• 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.

• Animal cells and systems
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• v.5 no.1
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• pp.37-44
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• 2001

Gonadal development, reproductive cycle, gonad index, meat weight rate, and first sexual maturity of the top shell, Omphalius rusticus were Investigated monthly by histological observations. Specimens were collected from the west coast of Korea during the period from January to December in 1999. O. rusticus is dioecious and oviparous. The gonad is widely situated on the surface of the digestive g1and located in the posterior spiral meat part in the shell. The ovary and the testis were composed of a number of oogenic follicles and several spermatogenic follicles, respectively. Ripe oocytes were approximately 120-130 $\mu$m in diameter. The meat weight rate peaked in June (27.7%), and then rapidly decreased in September (19.5%). Monthly changes in the gonad index in both sexes reached the maximum in June, and then sharply decreased in September. Percentages of first sexual maturity of female and male snails ranging from 9.0 to 9.9 mm in shell heights were 58.3% and 54.5%, respectively, and 100% in those over 11.0 mm in both sexes participated in reproduction. Reproductive cycle of this species can be categorized into five successive stages: in females, early active (October to April), late active (December to June), ripe (April to September), spawning (July to September) and recovery (September to January): in males, early active (November to March), late active (December to June), ripe (April to September), spawning (July to September) and recovery (September to December). Gonadal development, gametogenesis, reproductive cycle, and spawning were closely related to the seawater temperature.

• The Korean Journal of Malacology
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• v.24 no.2
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• pp.97-104
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• 2008

The gonad index, reproductive cycle and first sexual maturity of Sinonovacula constricta collected from Simpo, Kimje-gun, Korea were investigated by histological analysis. The gonad index(GI) in both sexes of S. constricta increased from April and reached a maximum in July when the water temperature rapidly increased. And then, the GI values gradually decreased by spawning from August through October. Monthly variations in the GI showed a close relationship with ovarian development. The reproductive cycle in females and males can be classified into five successive stages: early active stage(March to June), late active stage(May to July), ripe stage(July to September), partially spawned stage(August to October), spent/inactive stage(October to March). The percentage of first sexual maturations in female and male clams of 50.1-60.0 mm in shell length was over 50%, and for clams over 70.1 mm in shell length, it was 100%. Because harvesting clams < 50.1 mm in shell length could potentially cause a drastic reduction in recruitment, a measure including a prohibitory fishing size should be taken for adequate improved fisheries resource management.

• Animal cells and systems
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• v.3 no.4
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• pp.375-383
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• 1999

Gonadal development, gametogenesis, reproductive cycle, and first sexual maturity of Reishia clavigera were investigated monthly from July 1998 to June 1999 through cytological and histological observations. R. clavigera had separate sexes, and was an internal fertilizer. The ma1e penis was located near the two tentacles. The ovary and testis were composed of a great number of oogenic lobules and spermatogenic tubules, respectively. The size of ripe oocyte ranged from 130 to 140 ${\mu}$m in diameter. The peripheral cytoplasm of the germinal vesicle of the ripe oocyte in many cases were surrounded by smaller yolk granules, while the eccentric cytoplasm was occupied with larger ones. The reproductive cycle of R. clavigera could be classified into five successive stages: early active, late active, ripe, spawning, and recovery. Spawning of females occurred from early July to August when the seawater reached above 24.8$^{\circ}C$. Spawning of males occurred from early June to August in the water above 22.8$^{\circ}C$. Minimum size for sexual maturity of both sexes was above 10.0 mm in shell height. Each egg capsule was a cylinder or spindle in shape, 4-6 mm in length and 1-2 mm in width. Colors of newly spawned egg capsules showed yellowish white or pale yellow, while those with veliger larvae showed pale black, and released larvae or dead egg capsules showed black violet. The fecundity in an egg capsule ranged from 70 to 91 eggs (mean＝80.28 eggs).

