• Korean Journal of Ichthyology
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• v.7 no.1
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• pp.56-63
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• 1995

Ecological study of the Cynoglossus joyneri was conducted based on the specimens from the western coast of Korea from 1992 to 1994. Ecological characteristics of this species such as gonadal development, occurrence of larvae, stomach contents, and environmental conditions were investigated. Few larvae of Cynoglossus joyneri occurred in Kunsan coast. This coast is influenced by the freshwater input of the Mangyong and Kum River, especially during the summer. Therefore, the larvae of C. joyneri were considered to be spawned and grown during their early life stage in the high saline water in outer bay. Spawning occur from June to September, having the peak spawning period from July to August. Biological minimum size of matured fishes containing mature oocytes is about 143.5mm in total length, which requires about 20 months after hatching. The ranges of total length by age are as follows : 0-ring group(floating stage), 30~70mm ; 1-ring group, 49.0~133.0mm 2-ring group, 128.6~167.0mm ; 3-ring group, 169.0~202.0mm ; 4-ring group, 200.7~240.0mm. The major food items of young fish under 8cm were copepods and invertebrate larvae, and those of adult fishes were annelids(polychaets) in winter, and bivalves and shrimps in summer and autumn. Therefore, it can be assumed that the population of C. joyneri could be reduced due to the decrease of food organisms caused by the continuous reclamation activities in the inner bays of the west coast of Korea.

• Korean Journal of Ichthyology
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• v.7 no.1
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• pp.43-55
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• 1995

Based on the reproductive cycle of Rhodeus uyekii, the reproductive control mechanism was examined under the several combinations of photoperiod and temperature regimes at different phases of their reproductive cycle. In early spring, the gonads developed rapidly under the warm temperature condition(above $8^{\circ}C$), regardless of the photoperiod. In late spring or early summer, gonads intensely regressed under the high temperature condition(above $24^{\circ}C$), regardless of the photoperiod. Thus, it is concluded that the spawning period of R. uyekii is initiated by the rising of water temperature in spring and is terminated by the high temperature in early summer. In autumn, the gonadal recrudescence occurs under the conditions of artificial long daylength with warm temperature(15L/9D, $12^{\circ}C{\sim}20^{\circ}C$), whereas the gonads remain in the existing condition under the short daylength. Therefore, in autumn the gonadal recrudescence is prevented by the short daylength although the temperature is still in favorable condition. In bitterling, the responsiveness of the gonads to photoperiod varies clearly with seasons, which was declined during the winter but increased during the autumn. The critical photoperiod for maturation ranges 12~13 hours of light per day. The results indicate that the proper ranges of temperature and photoperiod for gonadal maturation of this species are from $8^{\circ}C$ to $8^{\circ}C$ and from 13L to 15L, respectively.

• Korean Journal of Ichthyology
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• v.12 no.3
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• pp.166-172
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• 2000

Growth of Ammodytes personatus was investigated based on the specimens collected in the costal waters of Shinsudo, Sacheon from March 20 to December 14, 1988. Age determination based on otolith. The rings in the otolith were used as the basis for age annulus. The time of ring formation was estimated to one time per year in May far 1st ring group and March for 2nd ring group. The spawning season peaked in December. It takes approximately 16 months for the first ring and 11 months for the second ring to form in the otolith. The opaque zone was formed and marked over summer at 1st ring group and spawning mark at 2nd ring group. The relationship between the total length(TL) and otolith radius(R), and body weight(BW) were represented respectively as follows: TL=29.17+182.9R, BW=$4.9{\times}10^{-8}TL^{3.9587}$. Von Bertalanffy growth model is $TL_t$ = 177.273 ($1_e^{-0.040(t+7.332)}$), Robertson growth model is $TL_t=\frac{150.275}{1+2.085e^{-0.099t}}$ and Gompertz growth model is $TL_t=157.551e^{-1.214exp(-0.069t)}$.

