• Korean Journal of Ecology and Environment
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• v.37 no.1 s.106
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• pp.130-136
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• 2004

In the present study, prey preference of juvenile fishes was examined using an experimental approach. Zooplankton composition, as a prey of the fish, was evaluated by taking into account the species as well as body size of juveniles in the aquarium. The predation of juvenile fishes is known to be an important factor in changes of zooplankton communities. In some previous studies at the regulated Nakdong River, the collapse of large cladcoerans and an increase in the rotifer population by selective predation during spring and summer were observed. This study focused on the predation of juvenile fishes such as Hyporhamphus sajori, Rhinogobius brunneus, and Opsariichtys uncirostris amurensis on zooplankton community structure in mesocosm scale experiments. These fishes selected the cladoceran Moina micrura with highest individual preference value (Manly/Chesson index)among zooplankton prey in the experimental aquarium. When the size-selective prey preferences of the juvenile fish were compared, both small (body size <2 cm) and large (body size >2cm) juveniles of O. uncirostris positively selected M. micrura. In the outdoor experimental tanks, juvenile fishes consumed the cladoceran M. micrura, resulting in an high abundance of the rotifer, Polyarthra spp. The results suggest that juvenile fish predation may play an important role in regulating the zooplankton community structure by reducing the cladoceran density and increase of rotifers in the Nakdong River during spring and summer.

• Korean Journal of Ecology and Environment
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• v.34 no.4 s.96
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• pp.310-318
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• 2001

In the large regulated Nakdong River, the Predation effect of juvenile fish on the zooplankton community was evaluated by gut and stomach analyses of fish in 1999. Juvenile fish of five species showed high density from May to early June when river discharge was low and water body became stagnant. During this period, large rotifers, Asplanchna spp. and Brachionus spp. declined and the decrease of cladoceran (Moina micrura and Bosminopsis deitersi) density was also obeserved. At this time, small rotifers including Polyarthra spp. reached maximum density. Gut analysis of fish demonstrated that small-sized juvenile fish (< 15 mm in total length)preferred large rotifers as well as cladocerans, while large sized fish (> 15 mm)selected only cladocerans. On the other hand, juvenile Micropterus salmoides of which size was larger than other juvenile fish consumed not only zooplankton but also other small juvenile fish. Based on these results, the decline of large rotifers and cladocerans during early summer in the river seems to be result of predation by juvenile fish. However, the period when juvenile fish maintained their high density was as short as one month and the decreased density of cladocera rapidly recovered as soon as juvenile fish became scarce. Such a short period of juvenile fish devel-opment in the river can be attributed to the consumption of juvenile fish by the young-of-the-year cohorts as well as adults of M. salmoides. The high trophic state of the river might permit the rapid recovery of the cladoceran community. The predation impact of juvenile fish in the Nakdong River seems to be affected by the existence of piscivore as well as high trophic status.

• Proceedings of the Korean Society of Fisheries Technology Conference
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• 2001.10a
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• pp.354-355
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• 2001

국내 수산자원은 어선세력의 증가와 어획기술의 발전에 의한 어획합력, 연안역 개발에 의한 산란 성육장의 축소 등으로 1970년대 이후로 자원감소의 현상이 현저하게 나타나고 있다. 효율적 자원조성을 위한 방안으로서 치어방류 사업이 근년 본격적으로 시행되면서 1999년에는 약 2,300만 마리의 치어방류를 하고 있으며, 방류효과에 대한 긍정적 평가가 조사 보고 되고 있다 (Sung, 1998). (중략)

• Development and Reproduction
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• v.4 no.2
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• pp.195-201
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• 2000

Sex differentiation process of the spotted sea bass, Lateolabrax maculatus, was investigated by histological method. The fish samples were collected from just after hatching to 365 days later. The primordial germ cells and genital ridge were appeared separately hanging under air bladder in 30-day larva (total length: 11.7~13.2 mm), and were unified into the undifferentiated gonads in 40-day larva (12.5~14.0 mm). The ovarian differentiation was started in 60-day juvenile (23.6~27.0 mm). The somatic tissues were elongated in tip of both ends of undifferentiated gonad and were fused each other. The complete ovarian cavity was appeared in 80-days juvenile(33.1~42.5 mm). The testicular differentiation was initiated in 70-day juvenile (24.8~31.6 mm). The rudiment of sperm duct was appeared in the center of the undifferentiated gonad. The meiosis of germ cells in the ovary was started in 168-day juvenile (88.0~115.4 mm). In 287-day juvenile (175.1~233.6 mm), the ovary was filled with both of chromatin stage and perinucleolus stage oocytes. The meiosis of male germ cells was started in 245-day juvenile (124.4~168.3 mm). However, the seminiferous tubules of testis were filled with numerous sperm in 365-day juvenile (162.5~253.8 mm). The sex ratio of male and female was 1:1.38. Considering these results, the spotted sea bass was showed differentiated type in sex differentiation and gonochorism in sexuality.