• 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.55 no.6
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• pp.927-937
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• 2022

The reproductive characteristics of Pacific anchovy, Engraulis japonicus were investigated using samples randomly collected from the southern waters of Korea between January and December 2021. We analyzed monthly changes in maturity stages, gonadosomatic index (GSI), egg diameter, fecundity, and fork length (FL) at sexual groups maturity of 50%, 75% and 97.5%, and sex ratio (female:male). GSI value showed two peaks in May and August; however, microscopic analysis of E. japonicus gonad tissue revealed that the spawning period was from March to October. The main spawning seasons for the entire populations were from April to June and August to September. The overall sex ratio was female-biased (1 females, 0.89 male). The fecundity (F) of female anchovies ranged from 429 eggs at an FL of 8.0 cm to 13,824 eggs at an FL of 14.9 cm and the relationship between FL and F was 0.0788FL^4.422. The FL at 50% group maturity was 8.26 cm for female anchovies. Based on the results, we suggest that the reproductive cycle in Pacific anchovies may be related to pulses in water temperature and the sexual cycle of the fish.

• Fisheries and Aquatic Sciences
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• v.26 no.4
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• pp.256-267
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• 2023

The suitability of any fish species for successful aquaculture requires basic information on its reproduction and growth. This study investigated some facets of the reproductive biology of Synodontis shall (Mochokidae) from River Siluko in Nigeria. Fish samples were collected forth-nightly for a duration of fourteen (14) months-March 2015 to April, 2016 with the assistance of artisanal fishermen. Fishes were identified using taxonomic guides and standard techniques were used for determination of sex ratio, gonad maturation and fecundity. Linear regression method was used to define the correlation between fecundity and fish length, body weight and ovary weight. Results showed that sex ratio did not indicate a significant divergence (p > 0.05) from the 1 male to 1 female distribution ratio (1:1.41). Gonad morphology revealed paired gonads. Testes and ovaries were classified into four maturity stages: immature, resting, ripening and ripe. Gonadosomatic index ranged from 0.04 to 5.68 (males) and 0.03 to 20.19 (females). Absolute fecundity ranged from 1,014 to 4,520 eggs (mean = 2,592 eggs) and did not correlate significantly (p > 0.05) to ovary weight. This study has contributed to existing data on the biology of freshwater fish species in Nigeria and provided valuable information for fishery management tools in the conservation and utilization of this valuable freshwater fish species.

• 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.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.52 no.5
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• pp.496-510
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• 2019

We investigated the reproductive characteristics of the sweetfish Plecoglossus altivelis, including changes in the gonadosomatic index (GSI), frequency of gonad developmental stages, and abundance of drifting larvae, in three streams (Gangjeong, Yeonoi, and Ongpo) on Jeju Island from May 2004 to December 2005. The GSI values of female P. altivelis in all Jeju streams began to increase in September and reached a maximum in October and November. Peak GSI values in males occurred in Gangjeong from October to November, in Yeonoi from November to January, and in Ongpo from September to October. The gonadal development of P. altivelis was classified into four stages: growth (March to October), maturity (September to December in females; July to December in males), spawning (September to January), and degeneration (October to March in females; after November in males). Drifting larvae were collected from October to January. These results suggest that the main spawning activity of P. altivelis in Jeju streams occurs from October to November. The information about the reproductive characteristics of P. altivelis obtained in this study is critical to fishery management for this species.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.57 no.1
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• pp.53-59
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• 2024

The reproductive biology of the Washington clam Saxidomus purpuratus, from Yeosu, Korea was investigated based on 699 individuals collected from January to December 2022. The sex ratio of this species was not significantly different from a 1:1 (male:female) sex ratio (P>0.05). Monthly changes in gonadosomatic index were analyzed to estimate the spawning season. The reproductive cycle of this species can be divided into the following stages: active (Jan.-Mar.), ripe (Mar.-Nov.), spent (Apr.-Dec.), and degenerative (Jun.-Dec.) stages. The spawning period ranged from March to December with the main periods being from April to June and from September to November. The shell length at 50% female group maturity (SL₅₀) was estimated to be 60.2 mm.