• Korean Journal of Veterinary Research
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• v.31 no.1
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• pp.33-40
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• 1991

For the observations of both the membrane properties and the excitability on the unfertilized eggs of female mice, changes of the membrane resistance and the membrane potential by hyerpolarizing current stimulation were recorded. As current-voltage relation was linear over the entire range (-180mV~+60mV), membrane resistance($R_m$) was calculated from the amplitude of electrotonic potential to a given stimulus current. Also the presence of anode-break excitation was confirmed. The results were as follows; 1. There was a linear relation between the membrane resistance and resting membrane potential, the expected input resistance was 61. 4M$\Omega$(resting membrane potential was $-18.9{\pm}8.7mV$, mean${\pm}$SD, n=30). 2. Transient depolarization with overshoot was generated just after hyperpolarizing current stimulus and showed the dependency of stimulus duration. 3. Transient depolarization lasted over 30ms, amplitude of these depolarization was increased by high $Ca^{{+}{+}}$(20mM) and inhibited by $Ca^{{+}{+}}$-antagonist, $Mn^{{+}{+}}$. 4. From the above results, it was suggested that the unfertilized mouse egg showed the characteristics of the excitable cell.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.33 no.6
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• pp.554-558
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• 2000

Reproductive biology of the female red tongue sole, Cynoglossus joyneri was investigated by means of histological methods. Gonadosomatic index (GSI) was the highest in June. Developmental pattern of oocytes was group-synchronous. Egg stalk and yolk nucleus were observed in the early growing oocytes. Reproductive cycle could be classified into the growing ($February{\~}May$), maturation ($May{\~}June$), ripe and spent ($June{\~}August$), and recovery and resting ($August{\~}February$). The absolute fecundity per individual ($TL 28.1{\~}30.8 cm$) was 2,197 and relative fecundity per g body weight was 18.0.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.4
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• pp.692-697
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• 2016

This study examined the effects of salinity and medium used on the induction of sexual reproduction for the mass production of the resting eggs in the marine rotifer Brachionus rotundiformis for 9 days. After exposure to various salinities, the mixis rate in all treatments began to increase on the third day and decreased after the 4th or 5th day. The resting eggs appeared on the 4th day at 10‰, 15‰, 20‰, 25‰. In particular, the fertilization rates with 33.3% and 31.3% at 20‰ and 25‰ on day 6 were higher than those of the others, respectively. Mean mixis rate for 9 day at 0‰ and 20‰ were the highest with 25.3% and 20.2%, respectively, and the fertilization rate (14.0%) at 25‰ was the highest. In the medium experiment used, the mixis rate in all treatments were similar to the results of the salinity experiment. The resting eggs were only found at 0% and 25% of the used medium treatments. While there were no significant differences in the mean fertilization rate of all treatments, the mean mixis rate (22.3%) in the 25% treatment was higher than that of the control (0% treatment). As a result, salt stress was more effective than using the used medium to induce sexual reproduction in B. rotundiformis. The optimal salinity was considered to be 20-25‰, which caused a high mixis and fertilization rate in the rotifer. These results provide basic data for the mass production of rotifer resting eggs.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.23 no.2
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• pp.141-144
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• 1990

Seasonal change in the reproductive pattern of the marine Cladoceran Podon polyphemoides, was studied using materials collected monthly during the period from January to December 1986 in Yongil Bay, Korea. The relative abundance of P. polyphemoides exceeded $10\%$ of total zooplankton in July. While the species remained as a minor components of the zooplankton community during the other periods of occurrence from June to December. Occurrence of sexual individuals of P. polyphemoides (males and gamogenetic females) in higher proportion in cold months ($30\%$ in November and $40\%$ in December) suggests that resting egg production of this species is largely confined to cold monthis in Korean waters as an overwintering strategy.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.30 no.4
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• pp.627-633
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• 1997

Gonad structure, germ cell development and reproductive cycle of the smallmouth scorpionfish, Scorpaena miostoma were investigated based on histological method. Samples were collected monthly in the vicinity of Suyoung Bay, Pusan, Korea from November 1995 to October 1996. The testis is seminiferous tubule type in internal structure. Seminiferous tubule consists of numerous testicular cysts which contain numerous germ cells in same developmental stage. The ovary consists of several ovarian lamellae originated from ovarian outer membrane. Oogonia originated from the inner surface of the ovarian lamella protrude to the ovarian cavity in oocyte stage, and they are suspended by the egg stalk. Biological minimum size of female and male were 12.5cm in total length. Gonadosomatic index (GSI) of female (3.81) and male (0.23) were the highest in October. Reproductive cycle was classified into the following successive stages: in female, growing stage $(May\~August)$, maturation stage $(September\~October)$, ripe and spawning stage $(November\~December)$, recovery and resting stage $(January\~April)$, and in male, growing stage $(June\~August)$, maturation stage $(September\~October)$, ripe and spent stage $(November\~January)$ and recovery and resting stage $(February\~May)$.

• Journal of Aquaculture
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• v.17 no.1
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• pp.30-38
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• 2004

To estimate the spawning period the annual change of gonadosomatic index (GSI) were examined from January 2000 to December 2001. Fecundity, spawning frequency and egg diameter were measured by ocular observation. Germ cell differentiation during gametogenesis, the reproductive cycle and the first sexual maturity of greenling Hexagrammos otakii were observed under light microscopy from January to December, 2000. GSI began to increase in August and reached the maximum in November when ovary was getting mature. The reproductive cycle of H. otakii can be divided into five successive stages in females: early growing stage (July), late growing stage (July to August), mature stage (September to October), ripe and spent stage (September to December), and recovery and resting stage (December to June). Males showed four successive stages : growing (June to August), mature (August to October), ripe and spent (September to December), and recovery and resting stage (December to May). According to the frequency distributions of egg diameter in spawning season, H. otakii could be one of polycyclic species spawning 2 times or more during one spawning season. Number of total eggs and mature eggs in the absolute fecundity were related to the standard length and body weight, respectively. Number of total eggs and mature eggs in relative fecundity were also proportional to the standard length, but rather these numbers decreased with body weight. Percentages of first sexual maturity of females and males in greenling were over 50% from 19.1 to 21.1cm in length, and 100% for fish over 25.1cm in length. Therefore, both sexes are ready to reproduce after one year old.

