• The Korean Journal of Malacology
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• v.22 no.2
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• pp.143-150
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• 2006

The gonad index, condition index, reproductive cycle and spawning of the pen shell Atrina (Servatrina) pectinata were investigated using samples from the subtidal zone of Nokdo on the Boryeong coastal waters of Korea. Samples were collected monthly by SCUBA divers for one year from January to December, 2001. A. (Servatrina) pectinata is dioecious and oviparous. The spawning season of this species occurred once a year from June to August, with the main spawning occurring between June and July when the seawater temperature was around $20^{\circ}C$. Ripe oocytes were about 60-65 ${\mu}m$ in diameter. The reproductive cycle of this species could be classified into five successive stages; early active stage (November to March), late active stage (February to May), ripe stage (April to July), partially spawned stage (June to August), and spent/inactive stage (August to October). Monthly changes in the gonad index reached a maximum (4.6) in May (ripe stage), thereafter, the GI values gradually decreased from June to August when spawning occurred continuously. Therefore, monthly changes in the GI values showed a similar pattern to the gonadal phase. The condition index (CI) of the meat part without the posterior adductor muscle reached the maximum in June (ripe and partially spawned stage) and the minimum in September (spent/inactive stage), Accordingly, monthly changes in the condition indice of the meat part without the posterior adductor muscle coincided with the gonadal phases.

• The Korean Journal of Malacology
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• v.27 no.3
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• pp.261-271
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• 2011

The gametogenic cycle, the spawning season and the biological minimum sizes in female and male Protothaca (Notochione) jedoensis were investigated by quantitative statistical analysis. In females, monthly changes in the percents of the follicle areas to the ovarian tissue areas and the percents of the oocyte areas to the ovarian tissue areas increased in February and reached the maximum in April, and then gradually decreased from May to July, with the spawning peak between June and July. In males, monthly changes in the percents of the testicular tissue areas to total tissue areas and the percents of the spermatogenic stage areas to the testicular tissue areas increased in February and reached the maximum in April, and then showed a rapid decrease from May to July. From these data, it is apparent that the number of spawning seasons in female and male P. (N.) jedoensis occurred once a year, from May to July. Therefore, P. (N.) jedoensis in both sexes showed a unimodal gametogenic cycle during the year. Compared the gametogenic cycle by quantitative statistical analysis in 2007 with the previous qualitative results of this species, the results of the gametogenic cycle calculated by quantitative statistical analysis showed some differentiations in the spawning seasons evaluated by the gonad index by qualitative histological analysis. The intervals of the beginning of two spawning seasons showed one month between the results of quantitative and qualitative analyses. The biological minimum sizes (considering to 50% of group sexual maturity) in female and male clams by quantitative analysis of this species are 32.01 mm in shell length in females and 30.58 mm in males, respectively. According to the mean shell length fitted to von Bertalanffy's equation, 30.58 and 32.01 mm in shell length were considered to be two years old. Therefore, we assume that both sexes of this population begin reproduction from two years of age.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.9 no.4
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• pp.251-255
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• 1976

Three hundred and sixty two specimens of Plecoglossus altivelis were randomly sampled from Chunji Stream in Seogwipo, Cheju-Do, during the period from 25 Aug., 1973 to 14 Feb., 1974 to investigate the relationship between total length and dody weight as well as the condition factor during the spawning period. Results obtained are summarized as follows : The relationships between total length and body weight are calculated as below, respectively : $W=0.008639\;L^{3.1806}$ : Prior to spawning period $W=0.01830\;L^{2.7689}$ : During spawning period The above equations differ each other significantly. Nevertheless, the significant difference is not found between sexes. The mean body length decreased during the spawning season. The fact seems to be caused by the death of large fish after spawning. The condition factor was $13.45\%_{\circ}$ on the average in August. The value decreased continuously from September, giving the minimum mean value of $10.25\%_{\circ}$ on Nobember 29. But the value increased again, showing $11.18\%_{\circ}$ in next February. Majority of the fish survived until next year was small ranging from 11 to 12cm in total length.

