• Korean Journal of Ichthyology
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• v.19 no.4
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• pp.306-317
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• 2007

Reproductive cycle with the gonad developmental phases, first sexual maturity, spawning frequency, sex ratio of the dusky mud hopper, Periophthalmus modestus were investigated by histological observations. Monthly variations of the gonadosomatic index (GSI) began to increase in May and reached a maximum in June when the gonad was getting mature during the period of higher ground (water) temperature-long day length. Changes in the GSI showed a negative correlation to the HSI, but coincided with the fatness index. The reproductive cycle can be classified into five successive stages: in female, early growing stage (April to May), late growing stage (April to May), mature stage (May to June), ripe and spent stage (June to August), and recovery and resting stage (August to March); in males, growing stage (April to May), mature stage (May to June), ripe and spent stage (June to August), and recovery and resting stage (August to March); According to the frequency distributions of egg diameters during the breeding season, Periophthalmus modestus is presumed to be a summer breeder, asynchronous group and polycyclic species to spawn 2 times or more during the spawning season. Total eggs and mature eggs in absolute fecundity and relative fecundity (per cm) increased with the increase of body length. Total eggs and mature eggs in absolute fecundity and relative fecundity (per g) did not increase with the increase of body weight. Percentages of first sexual maturity of females and males ranging from 5.1 to 5.5 cm in body length are over 50%, and 100% for fish over 7.1 cm in body length. The sex ratios of females to males over 5.1 cm in body length were not significantly different from a 1 : 1 sex ratio.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.25 no.5
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• pp.413-431
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• 1992

Gonadal development, fertilization and egg development in the maternal body and reproductive cycle of ovoviviparous rockfish, Sebastes inermis, were investigated histologically. Gonadosomatic index(GSI) of male and female were increased from September and reached maximum values in December. In the male, GSI decreased from January, but in the female maintained high values till February and decreased from March. Hepatosomatic index(HSI) was related to GSI conversely. In both sex, HSI increased from February and reached maximum in August as the gonad were degenerating and resting, and began to decrease from September as gonad were glowing. This ovoviviparous rockfish copulates in December. Fertilization with sperms maintained between ovulated oocytes in the ovary occurs in January mainly. Egg development in the ovarian cavity and discharging of hatched preiarva occurs from January to February. The reproductive cycle includes the successive stages: Growing(September), Mature (October-November), Ripe and Fertilization(Decembr-Janua), Egg development and Discharging of hatched larva(January-February), Degeneration and Resting(February-August). According to the frequency distribution of egg diameter and histological observation, the ovoviviparous rockfish discharged the prelarva at a time in a spawning season. The sexual maturation is first attained at 2 ages. All females and males reaches first maturity at body length of 17.1cm and 15.1cm respectively. The mean number of the embryos increased with the increase of the total length of female.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.36 no.3
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• pp.210-221
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• 2000

The population habitat and density of Korean scallops, Chlamys farreri, were investigated to estimate population ecological characteristics from samples randomly collected around Wando from November, 1998 to October, 1999. Age and growth of the Korean scallops were determined from their ring radii. Maturation and spawning were studied using data of ovary maturity stage, gonadosomatic index, and fecundity. Seawater temperature and specific gravity ranged from 7.6 to $25.9^{\circ}C$ and from 1.0188 to 1.0260, respectively. Also dissolved oxygen and pH ranged from 6.48 to 9.50 ppm and from 8.17 to 8.80. Rocky and gravel bottom had a maximum habitat density of $$28.83 inds/100m^2$$ , which accounted for 82.4 % of the overall habitat area. The relationship between shell length (SL, mm) and shell height (SH, mm) of the Korean scallops was fitted : SH=1.021 SL+2.211 $(R^2=0.989)$. The shell length-total weight (TW, g) relationship was $TW=0.0003; SL^{2.837};(R^2=0.980)$. Then von Bertalanffy growth parameters were estimated from a nonlinear regression method, and the values were as follows : $SH_{\infty}=117.4 mm$K=0.61/year,; and; t_0=-0.017 year., The 50 % maturity at age was 0.21 year with the shell height of 18.3 mm, and spawning occurred twice a year, that is, June/July and October. The relationship between fecundity (Fc) and shell length was$Fc=697.03 SL^{2.683}(R^2=0.984)$, and the fecundity-gonad weight (GW, g) relationship was Fc=10,076,090 GW+15,608,781 $(R^2=0.990)$.

