• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.54 no.1
• /
• pp.16-22
• /
• 2021

This study investigated the reduction in human norovirus (HNV) GII. 4 count in pacific oyster Crassostrea gigas using electron beam irradiation. Infectious HNV GII. 4 was detected using RT-qPCR (real time reverse transcription-quantitative polymerase chain reaction) with PMA (propidium monoazide)/sarkosyl. At electron beam doses 1, 5, 7, and 10 kGy, the count of HNV GII. 4 was 2.74, 2.37, 2.06, and 1.55 log copies/μL (control, 3.01 log copy/μL), respectively, confirming that as the irradiation dose increased, norovirus count reduced significantly (P<0.05). After PMA/sarkosyl treatment, the counts further reduced at the same irradiation dose, and 10 kGy showed significant differences between the non-treated and PMA/sarkosyl-treated samples (P<0.05). The Ed (decimal reduction dose of electron beam) value based on the first-order kinetic model was 7.33 kGy (R2=0.98). No significant difference was observed in the pH values of the control (6.2) and electron beam-irradiated samples at all doses (6.1). For sensory evaluation, the non-treated sample scored the highest in all categories (5.25-6.17), while the samples treated with 10 kGy showed the lowest score (4.67-5.33), although without statistical significance (P>0.05). Overall, our results suggest that 7 kGy electron beam is sufficient for the non-thermal sterilization of oysters without causing significant changes in quality.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.56 no.6
• /
• pp.810-817
• /
• 2023

Oysters are a highly consumed seafood throughout Korea, but they have a short shelf life because they support rapid microbial growth due to their of high moisture content and fragile muscle tissue. We examined natural food additives including lactic acid bacteria fermentation powder, rosemary extract, and lemon juice for their ability to preserve raw oyster Crassostrea gigas quality. Samples were stored at 4℃, and microbiological and physicochemical analyses were conducted. Among the natural additives tested, lemon juice was the most effective. Lemon juice was thus applied at different concentrations (50-300 ppm) to quantitatively assess its effect on total viable cell count, pH, glycogen, soluble protein, and turbidity. 200 ppm was confirmed to be optimal, and is projected to extend shelf life by 2 days compared to the control group.

• Development and Reproduction
• /
• v.27 no.3
• /
• pp.101-115
• /
• 2023

Environmental factors impact oyster growth, condition, and gonadal development, which is linked to gamete characteristics observed through histology. The reproductive cycle of bivalves is related to energy storage and utilization. Therefore, in this study, the year-round growth change and gonadal development of oysters were observed using histological analysis, and the biochemical composition changes were confirmed. The oysters used in this study are being nurtured in Gadeok-do, and 40 oysters were randomly sampled monthly from March 2021 to February 2022. Result of histological analysis of gonads, oysters were showed early development from December to February, late development from March and April, mature and ripe from May to July, spawned from August to October, and spent from November to December. Condition index values of oysters decreased in summer and autumn and increased again when entered the spent after spawning. The protein content of oysters was high in May, the maturity period, and the lipid content decreased during the spawning period. In addition, EPA and DHA, the major fatty acids of oysters, were low during the spawning period and high during the maturation period. As a result, this study suggested a close relationship between changes in oyster growth, biochemical composition, and the reproductive cycle.

• The Korean Journal of Malacology
• /
• v.31 no.2
• /
• pp.129-136
• /
• 2015

To introduce an oyster rack culture in tidal flat of Wando-gun, Korea, we investigated sanitary conditions from 2012 April to 2013 March in oyster growing waters and adjacent area in Wando. Average seawater temperature and salinity ranged $8.6-28.0^{\circ}C$ and 26.2-33.6 psu, respectively. The coliform group and fecal coliform of seawater ranged < 1.8-13.0 MPN/100 mL each. Only one of 60 samples was exceeded in the European criteria of fecal coliform. Influence of adjunct basin's pollution load on cultural waters was negligible, which half radius of dilution was not above 300 m. According to our observation, however, landing of oyster should be banned for at least 5 days after the heavy rainfall. Our findings meet the sanitary seawater criteria for domestic use and export of shellfish and classified as 'Class A' in European Community regulations for bivalve culture.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.31 no.4
• /
• pp.567-573
• /
• 1998

Cold storage of concentrated food phytoplanktons is a useful technique in supplying food organisms for artificial shellfish seed. One month after preservation at $4^{\circ}C$, we have measured survival rate of the concentrated food phytoplanktons, Pavlova lutheli, Isochrysis galbana, Isochrysis aff, galbana and Chaetoceros calcitrans. Thereafter we determined survival rate of oyster lavae fed fresh and concentrated diets and fatty acid compositions of the fresh and concentrated food phytoplanktons. Survival rate of concentrated planktons ranged from $23\%$ to $31\%$ after one month at $4^{\circ}C$. The survival rate of oyster larvae fed cold stored food appeared generally higher than those fed fresh harvested food. Especially, the highest survival rate were found in the larvae fed cold stored concentrated I. aff. galbana. EPA and DHA increased after cold storage and the highest level of DHA was detected in I. aff. galbana. As DHA can role as an important factor in determing nutritional value, it would be better to use concentrated I aff, gaibana kept in cold refrigerator for oyster seed production.