• Journal of Fisheries and Marine Sciences Education
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• v.26 no.4
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• pp.695-704
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• 2014

The purpose of this study was to obtain reference values of serum chemistry in Korean rockfish (Sebastes schlegeli), 5 juvenile (n=25) and 3 broodstock (n=15) subpopulations which were differentiated by cultured method. Serum samples were analyzed for the following commercial clinical kits: total protein, albumin, glucose, AST (aspartate aminotransferase), ALT (alanine aminotransferase), total cholesterol, free cholesterol, LDH (lactate dehydrogenase) and ALP (alkaline phosphatase). Significant differences were observed in the values of total protein, albumin, total cholesterol, AST, ALT, LDH and ALP between juvenile and broodstock subpopulations. In the comparison of total protein, albumin, total cholesterol and ALP, broodstock subpopulations showed higher levels. On the other hand, increased AST, ALT and LDH were observed in juvenile subpopulations. These results indicate that cultured method are major contributors to health-related physiology of Korean rockfish, juveniles and broodstocks.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.12 no.2
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• pp.86-93
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• 2007

We analyzed the aquatic insects and stomach contents of chum salmon (Oncorhynchus keta) fingerings which were collected at Namdae stream in Yangyang. A total of 6 orders, 25 family, and 52 species of aquatic insects have been found in the study area. The majority of prey eaten by chum salmon fingerlings was Diptera, which occupied 91.7% of prey items by number and 40.9% by wet weight. The food items from juvenile salmon stomachs were matched with living organisms in the river. Therefore it seemed that there was no food selectivity of juvenile chum salmon in Namdae stream. The stomach contents of masu salmon fry showed a similar pattern to the fingerlings of chum salmon. This result will provide information on the carrying capacity of Namdae stream for chum salmon.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.30 no.1
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• pp.62-71
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• 1997

The apparent nutrient digestibilities were examined by using chromic oxide indicator according to the various fecal collection methods in juvenile and adult Korean rockfish (Sebastes schlegeli). Feces were collected from three replicate groups of fish by dissection, stripping or decantation using fecal collector attached to fish rearing tank, respectively. The digestibilities of dry matter, protein, lipid, and energy were affected by fecal collection methods (P<0.01), but not affected by fish size. The digestibilities of nutrient determined by stripping or decantation methods were significantly higher than those determined by dissection method (P<0.01). No significant differences in the digestibilities of protein, lipid and energy were found between the stripping and decantation methods in adult fish (P>0.01). The digestibilities of dry matter, protein, lipid, energy, nitrogen-free extract, and total amino acids in juvenile and adult fish were 58, 93, 94, 79, 32, and $93\%$, and 61, 94, 96, 80, 29, and $94\%$, respectively, when they were measured by decantation method. Methionine, cystine and valine digestibilities were significantly lower than those of other amino acids in both juvenile and adult fish (P<0.01). Results indicate that stripping or decantation with fecal collector could be a reliable digestibility procedure for measuring the nutrient digestibilities in Korean rockfish.

• Proceedings of KOSOMES biannual meeting
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• 2009.06a
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• pp.167-169
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• 2009

넙치 치어에 대한 Naphthalene의 급성독성을 조사하기 위하여 대조구($0{\mu}g/\ell$), 1000, 1800, 3200, 5200, $10000{\mu}g/\ell$의 6개의 Naphthalene 농도구를 실정하여 24시간 동안 노출험을 실시하고 혈액학적 성상을 분석하였다. 넙치치어에 대한 Naphthalene의 24h-$LC_{50}$은 $2346.19{\mu}g/\ell$를 나타냈다. 넙치의 혈액학적 반응에서 헤마토크리트값은 5600, $10000{\mu}g/\ell$의 농도에서 대조구와 비교하여 유의하게 증가하였고, 글루코스는 $10000{\mu}g/\ell$의 농도에서 유의하게 증가 하였다. 삼투압 농토는 3200, 5600, $10000{\mu}g/\ell$의 농노 구에서 유의하게 증가하였다. 반면, 이온 분석 결과 $Na^+$, $K^+$은 5600 및 $10000{\mu}g/\ell$ Naphthalene 농도구에서 유의하게 증가하였으나 $Cl^-$는 큰 차이를 보이지 않았다.

• Proceedings of the Korean Society of Fisheries Technology Conference
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• 2000.05a
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• pp.298-299
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• 2000

바다목장화 사업의 일환으로 치어의 방류효과 제고를 위한 기초적 연구로서 조피볼락을 대상으로 자연산 치어와 양식산 치어의 마취내성을 조사하였다. 어류에 미치는 스트레스는 마취, 저산소, 공기노출, 기아, 염분 등 여러 가지가 있겠지만, 이중 마취에 대한 내성의 측정은 어류의 마취제들이 마취작용뿐만 아니라 그 자체가 어류에 대하여 스트레스 요인으로도 작용하므로(Smit et al., 1979; Barton et al. 1982; 정준기 등, 1994), 어류의 건강도를 판정할 수 있는 간단한 방법으로 이용이 가능하다. 따라서 자원조성용으로 조피볼락 치어를 자연 생태계인 바다에 방류하였을 때, 새로운 수서 환경에 대한 적응 능력 판정의 척도로서 자연산 및 양식산 조피볼락 치어의 마취내성과 공기노출 내성 시험을 실시하였다. (중략)

• Journal of Aquaculture
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• v.21 no.4
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• pp.304-308
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• 2008

Strength of juvenile black seabream (Acanthopagrus schlegeli) produced in the different types of hatchery for wild stock enhancement was evaluated in terms of resistances against anesthetizing agent, tricaine methane sulfonate (MS-222), and dry exposure. The working dosages of MS-222 varied significantly with two different water temperature and hatchery populations. Namely, water temperature $22^{\circ}C$ populations were less resistant against the chemical over water temperature $12^{\circ}C$ ones. MS-222 effects also differed with the fish with different growth histories. The fish seeds in collected from wild showed stronger resistances, earlier recoveries, and lower mortalities, compared to those cultured in land-based tank. Similar results were achieved in the juveniles challenged to dry exposure. These results suggest that wild population of black seabream are more resistant against anesthetic stress, expressed as anesthesia, recovery, and mortality, and further that the population are "healthier" than others.