• Korean Journal of Ichthyology
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• v.12 no.3
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• pp.192-202
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• 2000

Reproductive biology of the slimy, Leiognathus nuchalis was investigated by means of histological methods. Sex ratio was 1.81 : 1 in female to male. Developmental pattern of oocytes was group-synchronous. Testicular structure was restricted spermatogonial testis-type of tubular testis. The size of first group maturity is 7.5 cm in total length. Gonadosomatic index(GSI) of female was the highest in July(12.83) and the lowest in September(1.08). GSI of male was the highest in June(19.0) and the lowest in October(0.24). Hepatosomatic index(HSI) of female showed to be positively correlated with GSI. Thoracic spot index(TSI) showed to be the minimum value from May to July when the maturation and ripe season of gonad. Reproductive cycle of female could be classified into the growing(March~May), maturation(May~June), ripe and spent(June~August), recovery(August~November), and resting stage(November~March). Reproductive cycle of male could be classified into the multiplicative and growing(January~April), maturation(April~May), ripe and spent(June~August), recovery(August~October), and resting stage(October~December).

• The Korean Journal of Malacology
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• v.29 no.4
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• pp.313-323
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• 2013

Gonad development, the reproductive cycle, first sexual maturty and size at 50% of group sexual maturity (the biological minimum size) of Gomphina (Macridiscus) veneriformis were investigated for clams collected from the coastal waters of Donghae City, the East Sea of Korea by histological, and morphometric analysis. Monthly variations of the gonad index showed a pattern similar to that of the reproductive cycle. The reproductive cycle with the gonad developmental stages in female and male G. (M.) veneriformis can be classified into five successive stages: early active stage (December to March), late active stage (March to June), ripe stage (June to July), partially spawned stage (June to August), and spent / inactive stage (September to December). The spawning period continued from June to August, with a peak between July and August when the seawater temperature exceeds $20^{\circ}C$. The percentages of first sexual maturities of female and male clams ranging from 25.1 to 30.0 mm were 56.3% in females and 61.1% in males, and for clams over 30.1 mm shell length, it was 100%. Shell lengths at 50% of group sexual maturity (biological minimum size, $RM_{50}$) were 27.71 mm in females and 26.31 mm in males. Because harvesting clams < 26.31 mm in shell length could potentially cause a drastic reduction in recruitment, a measure indicating a prohibitory fishing size should be taken for adequate fisheries management.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.42 no.1
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• pp.41-47
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• 2009

The seasonal reproductive cycle of Gomphina melanaegis collected in the coastal area of Jumunjin, between April 2006 and March 2007, was analyzed. Maturation cycle parameters such as the gonad index (GI), ovarian egg diameter, frequency of developmental stages, protein content, and RNA/DNA variation in the gonads were analyzed monthly for the 40 samples. According to the indices from histological sections, the frequency of gonad developmental stages, and the oocyte diameter, this clam has a long-term partial spawning pattern from March to October. However, GI and nucleic acid values showed that the mature stage is from March to July and that the main spawning season is August. The peak RNA and DNA contents were good indicators of sexual maturation in females and males, respectively. The variation in protein content corresponded with the RNA/DNA ratios.

• Development and Reproduction
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• v.22 no.2
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• pp.175-182
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• 2018

In order to examine the effects of four different light spectra (white, red, green, and blue) on the oocyte maturation, the change of reproductive parameters, via brain-pituitary-gonad (BPG) axis in grass puffer, were investigated. After exposure four different light spectra for 7 weeks, the abundance of gonadotropin-releasing hormone (GnRH) mRNA which is a type of seabream (sbGnRH) and two different subunit of gonadotropin hormones mRNAs, follicle-stimulating hormone ($fsh{\beta}$) mRNA and luteinizing hormone ($lh{\beta}$) mRNA, were analyzed in the brain and pituitary. Histological analysis showed that the mature oocyte ratio in the green spectrum was higher than other light spectra-exposed groups. Gonadosomatic index (GSI) and oocyte developmental stage were also investigated in the gonad based on histological observations. GSI value with the presence of yolk stage oocytes was significantly increased in the green spectrum-exposed group when compared to that of the other light-exposed groups (white, red, and blue) (p<0.05). The abundances of sbGnRH mRNA and $fsh{\beta}$ mRNA in the green spectrum-exposed group were also significant higher than those of the other light spectra-exposed groups (p<0.05). These results indicate that the maturation of oocyte in grass puffer can be accelerated by exposure to the spectrum of green. To better understand the molecular mechanism for the maturation of oocyte in grass puffer, further study examining the relationship between oocyte development and its related genes is required.

