• Korean Journal of Fisheries and Aquatic Sciences
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• v.3 no.1
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• pp.7-18
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• 1970

The present paper deals with mortality and pathogenetic investigation of the oysters Crassostrea gigas cultured by tile coventional bamboo and hanging method in Kimhae and Koje-Do in 1969. The results of the investigation may be summarized as follows: 1. Mortality of the oysters by the bamboo method in Kimhae was $9.5\%$ in June, $10.2\%$ In July, $12.3\%$ in August and $12.1\%$ in September, respectively, 2. Mortality of the oysters cultured by the hanging method in Koje-Do was $2.4\%$ in June, $2.9\%$ in July, $30.7\%$ in October, $37.3\%$ in November and $30.0\%$ in December, respectively 3. The diseased oysters had severe inflammation, necrosis and multiple abscess in the epithelia of stomach, mid-gut, digestive tubules, blood vessels and gonads, mucous membrane and surrounding tissue. 4. From August gram negative bacteria were found in the nodules of connective tissue and multiple abscess of the diseased oysters. Particularly the connective tissue of the diseased oysters contained more bacteria than epithelia. 5. Since the bacteria are less abundant in the region of digenerated tissue, mortality of the oysters is not caused only by the infectious bacteria but seems that is also caused by other environmental factors such as extreme temperatures and salinities.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.47 no.5
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• pp.495-500
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• 2014

We examined chemical changes in oysters Crassostrea gigas and packing water that were sold after storage at 5, 10, and $20^{\circ}C$. The pH of oysters stored at $5^{\circ}C$ dropped to 5.81 after 10 days of storage, while that of oysters at $10^{\circ}C$ and $20^{\circ}C$ dropped to 5.37 after 8 days and to 5.04 after 4 days, respectively. The glycogen content of oysters stored at $5^{\circ}C$ decreased from 718.89 to 421.85 mg/100g during storage, while that of oysters at $10^{\circ}C$ decreased to 351.49 mg/100 g after 4 days. The turbidity and soluble protein in packing water increased slightly. The viable cell count of oysters did not exceed 6 log CFU/g after 10 days of storage at $5^{\circ}C$, but that of oysters at $10^{\circ}C$ did so after 8 days. Additionally, the viable cell count of packing water was lower than that of oysters. We performed a principal component analysis, where the first principal component (55.03%-57.24%) and second principal component (42.76%-44.97%) described most variation. The first principal component included the pH of oysters and packing water, and the glycogen content of oysters. A Pearson correlation between the first two principal components had a higher R value than that between other components. Freshness was evaluated using the pH of oysters and packing water, and glycogen. We found that soluble protein content was significantly associated with a lower pH and glycogen content.

• The Korean Journal of Malacology
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• v.15 no.1
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• pp.41-47
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• 1999

From September 1994 to April 1996, we observed the suspending time dependant meat increase (dry weight) for oysters at Pukman Bay in Korea. The oysters which suspended in September increased to 5 g in meat weight (dry weight) by January. Ones in June increased rapidly but lessened during summer and this stagnation of meat increase extended to autumn. It took long time to compensate for the loss of meat weight owing to spawning. Oysters suspended in July or August showed low growth or stagnation due to the high water temperature and spawning activities after suspending. However, meat weight showed sudden increasement after December and achieved 5 g at the late farm period. The meat increase of oysters suspended in October or November was very slow during entire growing period. Most of them did not achieved 5 g during farm period. The negative correlation was observed between meat growth and water temperature in September. Also, there was a high correlation between meat growth and chlorophyll-a. It was believed that deficiency of food organisms in the water column lead slow growth in terms of meat growth, particularly right after transplanting seed oysters to the farm. Our study suggests that proper time for transplanting oysters is between August and mid-September. However, the data indicate that good growth of oysters is depending upon amount of food available in the water column.

• Asian-Australasian Journal of Animal Sciences
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• v.26 no.7
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• pp.916-920
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• 2013

The triploid Pacific oyster, which is produced by mating tetraploid and diploid oysters, is favored by the aquaculture industry because of its better flavor and firmer texture, particularly during the summer. However, tetraploid oyster production is not feasible in all oysters; the development of tetraploid oysters is ongoing in some oyster species. Thus, a method for ploidy verification is necessary for this endeavor, in addition to ploidy verification in aquaculture farms and in the natural environment. In this study, a method for ploidy verification of triploid and diploid oysters was developed using multiplex polymerase chain reaction (PCR) panels containing primers for molecular microsatellite markers. Two microsatellite multiplex PCR panels consisting of three markers each were developed using previously developed microsatellite markers that were optimized for performance. Both panels were able to verify the ploidy levels of 30 triploid oysters with 100% accuracy, illustrating the utility of microsatellite markers as a tool for verifying the ploidy of individual oysters.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.7 no.2
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• pp.41-51
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• 1974

