• Journal of fish pathology
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• v.35 no.2
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• pp.225-230
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• 2022

Viral hemorrhagic septicemia (VHS) is one of the most serious viral diseases affecting farmed olive flounder (Paralichthys olivaceus) in Asian countries. VHS, caused by viral hemorrhagic septicemia virus (VHSV), occurs in over 80 different cultured and wild fish species worldwide. Our previous study demonstrated that VHSV infection can be restricted by adjusting the water temperature to over 17℃ from the host optima. We confirmed that the effective VHSV immersion vaccine treatment was a tissue culture infection dose (TCID) of 10^5.5 TCID₅₀/mL at 17℃. However, the safety of live VHSV immersion vaccines remains unclear. The objectives of this study were to 1) demonstrate the safety of the live VHSV immersion vaccine under co-habitant conditions and 2) estimate the pathogenicity of VHSV in live VHSV-vaccinated flounder at 10℃. No mortality was observed in olive flounder treated with the live VHSV immersion vaccine, and the vaccinated flounder challenged with VHSV did not transfer VHSV to naïve fish at 10℃ through cohabitation. VHSV titration was below the detection limit (< 1.3 log TCID₅₀/mL) in live VHSV immersion vaccine-treated flounder challenged with VHSV at 10℃. This study demonstrated that flounder treated with the live VHSV immersion vaccine were resistant to VHSV infection, and the live vaccine was also safe for naïve fish even at a water temperature known to be VHS infectious.

• Journal of fish pathology
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• v.36 no.2
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• pp.403-408
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• 2023

Mullet is an important marine aquaculture fish species in Korea, with a total of 7,237 tons produced as of 2022, making it the 5th most produced marine aquaculture fish species. In this study, ectoparasites presumed to be isopods were discovered in the fins of farmed flathead grey mullet (average weight 550 g), and the characteristics of the parasites were confirmed. The length of the parasite was 5 to 18 mm, and 3 to 7 parasites were infected per fish. To analyze the characteristics of the parasites, molecular biological identification and phylogenetic analysis were performed using the cytochrome c oxidase subunit I (COI) gene, and it was confirmed to be most closely related to Nerocila japonica in the Cymothoidae family. To confirm the parasite control effect, a direct exposure drug sensitivity test was conducted on five types of aquatic drugs and fresh water, trichlorfon was confirmed to be effective.

• Journal of fish pathology
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• v.35 no.1
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• pp.1-25
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• 2022

The aquaculture industry has developed rapidly over the last three decades and is an important industry that supplies over 15% of humans' animal protein intake; therefore, there is a need to increase production to meet the continuous demand. The fish cage farms on the southern coast (Kyengsangnam-do and Jeollanam-do) of Korea are critical resources in aquaculture because they account for approximately 90% of the national total fish cage farms by water area ratio. However, the current aquaculture environment is being gradually affected by climate change, which is a global issue, and its effects are expected to intensify in the future. Therefore, it is urgently imperative to accurately evaluate the effects of climate change on South Korean aquaculture industries and to develop social and national strategies to minimize damage to the fishing industry. The damage to fish farmed in cage farms on the southern coast is increasing annually and the leading causes are high and low water temperature and red tides, which are directly or indirectly related to climate change. At present, global warming can provide opportunities for aquaculture industrialization of fish or other novel species, with economic implications. However, despite such opportunities, the influx of new species can also cause problems such as ecological disturbances, increase in the reproduction frequency of microalgae such as red tide, increase in disease incidence, and occurrence and periods of high water temperatures in summer. The scale of farmed fish mortality is increasing due to the complex effects of these factors. Increased damages due to fish mortality not only have severe economic impacts on the aquaculture industry, but the social costs of responding to the damage and follow-up measures also increase. various active responses can reduce the mortality damage in fish farms such as improving the management skills in aquaculture, improved species breeding, efficient food management, disease prevention, proactive responses, and system-wide improvements. This review article analyzes the large-scale mortality cases occurring in fish cage farms on the southern coast of Korea and proposes measures to mitigate mortality and enhance responses to such scenarios.

• Journal of fish pathology
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• v.21 no.3
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• pp.259-270
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• 2008

Disease surveillance was performed to monitor the prevalence of fish pathogens in wild marine fish caught in coastal offshore water in Korea. A total of 333 of fish samples were collected at set net or fish market at landing port in Pohang (East Sea), Taean (Western Sea), Goseong and Tongyeong (Southern Sea) and 21 species of pathogens causing clinical infections to farmed fish were investigated. The detection rates of fish pathogens from Mugili formes, Tetraodontiformes, Pleuroneciformes, Sorpaeniformes, erciformes and Clupeiformes were 90.9, 61.1, 47.6, 43.6, 37.2 and 11.8%, respectively. Comparing with prevalence of diseases seasonally, both the detection rates of bacteria and parasite were higher than those of virus in April but the detection rates of parasites were distinctively higher than those of bacteria in August with high water temperature. Virus were detected in fish samples caught in the Western and Southern Sea in April. The detected parasites were Trichodina, Ichthyophthirius, Dactylogyrus, Microcotyle, Bivagina, Caligus, Alella and Myxobolus. Among the bacterial pathogens, Vibrio, Streptococcus, Photobacterium, Psuedomonas were predominant. Viral nervous necrosis virus (VNNV) and flounder lymphocystis disease virus (FLDV) were detected from the 6 species of fish virus examined in this study.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.33 no.2
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• pp.115-118
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• 2000