• Korean Journal of Ichthyology
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• v.22 no.3
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• pp.154-161
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• 2010

The reproductive ecology of the cardinalfish Apogon lineatus was examined using 4,300 specimens collected monthly from January to December 2006 in the coastal waters of Gori, Korea. Specimens ranged in standard length (SL) from 2.1 to 8.6 cm. They were distributed more in surface areas during summer and autumn and more on bottom areas during spring and winter. The gonadosomatic index (GSI) of females was highest in September and decreased until December, with the spawning season lasting from August to October. The monthly ratio of female to male did not significantly differ (${\chi}^2$-test, p>0.05). The size of 50% maturity was estimated at 5.43 cm SL and all females more than 7.0 cm SL were sexually mature. A. lineatus is a multiple spawner, spawning on more than one occasion in a single spawning season. The maximum egg diameter was 0.65 mm. Fecundity (F) ranged from 8,555 to 20,084 eggs, with a mean of 15,038 eggs. The relationship between fecundity and standard length was estimated as F=$334,851\;SL^{1.9876}$ ($R^2$=0.53). The relationship between fecundity and body weight(BW) was estimated as F=7,167.6 Ln (BW)-2,198.1 ($R^2$=0.33).

• Journal of Aquaculture
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• v.3 no.1
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• pp.89-125
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• 1990

In order to improve top shell seed production techniques spawning and larvae rearing were done in rearing tanks. Growth of young top shell in the nursing ground were also investigated. For induced spawning, top shells were maintained in still water during night time. Then they were treated with ultra violet iradiated sea water after dried up in air for 60 minutes. Spawning rate were 10 to $39.77\%$. It was found that young top shells moved in the growing grounds from nursing grounds when they reached approximately 30-40mm in shell heignt. Among main food algae for top shell in the natural growing grounds, sea mustard were melted away during June. Therefore, presence of another food algae such as Ecklonia cava or Sargassum spp. seems to be the main limiting factor for survival of top shell during summer. The tolerance of top shells ranging from 30mm to 60mm to low density of seawater for were tested at the temperature between 29.5 and $31.4^{\circ}C$. Hundred percent mortality occoured in 20, 55 and 90 hours after first stocking at the specific gravity of 1.010, 1.015, and 1.020, respectively.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.18 no.6
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• pp.571-580
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• 1985

Based on the data collected by R/V "Shinkai Maru" of the Japan Marine Fishery Resources Research Center during the period from April 1978 to April 1979, seasonal migration of Merluccius hubbsi was studied using the catch per fishing effort (tons/30 min. haul) and gonad maturity index (gonad weight /body weight X $10^3$). Merlurccius hubbsi are found in the area between $36^{\circ}S\;and\;54^{\circ}S$ along the coast of Arzentine and are abundant especially above the 100 fathoms in northern offshore of $48^{\circ}S$. It was observed that critical maturity body lengths (spawning minimum body length) in terms of gonad maturity index are 40 cm and 30cm in female and male respectively, while spawning seasons are from December to January and from November to December for female and male respectively. It was assumed that while the group which distrbutes in the north ($36^{\circ}S{\sim}39^{\circ}S$) in spring moves down south to $42^{\circ}{\sim}46^{\circ}S$ for spawning in summer (from December to January), the group which does not move or a part of this group which comes back to the north spawn in the area north of $42^{\circ}S$ throughout the long period except winter time (from July to August). Southern group as well might move north and spawn after mixing together with northern group at $42^{\circ}{\sim}46^{\circ}S$ area around the period of December to January,

• Korean Journal of Ecology and Environment
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• v.42 no.1
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• pp.58-66
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• 2009

The telemetry of eight adult manchurian trouts (Brachymystax lenok tsinlingensis) in the upper part of the Nakdong River, which is the southern limit of distribution of manchurian trout on the Korean peninsula, was used to examine migration patterns and evaluate characteristics of over-wintering and the spawning season between December, 2007 and May, 2008. Based on the tracking data, the tagged fish showed a limited migration between adjacent pools, moving only up to $8.6m\;day^{-1}$ during the winter season (December to February). Hydraulic conditions of over-wintering pool areas were, ca. 1m depth, slow moving surface water with areas of sand and gravel. The migration of tagged individuals was successful, moving up to $96.2m\;day^{-1}$ during the spawning season. Two tagged individuals (BL4, BL6) exhibited upstream migration, whereas others showed downstream movements. The timing of upstream migration of the two individuals was consistent with an increasing phases of water level and discharge. The fishes migrating toward the down stream moved to the wide pool areas downstream, where they spent the summer season for the growth.

