• Journal of fish pathology
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• v.34 no.2
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• pp.123-131
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• 2021

This study investigated the phylogenetic classification and pathogenicity of 6 infectious hematopoietic necrosis virus (IHNV) strains isolated from salmonid fish in Gangwon-do, Korea. Based on the nucleotide sequence of mid-G region, all six strains belong to J genotype, of which 5 are J-Nagano type and 1 J-Shizuoka type. In a challenge test, 5 isolates of J-Nagano type IHNV showed a various mortalities as 2 isolates induced a high mortality of 100% and the other 3 isolates induced mortalities of 50, 30, and 20% after intraperitoneal injection in rainbow trout (Oncorhynchus mykiss). Meanwhile no mortality was occurred by 1 isolate of J-Shizuoka type virus. Thus, it seems that there might be no relation between genotype and pathogenicity within IHNV J genotypes. This is contrary to previous studies where reported a higher pathogenicity of J-Shizuoka type virus than J-Nagano type virus in rainbow trout. Further examination will be required to clarify this since only one J-Shizuoka type virus was analyzed in this study.

• Korean Journal of Ichthyology
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• v.29 no.1
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• pp.75-79
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• 2017

About 10% mortality occurred in cultured rainbow trout Oncorhynchus mykiss at a marine farm in Jeju in 2014. Diseased fish showed markedly abdominal distension and distended stomach. Although parasites, bacteria or viruses were not isolated from diseased fish, numerous Candida sp. were isolated from distended stomach. In experimental infection with Candida sp., mortality was not observed in most fish and clinical sign of distended stomach was not observed in the fish. These results suggest that Candida sp. may not be the etiologic agent of stomach distension syndrome. This is the first report of stomach distension syndrome in seawater farmed rainbow trout in Korea.

• Journal of Korean Society of Water and Wastewater
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• v.20 no.4
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• pp.573-584
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• 2006

This study was carried out to investigate the causes of fish kills in the Yudeung Stream in Daejeon, Korea using literature reviews, governmental and our water quality monitoring data of the study site, rainfall data, intensive water quality monitoring during rainfall events, sediment pollutant contents and laboratory bioassay tests. Fish kill in urban streams can be caused by combined effect of reduction in dissolved oxygen concentration, increase in toxic material or increase in turbidity in waterbody due to introduction of surface runoff or effluent of combined sewer overflows after rainfall from the watershed areas. Despite of extensive and intensive field surveys and laboratory tests, it was found that those conventional methods have limitations to identify causes of fish kills in urban streams. It would be necessary to use dynamic water quality modeling to predetermine the range and level of water pollution in the stream and automatic water quality monitoring system that can collect water samples and detect water quality continuously.

• Journal of Korean Society of Water and Wastewater
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• v.20 no.4
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• pp.585-594
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• 2006

This study focused on the causes of fish kills and its prevention methods in Yudeung Stream, Daejeon, Korea. Intense field data, continuous water quality monitoring system and water quality modeling were applied to analyze the causes. Pollutant can be delivered to urban streams by surface runoff and combined sewer overflows in rainfall events. However, water quality analysis and water quality modeling results indicate that the abrupt fish kills in the Yudeung stream seems to be caused by combined effect of DO depletion, increase in turbidity and other toxic material. Excessive fish population in the study area may harm the aesthetic value of the stream and also has greater potential for massive fish kills. It is suggested to implement methods to reduce delivery of pollutants to the stream not only to prevent fish kills but also to keep balance of ecosystem including human uses. Frequent clean up of the urban surface and CSO, installation of detention basin will be helpful. In the long run, it seems combined sewer system has be replaced with separate sewer system for more effective pollutant removal in the urban area.

• Journal of Life Science
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• v.22 no.6
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• pp.788-793
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• 2012

High concentration of antibiotics has been used to treat the outbreak of edwardsiellosis caused by Edwardsiella tarda in aquaculture. However, not all of the bacteria have been killed with high concentrations of antibiotics treatment by the formation of persister cells with a dormant state. The main objective of this study was to kill persister cell using antibiotics with the addition of natural plant compounds. Antibiotics used in this study consist of 100 mg/ml florfenicol and 100 mg/ml amoxicillin. Ten natural plant compounds with persister cell inhibitor activity to E. coli were obtained from Protein Engineering and Systems Biology Lab. of Sungkyunkwan University. The persister cell inhibition activities of those natural plant compounds were evaluated in test tube. Concentrations of the antibiotics were in the ranges of 25~200 ${\mu}g/ml$. The persister cell formation was observed after 16 hours of culture. Persister cells were killed by antibiotics with natural plant compounds. Among ten natural plant compounds, Gynostemma pentaphyllum, Mallotus japonicus, and Orixa japonica showed persister cell formation inhibition activities. The optimal concentrations of G. pentaphyllum, M. japonicus, and O. japonica for the inhibitor of persister cell formation were 100 ${\mu}g/ml$, 100 ${\mu}g/ml$, and 200 ${\mu}g/ml$, respectively. In vivo study was carried out to evaluate the effect of the antibiotics with natural plant compounds using aquacultural fish, olive flounder, as test animals. G. pentaphyllum, M. japonicus, and O. japonica of 30 ${\mu}g/ml$, 10 ${\mu}g/ml$, and 10 ${\mu}g/ml$ with antibiotics reduced cumulative mortalities, showing the effectiveness of persister cell inhibition.

