• Korean Journal of Fisheries and Aquatic Sciences
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• v.53 no.1
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• pp.19-26
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• 2020

The maturity and spawning of pacific sand eels Ammodytes japonicus, was investigated using samples collected by gill net in coastal waters near Donghae, Gangwon-do, from January 2017 to December 2018. Monthly changes were analyzed in maturity stage, gonadosomatic index (GSI), egg diameter, fecundity (F), and total length (TL) at 50% group maturity. The average TLs of female and male A. japonicus were 18.5 and 18.1 cm, respectively. The spawning period was from November to March, with the peak from December to February based on monthly changes in GSI and maturity stages. The egg diameter during the spawning-capable stage was 300-1000 (main mode 500-600) ㎛. Fecundity ranged from 6,411 eggs at 16.7 cm fork length to 45,771 eggs at 24.7 cm fork length. The relationship between TL and F was F=0.00005TL^4.2715 (R²=0.7216), such that F increased with TL. TL at 50% group maturity was estimated to be 15.1 cm for both sexes.

• The Korean Journal of Malacology
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• v.22 no.1 s.35
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• pp.39-49
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• 2006

Ultrastructure of germ cell differentiation during supermatogenesis and the reproductive cycle in male Patinopecten yessoensis was studied by histological and cytological observations. The gonadosomatic index (GSI) in males rapidly increased and reached a maximum in April when seawater temperature gradually increased. Then the GSI gradually decreased from May through July when spawning occurred. Accordingly, monthly changes in the GSI in males coincided with testicular maturation and spawning periods. The sperm morphology of P. yessoensis belongs to the primitive type and showed general characteristics of external fertilization species. The head of the spermatozoon is approximately $3.50{\mu}m$ in length: the sperm nucleus and acrosome are approximately $2.90{\mu}m\;and\;0.60{\mu}m$ in length, respectively. The nuclear type of the spermatozoon is vase in shape, and the acrosome is cone type. The axoneme of the tail flagellum consists of nine pairs of microtubules at the periphery and a pair of central microtubules in the center The satellite body (which is formed by the centriole) and four mitochondria appear in the middle piece of the spermatozoon. The spawning period was from April through July and the main spawning occurred from May to June when seawater temperatures gradually increased. The reproductive cycle of this species can be classified into five successive stages; early active stage (September to November), late active stage (October to March), ripe stage (February to August), spawning stage (April to July), and spent/inactive stage (July to November).

• Korean Journal of Fisheries and Aquatic Sciences
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• v.42 no.3
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• pp.297-301
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• 2009

The water temperature from 1980 to 2000 and the anchovy catch from 1990 to 2000 in the southeastern portion of the South Sea of Korea were used to illustrate the influence of water temperature on the catch of the anchovy, Engraulis japonica. 1993 and 1998 were selected as poor and good fishing years therefore, the horizontal and vertical distribution of water temperature and catch per unit effort in these years was compared. When the anchovy catch was lower, the water temperature at 10 m was also about $0-2^{\circ}C$ lower than during a normal year, which resulted in the formation of a weak thermocline. Conversely, when the anchovy catch was higher, the water temperature at 10m was $0-2^{\circ}C$ greater than during a normal year, which resulted in the formation of a strong thermocline at around 20 m.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.38 no.4
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• pp.245-250
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• 2005

The maturity and spawning of Pacific cod, Gadus macrocephalus, was studied using samples caught by gillnets in the East Sea from January to December 2003. Monthly changes of maturity observed with the naked eyes for females showed that maturing Pacific cod appeared from August, and their numbers increased to $83\%\;and\;100\%$ in November and December, respectively. In January, mature and spawning Pacific cod were observed for the first time and composed over $40\%$ of the population. In February, the proportion of spawning individuals increased to over $50\%$, however, the mature individuals decreased to less than $10\%$. In March, mature fish were not found, and all were in an immature (spent) or spawning state. From April to July all fish remained in immature condition. The males maintained this trend with the females, whereas, mature males appeared from November to March. Monthly changes in the gonadosomatic index (GSI) of females and males showed higher values both in January and February and declined sharply in March. The lower value remained until October and then began to increase from November for the female population. For the males, however, this value remained lower until August, and then began to increase from September, and showed higher values in October through December than in January and February. These results indicated that the spawning season of Pacific cod was from December to March, and the main spawning season was from January to February, and the period of the spawning season was longer for males than the females. The diameter of the matured oocytes was 0.80-1.10 mm with a single mode of 0.95 mm. Fecundity was 1,300,000-9,400,000 in total length of 65-95 cm and the relationship between the total length (TL, cm) and fecundity (Fc) was Fc= $180,248\timesTL-10,883,638$. The total length at first maturity was observed at 57 cm for females and 47 cm for males. The size at $50\%$ group maturity was estimated to be 63.9 cm for females and 56.0 cm for males.

