• Journal of Aquaculture
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• v.20 no.3
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• pp.160-167
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• 2007

Embryonic and pre-leptocephalic larvae development of the eel, Anguilla japonica, are described following natural fertilization in the indoor tank of $23^{\circ}C$ water temperature. Following a routine hormone treatment technique for the brood stock, female eels were artificially matured by weekly intramuscular injections of salmon pituitary extracts (SPE) at a dosage of 20 mg/kg body weight (BW) for a total of 10-14 doses to induce ovarian maturation, while male eels received weekly intramuscular injections of human chorionic gonadotropin (HCG) at a dosage of 1 IU/g BW for a total of 6-10 doses to induce testicular maturation in a separate aquarium and induced natural spawning. Fertilized eggs of about 1.0 mm in diameter were pelagic and showed a typical discoidal cleavage. Hatching occurs 38 hrs after fertilization at a water temperature of $23^{\circ}C$. The newly hatched larvae measured about 3.0 mm in total length and the number of myomeres averages 42. Their mouths and anuses were opened at 4.5 days and the yolk sacs of the pre-leptocephalic larvae were almost absorbed at 6.5 days after hatching. Pre-leptocephalic larvae survive for 14.5 days. At this time they are $5.87{\pm}0.25mm$ in total length and have about 98 myomeres. However, morphological characterization of embryonic and pre-leptocephalic larvae were not different between natural fertilization and artificial fertilization by the dry method.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.29 no.4
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• pp.474-480
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• 1996

Physicochemical changes of milt during the spermiation period were investigated in black seabream (Acanthopagrus schlegeli) reared in recirculating seawater system. The spermiation period for the milt collection in cultured brood stock was from 11 April to 4 June. During the spermiation period, average milt volume (ml/100 g body weight) was $0.70{\pm}0.33\;ml$ and maintained high level from 2 May to 4 June. The total number of stripping spermatozoa per 100 g body weight reached the maximum value $(3.32{\times}10^{10})$ in 9 May, then decreased rapidly thereafter. Spermatozoa concentration per ml reached the minimum value in 2 May. There was no change in spermatocrit for the spermiation period. Total protein, total lipid, glucose and Na concentration in spermatozoa and seminal fluid were lower than those in plasma. Total protein, total lipid and K concentration in spermatozoa were higher than those in seminal fluid. The glucose concentration in spermatozoa and seminal fluid in April and May were significantly higher than those in June.

• Ecology and Resilient Infrastructure
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• v.2 no.3
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• pp.216-223
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• 2015

The conservation project to protect an endangered fish, Gobiobotia naktongensis was executed against declining the gene diversity of the fish after the construction of Youngju Dam in a sand-bed stream (Naeseongcheon Stream). We tried to move the populations of G. naktongensis from submerged planned sites to alternative habitats, bred artificially and augmented the juveniles to optimal habitat, and monitored the results of the restoration implementation. No entity of G. naktongensis was confirmed at the planned submerged sites despite attempting to capture more than 8 times and eventually the movement to alternative habitat could not be implemented. About 40 individuals of G. naktongensis were captured in the Naeseongcheon Stream and a total of 5,000 individuals were artificially spawned up. The population of juvenile inherited the genetic diversity from the brood stock. The bred juveniles were discharged at the selected optimal site that had a habit condition what was similar to their natural habitat. The micro-dispersion around the discharging area was found at the early stages of the augmentation. The re-capturing rate of discharged juveniles was reduced as time passed. The discharged juveniles seemed to adapt to the natural environment of Naeseongcheon Stream. The observation of their high abdominal distension and excrement demonstrated that the juveniles fed successfully in the discharging area. Therefore, securement of genetic homogeneity and enhancement of restoration population of G. naktongensis in upstream and downstream of Youngju Dam site from the artificial seed producing seemed to be primarily successful and long-term monitoring and analysis of the effect was expected to be necessary.

