• The Korean Journal of Malacology
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• v.20 no.1
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• pp.75-84
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• 2004

Reproductive cycle, the condition index, sex ratio of the Pacific oysters, Crassostrea gigas were investigated by histological and morphometric data. The specimens were collected in the two oyster farms of Geoje and Namhae, Gyeongsangnam-do, Korea, from November 1995 to October 1996. Growth of shell length in two regions was similar, but growth of total weight of the oyster in Namhae was faster than that in Geoje oyster farm. The spawning periods in female and male clams were from July to October in Geoje and from June to October in Namhae oyster farm. Ripe oocytes were approximately 50 m in diameter. The reproductive cycle of in females and males in Geoje and Namhae oyster farms can be divided into five successive stages: early developing, late developing, ripe, partially spawned and spent/inactive. Monthly changes in gonad developmental phases showed somewhat different patterns between female and male clams except for the spawning period. On the whole, however, monthly changes in the gonad developmental phases showed a similar pattern in the same sex. The sex ratios of females to males in Geoje and Namhae oyster farms were not significantly different from a 1:1 sex ratio ($x^2$ = 0.55 (p > 0.05) in Geoje and $x^2$ = 0.27 ( p > 0.05) in Namhae). Artificial induction of maturation by heating of adult oysters (two-year-old) was investigated from 17 January to 18 March in 1996. Maturity at the fixed water temperature group of $20^{\circ}C$ was 80%, it showed the highest maturity of experimental groups cultured for five weeks. The survival (%) of Crassostrea gigas in the raised water temperature experimental groups (15, 20, $25^{\circ}C$) were over 98.5%, as similar to the control group (100%). But, the survival of C. gigas in the fixed water temperature experimental groups (15, 20, 25, $30^{\circ}C$) were decreased with the increase of the water temperatures. In the fixed water temperature experimental group of $30^{\circ}C$, the survival was 51.1%. Base on these results, the fixed water temperature of $20^{\circ}C$ was the best condition for artificial induction of sexual maturation.

• Animal cells and systems
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• v.13 no.4
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• pp.447-452
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• 2009

We cloned the complete complementary DNA (cDNA) of a Pacific oyster (Crassostrea gigas) cytochrome P450 (CYP450)-related protein using rapid amplification of cDNA ends (RACE). The cDNA included a 1470 bp open reading frame that began with the first ATG codon at position 103 bp and ended with a TAG stop codon at position 1573 bp (GenBank accession EF451959). The sequence had all major functional domains and characteristics of previously characterized CYP450 molecules, including the heme-binding region (FGVGRRRCVG) and putative arginine codon (R) integral to enzymatic function. An NCBI/GenBank database comparison to other CYP450 genes revealed that the deduced C. gigas CYP450 amino acid sequence is similar to that of mouse (Mus musculus) CYP450 2D/II (28%, accession AK078880), rabbit (Oryctolagus cuniculus) CYP450 2D/II (28%, AB008785), and white-tufted-ear marmoset (Callithrix jacchus) CYP450 2D (28%, AY082602). Thus, although the C. gigas CYP450 we cloned appears to belong to the 2D type of the CYP450 group, it has low similarity to this type. CYP450 mRNA expression increased over 6 h in C. gigas gills at $30^{\circ}C$ and $10^{\circ}C$, and then decreased, indicating that CYP450 plays an important role in C. gigas exposed to water temperature changes. This finding can be used as a physiological index for Pacific oysters exposed to changing water temperatures.

• Korean Journal of Environmental Biology
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• v.20 no.3
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• pp.268-275
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• 2002

Seasonal variation in reproductive condition of the Pacific oyster Crassostrea gigas was investigated from a suspended cultured oyster population in Gosung Bay, South Korea using histological techniques, Gametogenesis of oysters initiated in February when water temperature reached 11 to $13^\circ{C}$. Increase in oocyte size and the number resulting in follicle expansion was observed from March to May First spawning of oysters observed in mid Jun when the surface water temperature reached 22 to $25^\circ{C}$. Spawning activity of oysters extended from mid June to late September with two marked spawning peaks in June and August. Most oysters collected from October to December exhibited few residual eggs in packed follicles exhibiting a typical spent condition. No gametes were observed from December to February from oysters collected in the Bay. Gonadal development of oysters in the Bay seemed to follow a seasonal fluctuation in environmental conditions such as water temperature and food availability in the water column. Spawning of oysters in late June was in part associated with sudden drop in salinity due to vast amount of freshwater input in the Bay after the summer flooding. Sex ratio of oysters was 59.5% male and 39.8% female. Less than 1 percent (0.6%) of the oysters examined were hermaphrodite; few eggs were observed in testis.

