• Journal of the Korean Society of Marine Environment & Safety
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• v.17 no.4
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• pp.367-373
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• 2011

We investigated the biological characteristics of the squid, Todarodes pacificus Steenstrup through the samples caught monthly in the Yellow Sea($32^{\circ}$ 30'N, $122^{\circ}E-37^{\circ}$ 30'N, $127^{\circ}E$) from 1985 to 1987. Monthly mantle length frequency were separated into Autumn spawning group and winter spawning group with Tanaka's method(1956) to determine the main group of the squids caught in the Yellow Sea. The ratio of winter spawning group was higher than that of autumn spawning group. Monthly gonadosomatic index of females increased on July in 1985, on October in 1986, and October in 1987 and decreased later in each year. That of males increased on June in 1985, on July in 1986, and June in 1987. The length of 50% group maturity of female was 20.7 cm mantle length(ML) in 1985, 17.9 cm ML in 1986, and 17.2 cm ML in 1987. The ratio of female was higher than that of male in the group over 24 cm ML, and the ratio of male was higher than that of female in the group under 24 cm ML. We concluded that the length of 50% group maturity of squids was affected by the density of the population status.

• The Korean Journal of Malacology
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• v.25 no.2
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• pp.127-133
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• 2009

The common octopus, Octopus vulgaris is commercially important species in Korea. Korean fishing vessels have actively caught it. However, the study of this species has been poorly known. Therefore, the purpose of this study is to provide information about maturation and spawning period of this species. Samplings have been monthly collected in Tongyoung and Sacheon of Gyeongsangnam-do, using traps. A total of 748 individuals were sampled from February 2007 to January 2008. We analyzed monthly changes in maturity stages, gonadosomatic index, total weight at 50% group maturity. The octopus total weight was between 128.6 and 3381.4 g. Females were distributed between 129.8 and 3381.4 g and males between 128.6 and 2378.4 g. The spawning periods were May to June and September. The total weight at 50% group maturity was estimated to be 919.6 g.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.48 no.5
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• pp.739-744
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• 2015

The sexual maturation and spawning time of female ocean sunfish Mola mola in Korean waters were studied by observing the gonads histologically. Specimens were purchased in a fish market in October 2013 and May, June, and October 2014. Nine females (total length 100-250 cm, gonad weight 31-3,470 g) and one male (total length 131 cm, gonad weight 60 g) were studied. Histologically, the ovaries became active in May and spawning began in July and continued until October. In July, mature oocytes and yolk globule stage oocytes were observed; parts of the gonad showed traces of spawning, while others had degenerated and absorbed any oocytes. By October, many oocytes had degenerated and been absorbed. Therefore, the approximate spawning period of ocean sunfish is from July to October based on histological changes in the gonads. The asynchronous oocyte development suggests that the ocean sunfish is a multiple spawner, as reported previously. The catch distribution data suggest that the waters around Jeju Island are a sunfish spawning area.

• Korean Journal of Ichthyology
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• v.23 no.2
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• pp.111-118
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• 2011

The maturation and spawning of filefish, Stephanolepis cirrhifer were investigated using samples randomly collected in the East Sea of Korea from August 2009 to July 2010. The total length at 50% group maturity of filefish was estimated to be 11.7 cm. Based on monthly changes in maturity stages and gonadosomatic index (GSI), the spawning period was estimated to be from June to September, and the peak spawning from August to September. The fecundity (F) ranged from 693,981 eggs to 7,383,429 eggs at 23.6 cm between minimum and maximum total length (TL) 13.3 cm and 23.6 cm respectively. The relationship between TL and F was expressed as F=$12.19TL^{4.208}$ ($R^2$=0.727). The sex ratio of male to female was 1 to 0.9.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.53 no.1
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• pp.103-106
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• 2020

We investigated the biological maturation of blackthroat seaperch Doederleinia berycoides in southern Korea waters, based on samples collected from March 2018 to February 2019. We analyzed monthly changes in maturity stage, gonadosomatic index (GSI) and total length (TL) at 50%, 75% and 97.5% group maturity. The spawning period was May to October in 2018. We estimated the TL at 50% group maturity as 27.0 cm for females in 2018. We estimated the TL of females at 75% and 97.5% group maturity as 28.7 cm and 32.7 cm, respectively, in 2018.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.39 no.6
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• pp.472-479
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• 2006

The sexual maturity and reproductive cycle of the common squid, Todarodes pacificus captured from the East Sea, Korea, between January 2004 and January 2006, were investigated by documenting changes in the gonadosomatic index (GSI), gonad development, and oocyte size frequency distribution. The GSI of females began to increase in July, reached a maximum in August, and then gradually decreased. The GSI of males increased from July to March. Using gonad histological observations, we identified four oocyte developmental stages. The changes in GSI and gonad tissue resulted in the classification of the annual reproductive cycle into the following four successive stages: immature (April to June), growing (June to July), mature (July to August), and ripe and spawning (August to March). According to the oocyte diameter size frequency distribution in the ovary, this species appeared to have asynchronous oocyte development and one spawning time.