• The Korean Journal of Malacology
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• v.31 no.3
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• pp.171-178
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• 2015

The reproductive ecology of freshwater bivalve, Unio douglasiae in Lake Uiam were examined from March 2014 to February 2015. The gonads distributed in reticular connective tissue, the dioecious clams take an internal fertilization and fertilized eggs are stored in the foster-sack in the gills, then the hatched juveniles are released outside after an ovoviviparous process. The gonad index (GI) began to increase in April, reached the maximum value in July and to decrease in August. The reproductive cycle of U. douglasiae can be divided into five successive stages: multiplicative stage (November to January), growing stage (February to March), mature stage (February to May), spawning stage (April to September), recovery stage (August to December). The spawning periods were from April to September, and the main spawning occurred between April and July. The shell length at 50% group maturity was estimated to be 29.4 mm.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.22 no.5
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• pp.342-350
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• 1989

Maturity and spawning of Crangon affinis were studied based on the histological observation. The samples were monthly collected in Nakdong estuary from June, 1988 to May, 1989. The gonad lies on the dorsal side of the thorax. The cavity in which it lies is located below heart and above hepatopancreas. Anterior part of ovary is fused roundly, and the posterior part shows a pair of tubule-like structure. Testis is bilaterally symmetrical; the anterior part shows convoluted tubule, and the posterior part consists of a pair of tubule. Seminal vesicle is connected and opened to the base of the fifth pereiopod. Gametogenesis of ovum and spermatozoon is being repeated in short period without seasonality, and it is formed simultaneously in the whole parts of germinal epithelium. Diameter of a ripe oocyte is ca. $430{\mu}m$. Spermatozoa is oval with distinct nucleoplasm. Reproductive cycle is performed in ca. 40 days. Crangon affinis spawns all year round except November. Incubation period of brooded eggs took $12\~14$ days before hatching in the aquarium at $21^{\circ}C\~24^{\circ}C\;and\;33\%_{\circ}$.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.39 no.4
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• pp.349-356
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• 2006

Gonad development in the sandfish Arctoscopus japonicus was investigated using a histological method. Specimens were collected monthly from April 2003 to March 2004, in the East Sea of Korea. The gonadosomatic index (GSI) of females began to increase in August, reached a maximum in November, and declined sharply in December. By contrast, in males, the GSI began to increase in June and reached a maximum in August. The annual reproductive cycle of A. japonicus can be divided into four successive stages in females: the early growing (January-March), late growing (April-August), ripe and spent (September-November), and recovery (December) stages. Males passed through early growing (January-April), late growing (May-July), ripe and spent (August-November), and recovery (November-December) stages. These results indicate that the spawning season was from October to December. The egg diameter of mature oocytes was 3.12$\pm$0.02 mm. The relationship between fecundity (F$_e$) and body length (BL) was F$_e$=0.4693BL$^{2.6825}$. Fecundity ranged from 483-2,254 eggs in a body length of 14.3-22.9 cm and increased with body length. The body length at 50% maturity was 14.80 cm, which corresponded to an age of 2.40 years.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.46 no.6
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• pp.835-842
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• 2013