• Korean Journal of Ichthyology
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• v.20 no.4
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• pp.263-271
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• 2008

The maturity and spawning of Korean flounder Glyptocephalus stelleri were investigated using samples randomly collected in the East Sea of Korea from May 2005 to September 2008. Gonadosomatic index began to increase in December and reached a maximum between March and May. After spawning it began to decrease from June. The spawning period was March to June, and the main spawning period was April to May. Annual reproductive cycles of this species can be divided into four successive stages; immature stage (July~November), maturing stage (December~February), mature stage (March~April) and spent stage (May~June). The fecundity ranged from 15,146 eggs at 24.1 cm (TL) to 101,491 eggs at 38.1 cm (TL). The relationship between total length (TL) and fecundity (F) can be expressed as $F=0.0004TL^{3.449}$ ($R^2=0.663$), with F increasing with TL. The TL at 50% group maturity ($TL_{50%}$) was estimated to be 25.6 cm.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.57 no.1
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• pp.78-91
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• 2021

This study analyzed the reproductive biology, fishing characteristics and changes in fishing business of Liparis tanakae, snailfish collected from September to March. It was the period when they were mainly caught from 2018 to 2020. The average length was generally small in September and October and was large in January and February. The average body weight was generally around 1,500 g and the average body weight in autumn was lower and in winter was higher. The sex ratio of male and female was 0.40:0.60 (��2 test, p < 0.05). The spawning period was estimated from October to February and the main spawning period was from December to February through the GSI. The egg diameter of matured staged female L. tanakae was 0.11-1.48 mm, which was the main spawning period and the relationship between body weight and fecundity was F = 1849TL0.1093 (r2 = 0.2401). The monthly catch of L. tanakae was high from November to February, the time of migrating to the coastal area. Coastal gillnet fishery showed the highest percentage of all fisheries catching Liparis spp. Liparis spp. were caught at a high rate in winter in Chungnam, Jeonbuk, Jeonnam and Gyeongnam region, and revenue and cost was increased since 2017. Assuming a situation where there is no catch of Liparis spp., the fishing profit that can be obtained was the highest in Gyeongnam region and the dependence on fishing of Liparis spp. by coastal gillnet fishery was high.

• The Korean Journal of Malacology
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• v.26 no.4
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• pp.261-265
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• 2010

Reproductive biology of the purplish Washington clam, Saxidomus purpuratus was investigated based on the samples captured in Jinhae Bay, the East China Sea from January to December 2002. The gonad index (GI) began to increase in January, reached the maximum value in March. The reproductive cycle of this species can be divided into five successive stages: the early active stage (from November to January), the late active stage (from December to February), the ripe stage (from February to May and October), the spawned stage (from May to December), and inactive stage (from November to December). The spawning period was from April to December, and the main spawning occurred between June and August. The shell length at 50% group maturity was estimated to be 71.85 mm. The Sex ratio of this species was not significantly different a 1:1 sex ratio (P > 0.05).

• Fisheries and Aquatic Sciences
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• v.10 no.2
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• pp.74-85
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• 2007

Pacific anchovy (Engraulis japonicus) eggs were collected during the spawning season (2000-2003) using a revised ring net in the coastal waters adjacent to the Geum River Estuary in the West Sea of Korea (Yellow Sea). Anchovy eggs were present from May to September, showing a peak in spawning from June to July when the water temperature and salinity were $17-27^{\circ}C$ and above 30.00 psu, respectively. During the main spawning season, no clear diel cycle (regarding the 24-h sampling period of dusk, night, dawn, and daytime) was detected in the vertical distribution of anchovy eggs near Eocheong Island (50-60m depth). Judging from the developmental stages of the collected eggs, it appeared that anchovies spawned mostly at night and that the eggs hatched at dusk and during the night. The density of anchovy eggs was high in the southwest-northeast direction in June, and spawners appeared to move offshore in July. Mean egg density was higher in June 2002 than in June 2003 when water temperatures and salinities were lower. This study on the spatiotemporal distribution of eggs will contribute to developing management plans for the Pacific anchovy in Korea.

• Korean Journal of Ichthyology
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• v.22 no.2
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• pp.83-89
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• 2010

We studied the maturity and spawning of Marbled sole Pleuronectes yokohamae from May 2006 to April 2007 in the Southern Sea of Korea. We analyzed monthly changes in maturity stages, gonadosomatic index (GSI), egg diameters, fecundity (F), total length (TL) at 50% group maturity, and sex ratio. The spawning period was November to February, and the main spawning period was December to January. The fecundity ranged from 75,155 eggs at 17.8 cm(TL) to 1,307,195 eggs at 36 cm (TL), and the relationship between TL and F was $F=3.656TL^{3.518}$ ($R^2$=0.872). The TL at first maturity was 17.8 cm and at 100% maturity, 32 cm. Thus, TL at 50% group maturity was estimated to be 19.8 cm. For sex ratio by length class, males were slightly predominant at sizes under 25 cm TL, but females were 100% at greater than 32 cm TL.

• Korean Journal of Ichthyology
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• v.18 no.4
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• pp.363-367
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• 2006

The maturity and spawning of brown sole, Pleuronectes herzensteini were investigated using samples randomly collected in the East Sea of Korea from April, 2003 to March, 2004. We analyzed monthly changes in maturity stages, gonadosomatic index (GSI), egg diameter, fecundity (F), total length (TL) at 50% group maturity, and sex ratio. The spawning period was February to May, and the main spawning period was March to April. The fecundity was 38,702 eggs at 22 cm (TL) to 133,085 eggs at 37 cm (TL), and the relationship between TL and F was $F=11.307TL^{2.628}$. The TL at first maturity was 15 cm and at 100% maturity, 21 cm. Thus, TL at 50% group maturity was estimated to be 17.8 cm, which corrensponded to the age of 3 years. The sex ratio was 60.2 for female and 39.8 for male, where the female population was seen to be slightly predominant.