• The Korean Journal of Malacology
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• v.26 no.3
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• pp.245-254
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• 2010

For the studies of germ cell development and maturation in the ovary, the gametogenic cycle and the number of spawning seasons per year in female Ruditapes philippinarum were investigated by quantitative statistical analysis using an Image Analyzer System. Compared with the results by qualitative and quantitative analyses, monthly variations in female gonad indice by qualitative histological analysis showed a pattern similar to that of the female gametogenic cycle calculated by quantitative statistical analysis. The number of spawning seasons occurred once per year, from June to October. In quantitative statistical analysis using an image analyzer system, monthly changes in the portions (%) of the ovary area to total tissue areas in females increased in March and reached a maximum in May, and then showed a rapid decrease from June to October when spawning occurred. And also monthly changes in portions (%) of follicle areas to the ovary area and in portions of oocyte areas to ovarian tissue areas in females began to increase in March and reached a maximum in May, and then. rapidly dropped from June to October when spawnig occurred. From these data, it is apparent that the number of spawning seasons occurred once per year, from June to October. Monthly changes in the number of the oocyte per $mm^2$ and in mean diameter of the oocyte in captured image which were calculated for each female slide showed a maximum in May and reached the minimum from December to February. Therefore, female R. philippinarum showed a unimodal gametogenic cycle during the year.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.56 no.5
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• pp.667-675
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• 2023

The Spanish mackerel Scomberomorus niphonius is an economically important fish species in the southwestern waters of Korea. This study aimed to provide insights into the reproductive biology of this species in the southwestern waters of Korea. We analyzed monthly changes in fork length (FL), maturity stages, and gonadosomatic index (GSI). Moreover, we measured the in FL at sexual group maturity of 50%, 75%, 97.5%, and sex ratio (female vs. male). The overall sex ratio of female and male was 1:0.8. GSI value showed the highest peak in May; however, the spawning period revealed by the microscopic analysis of gonad tissue of S. niphonius was from April to August 2020. The main spawning seasons for the entire populations was from May to June. The fork length at 50% group maturity was 53.3 cm for females and 53.1 cm for males. These results of spawning period of Spanish mackerel highlight the influences of water temperatures that were higher than those in the past, an increase in resource levels, and the level of Pacific anchovy resources flowing into the spawning ground.

• Journal of Aquaculture
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• v.12 no.3
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• pp.197-204
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• 1999

Successful produciton of seedlings for marine fish species are highly influenced by the aquisiton of sufficient number of good-quality eggs on required time. human chorionic gonadotropin has been used to induce successful ovulation for the purpose. Rabbitfish, siganus canaliculatus, is inhabited along the coast of Cheju Province and treated valuably for raw fish and fish roasted with seasoning. Female wild-captured rabbitfish (314 to 279 g in body weigth) were injected into intraperitoneal space with human chorionic gonadotropin (HCG) of 5,00,1,000, and 1,500 IU/kg body weight during spawning season of July 14 (trial 1), and July 27 (trial 2). Test fish in trial 1 were injected two times, first on July 14 and second on July 21 with one weekinterval because of no ovulation symptoms, but just one time in trial 2. All females injected both 1,000 and 1,500 IU/kg body weight ovulated in all trials. Among 500 IU/kg injection treatments, just one female ovulated in trial 1 showing 25% of ovulation rate, but none ovulated in trial 2. Ovulation was not occurred in control goups during test period. Time to reach ovulation after injection was 172 to 270 hours in trial 1 and 77 to 132 hours in trial 2, showing shorter as spawning season approached. Generally, ovulation of smaller females were late than that of larger ones. Gonadosomatic index (GSI) and pseudo-gonadosomatic index (Pseudo-GSI) were ranged 22 to 33% and 19 to 28%, respectively. One female spawned 406,200 to 1,032,000 eggs, and obtainable eggs per 100g of body weight were calculated by 130,000 to 190,000. Spawning rates were comparatively high by 96.0 to 98.4%. Rates to reach embryo-formation and hatching were higher in 500 high by 96.0 to 98.4%. Rates to reach embryo-formation and hatching were higher in 500 and 1,000 IU/kg treatments than in 1,500 IU/kg treatment. The result of present study demontrates that HCG treatment during spawning season could become very useful for ovulation of rabbitfish and the suitable dosage was suggested as 1,000 IU/kg of body weight.