• Korean Journal of Environment and Ecology
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• v.36 no.4
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• pp.381-389
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• 2022

This study investigated the ecological characteristics of Microphysogobio yaluensis at Dugye Stream of Geum River basin from January to December 2021. The river bed structure of this species' habitat was rich in pebbles and gravel. The water depth ranged from 12 to 85 cm with an average of 23 cm, which was shallow. The stream velocity was rapid at 1.03±0.34(0.72-1.47) m/sec. The ratio of females to males was 1:0.86. The age according to the total length-frequency distribution as of summer (June, July) indicated that the group with less than 50 mm (30.4-49 mm) in total length was one year old, the group with 50-69 mm was two years old, and the group over 70-92 mm was three years old. Both male and female fish sexually matured at 50 mm long and two years old in June and July. The spawning season was from July to August, and the water temperature was between 25.8℃ and 28.2℃ during the period. The prosperous spawning season was July. The matured eggs were yellowish and spherical with a mean diameter of 0.52±0.16 (0.33-0.77) mm, and the average number of eggs found in the ovaries of mature female fish was 2,593 (1,343-4,672). As for the food of M. yaluensis, only attached algae, which grow by attaching to stones and gravel of the stream rapids, were identified. The feeding habit of M. yaluensis was reported to be herbivorous, ingesting Cyanophyta, Chlorophyta and Bacillariophya. Also, the species belonging to Bacillariophya and Chlorophyta were abundant in Dugye Stream.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.6 no.3
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• pp.164-179
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• 2001

Spatio-temporal variation in species composition, abundance and distribution of fisheries resources caught by large purse seine off Korea from 1991 to 1994 was analysed. Out of 19 species, Scomber japonicus (54.7%), Sardinops melanostictus (20.4%), Trachurus japonicus (9.1%), and Scomberomorus niphonius (6.2%) were predominated in catch. These 4 pelagic fishes occupied 90% of total catch. Major pelagic fishes caught by large purse seine were dispersed to northward from spring to summer, and migrated to the southern wintering ground during winter. Fishing effort (number of haul) was high in summer, but catch per unit effort showed a peak in winter. The high CPUE in winter seemed to be related to aggregation of the pelagic fish to the wintering ground in the southern sea. After spawning, they were widely dispersed for feeding in warm months.

• Animal cells and systems
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• v.1 no.1
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• pp.99-105
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• 1997

Using three species of Korean frogs (Rana dybowskii, R. rugosa and R. nigromaculata), the annual spermatogenic pattern, the seasonal changes in the steroidogenic competence, and responsiveness of testis to gonadotropins in terms of testosterone secretion in vitro were examined. The spermatogenic pattern of R. dybowskii was classified as a discontinuous type since spermatogenesis stops completely after spawning in late winter (February) until mid-summer (July). In contrast, the pattern of R. nigromaculata and R. rugosa was classified as a potent continuous type since sperm was always present in the seminiferous tubules all year round. In all three species, the levels of testicular testosterone and that of testosterone secreted by testis following in vitro culture were very low in late summer (August), but increased thereafter until winter (hibernation period). Interestingly, responsiveness of testis in vitro to gonadotropins in terms of testosterone secretion increased markedly in November (early hibernation period). Specifically, bullfrog LH was more effective than FSH in stimulating the secretion of testosterone by frog testis in vitro during hibernation period. This fact suggests that testosterone secretion by testis during hibernation is at least regulated by the pituitary gonadotropin rather than environmental factors. Taken together, the data presented here suggest that testicular cycles of three species of Korean frogs are closely linked to their females breeding cycles, and are eventually controlled by various environmental cues.