首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 359 毫秒
1.
The risk of norovirus food poisoning from oyster consumption can be minimized by consumers, as thorough cooking can destroy norovirus. This paper uses data from 23 prefectures in Japan during 1970–2010 to examine how the demand for oysters responds to this manageable risk. We find that the incidence rate of norovirus has no effect on the price of oysters in prefectures that specialize in oysters for cooking, whereas it has significant negative impacts in prefectures that produce oysters to be eaten raw. These results indicate that consumers respond differently to manageable and non-manageable risks.  相似文献   

2.
  相似文献   

3.
  相似文献   

4.
The seasonal growth and survival of experimental batches of hatchery-reared spat of the European oyster (Ostrea edulis) and the Pacific oyster (Crassostrea gigas) was followed in North Wales during the period 1972 to 1975. Three methods of tray cultivation were compared. These were: (a) trays suspended from a raft in the Menai Straits, (b) trays supported on trestles on the foreshore of the Menai Straits, and (c) trays in a laboratory nursery system which were supplied with sea water from Conwy estuary via a pumped storage system.Growth of oysters in the nursery system was consistently inferior to that of oysters kept at either site in the sea. Although in several years there were significant differences between the growth of oysters on the raft and in trays supported by trestles, on average neither site consistently produced larger oysters.Survival was significantly better in the nursery system for both species of oyster, but no consistent differences in survival were observed between either site in the sea.Seasonal growth of both species of oyster as well as the mortality of O. edulis were positively related to temperature. It was concluded on the basis of cost that (i) cultivation in systems employing pumped sea water would not be viable in the long term, and (ii) raft cultivation would only be suitable for post-hatchery sized oysters up to about 5 g live weight.  相似文献   

5.
In order to evaluate the quality of oysters and whether a production method affects quality or not, a set of objective quantitative quality measures was developed. Eastern oysters (Crassostrea virginica) were cultured using two different treatments (never desiccated or desiccated daily with tidal exposure) and the meats were tested by textural, physico‐chemical and chemical analyses over a 25‐day cold storage period. Texture analyses parameters (cutting force and chewiness on oyster adductor muscles) were strongly correlated with storage time before the death of oysters and could be used as a quality indicator for oyster. Total volatile basic nitrogen (TVBN) could be used as freshness indicator for raw Eastern oysters, with the acceptability of 11 mg/100 g. Models for evaluating the quality of oysters were established that reflect the impact of a biofouling treatment on oyster's shelf life and texture attributes. The methods and quality indicators developed in this study were effective in evaluating the quality and freshness of Eastern oysters objectively, and could serve as routine quality check of oyster meat for the industry.  相似文献   

6.
Shrimp pond effluent water can contain higher concentrations of dissolved nutrients and suspended particulates than the influent water. Consequently, there are concerns about adverse environmental impacts on coastal waters caused by eutrophication and increased turbidity. One potential method of improving effluent water quality prior to discharge or recirculation is to use bivalves to filter the effluent. In this study, we examined the effects of the Sydney rock oyster, Saccostrea commercialis (Iredale & Roughley), on the water quality of shrimp pond effluent. Effluent from a shrimp farm stocked with Penaeus japonicus (Bate) was pumped directly into 34-L tanks stocked with different densities of oysters. Combinations of live and dead oysters were used to test the effects of three different densities of live oysters (24, 16 and 8 live oysters per tank). The concentrations of total suspended solids, the proportion of organic and inorganic matter, total nitrogen, total phosphorous, chlorophyll a and the total number of bacteria in the pond effluent water were determined before and after filtration by oysters. The oysters significantly reduced the concentration of all the parameters examined, with the highest oyster density having the greatest effect. Shrimp pond effluent contained a higher proportion of inorganic matter (72%) than organic matter (28%). The organic component appeared to be mainly detritus, with chlorophyll a comprising only a minor proportion. Filtration by the high density of oysters reduced the effluent total suspended solids to 49% of the initial level, the bacterial numbers to 58%, total nitrogen to 80% and total phosphorous to 67%. The combined effects of settlement and oyster filtration reduced the concentration of chlorophyll a to 8% of the initial effluent value.  相似文献   

