• The Korean Journal of Malacology
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• v.29 no.1
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• pp.65-76
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• 2013

We investigated the gametogenic cycle and spawning seasons of the male Chlamys (Azumapecten) farreri nipponensis by qualitative and quantitative analyses, and also the size at 50% of group sexual maturity was calculated by the data of first sexual maturity. In this study, the male gametogenic cycle of this species by qualitative analysis was divided into five successive stages: early active stage (January to March), late active stage (March to April), ripe stage (April to August), partially spawned stage (July to September), and spent/inactive stage (August to January). The male gametogenic cycle showed similar patterns with monthly changes in the gonadosomatic index and condition index. Particularly, spawning in male scallop occurred once a year from July to September, unlike the spawning period of this species (from June to August) reported by the previous researchers. In quantitative statistical analysis using an image analyzer system, the patterns of monthly changes in the percent (%) of the areas occupied by spermatogenic stages to the testis areas in males showed a maximum in June, and then sharply dropped from July to September, 2006. From these data, it is apparent that the spawning season of C. (A.) farreri nipponensis occurred once per year from July to early September, indicating a unimodal gametogenic cycle during the year. Shell heights at 50% of group sexual maturity (RM50) fitted to an exponential equation were estimated to be 49.90 mm in males (considered to be one year old), and it was 100% for male scallops over 61.0 mm (considered to be two years old).

• 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.

• Fisheries and Aquatic Sciences
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• v.21 no.11
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• pp.34.1-34.13
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• 2018

Sexual maturity ($L_{50}$), the length at which 50% of fish in a size class are mature, is a key aspect of domestication of new fish species because it guides the procedure for identification of appropriate broodstock size for artificial spawning. In this study, the $L_{50}$ was determined for 1083 Barbus altianalis samples obtained from Lake Edward and the Upper Victoria Nile. Gonads of freshly killed samples were examined macroscopically and verified with standard histological procedures for the maturation stages that were used to determine $L_{50}$. Oocytes and spermatogenic cell sizes were compared for fish obtained from both water bodies. Results indicated that there were no variations in macro gonad features observed for fish from Lake Edward and Upper Victoria Nile. Similarly, there were no significant differences in oocyte sizes (P > 0.05) between the two populations but significant differences in spermatogenic cell sizes were noted (P < 0.05) except for spermatozoa (P > 0.05). This however did not suggest peculiar differences between the two populations for staging the gonads. Consequently, no staging variations were suggested for both populations in determination of $L_{50}$. Sexual maturity was found in the same class size of fork length (FL) 20-24.9 cm and 35-39.9 cm for males and females from both water bodies, respectively. At this FL, however, males were too small, and for good selection of vigor broodstocks for spawning and conservation purposes, they are better picked from class size of 30-34.9 cm FL and above. These findings were crucial for integration of appropriate breeding size in spawning protocol by farmers and fisheries scientists conserving wild B. altianalis populations.

• Korean journal of applied entomology
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• v.57 no.4
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• pp.329-337
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• 2018

To increase the mating rate of Bombus ignitus used as insect pollinator, we investigated the sexual maturity time of B. ignitus. In investigating ovary development such as the number of eggs per ovariole and spermatheca size, the time of sexual maturity of queen was 10 days after eclosion. In case of male, the number of sperm was 246 thousand at immediately after eclosion, and was highest as 480 thousand at 9 days, and tended to show a dramatic decline at 35 days (87 thousand). The more mating time, the less the number of sperm. In consideration of number of sperms, the time of sexual maturity of male was 3-15 days after eclosion. In the sexual maturity time of queen in mating, the queen was not mated at immediately after eclosion, and showed a decrease in 20 days. In terms of the rate of mating and oviposition, the favorable time for mating of queen was 9-20 days. On the other hand, the male showed 3.3% of mating at immediately after ecolosion, showed the highest of 43.3% at 6 days after eclosion, and tended to decrease in 25 days. The sexual maturity time for mating of male was 6-20 days. In summary, our results indicate that sexual maturity time of B. ignitus in reproductive organs and mating is most favorable in 9-12 days after eclosion for queen and 6-9 days for male.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.53 no.1
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• pp.1-8
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• 2020

The reproductive biology of largehead hairtail Trichiurus japonicus, from near Jeju Island, Korea was investigated based on 4,384 individuals collected by commercial vessel from November 2016 to October 2019. There were more female specimens than male specimens (2.64:1). T. japonicus preanal lengths (PL) ranged from 10.5 to 53.5 cm; the relationships between PL and body weight (BW) were BW=0.0103PL^3.1293 for females and BW=0.0106PL^3.1251 for males. Monthly changes in gonadosomatic index were analyzed to estimate spawning season. The spawning period ranged from June to November. The size-frequency distribution of eggs suggested that T. japonicus exhibits multiple-spawning during a spawning period. The minimum size of females at maturity was 18.2 cm, while the size at sexual maturity was 25.0 cm.