A study of the sanitary quality of Pacific oysters (Crassostrea gigas) and growing waters associated with raft culture in Burley Lagoon, Washington was conducted. The study was sponsored by the Agency for International Development of the U.S. Department of State. The results obtained in this study are as follows: The average values of temperature, salinity and turbidity in the water showed that the values of bottom sample were slightly higher than top samples. The difference was about $0.3^{\circ}C$ for temperature, $0.5\%_{\circ}$ for salinity and 0.1 JTU for turbidity. The changes of temperature and salinity by tide generally followed the tide cycle pattern. Sanitary indicator microorganism concentrations in top water were generally higher than those in bottom water. In general, the levels of mean coliform and fecal coliform MPN's varied inversely with tide level indicating that the sources of these groups of microorganisms are the fresh water streams flowing into the estuary. The $35^{\circ}C$ plate counts were more stable at different tide levels. Mean values of coliform and fecal coliform MPN's in oysters demonstrated that levels in top oysters were generally higher than those in bottom oysters. However, mean values of $35^{\circ}C$ Plate count in oysters did not show this pattern. The mean levels of both coliform and fecal coliform MPN's in oysters also correlated inversely with tidal level. The accumulation ratios of oysters obtained during the study period ranged from 8.6 to 19.7 for mean coliform MPN and 16.9 to 44.3 for fecal coliform MPN. According to the results obtained from present study, one suggestion could be of considerable importance for the sanitary operation in hanging culture of pacific oysters. The results indicate that harvest of the oysters at high tide would result in lower levels of indicator organisms in the shellfish.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.45 no.6
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• pp.586-593
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• 2012

To identify the food component characteristics of seven oysters(four cultured oysters and two wild oysters Crassostrea gigas and one dendely lamellated oyster Ostrea denselamellos Korean name beotgul) in Korea, the proximate, fatty/amino acid, mineral compositions, texture, color, chemical and taste compounds were investigated. The proximate compositions were not significantly different between cultured and wild oysters, whereas beotgul had lower levels of crude protein, ash and lipid content, and a higher carbohydrate content. The amino nitrogen contents of the three main types were 232.8-258.2, 160.5-213.9, and 218.5 mg/100 g, respectively, and the salinities were 1.5-1.7, 1.5-1.8, and 0.9%, respectively. Regarding the muscle texture, the shearing forces were 95-114, 105-132, and 170 g, respectively. Amounts of total amino acids of cultured, wild oysters and beotgul were 9,004-10,198, 8,165-8,942, and 7,767 mg/100 g, respectively. The major amino acids were aspartic acid (Asx), glutamic acid (Glx), proline, alanine, leucine, phenylalanine, lysine and arginine. Regarding inorganic ions, beotgul had much lower Fe and S contents than the cultured and wild oysters. The major fatty acids of cultured and wild oysters were 16:0, 18:0, 16:1n-9, 18:1n-9, 22:1n-9, 16:4n-3, 20:5n-3, and 22:6n-3, and there was little difference between the two. Beotgul had a higher polyenes ratio, i.e., 20:5n-3, and a lower monoenes ratio than the cultured and wild oysters. The free amino acid contents of cultured, wild oysters and beotgul extracts were 1,444-1,620, 1,017-1,277, and 1,144 mg/100 g, respectively, and the major free amino acids were taurine, glutamic acid, glycine, alanine, tryptophan, ornithine, and lysine. There was a little difference in the glycine, tryptophan, ornithine, and arginine contents.

• Journal of Radiation Protection and Research
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• v.41 no.3
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• pp.245-252
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• 2016

Background: Ingestion of $^{210}Po$ laden seafood accounts for a substantial amount of the effective dose of $^{210}Po$. Among seafood items, mollusks, especially domestically produced oysters and mussels, are highly enriched in $^{210}Po$ and are consumed in large quantities in Korea. Materials and Methods: Oysters and mussels around the Korean coasts were collected from major farm areas in November 2013. Samples were spiked with an aliquot of $^{209}Po$ as a yield tracer, and they were digested with $6mol{\cdot}L^{-1}$ $HNO_3$ and $H_2O_2$. The $^{210}Po$ and $^{209}Po$ were spontaneously deposited onto a silver disc in an acidic solution of $0.5mol{\cdot}L^{-1}$ HCl and measured using an alpha spectrometer. The activity concentrations of $^{210}Pb$ and $^{210}Po$ were decay corrected to the sampling date, accounting for the possible in-growth and decay of $^{210}Po$. Results and Discussion: $^{210}Po$ activity concentrations in oysters were in a range from 41.3 to $206Bq{\cdot}(kg-ww)^{-1}$ and mussels in a range from 42.9 to $46.7Bq{\cdot}(kg-ww)^{-1}$. The $^{210}Po$ activity concentration of oysters in the turbid Western coast was higher than the Southern coast. The $^{210}Po$ activity concentration of the oysters was positively correlated ($R^2=0.89$) with those of the suspended particulate matter in the surface water. The calculated annual effective dose of $^{210}Po$ from oysters and mussels consumed by the Korean population was 21-104 and $5.01-5.46{\mu}Sv{\cdot}y^{-1}$. The combined effective dose due to the consumption of oysters and mussels appears to account for about $35{\pm}19%$ of that arising from seafood consumption in the Korean population. Conclusion: The annual effective dose of $^{210}Po$ for oysters in the Korean population was found to be higher than other countries. The total annual effective dose of $^{210}Po$ due to consumption of oysters and mussels consumed in Korea was found to be $76{\pm}42{\mu}Sv{\cdot}y^{-1}$, accounting for $28{\pm}16%$ of the total effective dose of $^{210}Po$ from food in Korea.