7.
In Maine's hatchery production of oysters, significant mortalities at the early juvenile stage have been associated with ciliate infestations. The predominant ciliate isolated from live infested oysters was identified as Uronema marinum. Feeding experiments, designed to identify the food source of the ciliate in the oyster tank environment, determined that U. marinum is a bacteriophage and not a histophage, thereby clarifying its role in the oyster mortalities.  相似文献   

8.
Abstract

Non-uniform steam distribution and large temperature differences are frequently found within the retort during pressure steam cooking of blue crabs. A precook treatment involving evacuation of air from the retort prior to introduction of steam was found to decrease this unevenness in temperature distribution. The conventional and modified treatments were compared by (1) determination of temperature profiles within a retort during the conventional cooking process and the modified process; and (2) testing the resulting product from the two processing methods for differences in meat moisture and pH. The modified process improved the temperature distribution and reduced cook time by up to 50%. Meat moisture content increased in crabs processed using the vacuum process while pH testing of the cooked meat showed little difference in meat from the two processes. It was concluded that the improved temperature distribution would shorten cook time and increase throughput, product yield, product safety, and process efficiency.  相似文献   

9.
  相似文献   

10.
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   

11.
To investigate the possibility of establishing oyster culture in Malta, growth trials with C. gigas and O. edulis were undertaken. The oysters were placed in floating cages at depths of 3 and 8 m at Marsaxlokk bay, Mistra bay and Rinella creek. These oysters were sampled at two-month intervals for their growth, meat-shell index and survival. The temperature, salinity, oxygen tension, chlorophyll-a levels and the levels of particulate matter in suspension in the water at the test sites were monitored concurrently. A programme of qualitative and quantitative analyses of the natural phytoplankton population was also carried out.O. edulis suffered catastrophic summer mortalities at all locations when the ambient temperature of the water reached about 25°C; this virtually rules out any possibility of starting any flat oyster industry using this system. As for C. gigas, Marsaxlokk bay 3 m appears to hold some promise for its culture. At this location, this species showed reasonable growth, relatively low mortality and normal shell growth. Although at Rinella overall growth of C. gigas was comparable to that at Marsaxlokk at 3 m, the Rinella oysters accumulated copper and exhibited abnormal and thickened shell growth with the result that the oysters were of a much inferior condition. Growth at Mistra (both depths) and Marsaxlokk 8 m was stunted.No clear correlation could be established between the performance of the oysters and the environmental parameters monitored. Several factors that may have been responsible for the observed differences in oyster performance are discussed. In particular, the nature of the water movements is thought to have played a key role in dictating the growth of the oysters.  相似文献   

12.
ABSTRACT

Experts in the oyster supply chain (farmers, retailers, and gourmet chefs) in The Netherlands have suggested that the European flat oyster (Ostrea edulis) has superior sensory qualities compared to the Pacific cupped oyster (Crassostrea gigas). However, scientific evidence is lacking. The aim of this study was to evaluate consumer preferences for these two oyster species and to determine the sensory properties of both species by consumers. Two-alternative forced choice tests were performed with the oysters involving a panel of 74 naïve consumers. No significant differences in preferences between the oyster species were observed by the consumers. Nine sensory attributes of both oyster species were evaluated. Consumers did not observe significant differences between species in the sensory attributes: overall odor intensity, sea odor, mud odor, sweetness, pungency, and firmness. The Pacific cupped oyster was perceived as significantly saltier and more intense in greenness than the European flat oyster. We concluded that only a few sensory properties of the European flat oyster and the Pacific cupped oyster are perceived as being different by untrained consumers.  相似文献   

