• Korean Journal of Fisheries and Aquatic Sciences
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• v.20 no.6
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• pp.501-508
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• 1987

Gonadal development, the annual reproductive cycle and the first sexual maturity of hen clam, Mactra chinensis were studied histologically. Sexuality of the species was dioecious. The gonads were irregularly arranged from the subregion of mid-intestinal 91an4 in visceral cavity to the reticular connective tissue of the foot. The ripe eggs were about $50-60\;{\mu}m$ in diameter, and they were surrounded by gelatinous membrane. The spawning period was from May to September when the water temperature ranged $18.5-27.0^{\circ}C$, with the peak in June and July. The annual reproductive cycle of Mactra chinensis could be classified into five successive stages; multiplicative, growing, mature, spent, and degenerative and resting. The monthly changes of the fatness coefficient closely correlated with the annual reproductive cycle. Percentages of the first sexual maturity of female and male clams were over $50\%$ among those individuals ranging from 3.5 to 3.9cm, and $100\%$ in those over 5.0cm in shell length.

• The Korean Journal of Malacology
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• v.27 no.1
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• pp.15-27
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• 2011

This study was performed to observe ultrastructure of the gill and to ascertain the effect of salinity on histopathological and ultrastructural changes in the gill of the Japanese clam, Corbicula japonica. Experimental period was 7 days. Experimental groups consisted of control, 5, 10, 20 psu. $LC_{50}$ (96 h.) by the probit was 19.55 psu. Mortality was significantly different from the control (p < 0.05). Inner demibranch of the gill of C. japonica was wider 1.37 times than outer demibranch (p < 0.001). The filament zone on the plica can be distinguished by the six epithelial celll cell; frontal ciliated epithelium ($7{\mu}m$), latero-frontal ciliated epithelium ($5{\mu}m$), postlatero-frontal epithelim ($3{\times}8{\mu}m$), and lateral ciliated epithelium ($5{\mu}m$) in the frontal zone, endothelial cellin the intermediate zone, and abfrontal cell in the abfrontal zone. It had one type of secretory cell that was filled with fibrous substances of low electron density. The gill of C. japonica exposed to 5 psu for 7 days was observed partially disappearance of the cilia, and glycogen granule in the filament. In the 10 psu, gill appeared partially modification of epithelial cell and destruction of the glycocalyx. Gill exposed to 20 psu was extended nuclus of the ciliated epithelial cell, destruction of the organelles, and observed glycogen granules infiltration and numerous vacuoles. Moreover, more than 50% filaments were observed that come out chitinous rod from disappearance of epithelial cell in the filament. Therefore, the destruction of the cilia and epithelial cell induce physiological activity and it may be leading directly to death.

• The Korean Journal of Malacology
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• v.29 no.1
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• pp.15-21
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• 2013

Nitric oxide (NO) is an important intra-intercellular signaling molecule that regulates many physiological processes and participates in the development some pathological conditions in animals. In this study, we compared different methods for determining NO concentration in the hemocytes of Manila clam Ruditapes philippinarum. For measuring the intracellular NO levels, we used the specific fluorescent probe 4,5-diaminofluorescein diacetate (DAF-2 DA), and the quantification methods that were compared were based on image analysis, spectrophotometry, and flow cytometry. NO concentration could be determined using all the 3 methods, and the concentration varied significantly depending upon the presence of NO regulators in the hemocytes; NO concentration increased in the presence of L-arginine, while it decreased in the presence of N-nitro-L-arginine methyl ester. In particular, it is found that estimation of NO using a flowcytometry is more economical, reliable and accurate compared to image analysis and spectrophotometry. Accordingly we believe that determining NO concentration by using flowcytometry will be useful in evaluating physiological and pathological conditions in marine bivalves.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.27 no.5
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• pp.549-559
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• 1994

