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1.
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.  相似文献   

2.
Growth and mortality of sibling triploid and diploid Sydney rock oysters, grown at two tidal heights, three stocking densities and three different sites on the Camden Haven River estuary, were compared. Triploids grew faster than diploids. The majority of the growth rate difference occurred after the oysters reached 2 years of age. By 3.2 years, triploids were 49% heavier than diploids. Oysters grown intertidally were larger than those grown subtidally. Oysters stocked at the lightest density of 2 L per basket grew to a significantly larger size than baskets stocked at 3 or 4 L. Growth rates were significantly different at the three sites. Growth was reduced the further the oysters were from the mouth of the estuary. There was no significant difference in mortality between ploidy level, but there were differences between tidal heights, stocking densities and sites. Intertidal oysters suffered higher mortality than subtidal. Oysters stocked at the highest density had a significantly higher mortality than the lowest density; neither of these was significantly different from the medium density. The site closest to the mouth of the estuary had significantly lower mortality than the middle and upper estuary sites.  相似文献   

3.
The Pacific oyster, Crassostrea gigas, is cultivated intertidally in Kinmen Island by both a traditional way of growing oysters on the surface of stone blocks, nicknamed “rock oysters”, and a recently introduced and more efficient way of hanging them in clusters on horizontal nylon lines, i.e. “hanging oysters”. We investigated the growth and mortality of both types of oysters from late July to early December 2003, and measured condition index (CI) and rates of oxygen consumption and ammonium excretion for the hanging oyster. Growth of oyster shells stopped in early October for the hanging oysters and early December for the rock oysters. Mortality rates were higher for hanging oysters than rock oysters. Hanging oyster's O/N ratio and CI, determined by a home-made CI meter that measured the volume of oyster's inner shell cavity with high precision, decreased significantly in October. Hanging oysters were apparently in poor physiological condition during the winter Monsoon, which is characterized by cold and persistently strong wind. On Kinmen Island the monsoon season begins in late September and is accompanied by declining seawater temperature and high seston loads in oyster farms. Chlorophyll a concentrations and seston food quality decreased significantly in early October after the winter Monsoon began. The hanging oyster's poor acclimation to the local climate was probably caused by the import of its spat from southwest coast of Taiwan where it is warmer than Kinmen Island in fall and winter. We recommend that oyster growers collect spat locally or from areas of similar climate.  相似文献   

4.
Annual growth and survival rates were measured for blood arks Anadara ovalis (Bruguière 1789) cultured in mesh bags that were placed at the spring-low-water mark in soft-bottom sediments of the Skidaway River, Georgia. The feasibility of growing the arks to a marketable size using this technique was assessed by determining the effects of stocking density and biofouling on growth and survival. Two replicate densities of 190 (low) and 400 (high) arks per mesh bag (mean shell length 31.97 mm) were planted in early September 1999. In April 2000, the arks cultured at the lower density had a significantly larger size (44.99 mm) than at the higher density (43.83 mm), with growth rates of 1.85 mdmo, and 1.69 mm/mo, respectively. Growth decreased considerably in the subsequent months (low: 0.17 mm/mo; high: 0.30 mm/mo). There was no significant difference in ark size between treatments after a year's growth in late August 2000 (low: 45.76 mm, 1.15 mm/mo; high: 45.31 mm, 1.11 mm/mo). Similarly, no significant difference in annual survival rates between stocking densities occurred (low: 42.89%; high: 40.25%). The present findings indicate that this method of growing arks to market size has potential to contribute to future endeavors to develop an aquaculture fishery for the blood ark in the coastal waters of Georgia.  相似文献   

5.
A new method of oyster cultivation, the Stanway oyster cylinder, has been investigated in the Bay of Arcachon since 1989. A comparative study was carried out between the growth of spat and 18-month-old Crassostrea gigas oysters, in cylinders and in traditional bags. The growth in height and in whole weight was lower in cylinders. In contrast, the tests showed a better quality of the meat, with higher condition index and higher carbohydrate content, and a better quality of the shell, with higher density and better shape. Therefore, because of the improvement in oyster quality, the use of the cylinder seems to be advantageous for the Arcachon oyster industry.  相似文献   

6.
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.  相似文献   

7.
The production of unattached hatchery-reared oyster seed has encouraged the initiation of oyster cultivation in new areas throughout the British Isles, and has led to innovations in methods of handling and growing-on oysters. Strangford Lough, Northern Ireland is an area with no traditional oyster fishery, and the introduction of the fast growing pacific oyster has led to consideration of the most feasible method of cultivating this species. Although raft culture to market size has known advantages, it is normally associated with oysters attached to cultch. However, off-bottom culture by growing unattached oysters intertidally in trays held off the sea-bed is an alternative, which provides higher survival, better growth, higher stocking densities and complete cropping compared with traditional sea-bed culture. Considering these advantages, tray cultivation may be economically justifiable, especially in an area without an existing oyster fishery.  相似文献   