• The Korean Journal of Malacology
• /
• v.24 no.2
• /
• pp.109-119
• /
• 2008

In order to investigate the possibility of yearly-harvest, we carried out growth experiment(shell height, meat weight and condition index) for of the artificial oyster spat, which suspended in three different times before the season for natural spat around coastal waters of Gyeongnam Province. Shell growth of spats suspended in June showed higher than those in April and May. In meat weight, the growth of spats was significantly elevated from October, of which significant difference was observed depending on growing farms(Gosung$\geq$80 mm) and October on the meat weight level($\geq$5 g).

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.18 no.5
• /
• pp.471-476
• /
• 1985

In order to set up a predictive model for effective spat collection of Pacific oyster, Crassostrea gigas, the survival rate and time required at each developmental stage of drifting larvae were surveyed during the period from June 13 to October 16 in 1984 at the main oyster farming area, Hansan Bay, the southern part of Korea. The advent of D-shape larvae ca. $72{\times}61{\mu}m$ long had two peaks in that area : July 16 and September 20. Umbo-shape larvae ca. $189{\times}217{\mu}m$ and full grown larvae co. $303{\times}308{\mu}m$ long also showed two peaks: July 21 and September 25 for the former, and July 28 and September 30 for the latter. About five days were required for D-shape larvae to develop to umbo-shape larvae. The instantaneous death rate was 0.24 and the daily survival rate 0.78 with a mean survival rate of $29.38\%$, at this intermorphological stage. The turnover time of umbo to full grown larvae varied from five to seven days with a instantaneous death rate of 0.15, daily survival rate of 0.86 and mean survival rate of $38.54\%$. Ten to twelve days were required for each group of the D-shape larvae to reach a full grown stage, and their mean survival rate was $11.32\%$ during this developmental period.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.30 no.5
• /
• pp.794-803
• /
• 1997

Long line suspended culture of oysters has been started commercially in Hansan-Koje Bay since 1969. However, its Annual production has been decreased and culturing periods extended in recent years. So, we investigated environmental parameters and food organisms to identity the causes of poor fatness of oysters in Hansan-Koje Bay from February to November, 1994. As the result, the Water quality of Hansan-Koje Bay was found to be good for culture. For example, the mean concentration of COD was $1.35mg/\ell$, phosphate phosphorus was $0.30{\mu}g-at/\ell$ and dissolved inorganic nitrogen was $4.68{\mu}g-at/\ell$. However, the Hwado island and the inner part of the Hansan-Koje Bay were found to be eutrophicated due to various contaminants transported by land-based activities. But in the central pan of the Hansan-Koje Bay where the oyster farms Have been developed densely, the level of nutrient concentration was very low. During the study period, the dominant species of phytoplankton was Chaetoceros spp. with the percentage of $72.6\%\~87.8\%$ and the mean values of Chlorophyll-a concentration and phytoplankton standing crops were $2.05mg/m^3\;and\;188ind./m\ell$, respectively. The distribution of these parameters also showed similar trends those of nutrients. Especially, chlorophyll-a contents was very low with the concentration of below $0.5mg/m^3$ at central part of the Bay, Juklimpo. The fatness of oysters and the eutrophic index in this area were $18.1\%$ and 0.54, respectively. These values were lower than those of other culturing farms in the southern coastal areas in Korea. Therefore, we estimated that the insufficient food supply due to the low level of nutritional status was the major factors affecting the poor fatness of the Pacific oysters in Hansan-Koje Bay.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.15 no.1
• /
• pp.42-46
• /
• 1982

Followings are the results of growth of Pacific oysters transplanted from the temperate waters of Korea in February 1981, and cultivated upto early July in the tropical waters of Ambong Bay in Malaysia: The shell length increased from 5.78 mm in February to 25.01 mm in July, and the shell height increased from 7.33 mm in february to 38.91mm in July. The meat weight progressively increased and reached the maximum value of 1.66g in May, but then gradually decreased until July, and the fatness varied from $28\%$ of maximum in March to $11\%$ of minimum in July-Survival rate was $47\%\;and\;39\%$ of the initial number in June and July respectively.

• Asian Pacific Journal of Cancer Prevention
• /
• v.17 no.9
• /
• pp.4185-4197
• /
• 2016

Chronic arsenicosis is a major environmental health hazard throughout the world, including India. Animals and human beings are affected due to drinking of arsenic contaminated ground water, due to natural mineral deposits, arsenical pesticides or improperly disposed arsenical chemicals. Arsenic causes cancer with production of free radicals and reactive oxygen species (ROS) that are neutralized by an elaborate antioxidant defense system consisting of enzymes and numerous non-enzymatic antioxidants. Dietary antioxidant supplements are useful to counteract the carcinogenesis effects of arsenic. Oyster mushroom lectins can be regarded as ingredients of popular foods with biopharmaceutical properties. A variety of compounds have been isolated from mushrooms, which include polysaccharides and polysaccharopeptides with immune-enhancing effects. Lectins are beneficial in reducing arsenic toxicity due to anticarcinogenetic roles and may have therapeutic application in people suffering from chronic exposure to arsenic from natural sources, a global problem that is especially relevant to millions of people on the Indian subcontinent.