn at four localities. Weight increases averaged 40% and mortality 8%.The growth rates calculated from weight increases were two to three times greater than those expected from normal intertidal culture traditional of Australia. The estimated time to convert spat to plate oysters was 4 months for summer and autumn crops.     

Growth of the European flat oyster in the Mediterranean Sea (Murcia, SE Spain)

Growth of the natural European flat oyster (Ostrea edulis L.) spat from the Mar Menor (Murcia, Spain) was studied in the Mediterranean Sea over 18 months. The oysters were cultured in two types of containers, stackable plastic Galician trays and plastic mesh pots, deployed at a depth of 15 m hung from a long-line. Two size classes of spat were used, Class I spat (initially 53 mm in size and 19 g in weight) and class II spat (initially 31 mm, 4 g). The best results were observed in the class I oysters grown in the trays, which yielded a substantial biomass (24.77 kg m^–2), the survival rate was 69% and commercial size (60 mm) was attained by all the oysters within 9 months of the start of the experiment. The observed growth of the class II oysters was poor, attaining a mean of not more than 50 mm and 18 g; the survival rate ranged between 25–74% and only between 8–13% of the class II spat attained commercial size.     

Impact of Feeding Status on the Efficacy of Depuration for Decontaminating Vibrio parahaemolyticus in Pacific Oysters (Crassostrea gigas)

Vibrio parahaemolyticus causes acute human gastroenteritis and is often linked to consumption of raw oysters. Previous investigations indicated that refrigerated seawater depuration at 12.5°C could significantly reduce V. parahaemolyticus contamination in Pacific oysters; however, further optimization is necessary to achieve the regulatory target of >3.52 log most probable number (MPN)/g reduction. The current study investigated influences of algal feeding on efficacy of depuration to reduce V. parahaemolyticus in raw oysters. A V. parahaemolyticus cocktail (10290, 10292, 10293, BE 98–2029, 027-1c1) was mixed in artificial seawater (70 L) to inoculate oysters (n = 35) at 4–5 log MPN/g. Inoculated oysters were subjected to depuration with feed (algae = 0.036 ml/gram of oyster) and without feed at 12.5°C. Oysters (n = 5) were analyzed for V. parahaemolyticus using a three-tube MPN method after 0, 1, 3, 5, and 6 days of depuration. Depuration (6 days) achieved average V. parahaemolyticus reductions of 2.75 log MPN/g and 3.03 log MPN/g in the fed and unfed systems, respectively; however, feeding status did not significantly impact the efficacy of depuration to reduce V. parahaemolyticus in Pacific oysters. Further optimization of depuration is necessary to achieve the regulatory target for V. parahaemolyticus decontamination in raw oysters.     

The Effects of Stocking Density,Bag Mesh Size,and Bottom Sediment on the Growth and Survival of the Eastern Oyster,Crassostrea virginica,with Emphasis on Controlling Oyster Spat Fouling

This study was designed to determine if oyster spat fouling upon adult oysters, Crassostrea virginica, cultured in coastal Georgia could be controlled by stocking density, bag mesh size, substrate type, and tidal level (intertidally or subtidally). Oyster gowth and survival was also monitored for each treatment. Sediment type had no effect on the number of spat per oyster either in intertidal or subtidal areas. Greater growth occurred in subtidal bags placed on sandmud and sandclay substrates. Intertidal mud and sandhnud bottom treatments showed the least growth. Survival of oysters grown intertidally (64%) was better the those cultured subtidally (27%). Mesh size of the oyster growing bags -had no effect upon oysler fouling or growth (shell length) and survival of the oysters they contained. Stocking density did affect oyster fouling, with lower fouling per oyster in higher density treatments. Density had no effect on oyster growth (shell length) or survival at the levels tested. Heavy fouling occurred on all oysters in the mesh and stocking density experiments while they were suspended off-bottom, but an I l -fold decrease in fouling occurred after bags were placed on the sublidal river bottom.     