• Development and Reproduction
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• v.12 no.3
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• pp.261-266
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• 2008

In the present study, we investigated in vivo effects of Manchurian trout recombinant gonadotrophin hormone (mt-rGTH) on the induction of maturation in female eel, Anguilla japonica. The brood stock, female eel (450$\pm$50 g) were weekly injected intramuscularly with different doses of 0.1, 1, 10 ${\mu}g\m{\ell}$/fish (mt-rFSH or mt-rLH) for 10 week. The effects of r-mtGTH were analyzed by gonadosomatic index (GSI), ovarian follicle diameter and sex steroid levels. All groups did not exhibit significant differences in the GSI values. Whereas plasma testosterone (T) and estradiol-17$\beta$ (E2) levels did not change significantly in control group, plasma levels of T and E2 by injection of the r-mtFSH or r-mtLH were increased at 2 or 4 week after injection. In addition, injection of the mt-rFSH (1, 10 ${\mu}g/m{\ell}$/fish) or mt-rLH (0.1, 1, 10 ${\mu}g/m{\ell}$/fish) significantly increased follicle diameters comparing to the control group. These results demonstrate that the recombinant hormone may affect early ovary development and maturation in female eel. Taken together, these results suggest that the recombinant Manchurian trout FSH and LH are effective for reproductive activities in female eel.

• Journal of Aquaculture
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• v.20 no.4
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• pp.219-225
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• 2007

This study investigated the correlationship between artificial maturation season and reproduction coefficient of cultured eel Anguilla japonica from May (spring) to next January (winter). The brood stock, female eels ($400{\sim}600\;g$) were artificially matured by weekly intramuscular injections of salmon pituitary extracts (SPE, 20 mg/fish) to induce a completion of vitellogenesis. After completion of vitellogenesis, final oocyte maturation and ovulation was induced by injection of $17{\alpha}$, $20{\beta}-dihydroxyprogesterone$ (DHP) at about $2\;{\mu}g/g$ body weight. Most fish ovulated $15{\sim}18\;h$ following the DHP injection. The ovulated fish were induced to natural spawning or artificial fertilization by the dry method. Males ($200{\sim}350\;g$) were received weekly intramuscular injections of human chorionic gonadotropin (HCG) at a dosage of 1 IU/g body weight to induce testicular maturation and spermiation. Seasonal reproduction coefficient which includes the rate of ovulation, buoyancy, fertilization and hatching of eggs in the artificially matured eel during spring to summer ($May{\sim}July$) were significantly higher than the other season, while there were no significant difference among spring and summer (P<0.05). Furthermore, the number of eggs spawned and larvae hatched in the artificially maturated eel during spring to summer ($May{\sim}July$) were significantly higher than the other season, while there were no significant difference in spring and summer (P<0.05). These results indicate that artificial maturation by hormone treatment of A. japonica was successful only during spring to summer, which is the maturation period in the wild stock in nature. Consequently, it is possible to determine the period of artificially induced sexual maturity by the reproduction coefficient which includes the rate of ovulation, buoyancy, fertilization and hatching of eggs in the cultured eel A. japonica.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.1
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• pp.49-54
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• 2017

We collected and reared Theragra chalcogramma walleye pollock brood-stock for use in natural spawning tests and undertook to obtain domestic pollock via fertilized egg capture, development of fertilized eggs, and absorption of yolk sac after hatching. Whole pollock were caught with trammel and set nets and immediately placed in a deep-sea water tank. Adults were the most common pollock age group (43.0%; n = 86) among the 254 pollock captured in March 2014 with 57.9% (n = 147) being captured off Southern Gosung, Korea. The main spawning period of pollock is February (spawning phase of 91% of pollock). From the deep-sea tank, we collected 1640 mL of naturally fertilized eggs (~820,000 eggs) from 12 spawning events occurring between February 4 and 22 2015. The floating/ live eggs were maintained in deep-sea water tanks at $5.5{\pm}0.2^{\circ}C$. Egg size was $1.5{\pm}0.03mm$. Six hours after fertilization the eggs were at the 2 cell stage, and the eggs hatched approximately 340 hours after collection. At hatching, larval length and yolk sac area were $5.2{\pm}0.25mm$ and $9.5{\pm}1.00mm^2$ (100%), respectively. Four days after hatching, the yolk sac area was $2.2{\pm}0.53mm^2$ ($23.1{\pm}5.55%$). This is the first report of collection of naturally fertilized eggs from pollock and their subsequent hatching while held in an indoor deep-sea water tank. The results suggest that such collection could assist in the recovery of pollock resources and the possibility of domestic rearing of cultivated larvae.