• Animal cells and systems
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• v.11 no.2
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• pp.227-234
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• 2007

Spermatogenesis, the reproductive cycle, and the size at first sexual maturity in male Mactra chinensis were investigated by cytological and histological observations. The spermatozoon exhibits a primitive type morphology and is similar to those of other bivalves in that it contains a short midpiece with four mitochondria surrounding the centrioles. The morphologies of the sperm nucleus type and the acrosome shape of this species are cylindrical and modified cap-like, respectively. The spermatozoon is approximately $40-45\;{\mu}m$ in length including the sperm nucleus (about $1.46\;{\mu}m$), acrosome (about $1.20\;{\mu}m$) and tail flagellum. The axoneme of the sperm tail flagellum consists of nine pairs of microtubules at the periphery and a pair at the center. The axoneme of the sperm tail shows a 9+2 structure. The spawning period of this species lasts from June to September, and the main spawning occurs in July and August, when the seawater temperature is greater than $20^{\circ}C$. The percentage of individual male clams at first sexual maturity was 56.5% for those whose shell lengths were 35.1-40.0 mm, and 100% for over 45.1 mm. Accordingly, harvesting clams <35.1 mm in shell length could potentially cause a drastic reduction in recruitment, and 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.53 no.1
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• pp.50-56
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• 2020

Determination of the precise size at sexual maturity is very important for science-based stock assessment and fisheries resource management. In this study, two different models, (1) a visual method and (2) a gonadosomatic index (GSI) method, were employed to estimate length at sexual maturity of the small yellow croaker Larimichthys polyactis in the Yellow Sea of Korea. The visual method is a common qualitative method using visual gonadal identification. Conversely, the GSI method is a quantitative method using the GSI, which can be easily and precisely collected. We compared results from these methods to determine the best approach, and to examine the practicality of the GSI method. Logistic regression of the maturity ogive was conducted using a general linear model (GLM) with the R statistics program. Also, the bootstrapped 95% confidence intervals of all estimates were calculated. The best-fit model was the visual method (R_Mc²=0.805, AUC=0.989, L₅₀=15.1). Among models using the GSI method, the model computing GSI_ref=0.94 was the best-fit model (R_Mc²=0.792, AUC=0.989, L₅₀=15.2). There was no significant difference between the two models, evidencing the effectiveness and accuracy of the GSI method.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.35 no.4
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• pp.380-385
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• 2002

The sand shrimp, Crangon hakodatei commonly occured in the southern coast of Korea. The population structure, growth, mortality, and size at sexual maturity of C. hakodatei were examined by the samples collected from the coastal area of Geoje Island, Korea from October 2000 to October 2001. For estimation of parameters of growth and mortality, monthly length-frequency data were analysed by ELEFAN. Parameters of growth were estimated, using the modified yon Bertalanffy growth function model. The female grew faster and reached larger size at the same age than the male, There was a breeding season showing a peak in winter (January to february). Total mortality by length-converted catch curve was estimated at $3.10 yr^{-1}$, fishing mortality was $0.62 y^{-1}$ and natural mortality was $2.48 yr^{-1}$. The size at $50\%$ sexual maturity for the female ranged from CL 11.00 to 11.50 mm.

• Journal of Aquaculture
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• v.22 no.1
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• pp.92-99
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• 2009

Population dynamics and sexual maturity of Neomysis japonica (Ishikawa and Oshima, 1951) were investigated from a shrimp farm in Tae-an, Korea. N. japonica was collected monthly at the shrimp farm belonging to the Marine and Fisheries Research Institute, the Soonchunhyang University from October 2002 to September 2003. The proportion of female was higher than that of male. The mean carapace length of male (2.42 mm) was larger than that of female (2.31 mm). Brood size increased with increasing female body size. The size of N. japonica at 50% sexual maturity was approximately 4.4 mm. N. japonica females grew faster and reached larger size than males. The mortality rate (z) calculated by length-converted catch curves was $3.46\;yr^{-1}$. The annual recruitment pattern of N. japonica had two major peaks. Log-transformed total length was significantly related with log-transformed carapace length.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.36 no.6
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• pp.646-653
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• 2003

Investigations were made on the population structure, sex ratio, growth, and recruitment patterns of Leptochela sydniensis in the southwestern coastal areas of Korea, between May 2000 and December 2001. Spawning period, fecundity, brood loss, reproductive output, and size at sexual maturity also were examined. The results of the sex ratio showed that females were more numerous than males during the overall study period. Parameters of growth were estimated using the modified von Bertalanffy growth function (VBGF) model incorporating seasonal variation into growth. Females grew somewhat faster and reached a larger size than males $(L\infty=12.80\;mm\;CL\;and\;K=0.70\;yr^{-1}\;or\;females,\and\;L\infty=12.08\;mm\;CL\;and\;K=0.69\;yr^{-1}$ for males). The structure of recruitment patterns obtained by the FiSAT program indicated one normally distributed group. Based on the occurrence of ovigerous females and the gonadosomatic index (GSI), the main spawning season was from June to August. Analysis of covariance indicated that brood loss was not observed during the incubation period. The size at which $50\%$ of females are mature is estimated as 5.48 mm CL.