• Journal of Aquaculture
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• v.21 no.4
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• pp.252-258
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• 2008

Gonadal development and reproductive cycle of the ark shell Scarpharca subcrenata were investigated by histological observations. Samples were collected monthly from March 2007 to February 2008 in the Yeoja Bay, Yeosu, Jeollanam-do, Korea. S. subcrenata was dioecious. The gonads consist of a number of oogenic follicle and acinus. Monthly changes in the gonad index reached a maximum in June and a minimum in September. Monthly changes in the condition index reached a maximum in April and a minimum in September. The reproductive cycle of this species can be divided into five successive stages: early active stage (January to April), late active stage (March to June), ripe stage (May to August), spent stage (July to September) and recovery and resting stage (September to March). The main spawning of S. subcrenata occurred in July and August in Yeoja Bay. The sex ratio of female to male was not significantly different from 1:1.

• The Korean Journal of Malacology
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• v.16 no.1_2
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• pp.35-41
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• 2000

We investigated the gonad index (GI), gonadal development, the reprodutive cycle and first sexual maturity of the venus clam, Cyclina sinensis by histological observation. Samples were collected from the intertidal zone of Komso Bay, Chollabuk-do, west coast of Korea, from April 1998 to March 1999. This clam is dioecious and oviparous. Monthly changes in the gonad index (GI) showed a similar pattern to the reproductive cycle. Ripe oocytes are about 90-100 ㎛ in diameter. The spawning period was between early July to September, and the main spawning occurred between July and August when the sea water temperature was over 20$\^{C}$ The reproductive cycle of this species can be divided into five successive stages: early active stage (February to April), late active stage (March to June), ripe stage (April to August), partially spawned stage (July to October), and spent / inactive stage (September to February). Percentages of first sexual maturity of female and male clams measuring 26.1-30.0 ㎜ in shell length were 53.3% and 62.5%, respectively, and 100% for the clams > 41.0 ㎜. It is assumed that both sexes begin reproduction at about two years age.

• The Korean Journal of Malacology
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• v.20 no.1
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• pp.65-73
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• 2004

Gametogenesis, changes of gonad bulk index (GBI), monthly variation in oocyte diameter, reproductive cycle and spawning with lunar cycle of the top shell, Trochus niloticus were investigated by histological examination. The specimens were sampled in the coastal waters of Chuuk Island, Micronesia, form November 1999 to September 2000. T. niloticus is a gonochorism, and the female and male were present in an approximately 1:1 ratio (p > 0.05). The ovary contained with the oocyte of yolk stage, the testis composed of the spermatid and spermatozoa at around the year. Monthly GBI were higher at February, March, April and June than the other months. Major spawning occurred between April and May, and June and July but the individuals of partially spawning were presented throughout the year. GBI with lunar cycle were higher at the full moon than the other lunar phase. These results suggest that the spawning occurred between the full moon and last quarter moon.

