• Ocean and Polar Research
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• v.44 no.4
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• pp.319-329
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• 2022

The paramyxean parasite Marteilioides chungmuensis infects the cytoplasm of the eggs of Pacific oysters Crassostrea gigas , resulting in spawning failure of the infected females. Such infected eggs appear as bump-like nodules on the body in late fall when most of the uninfected females complete spawning. In this study, we estimated the quantity of the infected eggs using an enzyme-linked immunosorbent assay (ELISA), which is destroyed by M. chungmuensis parasitism. In December, the infected oysters collected from Tongyoung on the south coast exhibited numerous yellowish bump-like nodules as signs of infection. In histology, the infected oysters exhibited mature eggs in the follicle, which were heavily infiltrated by hemocytes. ELISA indicated that the infected egg mass accounted for 7.52±5.50 percent of the body weight, suggesting the ovarian parasite causes substantial reproductive loss. Histology also indicated that the infected oysters are in a poor nutritional condition, as the digestive gland atrophy (DGA) level is comparatively higher than the uninfected oyster. The total carbohydrate contents in the infected oysters (108.68±44.41 mg/g dry wt) were significantly lower than in uninfected oysters (269.76±50.97 mg/g dry wt), suggesting that M. chungmuensis parasitism also affected the energy storage capacity of the host during the resting stage.

• Journal of Food Hygiene and Safety
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• v.21 no.4
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• pp.238-243
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• 2006

The populations of V. parahaemolyticus were enumerated in oysters collected in wholesale seafood markets in Seoul and tested in various possible condition. The populations of oysters soled in the markets were ranged $<2\sim1.4\times10^6$ MPN/100 g from April to November in 2005. In the case of oysters added with V. parahaemolyticus of $4\times10^3$ CFU/100 g, the highest population numbers were $1.4\times10^7$ CFU/100 g, $5.4\times10^5$ CFU/100 g and $2.7\times10^4$ CFU/100 g at $36^{\circ}C$ after culturing for 15 hours, at $25^{\circ}C$ after 15 hours and at $4^{\circ}C$ after 15 hours, respectively. But the difference of the populations of V. parahaemolticus in oysters stored in the icebox with ice for bulked sale and displayed in stalls on ice for the small packaged sale was not significant. In the case of oysters carried with ambient temperature at $30.8^{\circ}C$, the V. parahaemolyticus density was dramatically increased from $2.7\times10^5$ to $1.4\times10^8$ MPN/100 g. It was indicated it is important to carry the oysters to home with ice after purchase. Even after the washing two times with 21 tap water, the common cooking method in Korea was not greately make the decrease of V. parahaemolyticus density from $1.4\times10^8$ MPN/100 g to $9.0\times10^5$ MPN/100 g. So it is noticed to stored in low temperature after cooking, especially in hot seasons.

• The Korean Journal of Malacology
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• v.29 no.4
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• pp.273-281
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• 2013

In order to evaluate how the effects of aquacultural environment, such as temperature, salinity, DO, SS, Chlorophyll-a, COD and nutritive salts on Cupped oysters, an investigational study was conducted between September to December of 2011. During the study, different intermediate cage farms on the surface of the sea were used to culture and compare the growth and survival rate of the Cupped oysters in different fishing environments. The different intermediate cage farms used were Wonsando-ri, Chang-ri, and Pado-ri. In January of 2012, these oysters were transplanted to a horizontal net farm in a mudflat until July of that year. The adaptation rates of the Cupped oysters were tested at differential exposure times at varying intertidal periods. Wonsando-ri showed the highest water temperature and Chlorophyll-a levels, while the salinity was found to be within range of stable conditions among all three intermediate cage farms. Once the Cupped oysters were at the horizontal net farm, the growth was measured at distinct tidal exposure time of 1, 3, and 5 hours, whereby the growth rate was highest at 3, 1, and 5 hours, respectively. In addition, the oysters cultivated in intermediate cage farms had longer shell lengths compared to shell heights, while oysters cultured in the horizontal net farm had larger shell heights than shell lengths.

• Ocean and Polar Research
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• v.34 no.2
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• pp.151-163
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• 2012

Digestive cells of the bivalves have a highly developed lysosomal system and the system is known to be sensitive to changes in environmental qualities. In this study, we measured lysosomal responses of the digestive cells in wild oyster, Crassostrea gigas using frozen section. Oysters were collected in June 2010 from intertidal areas in the inner and outer bay of Gwangyang off the south coast of Korea. From the tissue sections, we measured the digestive cell lysosomal membrane stability (LMS), level of neutral lipids (NL), lipofuscin (LF) and the digestive gland atrophy (DGA). The DGA and condition index of oysters from the inner bay were significantly lower (P<0.05). The statistical test indicated that LMS levels of oysters in the inner bay and the outer bay were not significantly different since a shorter activity was displayed by oysters from the inner bay than that of oysters in outer bay. The LF deposition level of the oysters in the inner bay displayed significantly higher levels than the outer bay (P<0.05). In contrast, the NL accumulation measured from oysters in outer bay was significantly higher than the level observed in the inner bay (P<0.05). Different levels of DGA and LF that were observed in the inner and outer bays were thought to be associated to different level of environmental contamination and these two assays are considered to be good biomarkers.

• The Korean Journal of Food And Nutrition
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• v.10 no.3
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• pp.320-324
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• 1997

The number of Vivrio vulnificus strain 29307 was assessed for oysters treated with acetic, lactic, citric, and alginic acids during storage at 15$^{\circ}C$. When oysters were dipped with 0.5% acetic, 0.5% lactic, or 0.5% citric acids for 3 min, V. vulnificus was not detected after 4 days of storage. V. vulnificus in the treatment of 3% alginic acid (AL) containing 2% acetic acid (AA) was not detected after 2 days of storage, while it was isolated in the controls for 4 days of storage. Based on these results, the combination of AL and AA was more effective for preventing the growth of V. vulnificus in oysters than the treatments of the acid alone.