8.
Abstract. Production of Pacific oysters was studied under pilot-scale conditions in Baynes Sound, British Columbia, using common bottom culture strategies. Four seeding treatments, each with a different seed per cultch density were cultured: wild-caught seed 5mm in shell height at 10 seed per cultch piece and hatchery produced seed 1-2 mm in shell height at densities of 11, 40 and 105 per cultch piece. The cultch material for all treatments was Pacific oyster shell. All seed was reared for approximately 1 year in a seed nursery located at the 2.2-m tidal level then transferred to a 1-m tidal level grow-out plot until harvest 4 years later in May 1988, Clusters of large numbers of oysters were separated and evenly distributed within the plots when the oysters attained a shell height of 60-100 mm. During the first year, growth was slow and mortalities were relatively high. All treatments produced oysters of similar size at harvest. The proportion surviving at harvest was substantially higher for the wild oysters which were initially larger at time of planting. Within the hatchery treatments proportional survival per cultch piece was inversely related to initial density on the shell; however, total production per cultch piece was positively related to initial density. Most efficient use of seed is attained at lower densities per shell; however, most efficient use of cultch and effort to handle cultch is attained at high densities.  相似文献   

9.
Studies on larval settlement and growth of the commercial scallop Aequipecten tehuelchus were carried out over a 2-yr period in San Matias Gulf, Argentina. Gonadal index was used to indicate spawning and spat collectors were deployed when spawning began. Artificial spat collectors (mono-filament bags filled with thin shrub branches) were placed at a depth of 25 m in two areas of the Gulf during two seasons (1989–1990 and 1991–1992). Maximum settlement occurred by mid-February during the first season and by mid-January in the second season. Larger numbers of spat were found in collectors placed near the sea bottom. After settlement, spat were removed and placed in cages for growout. Scallops reached the average commercial size (60 mm shell height) 16 mo later. Mortality rate during the entire period was 10%.  相似文献   

10.
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.  相似文献   

11.
Juveniles of Pinctada mazatlanica and Pteria sterna were collected with artificial collectors from Falsa Bay, Baja California Sur, Mexico during a 12 month experimental period. Filament substrate artificial collectors contained in 2 mm plastic mesh bags (25 ± 25 cm) were deployed from the surface to 17 m of depth, and replaced monthly. Pinctada mazatlanica had the greatest recruitment (12 juveniles/cm2) in late summer and P. sterna (5 juveniles/cm2) in winter. Maximum spat collection from September 1986 to April 1987 occurred at 10 m depth for P. mazatlanica and at 4–7 m depth for P. sterna . However, peak spatfall under 11m depth occurred from late July to August 1987. The mean prodissoconch shell height was 254 μ m (SE = 0.003; N = 50) for P. mazatlanica and 313 μm (SE = 0.004; N = 50) for P. sterna . The growth equations for the first five weeks of both species, based on the prodissoconch shell height and the maximum spat height (measured from the umbo to distal edge) are presented.  相似文献   

12.
Temperature and quality of the available food are important factors that influence the physiology of oysters; however, the combined effects have not been well studied. We evaluated the impacts of the temperature and diet on the growth, survival and biochemical composition in the Pacific oyster Crassostrea gigas spat, cultured in the laboratory for 8 weeks at 23, 26, 29 and 32°C and fed Isochrysis sp.‐Pavlova lutheri (IP) and Dunaliella tertiolecta (Dt). The growth and biochemical composition showed a pattern, which changed in response to rising temperature. The shell length was significantly longer, in spat fed the IP diet, except at 32°C, where both diets produced poor growth results. The survival was <50% after 5 weeks at 32°C, whereas at all other temperatures it was >88%. High temperatures directly increased lipids and saturated fatty acids, while the proteins, carbohydrates and unsaturated fatty acids decreased. High temperatures achieved in the environment, as those reached on clear summer days during low tides, are an important stressor in oyster spat, especially when the quality of the available food is poor.  相似文献   

13.
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.  相似文献   

14.
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 (34 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.  相似文献   

15.
Biofouling on the periostracum of pearl oysters and on the cages has been considered as a stress factor causing mortality of the farmed stock, reducing growth rates and also affecting pearl quality. In farming experiments using the pearl oyster, Pinctada fucata, at Kollam Bay (India), biofouling was found to be a problem. This study was conducted to understand the effect of fouling on the mortality of pearl oysters kept in suspended culture, to identify the main foulers, the seasonal variation in biofouling and species successions in the community with reference to abiotic factors. The average monthly mortality rate (MR) was estimated as 0.117 ± 0.002 and the monthly variations were significantly different (P < 0.01). The total fouling (0.163 ± 0.002 g/g oyster) and biofouling weights (0.166 ± 0.007 g/g oyster) were high in December when the fouling community was composed of several species and dominated by the ascidian, Didemnum sp. December was also the period when the MRs peaked indicating that this organism was the main cause of mortality in pearl farms in Kollam Bay. A clear seasonality in the fouling community (25 species belonging to nine phyla) has been observed in the present study. On the basis of this study, monthly cleaning of oysters is advocated except during December, January, and March when the cleaning should be fortnightly.  相似文献   