• Fisheries and Aquatic Sciences
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• v.9 no.1
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• pp.7-13
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• 2006

Using biochemical methods, we determined the potential of local female shrimp populations as breeding stock to select the best adult prawns for improving larval production. As condition indexes, we selected total RNA, DNA, their ratio, and trypsin activity. The DNA content in the pleopods of each local population was similar, i.e., between $0.90{\pm}0.06\;and\;1.02{\pm}0.04(SE){\mu}g/mg$. In comparison, the RNA contents differed markedly between $2.00{\pm}0.09$ and $0.96{\pm}0.08\;{\mu}g/mg$. Therefore, the RNA/DNA (R/D) ratio in the pleopod could be used as a condition index because it represents a biochemical characteristic of the population. The mean pleopodal R/D ratio of the Goheung population was the highest at $2.52{\pm}0.19$, which indicated the best condition. Trypsin activity was influenced little by shrimp condition and more by the amount of food ingested. The gonadosomatic index (GSI) and R/D ratio in the gonads provided offsetting information about the instantaneous gonad maturity. The Goheung population had the highest instantaneous GSI, despite some spawning. Based on the condition indexes and time of gonad maturation, the Goheung shrimp population is suitable for use as breeding stock.

• Journal of Aquaculture
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• v.22 no.1
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• pp.34-41
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• 2009

Gonadal development and reproductive cycle of the granular ark Tegillarca granosa were investigated by histological observations. Samples were collected monthly from January to Decemberry 2002 in the Yeoja Bay of Yeosu, Jeollanam-do, Korea. T. granosa was dioecious. The gonads consist of a number of oogenic follicle and acinus. Monthly changes in the gonad index reached a maximum in June and a minimum in August. Monthly changes in the condition index reached a maximum in July and a minimum in September. The reproductive cycle of this species can be divided into five successive stages: early active stage (March to May), late active stage (April to June), ripe stage (May to July), spent stage (July to August) and recovery and resting stage (September to March). The spawning of T. granosa occurred in July and August in Yeoja Bay. The sex ratio of female to male was not significantly different from 1:1.

• Fisheries and Aquatic Sciences
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• v.1 no.1
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• pp.82-93
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• 1998

Monthly changes of the gonad follicle index (GFI), reproductive cycle, egg-diameter composition, first sexual maturity of the Pacific oyster, Crassostrea gigas, were studied based on the samples which have been collected from the intertidal zone of Poryong west coast of Korea, from January to December, 1996. C. gigas, is dioecious, while a few individuals are alternatively hermaphroditic. Monthly variation of gonad follicle index (GFI) used for determination of spawning period, coincided with the reproductive cycle. GFI increased from April when seawater temperatures gradually increased and reached the maximum in May. And then, GFI sharply decreased from June to September due to spawning. Reproductive cycle of this species can be divided into five successive stages: in females, early active stage (March to April), late active stage (April to May), ripe stage (May to August), partially spawned stage (June to September) and spent/inactive stage (September to February); in males, early active stage (February to March), late active stage (April to May), ripe stage (May to September), partially spawned stage (June to September) and spent/ inactive stage (September to February). The diameter of fully mature eggs are approximately 50um. Spawning occurred from June to September, and two spawning peaks were observed in June and August when the seawater temperature was above $20^{\circ}C$. Percentages of the first sexual maturity of males of 20.1-25.0 mm in shell height were over $50\%$, while those of females of 25.1-30.0 mm in shell height were over $50\%$. All the males of > 30.1 mm and all the females of ^gt; 35.1 mm completed their first sexual maturity. The results suggest that C. gigas has a protandry phenomenon. Sex ratios of 919 oysters observed were 453 females $(49.29\%)$, 429 males $(46.68\%)$, 16 hermaphrodites $(1.74\%)$, and 21 indeterminate individuals $(2.29\%)$. In age class I, sex ratio of males were $64.00\%$, thus, a higher percentage than that of females. It was noted that $64.00\%$ of the young males (age class I) were more functional than females in age class I, but 2-3 year-old oysters showed higher percentage of females. Percentages of hemaphrodites in 2-3 year classes were relatively higher than those in other year classes. Histological pattern of hermaphrodites can be divided into two types: Type I (hermaphrodite having a number of newly formed developing oocytes on the oogenic tissues within a degenerating spermatogenic follicle after discharge of numerous spermatozoa) and Type II (hermaphrodite having two separate follicles in the same gonad).