• Korean Journal of Fisheries and Aquatic Sciences
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• v.30 no.5
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• pp.804-808
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• 1997

The genetic differentiation and characteristics of two oyster populations (Crassostrea gigas) in Korea were assessed based on the restriction fragment length polymorphisms (RFLP) analysis and the restriction patterns of subcloned mtDNA. The restriction fragments of twenty individuals in West Sea revealed an identical pattern, determined by 8 restriction enzymes. On the other hand, two haplotypes having variation at the HindIII site were shown in the specimens from South Sea; minor haplotypes (4 of 20) were similar to the results obtained from individuals in West Sea while major haplotypes were different from those in West Sea. It was suggested that oysters (C. gigas) of West Sea might have been introduced to South Sea. Each mitochondrial DNA from two oyster populations in Korea and from one in Japan was divided to three parts and subcloned into pUC19 to use in genetic studies effectively. Restriction map was constructed based on the cleavage pattern by multiple restriction enzymes.

• Fisheries and Aquatic Sciences
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• v.9 no.4
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• pp.140-145
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• 2006

We measured activities of the ubiquitous tripeptide non-protein thiol (L-${\gamma}$-glutamyl-L-cysteinyl-glycine), glutathione (GSH), which is believed to playa fundamental role in detoxifying xenobiotics in biological systems, as a metabolic biomarker for benzo(${\alpha}$)pyrene and Aroclor 1254 exposure in the Pacific oyster Crassostrea gigas. Reproductive oysters were exposed to the pollutants for 50 days by the algal vectoring method in which the oysters were fed with concentrated standard algal foods grown in culture media containing Aroclor 1254 (0, 5, 50, 500 ng/g) or benzo(${\alpha}$)pyrene (0, 10, 100, 1,000 ng/g). Both pollutants induced maternal GSH activities in 10 days in a dosage-dependent manner (p<0.05), although Aroclor 1254 was stronger. The pollutant-driven GSH elevation persisted for 20 to 30 days depending on the pollutants and concentrations. Thereafter, a drastic decline in the GSH activity was observed due to metabolic failure, after which the oyster GSH remained at low levels throughout the remainder of the experiment. The pollutant exposures influenced maternal reproductive output in terms of fertilization, hatching, and morphology. These results imply that changes in activity of the GST-catalyzing molecule can be used as an oyster biomarker for Aroclor 1254 and benzo(${\alpha}$)pyrene exposure.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.47 no.6
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• pp.853-859
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• 2014

The goal of this study was to evaluate the effects of cryoprotectants [dimethyl sulfoxide (DMSO), methanol, polyethylene glycol, and propylene glycol], cryoprotectant concentrations (10% and 20%), equilibration time (3, 10, and 30 min), cooling rate ($3^{\circ}$, $5^{\circ}$, $7^{\circ}$, and $10^{\circ}/min$), and straw size (0.25 and 0.5 mL) for sperm cryopreservation of tetraploid Pacific oysters. There was a significant difference among the four cryoprotectants, with 10% DMSO yielding the highest post-thaw survival and activity index of sperm. A significant relationship was observed between the cryoprotectant and its concentration. The sperm with equilibration times of 30 min yielded higher post-thaw survival and activity indices than those with 3 and 10 min equilibration times. The sperm cooled at a rate of $5^{\circ}/min$ yielded the highest post-thaw survival and activity index, and the results were significantly different from those observed for cooling at $7^{\circ}$ and $10^{\circ}/min$. Post-thaw survival and activity indices of sperm using a 0.25-mL straw were significantly higher than those using a 0.5-mL straw.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.51 no.5
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• pp.535-541
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• 2018

This study evaluated the sanitary state of seawater and shellfish in Yongnam-Gwangdo area from January 2014 to December 2016. The sampling stations for sanitary survey in Yongnam-Gwangdo area were composed of 41 seawater stations and 5 oyster Crassostrea gigas stations. The samples were collected monthly at each station. Shellfish-borne disease is associated with bacteria and viruses in the presence of fecal coliforms. Bacteriological pollution levels of shellfish increase with seawater quality. Therefore, fecal coliforms are very important criteria for evaluating the safety of fisheries in coastal areas. The geometric mean and the estimated 90th percentile ranges of total and fecal coliforms for seawater were 1.8-11.7, 2.8-233.6, <1.8-6.7 and 1.8-100.2 MPN/100 mL, respectively. The range of E. coli levels for oysters was <20-1,300 MPN/100 g. Based on various standards, the sanitary condition in Yongnam-Gwangdo area was evaluated as follows: clean area (Korean criteria), conditionally approved area (US criteria) and class B (EU criteria).

• Korean Journal of Fisheries and Aquatic Sciences
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• v.19 no.6
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• pp.593-598
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• 1986

The growth of the pearl oyster, Pinctada fucata was compared between two areas, Hansan Bay and Ilkwang located in southern part and in southeast part of Korean waters respectively, from November 1984 to June 1986. The pearl oysters in Hansan Bay grew from 2.53cm to 6.07 cm in shell length in 17 months, while those in Ilkwang grew from 2.53 cm to 4.07 cm in 19 momths. Shell height, shell breadth and total weight of the pearl oysters in Hansan Bay also showed more rapid growth than those in Ilkwang. The relative growth of shell breadth to shell length in specimens between Hansan Bay and Ilkwang showed a significant difference indicating that the value in Ilkwang is bigger than that in Hansan Bay, It is also suggested that Hansan Bay is a good area for the growth and Ilkwang, an area worth wintering of the pearl oyster.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.49 no.6
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• pp.772-778
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• 2016