16.
In order to study the possibility of gaining commercial benefit from culturing an excess of one sex of the Pacific oyster (Crassostrea gigas), comparative data on the growth rate and condition of male and female oysters are reported. Historically, measurement of sex‐specific growth rate in oysters has been overlooked or confounded by protandric sex. The recent conclusion that the sex ratio of Pacific oysters is predominantly under genetic rather than environmental control introduces the possibility of manipulating sex ratio for commercial gain if they exhibit asynchronous sex‐specific growth rates. Pacific oysters were cultured intertidally in Smoky Bay, south Australia. The observations, made over the 7‐month gametogenic cycle from August to February to ensure no sex reversal, were of growth rates of male and female oysters and ambient chlorophyll a concentrations. Mean shell growth of female oysters was significantly faster than that of males (4.5 ± 3.3 compared with 3.8 ± 3.2 μm day?1 mm?1 total length). Sex‐specific asymmetries in length and weight were generally significant and increased in magnitude during the 7‐month study period, suggesting potential commercial benefits from increasing the proportion of cultured female oysters. The fastest increase in the sex‐specific disparity in growth and condition came after the October chlorophyll a peak, suggesting that females utilize blooms more efficiently than males. Our results compare favourably with methods currently used to increase oyster growth (e.g. triploidy can provide growth gains of 13–51%).  相似文献   

17.
We evaluated growth and survival rates of Pinctadaimbricata in relation to environmental changes during nine months insuspended and bottom culture in the Golfo de Cariaco, Venezuela. Juveniles,measuring 13 mm in length, were cultured using two methods, (1) inSpanish-type baskets suspended at 3–4 m in depth from a longline and (2) in baskets embedded on the seabed (7–8 m indepth). At monthly intervals, we quantified mortality and took a sample ofoysters to determine shell length (dorsal-ventral axis) and the dry mass of theshell, muscle and remaining tissues. We also quantified the dry mass of foulingon the shells (a potentially important environmental factor). Survival rateswere slightly higher in suspended culture (98–100%), although notsignificantly higher than on the bottom. The growth rate was higher in suspendedculture than on the bottom culture, and the difference between culture methodswas greater for tissue and shell biomass than for shell dimensions. At the endof the study, oysters measured 55 mm in shell length for oysters insuspension and 45 mm for those on the bottom. Although growth wasnot significantly correlated with any environmental factor, it tended toincrease with increases in chlorophyll a during periods ofupwelling, thus suggesting that phytoplankton abundance enhanced the growth ofPinctada imbricata. The pearl oyster Pinctadaimbricata should be an excellent species for aquaculture activities,given its high rates of growth and survival in suspended culture and itseconomic importance in the Caribbean region.  相似文献   

18.
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.  相似文献   

19.
We investigated the effects of culture mode (intertidal and off‐bottom suspended culture) and initial stocking density (5%, 10%, 35% and 70% bottom cover) on survival, growth and condition indices of three size cohorts (16, 22 and 32 mm initial shell length) of the basket cockle, Clinocardium nuttallii, during a second year of grow‐out. In addition, we evaluated the effects of depth (2, 4 and 6 m) in suspended culture. All size cohorts demonstrated significantly higher growth rates, soft‐tissue biomass and condition indices in the off‐bottom suspended system compared to the intertidal one. In suspended culture, however, C. nuttallii exhibited sub‐optimal survival, shell deformities and heavy fouling. For all size cohorts, stocking density had a significant effect on most growth and condition parameters, except meat yield indices, in both culture modes. An initial maximum stocking density of 10% cover is recommended for all size cohorts. Culture depth did not have a consistent statistically significant effect on any of the growth or condition parameters. Depending on the grow‐out scenario, stocking density and harvestable size chosen, the cumulative harvestable proportion after the second year of grow‐out constituted 15.5–63.1% of the seed planted. Our results could be used to develop and improve culture techniques for C. nuttallii and other cockle species.  相似文献   

20.
XLP涂料对合浦珠母贝成活率、生长及附着生物量的影响   总被引：2，自引：0，他引：2  
研究了XLP防污涂料对合浦珠母贝Pinctada fucata成活率、生长及附着生物量的影响。经XLP防污涂料处理后的贝,其附着生物量明显低于对照组;经防污涂料处理后的养殖网笼具,其附着生物量也明显低于对照组;贝和养殖网笼具同时用XLP防污涂料处理时,防生物附着的效果最好。经XLP防污涂料处理后,处理前期（30～60d）合浦珠母贝养殖成活率与对照组的成活率接近,或者略低于对照组;养殖120d后试验组成活率则高于对照组。使用XLP防污涂料处理后养殖120d,合浦珠母贝的个体大小及体重高于对照组。试验结果表明,使用XLP防污涂料能有效防御污损生物附着,有利于合浦珠母贝的养殖。  相似文献   

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