Razor clam, Solen (Solen) strictus, was collected between May 1989 and July 1990 on a macrotidal flat, Inchon, Korea. The population sampled at just above mean sea level had a mean density of 126 individuals/$m^2$. Age was determined for 872 specimens by counting annuli, a series of closely-spaced concentric growth lines. According to the fatness index spawning seemed to have occurred once per year in June, and the first recruits for the 1989 year cohort population were found in July. Solen (Solen) strictus on the Chokchon tidal flat reached a shell length of 6.2 cm in four years. Mean growth in shell length can be described by the von Bertalanffy function, which yielded estimates of growth parameters equivalent to $L_{\infty}=81.865\;mm$ shell length and K=0.320 per year: $$L_{t}=81.865(1-e^{-0.320(t+0.487)})$$$$W_{t}=7.173(1-e^{-0.320(t+0.487)})^3$$

• Korean Journal of Fisheries and Aquatic Sciences
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• v.27 no.1
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• pp.59-68
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• 1994

The effects of silt and clay, water temperature and salinity on the metabolic activities: rates of respiration, filtration and nitrogen excretion in the clam, Mactra veneriformis, were investigated in ranges of $0{\sim}250ppm,\;15{\sim}25^{\circ}C\;and\;10{\sim}30\%0$ respectively. The weight specific respiration rate decreased with shell length and significantly declined at lower temperatures and lower salinity levels. Average respiration rates, filtration rates and ammonia excretion rates of the clam groups declined as water temperature was lowered. The respiration rate(R) and the filtration rate(F) decreased as the concentration of silt and clay(C) increased, the relationships between the two parameters were expressed as a regression line, R=a+b LogC and LogF=a+b LogC, respectively. On the rearing experiment treated with 50ppm of silt and clay, the relationship between the accumulative mortality(M) and the elapsed day(T) was $M=0.0186T^{2.7965}$, and the median lethal time was calculated at 16.8 days. From the rearing experiment, both rate of respiration and ammonia nitrogen excretion of experimental groups and control groups decreased with elapsed days, the rates of experimental groups, especially declined more compared with those of the control groups.

• Korean Journal of Food Science and Technology
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• v.8 no.4
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• pp.219-224
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• 1976

The appearance of organochlorine pesticide residues in shellfish, seaweed, mud and water samples collected from south coast of Korean peninsula in September 1974 was surveyed to obtain the following results. 1) The residues in shellfish samples were found to be in the orders of Choongmoo > Yeosoo > Busan > Mokpo area, top-shell >short-necked clam > mussel > hard clam > red-shell, aldrin > ${\alpha}-BHC$ > heptachlor> ${\gamma}-BHC$ > dieldrin > heptachlor epoxide > endrin and in the range of $0-49\;{\mu}g/kg$ edible fresh muscle. 2) The residues in seaweed samples from Wando area were found to be in the orders of tangle > green laver > laver, ${\alpha}-BHC$ > ${\gamma}-BHC$ > aldrin > dieldrin > heptachlor > heptachlor epoxide > endrin and in the range of $0-60\;{\mu}g/kg$ dry matter. 3) The residues in water samples were found to be in the orders of Yeongsan River > Nakdong River > Seomjin River > Choongmoo shellfish farm, ${\alpha}-BHC$ > ${\gamma}-BHC$ > aldrin > heptachlor > dieldrin > heptachlor epoxide > endrin and in the range of $0-180\;{\mu}g/kl$ while those in mud samples were in the order of ${\alpha}-BHC$ > ${\gamma}-BHC$> aldrin > dieldrin > heptachlor > heptachlor epoxide > endrin and in the range of $0.7-18\;{\mu}g/kg$ dry matter. It should be noted that BHC contents of water samples from Yeongsan and Nakdong rivers were far above the recommended environmental levels in USA.