• 한국해양학회지
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• v.15 no.1
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• pp.8-16
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• 1980

The seed of Japaness oyster, Crassostrea gigas(Thunberg), cultivated along the southerncoast of Korea have been transplanted and cultivated in both the Seonyu island and the Eocheong island of the western coast of Korea. The present study was carried out to investigate the growth of transplanted oysters, environmental factors influencing their fatness, and differences of two areas between the Seonyu island and the Eocheong island during the period from April to November, 1978. The results obtained were as follows: 1. Maximum height of the shell was 69.2mm (58.4mm on the average) in the island of Seonyu and 64.8mm(53.2mm) in the island of Eocheong, respectively. 2. The fatness of the oysters measured in the island of Seonyu (5.2g/month) was greater than in the island of Eocheong (2.5g/month) 3. The shell height was increased with high temperature while, the shell fatness with low temperature. 4. The growth rate of the transplanted seed oysters was twice as much as that of native ones in the western coast of Korea. 5. Environmental conditions of Seonyu island were more favorable in cultivating oysters than those of the Eocheong island.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.12 no.4
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• pp.255-259
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• 1979

Depuration of extraneous substances such as bottom deposit, feces and coliforms from live oyster has been studied. Coliform accumulation of bottom cultured oysters was much higher than that of raft or long line cultured oysters. When the depuration tank designed in this study was adopted, the depuration rate could be diminished to about $50\%$ within one hour treatment. Tho most effective conditions of the tank water for depurating live oysters wer $22^{\circ}C$ in temperature, 8.80 in pH and below about 2 ppm of residual chlorine concentration.

• The Korean Journal of Malacology
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• v.29 no.3
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• pp.217-223
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• 2013

The morphological relations and physiological characteristics of the triploid and diploid oysters (Crassostrea gigas) in Taean area, west coast of Korea, were investigated from May 2012 to April 2013. Mophometric analysis indicated that the triploid oysters have the same shell length to shell height ratio but higher shell depth to shell height ratio than diploids. Consistent with morphological characteristics, triploid oysters showed greater values of fatness, condition index and RNA/DNA ratio during the period of experiment. The DNA concentration in adductor muscle and mantle of triploid were either lower or equal to the nucleic acids of diploid. However, RNA/DNA ratio were significantly higher than diploid. It appears that RNA/DNA ratio could be a useful indicator of health condition of triploid and diploid oysters when taken in correlation with the morphological indices.

• Development and Reproduction
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• v.26 no.4
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• pp.165-174
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• 2022

Three proteins [myosin heavy chain (MHC), filamin-C fragment (FIL-C), and actin 2 (ACT2)] were identified in adductor muscle from diploid and triploid Pacific oysters (Crassostrea gigas) and the relationship between the condition index (CI) and mRNA expression of these genes was investigated, together with the mRNA expression of molluscan insulin-related peptide (MIP), C. gigas insulin receptor-related receptor (CIR), and insulin-like growth factor binding protein complex acid labile subunit (IGFBP-ALS). Monthly changes in the CI were similar to the changes in the tissue weight rate in both groups. ACT2 and MHC mRNA expression was statistically higher in the triploid than the diploid, while FIL-C mRNA expression was significantly higher in the diploid (p<0.05). The MIP, CIR, and IGFBP-ALS mRNA expression of the diploid oysters were all significantly higher in July than in other months (p<0.05). The MIP, CIR, and IGFBP-ALS mRNA expression in the triploid oysters was high in July, but there were no significant differences (p>0.05). Changes in the expression levels of the genes investigated in this study could be used as intrinsic indicators of the annual growth, maturity, and spawning period of cultured diploid and triploid C. gigas in Tongyeong, Korea.

• Parasites, Hosts and Diseases
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• v.55 no.4
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• pp.399-408
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• 2017

A survey was performed to know the recent infection status of digenetic trematode metacercariae in clams and oysters from 4 sites in western coastal regions of the Republic of Korea (=Korea). Four species of clams (Mactra veneriformis, Ruditapes philippinarum, Cyclina sinensis, and Saxidomus purpuratus) were collected from Taean-gun, Chungcheongnam-do (Province), Buan-gun (County) and Gochang-gun, Jeollabuk-do, and oysters, Crassostrea gigas, from Shinan-gun, Jeollanam-do were transferred to our laboratory on ice and examined by the artificial digestion method. The metacercariae of Himasthla alincia were detected in 3 species of clams, M. veneriformis, R. philippinarum, and C. sinensis from the 3 surveyed areas. The positive rate and the mean density per clam infected were 98.9% (30.8 metacercariae) in M. veneriformis, 60.0% (5.0) in R. philippinarum, and 96.0% (28.4) in C. sinensis. The positive rate (mean density) of Acanthoparyphium tyosenense metacercariae in M. veneriformis was 50.0% (2.1) from Taean-gun and 70.0% (2.8) from Gochang-gun. The metacercariae of Parvatrema spp. were detected in M. veneriformis and R. philippinarum from Taean-gun and Gochang-gun; the positive rate (mean density) was 63.3% (4,123) and 50.0% (19) in M. veneriformis, and 6.7% (126) and 100% (238) in R. philippinarum from the 2 regions, respectively. The metacercariae of Gymnophalloides seoi were detected in all 30 oysters from Shinan-gun, and their average density per oyster was 646. From the above results, it has been confirmed that more than 3 species of metacercariae are prevalent in clams from the western coastal regions, and G. seoi metacercariae are still prevalent in oysters from Shinan-gun, Jeollanam-do, Korea.