• Korean Journal of Ichthyology
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• v.7 no.1
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• pp.33-42
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• 1995

The reproductive cycle of the bitterling, Rhodeus uyekii was studied to observe the annual variations of gonadosomatic index(GSI), size frequency distribution of egg, ovipositor length and histological changes of gonad. GSI began to increase from February when the water temperature started to increase, and reached the maximum value in May, whereas it began to decrease from July and reached the minimum value in August which in the highest water temperature season. It began to incerase again but showed low value from September to November. The GSI remained stable thereafter. Monthly changes in GSI, ovipositor length, frequency of egg diameter and gonadal histology showed that the annual reproductive cycle was classified into the following successive phases : primary growing phase from September to November, quiescent phase in December, secondary growing and mature phase from January to February, ripe and spawning phase from March to June, and recovery and resting phase from July to August.

• Fisheries and Aquatic Sciences
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• v.6 no.2
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• pp.51-58
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• 2003

The gonadal development and the gametogenic cycle and the fine structure of ripe germ cells of the cultured Pacific oyster, Crassostrea gigas were investigated using oysters monthly collected from the southern coast of Korea from October 2000 to September 2001. Monthly changes in the condition index were similar to that of meat weight rate and the highest value was observed in between April and May, and the lowest value in August. The external colors of the testis and the ovary were milky white and yellowish, respectively. The spawning period of the Pacific oyster was continued from May to September, with a peak in July. The gametogenic cycle could be classified into five successive stages: multiplicative stage (December to March), growing stage (March and April), mature stage (April to June), spawning stage (June to August) and resting stage (August to January). Variety of egg yolk granules, lipid granules, mitochondria, and endoplasmic reticula were observed in cytoplasm of ripe oocyte. The spermatozoon consisted of the head, middle piece and tail; including cap-shaped acrosome with domed structure, elliptical shaped nucleus, four mitochondria, two centrioles and flagellum.

• Fisheries and Aquatic Sciences
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• v.2 no.2
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• pp.142-148
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• 1999

Monthly changes in the gonad index (GI), egg-diameter composition, gonadal development, reproductive cycle of the ark shell, Scapharca subcrenata, were investigated by histological method and morphometric data. This species is dioecious and oviparous. The gonad is located among the subregion of mid-intestinal gland, digestive diverticula and the outer fibromuscular layers compacted by the fibrous connective tissues and muscle fibers. The gonad index sharply increased in May, reached the maximum value in June, and then gradually decreased from July to December. The reproductive cycle of this species can be divided into six successive stages: early active stage (January to May), late active stage (June to July), ripe stage (June to August), partially spawned stage (July to September), degenerative stage (August to December), and resting stage (January to April). S. subcrenata spawns once a year between July and early September, and the main spawning occurred between July and August when the water temperatures were above $20^{\circ}C$. This evidence suggest that timings of maturation and spawning are closely related to water temperatures. Even though the spawning period was once a year, it is assumed that the number of spawning frequencies (broods) may occur more than twice during the spawning season.

• The Korean Journal of Physiology
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• v.28 no.2
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• pp.215-224
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• 1994

The presence of a calcium current $(i_{Ca^{2+}})$ passed via a specific channel was examined in the unfertilized hamster egg using the whole-cell voltage clamp technique. Pure inward current was isolated using a $Ca^{2+}-rich$ pipette solution containing 10 mM TEA. This current was independent of external $Na^+$ and was highly sensitive to the $Ca^{2+}$ concentration in the bathing solution, indicating that the inward current is carried by $Ca^{2+}$. The maximal amplitude was $-4.12{\pm}0.58nA\;(n=12)$ with 10mM $Ca^{2+}$ at -3OmV from a holding potential of -8OmV. This current reached its maximum within 20ms beyond -3OmV and decayed rapidly with an inactivation time constant $({\tau})$ of 15ms. Activation and inactivation of this $i_{Ca^{2+}}$ was steeply dependent on the membrane potential. The $i_{Ca^{2+}}$ began to activate at the lower voltage of -55 mV and reached its peak at -35 mV, being completely inactivated at potentials more positive than -40 mV. These result suggest that $i_{Ca^{2+}}$ in hamster eggs passes through channels with electrical properties similar to low voltage-activated T-type channels. Other results from the present study support this suggestion; First, the inhibitory effect of $Ni^{2+}\;(IC_{50}=13.7\;{\mu}M)$ was more potent than $Cd^{2+}\;(IC_{50}=123\;{\mu}M)$. Second, $Ba^{2+}$ conductance was equal to or below that of $Ca^{2+}$. Third, $i_{Ca^{2+}}$ in hamster eggs was relatively insensitive to nifedipine $(IC_{50}=96.6\;{\mu}M)$, known to be a specific t-type blocker. The physiological role of $i_{Ca^{2+}}$ in the unfertilized hamster eggs remains unclear. Analysis from steady-state inactivation activation curves reveals that only a small amount of this current will pass in the voltage range $(-70{\sim}-30\;mV)$ which partially overlaps with the resting membrane potential. This current has the property that it can be easily activated by a weak depolarization, thus it may trigger a certain kind of a intracellular event following fertilization which may cause oscillations in the membrane potential.