13.
We used mitochondrial (mt) DNA barcoding to evaluate the species diversity of oysters sampled from the coast of Okinawa Island, Japan. Our analysis revealed the presence of a hitherto-unrecognized population of the Portuguese oyster Crassostrea angulata, a putative species closely related to the Pacific oyster C. gigas. Forty-eight Okinawan oyster specimens were collected and subjected to species diagnosis trials based on mtDNA barcodes. Of the 30 Crassostrea specimens, 17 were identified as C. angulata, seven as C. gigas and six as C. bilineata (syn. C. iredalei). The remaining 18 Saccostrea specimens formed several divergent clades in phylogenetic trees, although they could not be identified to species level because of the confounding taxonomy of the Saccostrea species complex. Our results stress the necessity for reviewing the species diversity of Okinawan oysters.  相似文献   

14.
Several small beds of the Portugese oyster (Crassostrea angulata Lam.) were found on the bottom of a sea inlet in the Po river delta. In order to establish the possibilities of oyster culture there, a preliminary study of the growth and reproductive cycle of oysters kept in plastic trays from February, 1972 throughout March, 1973, was conducted. At monthly intervals (a) salinities and temperatures of the water, (b) mean growth and weight of 50 specimens and (c) histological data on the condition of the gonads, were recorded.The first results indicate that environmental conditions in the sea inlet are optimal for Crassostrea angulata and therefore that it would be a suitable place to develop the culture of oysters, before the complete disruption of the bottom by the undisciplined local fishermen takes place.  相似文献   

15.
Many oyster handling and processing devices require oysters to enter in a specific orientation. Unfortunately wild caught oysters exhibit great variability in shape and configuration. Thus, orienting them automatically is challenging. Orientation and transfer devices were developed and the efficiency of both orienting single wild caught oysters from the Chesapeake Bay region and transferring them from the orientation device to an exit conveyor were determined.The computer program, OYSORS, developed to control the orienting device was found to be able to orient only 51% of the oysters within ±0.35 radians when using only the basic program and 68% when using the basic program plus the Adjust modification. The total orientation and transfer system efficiency using the Adjust algorithm was determined for oysters from three oyster bars in the Chesapeake Bay Region: Tangier Sound, Wicomico River, and Potomac River. The total system was found to be able to orient and transfer oysters while holding their orientation within ±0.35 radians for between 50 and 66% of the oysters depending on the origin of the oysters. The transfer system alone was shown to be able to transfer oysters from the orienter to the exit conveyor within an allowable deflection of ±0.17 radians in 75–95% of the oysters depending on the origin of the oysters. It was shown that the transfer system was actually able to correct the orientation of some of the oysters incorrectly oriented by the computer program OYSORS.  相似文献   

16.
In the present study, hybrid and inbred oysters were produced by factorial hybridization between two closely related species, the Pacific oyster Crassostrea gigas and the Portuguese oyster C. angulata. Tissues samples were used for the analysis of total lipid content (TLC) and fatty acid composition (FAC). In general, FAC but not TLC in hybrid oysters was significantly different from inbred oysters. Hybrid oysters have significantly lower ∑SFA composition but higher ∑PUFA composition than inbred oysters, with heterosis for ∑SFA, ∑MUFA and ∑PUFA of ?6.03%, ?6.53% and 14.31% respectively. Moreover, hybrid oysters have significantly higher EPA + DHA content and n3/n6 PUFA ratio than inbred oysters, indicating higher lipid nutritional quality than inbred oysters. Among them, the hybrid ♀ C. gigas × ♂ C. angulata appears to be the most nutritious. These results indicated that the lipid nutritional quality of oysters can be improved by hybridization.  相似文献   