To develop a value-added product from individually quick-frozen oysters Crassostrea gigas (IQFO), we prepared a retort pouched oyster soup (RPOS) from IQFOs and characterized its processing conditions and quality metrics. We found that the most appropriate manufacturing process for the RPOS consisted of half-thawing and washing raw IQF oysters, blanching, adding them to the retort pouch along with other ingredients (base soup stock, IQF oyster extract, radish, bean sprouts, garlic, and red pepper), sealing, retort sterilization ($120^{\circ}$, F0-value 10 min.), cooling, and packaging inspection. The moisture, crude protein, pH and salinity of the RPOS were 91.0%, 2.8%, 6.20 and 0.9%, respectively. The total amino acid content of the RPOS was 2,163.8 mg/100 g, and the main amino acids were glutamic acid, aspartic acid, leucine, proline, lysine and arginine. The primary inorganic ions were Na, K, S and Zn. In taste compounds, total free amino acid content was 313.4 mg/100 g, and the main free amino acids were glutamic acid, taurine, proline, hydroxyproline, aspartic acid, glycine, alanine, valine, lysine and arginine. This RPOS has good storage stability and organoleptic qualities compared with commercial retort pouched shellfish soup, and is suitable for commercialization as a value-added instant seafood soup.

• Journal of Microbiology and Biotechnology
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• v.26 no.8
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• pp.1398-1403
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• 2016

The simultaneous detection and accurate identification of hepatitis A virus (HAV) is critical in food safety and epidemiological studies to prevent the spread of HAV outbreaks. Towards this goal, a one-step duplex reverse-transcription (RT)-PCR method was developed targeting the VP1/P2B and VP3/VP1 regions of the HAV genome for the qualitative detection of HAV. An HAV RT-qPCR standard curve was produced for the quantification of HAV RNA. The detection limit of the duplex RT-PCR method was 2.8 × 10¹ copies of HAV. The PCR products enabled HAV genotyping analysis through DNA sequencing, which can be applied for epidemiological investigations. The ability of this duplex RT-PCR method to detect HAV was evaluated with HAV-spiked samples of fresh lettuce, frozen strawberries, and oysters. The limit of detection of the one-step duplex RT-PCR for each food model was 9.4 × 10² copies/20 g fresh lettuce, 9.7 × 10³ copies/20 g frozen strawberries, and 4.1 × 10³ copies/1.5 g oysters. Use of a one-step duplex RT-PCR method has advantages such as shorter time, decreased cost, and decreased labor owing to the single amplification reaction instead of four amplifications necessary for nested RT-PCR.

• 한국해양학회지
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• v.1
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• pp.49-55
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• 1971

After the heavy precipitation from April 1969 to September 1970, more than 1.359 10$\^$6/㎥ of fresh water was discharged through diversion channel of the Namgang Dam. The sands and muds in the northern Sachon Bay were moved and swept away by the strong southsard flow which was observed to be speedier than five knots. The shellfish culture facility as well as the oysters and bivalves were buried. In Sachon Bay, a southward surface ebb current of approximately one knot stratifies above the northward flow of approximately 0.5 knot, which seems to be similar to the salt wedge estuary. The stratified current is responsible for the breaking of the gill nets and other fishing gears. The salinity of sea water in Chinju Bay decreased remarkably and the abnormal low salinity water lower than 5 was distributed in Sachon Bay. The low salinity water front was observed in eastern Chinju Bay and the Samchonpo Channel, where the salinity was increased from 4.6 to approximately 30 within half a tidal cycle. These caused the oysters and bivalves die, and drove anchovies and octopus out to the sea and prevented them from approaching the bay. The decrease of salinity causes the decrease of density and osmotic pressure of sea water. Turbid water would prevent the sunlight from penetrate into deep layer.

• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.6
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• pp.684-689
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• 2017

We examined the possibility of developing an early monitoring system using the shell valve movement activity of Pacific oyster (Crassostrea gigas) for early detection of low salinity water in coastal areas. At salinity levels of 30 psu and 20 psu, SVMs were detected $7.32{\pm}3.21times/hr$ and $7.11{\pm}3.90times/hr$, respectively, The patterns and times of SVMs were not significantly different between the two experiment phases. However, at 10 psu and 5 psu, shell valves were observed to be permanently closed in all experiments. Under combined condition (Group 1: temperature $15^{\circ}C$ ${\times}$ salinity 15 psu), SVMs were observed from 20 psu to 30 psu over a 2 - 3 hr period, and then remained closed. In Group 2 (temperature $30^{\circ}C$ ${\times}$ salinity 15 psu), SVMs were observed, which indicated that the physiological condition of the oysters reached a critical point. Thus, it may be possible to utilize SVMs as an early warning signal for low salinity water.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.53 no.6
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• pp.842-850
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• 2020

The objective of this study was to evaluate the effect of the depuration process (artificial seawater sterilization using UV light) for extending the shelf life of raw oyster Crassostrea gigas and maintaining food quality. To confirm the effects of depuration, microbiological (viable cell count) and several physiochemical analyses (pH and glycogen levels in shucked oyster and pH, soluble protein, and turbidity in filling water) were carried out during the storage of raw oysters. The results showed that depuration could effectively extend the shelf life (2-3 days) of raw oysters with minimal change in food quality, including pH and glycogen content. Thus, the depuration process proposed in this study could successfully be applied to processing practices for other shellfish to extend their shelf life and contribute to the management of seafood safety issues.