Experimental test of oyster restoration within eelgrass

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Molecular cloning and expression of the heat shock protein 70 gene in the Kumamoto oyster <Emphasis Type="Italic">Crassostrea sikamea</Emphasis>

Episodes of summer mortality of the Kumamoto oyster Crassostrea sikamea are a major problem for its cultivation. Expression of the heat shock protein 70 (HSP70) is induced by various environmental stresses, including heat. We cloned and sequenced hsp70 complementary DNA from C. sikamea to investigate the relationship between hsp70 expression and heat tolerance in this oyster. Quantitative real-time polymerase chain reaction was performed using gill tissue dissected from oysters before and after heat shock for 1 h. The results showed hsp70 expression was faster and greater in oysters cultured at 20–22 °C than at 10–12 °C, and survival was lower among oysters cultured at 20–22 °C than at 10–12 °C. Moreover, heat tolerance was investigated by a 1-h pre-heat treatment, followed by exposure to heat shock conditions 5 days later. Survival was higher and hsp70 expression was notably lower in oysters that received the pre-heat treatment compared with those that did not. We conclude that a pre-heat treatment of only 1 h may be useful for inducing heat tolerance in C. sikamea, and that a low level of hsp70 expression after heat shock is an important index in selecting for high heat tolerance in these oysters.     

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.     

New oyster on-growing container for German mariculture operations

The hydrographic and climatic situation along the German coast requires specially adapted equipment for mariculture enterprises. The containers used in the past for the on-growing of oysters (Crassostrea gigas Thunberg) in shallow sea areas provided results which gave reason for developing a new type of container which was to be more economic and produce a high quality oyster of uniform shape.Small prototype containers, based on a galvanized iron construction, were built and placed at different sites along the coast. They held 1680 oysters, each of which were re-attached with cement onto square mesh plastic netting which was stapled on oak frames. On these frames, which were handled like drawers, the oysters had optimal conditions which were believed to be better than on a natural oyster bed. Each oyster had its own space of 7 cm by 8 cm wide and 10 cm high and was not handled until it reached market size. Good water exchange was provided by the open construction of the container which also gave protection against predators by means of a complete mesh cover.     

The effets of feed water flow rate on the growth of aquacultured Crassostrea virginiea in Hawaii

Selected nursed C. virginica with an initial average weight of 3.59 g were grown in vertical suspension in a tank which was divided into three chambers. The oysters were divided into three groups, glued onto strips of polyvinyl chloride and suspended in the three chambers. They were fed commercial shrimp pond effluent at the following flow rates: 4.00 liter/ day/g (high), 1.33 liter/day/g (medium), and 0.45 liter/day/g (low)^*. After 209 days the final average weights of the oysters were 66.43 g, 53.67 g and 40.65 g. The average recorded dissolved oxygen concentrations of the effluent of the three chambers were 7.0 ppm, 6.0 ppm and 5.2 ppm, respectively. The survival rates were 90.56, 73.33 and 52.12% and the percentages of oysters 55 g or larger on the harvesting day were 91.67, 76.69 and 8.33% for the high, medium and low feed water flow rates. Up to an average weight of about 20 g, there was no significant difference between the growth rate of the oysters receiving 4.00 liter/day/g and those receiving 1.33 liter/day/g. All of the oysters grew rapidly during a period of increased temperature and decreased salinity towards the end of the grow-out period.     

Analysis of growth and first reproduction of hatchery‐reared juvenile Cortez oyster (Crassostrea corteziensis) in northwestern Mexico: proposal of a minimal fishing size

This study presents complimentary data of early growth and age/size of first reproduction of hatchery‐reared Crassostrea corteziensis juveniles cultivated in the field for 9 months. Samples of oysters and gonads were collected monthly to determine absolute growth and growth rates, as well as overall gonad development. At the end, adult oysters ranging 75.6 ± 0.62 mm shell height (SH) yielded a mean growth rate of 0.308 mm day⁻¹, which is among the highest reported for the species. Gametogenesis began in March–April and spawning occurred during August and September. Males outnumbered females at smaller sizes, but female were more abundant at larger sizes. From planting time in the field, the age/size of first maturity was 3.25 months for males (42 mm SH) and 4.5 months for females (54 mm SH), with a mean population age of 4.75 months for males (size range 55–59 mm) and 5.25 months for females (60–64 mm). Based on these results, and the time needed for hatchery care prior planting juveniles in the field (2.25 months), we propose limiting fishing of wild oysters to sizes >65 mm height to allow them to breed at least once and contribute to restoring wild populations.     