• Parasites, Hosts and Diseases
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• v.36 no.3
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• pp.163-170
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• 1998

An epidemiological survey was performed to know the infection status of oysters with Gwmnophclloides seoi metacercariae in 7 islands of the West Sea known as the habitat of paleartic oystercatchers . Hcemntopus ostralegus osculans, in Korea. The surveyed areas were Aphaedo (Shinan-gun. Chollanam-do) Jangiado, Sonyudo and Munyodo (Okdo-myon, Kunsan-shi, Chollabuk-do), Yubudo (Changhang-up, Sochon-gun Chungchongnam-do), and Polumdo and Chumoondo (Sodo-myon, Kangwha-gup, Inchon ski). The oysters collected from Aphaedo, the known endemic focus, were examined monthly from August 1995 to October 1996 for observation of any seasonal variation of the metacercarial density. The average metacercarial burden was 761-2,077 by month, but the seasonal variation of the metacercarial density was not obvious. A total of 54 metacercariae was detected in 63 oysters collected from Yubudo. Out of 30 oysters from Sonyudo, 25 (83.3%) were infected with 1-66 metacercariae (12.6 in average). All of 50 oysters (100%) from Munyodo were infected with 3-162 metacercariae (53.5 in average), Only 4 metacercariae were detected in 100 oysters from Chumoondo. However, no metacercariae were found in 55 oysters from .Tangjado and 50 oysters from Polumdo. From the above results, it was confirmed that G. seoi is still highly prevalent in oysters from Aphaedo, and several islands of the West Sea known as the habitats of paleartic oystercatchers are new endemic areas of this fluke.

• The Korean Journal of Malacology
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• v.30 no.3
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• pp.189-196
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• 2014

A significant production decrease has been witnessed for the Pacific oysters, Crassostrea gigas farmed in the western coastal waters of Korea, presumably by the loss of physiological viability. We evaluated the viability in terms of health indicators, the condition indices and hemocyte apoptosis rates of the oysters inhabiting two representative farming sites, Incheon and Taean each with different environmental variables. In our monthly measurements for the whole year 2013, the indicators were location specific. The condition indices of Incheon were highly variable, 1.67-8.58%, while those of Taean were less, 2.28-5.57%. The condition indices decreased during the spawning seasons, July and September in common. The two oysters exhibited also differed in the apoptotic activities of hemocyte, highly active, 4.03-30.15% for Incheon oysters and less active, 2.87-17.48% for Taean oysters. One thing we could identify was the two measurements were adverse during the critical seasons of spawning, reminiscent of being a useful tool for a health indicator for the oysters. Similar trend was also observed in the time when change in temperature was extreme. The findings in this study are highly indicative of health indicators for the oyster aquaculture.

• Parasites, Hosts and Diseases
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• v.49 no.3
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• pp.229-234
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• 2011

In order to assess changes in the activity of immunecompetency present in Crassostrea gigas infected with Marteilioides chungmuensis (Protozoa), the total hemocyte counts (THC), hemocyte populations, hemocyte viability, and phagocytosis rate were measured in oysters using flow cytometry. THC were increased significantly in oysters infected with M. chungmuensis relative to the healthy appearing oysters (HAO) (P<0.05). Among the total hemocyte composition, granulocyte levels were significantly increased in infected oysters as compared with HAO (P<0.05). In addition, the hyalinocyte was reduced significantly (P<0.05). The hemocyte viability did not differ between infected oysters and HAO. However, the phagocytosis rate was significantly higher in infected oysters relative to HAO (P<0.05). The measurement of alterations in the activity of immunecompetency in oysters, which was conducted via flow cytometry in this study, might be a useful biomarker of the defense system for evaluating the effects of ovarian parasites of C. gigas.