Flathead flounder Hippoglossoides dubius is a commercially important fish in the coastal waters of Gangwon Province, which is its spawning ground and breeding habitat. A total of 1,669 gonads were sampled monthly from February 2011 to May 2013 to investigate ecological characteristics, such as variations in maturation and spawning by gonad index, visual maturity stage, histological observations and oocyte diameter. Males were numerically dominant over females in the fishing grounds year round. The spawning season was from January to April, and the peak was from February to March. Oocyte number as a measure of fecundity was between 27,372 and 915,209 eggs with a length range of 26.0-48.7 cm TL, while the largest oocyte grew to 0.9-1.4mm in egg diameter during its spawning season. The relationship between fecundity and total length was $F=0.0016TL^{5.2539}$. The smallest mature lengths of the females and males were 28.4 and 22.6 cm respectively, and the 50% mature lengths of females and males were 32.9, 26.9 cm respectively.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.33 no.3
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• pp.184-191
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• 2000

Gametogenesis and the reproductive cycle of the marsh clam, Corbicula leana(Prime} were investigated monthly Hyongsan estuary, Korea from January to December 1998 by histological observation. C. leana had separate sexes, and oviparous. The gonads were located between the sub-region of mid-intestinal gland in visceral cavity and reticular cennective tissue. The ovary and testis were composed of a number of ovarian and testicular tubules, respectively, Mature oocytes were characterized by germinal vesicles with nucleoli and their sizes ranged $70\;to\;80{\mu}m$ in diameter. A number of mesenchymal tissues and pigment granular cells were distributed in the growing oocytes and spermatocytes during early developmental stages. With the further development of gonad, these tissuse and cells gradually disappeared. The monthly changes in the fatness index were closely related to reproductive cycle. Minimun size for sexual maturity was reached over 10.0 mm in shell length. The reproductive cycle could be classified into 6 stages : multiplicative (March to April): early growing and growing (May to June), mature (July to August), spent (September), degenerative (October) and recovery (November to February).

• Development and Reproduction
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• v.20 no.4
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• pp.305-314
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• 2016

The marine medaka, Oryzias dancena is a suitable sample as a laboratory animal because it has a small size and clearly distinguishes between female and male. Data on the growth and maturity of the diploid and triploid sea cucurbit species suitable for laboratory animals are very useful for studying other species. Triploidy was induced in the marine medaka by cold shock treatment ($0^{\circ}C$) of fertilized eggs for 45 min, applied two minutes after fertilization. The diploid and triploid male fish were larger than their female counterparts (P<0.05), and the concentrations of thyroid stimulating hormone (TSH) and thyroxine (T4) were higher in the induced triploids over 1 year (P<0.05). In both the diploid and tri-ploid groups the concentrations of TSH and T4 were higher in the male fish than in the females (P<0.05), while the testo-sterone and estradiol-$17{\beta}$ concentrations in the induced triploids were lower than in the diploids (P<0.05). The gonadosomatic index (GSI) of the triploid fish was lower than that for the diploids, and the GSI for females in each ploidy group were higher than that for the males. For both groups the GSI was highest at 4 months of age, and decreased thereafter to 12 months. Analysis of the gonads of one-year-old triploid fish suggested that the induction of triploidy probably causes sterility in this species; this effect was more apparent in females than in males.

• Development and Reproduction
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• v.27 no.3
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• pp.101-115
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• 2023

Environmental factors impact oyster growth, condition, and gonadal development, which is linked to gamete characteristics observed through histology. The reproductive cycle of bivalves is related to energy storage and utilization. Therefore, in this study, the year-round growth change and gonadal development of oysters were observed using histological analysis, and the biochemical composition changes were confirmed. The oysters used in this study are being nurtured in Gadeok-do, and 40 oysters were randomly sampled monthly from March 2021 to February 2022. Result of histological analysis of gonads, oysters were showed early development from December to February, late development from March and April, mature and ripe from May to July, spawned from August to October, and spent from November to December. Condition index values of oysters decreased in summer and autumn and increased again when entered the spent after spawning. The protein content of oysters was high in May, the maturity period, and the lipid content decreased during the spawning period. In addition, EPA and DHA, the major fatty acids of oysters, were low during the spawning period and high during the maturation period. As a result, this study suggested a close relationship between changes in oyster growth, biochemical composition, and the reproductive cycle.