Growth of American oysters increased by polyploidy induced by blocking meiosis I but not meiosis II

Triploidy in American oysters (Crassostrea virginica) was induced by blocking polar body formation with cytochalasin B. Triploid oysters created by treatment during meiosis I grew faster during the first 3 years of life than did diploid siblings. Triploid oysters created during meiosis II grew at the same rate as their controls. Because heterozygosity was higher in oysters created during meiosis I than in other groups, the increased growth must be due to heterozygosity rather than to triploidy per se.     

Fouling and predation; how do they affect growth and survival of the blacklip pearl oyster, Pinctada margaritifera, during nursery culture?

This paper reports on 5 experiments conducted to assess the effect of cleaning regime and predation on growth and survival of blacklip pearl oyster (Pinctada margaritifera) juveniles in north Queensland, Australia. P. margaritifera juveniles with a mean (±SE) dorso-ventral shell height (DVH) of 4.5 ± 0.1 mm were placed into plastic mesh trays and cleaned either every 4 or 8 weeks or left uncleaned for 16 weeks. Cleaning regime had a significant effect on growth and survival (P < 0.005). Lowest DVH (16.2 ± 1.0) was shown by oysters in uncleaned trays during 16 weeks compared to oysters in cleaned trays; however, there was no significant difference in DVH between oysters held in trays cleaned every 4 (19.4 ± 1.2) or 8 weeks (21.2 ± 0.8). In contrast lowest survival was shown by oysters held in trays that were cleaned every 4 weeks (30 ± 5%), but no differences were noted between oysters cleaned every 8 weeks (63 ± 4%) and oysters that were left uncleaned for 16 weeks (75 ± 8%). Predators of P. margaritifera in northern Australia included crabs, stomatopods, flatworms, gastropods and fish. The stomatopod, Gonodactylus falcatus, was the most destructive predator with individuals consuming in excess of 20 juvenile pearl oysters per week. The leather jacket, Paramonocanthus japonicus, did not kill pearl oysters, but trimmed the margin of oysters shells significantly reducing DVH when compared to control groups cultured without fish. Removing predators monthly had a significant effect on growth of pearl oysters compared to oysters in non-inspected trays; however monthly inspection of culture trays did not significantly improve oyster survival. This revised version was published online in August 2006 with corrections to the Cover Date.     

Experimental deepwater culture of the Sydney rock oyster (Saccostrea commercialis). VI. Commercial oyster cage systems

A growout cage that retains oysters, excludes predators and reduces maintenance is described; it is cut from 200 mm (8 in) steel reinforcing mesh as kitset units and then hot dip galvanised. Each cage is 2.2 m long, 0.8 m wide and 1.0 m deep (88 × 22 × 40 in) and contains five floors which are 203 mm (8 in) apart. The floors and the walls are covered with 19 mm ($\text{3}\text{4}$ in) galvanised wire mesh, or high density polyethylene plastic mesh. These cages may be slung from rafts, fitted with individual flotation or lowered to the bottom with a marker buoy; they weigh approximately 70 kg (154 lb) empty and about 220 kg (484 lb) when harvested. Each cage crop consists of approximately 2.5 bags totalling about 150 kg (330 lb), and in good growing areas three to four crops have been harvested from each cage per year. In two such crops culled spat (22–29 g whole wet weight) were converted to plate (first grade) oysters (40–67 g); in the other two, seconds (29–40 g) were converted to plate oysters. Growth rates, stocking densities and mortality data are given for 11 crops.     

Grow-out culture of tropical abalone, Haliotis asinina (Linnaeus) in suspended mesh cages with different shelter surface areas

Thisstudy investigated the effects of shelter surface area (SSA) on the feeding,growth and survival of the donkey-ear abalone, Haliotisasinina reared in mesh cages (0.38×0.38×0.28m) suspended in flow-through tanks (water volume = 6m³). Cages had sections of polyvinylchloride (PVC) thatprovided shelters with surface area of 0.22 m², 0.44m² and 0.66 m².Hatchery-produced abalone with initial shell length of 32 ± 1mm and wet weight of 7.5 g were stocked at 50individuals cage^?1 that corresponded to stocking densities ofca. 227, 113 and 75 abalone m^?2 of SSA. The ratios of sheltersurface area to cage volume (SSA:CV) were 5.5, 11 and 16.5. Abalones wereprovided an excess red seaweed Gracilariopsis bailinae(= Gracilaria heteroclada) at weekly intervals overa 270-day culture period. Feeding rates (18–20% of wet weight), foodconversion ratio (26–27) and percent survival (88–92%) did notdiffer significantly among treatments (p > 0.05). Body size at harvest rangedfrom 56 to 59 mm SL and 52 to 57 g wet body weightwith significant differences between abalone reared at SSA 0.22m² and 0.66 m² (p < 0.05).Abalone reared in cages with 0.66 m² SSA grewsignificantly faster at average daily growth rates of 132 μm and188 mg day^?1. Stocking densities of 75–113m^?2 SSA in mesh cages suspended in flow-throughtanks resulted in better growth of abalone fed red seaweed.     