• Korean Journal of Ichthyology
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• v.36 no.3
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• pp.209-219
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• 2024

A survey was conducted in 2011 to investigate the reproductive ecology and spawning behavior of the natural monumental and endangered species, Cobitis choii. C. choii exhibits sexual dimorphism with the development of lamina circularis on the second pectoral fin ray in males at one year old, facilitating easy differentiation between males and females. A total of 1,288 females and 881 males were collected from January to December, resulting in a sex ratio of 1 : 0.68. The spawning season was estimated to be from late June to early July (spawning peak from late June, with water temperatures ranging from 22 to 25℃), coinciding with a sharp decrease in the condition index. Gonadal maturity was observed with maturity indices of 17.5±2.11% for females and 2.9±0.46% for males, with fecundity of 2,444±838 eggs and egg size of 0.75±0.05 mm. Spawning behavior was induced by hormone injection (Human Chorionic Gonadotropin, HCG) in laboratory conditions. Experimental results revealed that males and females paired in a 1 : 1 ratio before spawning. Males pressed the abdomen of females using their lamina circularis to induce spawning, followed by immediate fertilization. Spawning behavior was repeated 15 to 25 (average 20) times per pair of males and females, and 80 to 120 eggs were spawned per time, and the total amount of spawned eggs were 2,500±250 on average.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.41 no.4
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• pp.253-260
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• 2008

Gonadal development, gametogenesis, reproductive cycle, spawning, relative weight of flesh, and onset of sexual maturity of the murex shell, Ceratostoma rorifluum, collected from the rocky intertidal zone of Daehang-ri, Buan-gun, Jeollabuk-do, Korea were investigated monthly from January to December 2005 both cytologically and histologically. The gonads were widely placed on the digestive gland located in the posterior spiral fleshy part in the shell. C. rorifluum had separate sexes, and was an internal fertilizer. The sex ratio of females to males was approximately 1:1. The ovary and testis contained a great number of oogenic follicles and spermatogenic tubules, respectively. The oogonia and fully ripe oocytes were $15-19{\mu}m$ and $150-160{\mu}m$ in diameter, respectively, and the cytoplasm of the ripe oocytes contained a number of yolk granules. The relative weight of flesh reached a maximum in August($39.35{\pm}0.40%$), and then decreased rapidly in November($32.75{\pm}1.20%$). The percentages of female and male snails at first sexual maturity with shell heights ranging from 12.1-14.0 mm were 60.0% and 52.9%, respectively, while 100% of the snails of both sexes with shell heights over 18.1 mm were reproductively active. Based on the gonadal development and histological observations, the reproductive cycle of the snail could be categorized into five successive stages: early active(December to May), late active(March to July), ripe(June to September), spawning(July to October), and recovery(October to March). C. rorifluum spawned once a year between July and October, and the majority of spawning occurred in September when the seawater temperature exceeded $23.5^{\circ}C$.

• The Korean Journal of Malacology
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• v.21 no.2 s.34
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• pp.95-105
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• 2005

Gonadosomatic index, reproductive cycle, spermatogenesis and first sexual maturity of Chlamys farreri were investigated by cytological and histological observations, from January 1998 to December 1999. The gonadosomatic index (GSI) rapidly increased in April and reached a maximum in May when seawater temperature rapidly increase. Then the GSI gradually decreased from June to August when spawning occur. Accordingly, monthly changes in the GSI in males coincide with the reproductive cycle. The spermatozoon of Chlamys farreri is the primitive type found in external fertilization species. The head of the spermatozoon is approximately $2.75{\mu}m$ in length including the acrosome measuring about $0.50{\mu}m$ in length, and its tail was approximately $20{\mu}m$, the axoneme of the tail flagellum consists of nine pairs of microtubules at the periphery and a pair at the center. Five spherical mitochondria around the centriole (the satellite body) appear in the middle piece of the sperm. The spawning period was from June to August and the main spawning occurs from July to August when seawater temperatures are greater than $20^{\circ}C$ The reproductive cycle of this species can be categorized into five successive stages; early active stage (January to March), late active stage (March to April), ripe stage (April to August), partially spawned stage (June to August), and spent/inactive stage (August to January). Over 50% of male scallops attained first sexual maturity between 50.0 and 60.0 mm in shell height, and 100% of those over 60.0 mm in shell height achieved maturity. Accordingly, we assume that male individuals begin reproduction at three years of age.

• 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).