• Journal of Aquaculture
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• v.18 no.3
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• pp.200-206
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• 2005

We previously pointed out that the polluted sediment elutriate manifestly affected the early events of reproductive outputs in the Pacific oysters, Crassostrea gigas. A serial dilution of priority xenobiotic sediment elutriates determined by gas chromatography/mass spectrometry (GC/MS) were exposed to gametes of the oyster with different stress burdens to detail the maternal stress transfer to its reproductive outputs. There was an apparent critical concentration over which survival and morphogenesis were significantly affected with more profound damage in morphogenesis. The critical concentration which drives mortality and abnormal morphogenesis of the larvae corresponded to a dilution between 10 and 20% of our elutriate. The adverse effects of the early lives by the xenobiotic exposure over the critical concentration were magnified by the maternal stress from the exposed benzo(a)pyrene (BaP), one of the priority polyaromatic hydrocarbons (PAHs) during the maturation condition. These results indicate that maternal transfer of the xenobiotic compounds from oysters living in the contaminated location might represent a significant adverse effect to their larval population of wild seeds.

• The Korean Journal of Malacology
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• v.28 no.3
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• pp.259-267
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• 2012

Due to the oil spill incident in December 2007, every facility of oyster culture was removed in western coast especially in Taean and Seosan. To restore oyster resources in Taean and Seosan, we brought oyster seeds from southern area and monitored their growth. In addition we monitored the culture environment throughout the year, and observed the number of oyster larvae and attached spats on collectors during summer. The factors of water environment were appropriate for oyster culture in both study area. The growth of shell height was larger in Uihang-ri, Taean than Jungwang-ri, Seosan. Spawning was more intensive in a short time in Jungwang-ri, Seosan than Uihang-ri, Taean. The number of oyster larvae and spats of collectors were much more in Jungwang-ri, Seosan than Uihang-ri, Taean. This study showed that transplantation of healthy oyster seeds from southern area can be a way of restoration of oyster resources in western coast. In addition, systematic approaches are necessary by building a better understanding of regional characteristics to restore and enlarge the oyster culture farms in western coast. In summary Uihang-ri, Taean will be appropriate for cultivation farms and Jungwang-ri, Seosan for seedling grounds to increase oyster culture productivity.

• Proceedings of the Korean Society of Fisheries Technology Conference
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• 1997.06a
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• pp.173.1-174
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• 1997

• Environmental Analysis Health and Toxicology
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• v.25 no.2
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• pp.161-168
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• 2010

The observed the toxic effect of WSF (Water Soluble Fraction) on development time, development rate, attachment rate, survival rate and growth of the larva during the early stage of the Pacific oyster, Crassostrea gigas. The time required early juvenile from the fertilized eggs exposed to crude oil (WSF) was about 13 hours in control group. But that of the crude oil dose group takes 12 hours, with shorter compared to control group. Development and attachment rate of the oyster significantly higher in 0.4 and 0.8 mg/L WSF compared to control group (P<0.05) but significantly lower more than 1.6 mg/L WSF (P<0.05). Survival rate of the oyster larva significantly higher in 0.4 and 0.8 mg/L WSF compared to control group (P<0.05) but significantly lower more than 2.4 mg/L WSF (P<0.05). Survival rate of spot showed no significantly difference compared to control group (P>0.05). Shell growth of the oyster were significantly lower more than 1.6 mg/L WSF compared control group (P<0.05). The effect concentration of crude oil showed that more 0.4 mg/L in development and attachment rate and more 1.6 mg/L in growth. Also, chronic exposure of crude oil even effect also in low concentration.

• The Korean Journal of Malacology
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• v.29 no.3
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• pp.251-258
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• 2013

This study aims to find out a suitable cryoprotective agent (CPA) for cryopreservation and its optimum concentration in order to conduct planned artificial seed production of Pacific oyster, Crassostrea gigas and to preserve superior sperm. For this, we tried to understand toxicity and the effect of cryopreservation by CPA type and concentrations first and then looked into cell damage of the sperm after thawing. Toxicity analysis on the sperm of Pacific oyster according to different CPA and immersion time shows that dimethyl sulfoxide (DMSO) comes first when it comes to survival rate and mobility followed by ethylene glycol (EG), glycerol and methanol. To identify the optimum CPA and its level, filtered seawater was used as a diluent before cryopreservation for 30 days. As a result, cryopreserved sperm of Pacific oyster with 15% of DMSO showed the highest survival rate and activation. Also, we observed the cryopreserved and thawed sperm with Scanning electron micrographs by CPAs and concentrations. Consequently, DSMO showed the lowest cell damage followed by EG, methanol, glycerol and the level was 15, 20, 10, 5% respectively. In a nutshell, it is proven that the optimum CPA and its level is 15% of DMSO.

• Proceedings of the Malacological Society of Korea Conference
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• 2002.11a
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• pp.13-13
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• 2002

• 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.