• Korean Journal of Ichthyology
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• v.31 no.4
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• pp.201-207
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• 2019

Temperature is one of the most important criteria considered in species preference for aquaculture. Acute drop in temperature during winter is a cause of disease and mass mortality in farmed fish. This study was carried out the low water temperature tolerance, oxygen consumption, hematologic and histological responses to use as basic data for the management of fish farming which frequently cause death due to winter water temperature drop. Low-lethal water temperature for 4 days of file fish Thamnaconus modestus (4day-LT₅₀) was 6.97℃ (6.69~7.27℃). Oxygen consumption rate decreased with decreasing water temperature, showing a significant difference between water temperatures. SOD activity increased significantly at 6℃ experimental group than control group (10℃) (p<0.05), but CAT did not show any significant difference between experimental temperatures (p>0.05). Cortisol increased with decreasing experimental water temperature compared to control group. Histological changes in the liver include decreased blood vessels in the blood vessels, proliferation of acid cells, condensation of the nucleus, atrophy of pancreatic exocrine gland cells, and enzyme source granules.

• The Journal of the Korea Contents Association
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• v.22 no.3
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• pp.71-80
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• 2022

In the past, fish diseases were bacterial in aqua farms, but in recent years, the frequency of fish diseases has increased as they have become viral and mixed. Viral diseases in an enclosed space called a aqua farm have a high spread rate, so it is very likely to lead to mass death. Fast identification of fish diseases is important to prevent group death. However, diagnosis of fish diseases requires a high level of expertise and it is difficult to visually check the condition of fish every time. In order to prevent the spread of the disease, an automatic identification system of diseases or fish is needed. In this paper, in order to improve the performance of the disease identification system of Paralichthys olivaceus based on deep learning, the existing pre-processing method is compared and tested. Target diseases were selected from three most frequent diseases such as Scutica, Vibrio, and Lymphocystis in Paralichthys olivaceus. The RGB, HLS, HSV, LAB, LUV, XYZ, and YCRCV were used as image pre-processing methods. As a result of the experiment, HLS was able to get the best results than using general RGB. It is expected that the fish disease identification system can be advanced by improving the recognition rate of diseases in a simple way.

• Korean Journal of Ichthyology
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• v.28 no.1
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• pp.1-8
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• 2016

This study was conducted to investigate the physiological responses of sevenband grouper, Epinephelus septemfasciatus at low temperature condition in winter season. Water temperature was dropped from $12^{\circ}C$ to $5^{\circ}C$ by two different interval (interval I: $-1^{\circ}C/24h$ and interval II: $-1^{\circ}C/8h$). The experimental fishes were exposed for 9 days at each water temperature condition, and were observed survival rate. The blood sample was collected from fishes for analysis of cortisol, glucose, total protein (TP), and electrolytes ($Na^+$, $Cl^-$, $K^+$). Mortality of fish was not observed until $5^{\circ}C$. The mortality (12 individuals) began after 170 h and all fish were death after 174 h in interval I case, whereas the mortality (9 individuals) began after 72 h and all fish were death after 76 h in interval II case. Little different was observed in the physiological responses, but trend was similar between two intervals. The physiological metabolism of plasma cortisol and glucose were increased rapidly, and swimming ability and respiration response was faster at $7^{\circ}C$. This result means that the critical temperature of sevenband grouper was $7^{\circ}C$ at low water temperature condition.

• Journal of fish pathology
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• v.18 no.2
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• pp.157-165
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• 2005

A new disease causing mass mortality of farmed snakehead (Channa arga) has emerged in Korea over the summer of 2005. The affected fish showed no specific external signs with the exception of a distended abdomen and hemorrhaging around the anus. After opening the abdomen, the visceral organs, liver, spleen and kidney, present numerous white nodular structures. Histopathological examination revealed these nodules to be evidence of granulomas in the visceral organs. A Gram-positive, filamentous bacterium was isolated from all of the affected fish. Development of primers for a genus-specific peR assay for Nocardia, following analysis of the sequences of the complete 16S rRNA genes from Nocardia spp. and non-Nocardia bacterial genes, allowed identification of the causative organism as Nocardia. This is the first report of a nocardial infection of fish in Korea.

• Korean Journal of Environmental Biology
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• v.28 no.3
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• pp.143-149
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• 2010

The pathogens and community structure of the fishes in Taehwa river were investigated from March 2007 to January 2009. During the study period, 3,504 individuals belonging to 35 species, 17 families and 9 orders were collected. The numerically dominant and subdominat species were Opsarichthys uncirostris (relative abundance 39.7%) and Hemibarbus labeo (relative abundance 30.9%). There were five Korean endemic species (20.8%) including Squalidus chankaensis tsuchigae, Zacco koreanus, Cobitis hankugensis, Coreoperca herzi, Odontobutis platycephala. The large fishes like Hemibarbus labeo or Opsarichthys uncirostris were gathered around the Samho bridge, sampling site 2 according to a season. The reaction to which two kinds of fish pathogenic virus is all negative and no fish pathogenic bacteria was isolated from 220 individuals. The fish pathogenic parasite not present variously with 7 species. Especially, Trichodina sp. was detected monthly and the infective density was high. But it is cosidered that temporary overcrowding of fish is not influenced mass mortality causing diseases in the specific site of river.