• Journal of Aquaculture
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• v.16 no.3
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• pp.179-186
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• 2003

Reproductive cycle, gonadal development and the spawning period of the Korean anchovy Coilia nasus were investigated by histologhical observations. Samples were collected at the coastal area of Geumgang dyke which is connected to Gunsan and Janghang, Korea, from February 2002 to January 2003. C. nasus is dioecious; the ovary consists of a pair of saccular structure with many ovarian lobules, and the testis consists of a pair of lobular structure with many testicular lobules and connected to the posterior seminal vesicle. Monthly changes in the gonadosomatic index (GSI) began to increase in April when seawater temperature increased and reached the maximum in June when the ovary was getting mature, the summer season of longer day length with higher water temperature. The reproductive cycle can be classified into five successive stage in females: early growing stage (February to March), late growing stage (March to April), mature stage (May to June), ripe and spent stage (June to July), and recovery and resting stage (July to January): in males, the cycle can be divided into four successive stages; growing stage (February to April), mature stage (May to July), ripe and spent (June to July), and recovery and resting stages (July to January). According to the frequency distributions of egg diameters in the spawning season. C. nasus is presumed to be summer spawning species and polycyclic species to spawn 2 times or more during the spawning season.

• The Korean Journal of Malacology
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• v.27 no.1
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• pp.43-53
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• 2011

The gametogenic cycle and the spawning season in female and male Cyclina sinensis were investigated by quantitative statistical analysis using an image analyzer system, and the biological minimum size (the size at 50% of sexual maturity) was calculated by combination of quantitative data by size and von Bertalanffy's equation. Compared the gametogenic cycle by quantitative statistical analysis with the previous qualitative results in female and male C. sinensis, monthly changes in female and male gametogenic cycles calculated by quantitative statistical analysis showed similar patterns to the gonadal stages in female and male reproductive cycles by qualitative histological analysis. Comparisons of monthly changes in the portions (%) of each area to eight kinds of areas by quantitative statistical analysis in the gonads in female and male C. sinensis are as follows. Monthly changes in the portions (%) of the ovary areas to total tissue areas in females and also monthly changes in the portions of the testis areas to total tissue areas in males increased in March and reached the maximum in May, and then showed a rapid decrease from June to October. Monthly changes in the portions (%) of oocyte areas to ovarian tissue areas in females and also monthly changes in the portions of the areas of the spermatogenic stages to testis areas in males began to increase in March and reached the maximum in June in females and males, and then rapidly dropped from July to October in females and males when spawnig occurred. From these data, it is apparent that the number of spawning seasons in female and male C. sinensis occurred once per year, from July to October. Monthly changes in the number of the oocytes per mm2 and in the mean diameter of the oocyte in captured image which were calculated for each female slide showed a maximum in May and reached the minimum from December to February. Therefore, C. sinensis in both sexes showed a unimodal gametogenic cycle during the year. The percentage of sexual maturity of female and male clams ranging from 25.1 to 30.0 mm in length was over 50% and 100% for clams over 40.1 mm length. In this study, the biological minimum size (sexually mature shell lengths at 50% of sexual maturity) in females and males were 26.85 and 26.28 mm, respectively.

• Journal of Aquaculture
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• v.13 no.3
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• pp.197-206
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• 2000

At the Poryoung coast, the spawning season of the mullet, Chelon lauvergnii lasts from May to June. A combination of rotifer, Rotifer nauplii and synthetic feed supported significantly (P < 0.05) better survival and growth of 1-day old mullet larvae during 70-day rearing experiment than the other feeds consisting of rotifer or rotifer + Artemia nauplii. Significantly higher growth and survival were also observed, when the larvae were fed on rotifer, that were harvested from culture enriched with masimaTR, or Artemia nauplii from culture enriched with cuttlefish liver oil, At the feeding density of 97-98 individuals /200 l, the mullet larvae displayed maximum growth and survival in aquarium each with 100 larvae /200 l.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.45 no.5
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• pp.499-506
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• 2012

We estimated the population size and fishing mortality of Pacific cod Gadus macrocephalus during the spawning season in waters off Woipo, Geoje Island, Korea, using a mark-recapture method. We marked and released 51 cod>50 cm in total length; six were recaptured by local fishermen during the period from December 15 to 31, 2009. The estimated population size was ca. 180,000 and the fishing mortality of the exploitable cod was 26%. Although we could assume a closed population due to the short survey period, we evaluated the uncertainty in the estimates by applying bootstrap resampling because the sample size was small. The estimated 95% confidence interval was 94,000-568,000 for the population size and 8-49% for fishing mortality. Our study demonstrated that the application of mark-recapture methods and bootstrap resampling can be useful in stock assessment for fisheries management in Korea, but requires a larger sample size, spatially extensive coverage, and sophisticated mark-recapture models based on a refined sampling design for reliable stock assessment and biological reference points in sustainable cod management.