When should pearl oyster,Pinctada margaritifera (L.), spat be transferred from the hatchery to the ocean?

Hatchery propagation of pearl oysters is relatively new and optimal hatchery protocols are still being developed. While in the hatchery, pearl oyster spat are supplied a constant and reliable food source and are protected from fluctuations in environmental conditions and predators. This study investigated the hypothesis that retaining blacklip pearl oyster, Pinctada margaritifera (L.), spat in the hatchery for longer periods, prior to transfer to the ocean, would improve growth and survival during early nursery culture. Results showed that the longer spat were retained in the hatchery, the smaller their average size at grading (3.5 months of age). At grading, spat transferred 3 weeks after settlement had a mean dorso–ventral shell height (DVH) of 9.2 ± 0.4 mm with 34% of individuals retained on a 10‐mm mesh. However, spat retained in the hatchery until 5, 7 and 9 weeks after settlement, had a mean DVH of 9.0 ± 0.4, 7.8 ± 0.3 and 6.3 ± 0.4 mm respectively. Only 10% of spat transferred 9 weeks after settlement were retained on a 10‐mm mesh at grading. The results probably reflect superior nutrition available in the ocean and indicate that pearl oyster spat should be transferred from the hatchery as soon as possible after settlement in order to maximize growth.     

Mortality associated with OsHV-1 in spat Crassostrea gigas: role of wild-caught spat in the horizontal transmission of the disease

The French oyster production of Crassostrea gigas is based on two sources of spat: wild-caught (WC) and hatchery-produced (HP). Massive mortality related to the ostreid herpesvirus type 1 (OsHV-1) has affected both sources in France since 2008. We investigated the mortality in juvenile C. gigas due to the horizontal transmission of OsHV-1 within (separated condition) and between (mixed condition) the two spat sources in three environments from April to June 2010. In the separated condition, no mortality was observed in the HP batches, while the WC batches experienced moderate to high mortality (40–80 %). In contrast, the WC and HP batches experienced high mortality in all tested environments for the mixed condition. At the beginning of the trial, the HP batches were all negative for OsHV-1 DNA detection by real-time PCR, while the WC batches were all positive for OsHV-1 DNA detection by real-time PCR, even though the percentage of virus DNA-positive oysters and viral load were low. During the experiment, all batches that exhibited mortality were positive for OsHV-1 with a high viral load, while OsHV-1 was never detected for the HP batches of the separated condition. Together, our results demonstrated that OsHV-1 was horizontally transmitted from the WC oysters to the HP oysters. Our study is the first to indicate that the mortality related to OsHV-1 in HP oysters can be avoided using ponds or tanks. However, these oysters were always protected from OsHV-1, and HP oysters could also experience mortality and spread the disease similar to the WC oysters if such care is not used. Finally, the persistence of OsHV-1 at a sub-clinical level in certain oysters supports the hypothesis that the virus can be reactivated and cause viral replication. The use of the two spat sources is discussed to better understand the spread of the disease among oyster stocks.     

Resistance of Ostrea edulis to Bonamia ostreae infection

Preliminary studies showed that oysters from a population of Ostrea edulis infected with Bonamia ostreae since at least 1963 have a substantial degree of resistance to the infection in comparison with oysters from a population with no prior exposure history to the disease. Over a 46-week period and under identical environmental conditions, 99% of non-resistant oysters exposed to the disease died while only 26% of a population of resistant oysters died. The surviving resistant oysters had lesions which indicated a chronic infection and possible degradation of the parasite within the tissues. The resistant oysters may offer a management option for the reestablishment of Ostrea edulis culture in disease enzootic areas where the parasite has virtually eliminated non-resistant populations.