• Journal of the Korean Society of Food Science and Nutrition
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• v.32 no.2
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• pp.161-166
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• 2003

This study attempted to fortify Kimchi with water extracts of shells of shellfishes (corb shell, short neck clam, taste clam, ark shell, top shell, oyster) as natural resource of calcium. Kimchi added with the shell extracts in 5% were fermented at 1$0^{\circ}C$ with measurements in chemical, microbiological and sensory qualities. Calcium content of shellfish shells before water extraction was in the range of 25.57~38.78%. Kimchi added with the extracts showed higher pH, lower acidity, lower total aerobic bacterial count and higher lactic acid bacteria count compared to control Kimchi without any addition. After 7 day fermentation the Kimchi added with the extracts also showed higher ash and calcium contents compared to control products (3.3~5.0 vs. 2.8~3.0% and 300~376 vs. 70~95 mg%). Kimchi with oyster shell extract gave the most pronounced effect in ash and calcium contents. The addition of extract made Kimchi crisper and less sourer oganoleptically. In the overall acceptability, the Kimchi fortified with the shell extracts were better than control after 14 day fermentation.

• Journal of the Korean Society of Food Science and Nutrition
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• v.36 no.7
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• pp.926-931
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• 2007

Diarrhetic shellfish poisons (DSP) such as okadaic acid (OA), dinophysistoxin-1 (DTX1), pectenotoxin-1(PTX1), PTX2, PTX6 and yessotoxin (YTX) were determined simultaneously by LC-MS/MS and mouse bioassay in the shellfishes (oyster, mussel, Washington purple clam, ark shell, scallop and short necked clam) collected at Tongyeong, from March to September, 2006. Oyster and mussel were found to contain DSP (0.05${\sim}$0.1 MU/g) in March by mouse bioassay; however, no DSP components were detected on the LC-MS/MS. Also, a small amount of DTX1 (0.05 ${\mu}g/g$) in mussel (June) and OA (0.01${\sim}$0.02 ${\mu}g/g$) in 5 species of shellfishes(August) were determined by LC-MS/MS.

• The Korean Journal of Malacology
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• v.31 no.2
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• pp.123-127
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• 2015

${\beta}$-Glucan is a polysaccharide that is widely used as an adductive in fish feed to facilitate immune stimulation. This study aimed to investigate the effect of ${\beta}$-glucan on immune responses in the Manila clam Ruditapes philippinarum. For this purpose, three groups of R. philippinarum were exposed to 0%, 0.1%, or 1% ${\beta}$-glucan in sea water for 1 hr/day for 2 weeks using an immersion method. Thereafter, two immune parameters-phagocytic rate and antibacterial activity-were measured. R. philippinarum exposed to 1% ${\beta}$-glucan showed an approximate 30% significant increase in phagocytic rate. In addition, ${\beta}$-glucan significantly limited the growth of the pathogenic bacteria Vibrio tapetis, V. parahaemolyticus, and V. ordalii. Moreover, the mortality rates of ${\beta}$-glucan-treated clams decreased during a 17-day experiment. Our study suggests that treatment with ${\beta}$-glucan significantly increases the immune responses in R. philippinarum, and that immersion is a simple and effective method for immune stimulation in this species.

• Journal of the Korean Society of Marine Environment & Safety
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• v.21 no.5
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• pp.484-491
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• 2015

The productivity of Manila clam(Ruditapes philippinarum) aquaculture farm is closely related to suitable site selection, so it is essential to assess the habitat suitable for aquaculture species in order to manage yield. This study evaluated the habitat suitable index(HSI) with 9 sites for tidal flat farm, Gochang(Hajun) on May 2014. The suitability index was selected Growth(hydrodynamics, chlorophyll a), Survival(sediment-sand, silt-clay) and Water Environment(dissolved oxygen, salinity). Both Weight and No weight were tried for objective judgment as HSI scoring method. As a result, it shows lower tidal flat(HSI; No weight: 0.60~0.76, Weight: 0.47~0.70) is higher than upper(HSI; No weight: 0.25~0.27, Weight: 0.09~0.10), hydrodynamics and sediment particle size are the most effective. This research can consider the potential suitable site for Manila clam through scientific approach, and provide the basis for optimal management practices in tidal flat farm.