17.
The Australian edible oyster industry has been severely impacted by disease and declining yields since the 1970s. Selective breeding of Saccostrea glomerata is one measure addressing these problems by producing fast‐growing, disease‐resistant oysters. Farmers report that selected oysters have different growth characteristics than their wild counterparts using conventional grow‐out methods. This study investigated how different grow‐out methods influence commercially valuable oyster characteristics including shell length, shape, surface growth deformities and meat condition. In June 2015, selectively bred S. glomerata spat were deployed in two estuaries (Hawkesbury River and Georges River) in NSW, Australia, using three grow‐out methods (fixed trays, Stanway cylinders and floating baskets). In November 2015, oysters were transferred among grow‐out methods to test for the effects of changing grow‐out methods on oyster growth patterns. Oysters transferred from baskets to cylinders and from trays to cylinders had, on average, deeper and wider shells, a higher meat condition and fewer shell surface deformities than oysters in other grow‐out method combinations. However, these oysters were smaller than oysters not grown in cylinders. While there were some differences in growth patterns between the estuaries, overall it was the grow‐out methods that most influenced oyster characteristics. This was attributed to differences in the amount and magnitude of movement oysters experienced in the grow‐out methods, as recorded by motion sensors. This study demonstrates how grow‐out methods can be managed to achieve desired growth trajectories and therefore improve marketability among selective bred S. glomerata.  相似文献   

18.
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.  相似文献   

19.
During 1977–1978 the spawning season of the Port Lincoln oyster (Ostrea angasi Sowerby) extended from about mid-October to early March. Between 5.6% and 21.4% of randomly sampled adult oysters (larger than 68 mm in length) were incubating larvae and between 0.91 and 1.33 broods of larvae were produced per adult oyster. Large oysters (68–94 mm in length) had a mean of 12.1 × 105 larvae per brood. The incubation period under natural and laboratory conditions ranged from 15–22 days and there are similarities in the breeding biology of O. angasi, the European oyster (Ostrea edulis L.) and the Olympia oyster (Ostrea lurida Carpenter).  相似文献   

20.
Current shrimp pond management practices generally result in elevated concentrations of nutrients, suspended solids, bacteria and phytoplankton compared with the influent water. Concerns about adverse environmental impacts caused by discharging pond effluent directly into adjacent waterways have prompted the search for cost‐effective methods of effluent treatment. One potential method of effluent treatment is the use of ponds or raceways stocked with plants or animals that act as natural biofilters by removing waste nutrients. In addition to improving effluent water quality prior to discharge, the use of natural biofilters provides a method for capturing otherwise wasted nutrients. This study examined the potential of the native oyster, Saccostrea commercialis (Iredale and Roughley) and macroalgae, Gracilaria edulis (Gmelin) Silva to improve effluent water quality from a commercial Penaeus japonicus (Bate) shrimp farm. A system of raceways was constructed to permit recirculation of the effluent through the oysters to maximize the filtration of bacteria, phytoplankton and total suspended solids. A series of experiments was conducted to test the ability of oysters and macroalgae to improve effluent water quality in a flow‐through system compared with a recirculating system. In the flow‐through system, oysters reduced the concentration of bacteria to 35% of the initial concentration, chlorophyll a to 39%, total particulates (2.28–35.2 µm) to 29%, total nitrogen to 66% and total phosphorus to 56%. Under the recirculating flow regime, the ability of the oysters to improve water quality was significantly enhanced. After four circuits, total bacterial numbers were reduced to 12%, chlorophyll a to 4%, and total suspended solids to 16%. Efforts to increase biofiltration by adding additional layers of oyster trays and macroalgae‐filled mesh bags resulted in fouling of the lower layers causing the death of oysters and senescence of macroalgae. Supplementary laboratory experiments were designed to examine the effects of high effluent concentrations of suspended particulates on the growth and condition of oysters and macroalgae. The results demonstrated that high concentrations of particulates inhibited growth and reduced the condition of oysters and macroalgae. Allowing the effluent to settle before biofiltration improved growth and reduced signs of stress in the oysters and macroalgae. A settling time of 6 h reduced particulates to a level that prevented fouling of the oysters and macroalgae.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号