The production of cultured coho salmon (Oncorhpchus kisutoh) in Korea has being increased year after year. Smolt being reared in freshwater suffer transferring into seawater and are farmed in cages for fattening. This handling processes including transportation, confinement into cages are unavoidable stress to fish in salmon farming and often end up to mass mortality, This study aimed to investigate the impact of handling process on the stress responses of coho salmon. The indicator of stress was measured by cortisol to be a first response, and for the second response test, glucose, triBlyceride, cholesterol, lactate and electrolyte of $K^+, Na^+, Cl^-$ in serum and the activities of alanine aminotrtnferase (ALT), aspartate aminotransferase(AST) and lactate dehydrogenase (LDH) were analyzed. As a result, the concentration of cortisol, glucose as well as LDH activity were significantly increased, whereas others showed no difference comparing with control group. It obviously demonstrated that handling process made fish stressful.

• Fisheries and Aquatic Sciences
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• v.21 no.6
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• pp.17.1-17.7
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• 2018

This study investigated the trend in emaciation infection outbreak in olive flounder (Paralichthys olivaceus) of Jeju island, South Korea, during 2014-2015. A total of 900 fish were systematically examined by PCR method using the EM-F/EM-R primer set in April, May, September, November, and December 2014, and the infection rate was recorded. In 2015, the same examination was conducted in March, May, July, and October but with 660 fish. It was found that the infection rate was 18.3~71.6% in 2014, which increased to 16.3~90.3% in 2015. Furthermore, September and December in 2014 and March, July, and October in 2015 showed a relatively higher infection rate. According to the infection trend analysis, which depended on the sample size, the infection occurred in all of fish sizes in this study and 11~30 cm fish group showed the highest infection rate. Histological examination confirmed that the kidney areas of the emaciating infected olive flounder contained several spores of $4{\sim}9{\mu}m$, and in severe cases, the elimination and destruction of tissue were confirmed by PCR. Thus, an important portion of farmed olive flounders in the Jeju region suffers from emaciation disease. This epidemiological survey serves as a useful reference on the emaciation disease of cultured olive flounders in Jeju

• Journal of Food Hygiene and Safety
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• v.27 no.3
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• pp.290-294
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• 2012

Vibrio spp. and Streptococcus spp. have caused a considerable disease of farmed fish and economic loss in fish farming and seafood industry. In this study, the efficacy of an aquatic disinfectant tablet composed to calcium hypochlorite was evaluated against V. anguillarum and S. iniae. A bactericidal efficacy test by broth dilution method was used to determine the lowest effective dilution of the disinfectant following exposure to test bacteria for 30 min at $4^{\circ}C$. An aquatic disinfectant tablet and test bacteria were diluted with distilled water (DW), hard water (HW) or organic matter suspension (OM) according to treatment condition. V. anguillarum on the DW, HW and OM condition was completely inactivated with 16,000 15,000 and 13,000 fold dilutions of the disinfectant, respectively. On the DW, HW and OM condition, S. iniae was absolutely inactivated with 17,000 16,000 and 14,000 fold dilutions of the disinfectant, respectively. As an aquatic disinfectant tablet possesses bactericidal efficacy against fish pathogenic bacteria such as V. anguillarum and S. iniae this disinfectant solution can be used to control the spread of fish infective bacterial diseases.

• Journal of Fisheries and Marine Sciences Education
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• v.28 no.5
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• pp.1444-1458
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• 2016

The expansion of high-density aquaculture in the limited waters has caused a wide variety of problems. The problems include environmental problems nearby aquaculture sites, growth rate of aquatic organisms, quality decline of farmed fish and price fall in the market. The phenomenon of aquaculture industry happens in not only inshore but also offshore. Therefore, the fisheries authorities have been changing their policy paradigms from mass production to sustainable production based on ecosystem. Other countries, however, focusing on relieving poverty and providing protein from fish production have not recognized the degree of seriousness. When it comes to enhancing the problems, National Institute of Fisheries Science has been developing the technology of Integrated Multi-Trophic Aquaculture (IMTA) to reduce and to prevent contaminants from fish and aquaculture sites, remained feed from fish farming process. In long-terms of view, the system is one of the most sustainable fishery production methods based on ecosystem. As integration of nutrient feed system from aquatic organisms is firmly established, the earlier mentioned problems will be diminished gradually. In term of the substantiality, this study was conducted. The research on management system for IMTA also has been incorporated. This study also investigated the features and current status of IMTA and demonstrated the developed management system and direction for the future advancement.

• Journal of Microbiology and Biotechnology
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• v.29 no.8
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• pp.1324-1334
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• 2019

Fish mycobacteriosis is a common bacterial disease in many species of freshwater and marine fish and has caused severe loss of fish production. Mycobacterium marinum has been the most prevalent pathogen observed in several outbreaks of mycobacteriosis of farmed sturgeons in China. However, the immune responses and pathology of sturgeons in mycobacterial infection are rarely studied. Therefore, we used the Illumina RNA-seq method to analyze the transcriptome profile of Acipenser schrenckii challenged with Mycobacterium marinum. To begin, 168,220 non-redundant contigs were acquired from the infection and control groups, and among these, 33,225 contigs have acquired annotations. A total of 4,043 differently expressed (DE) contigs between the two groups were identified, and among these, 2479 were up-regulated and 1564 were down-regulated in the infected fish. A total of 1,340 DE contigs with acquired annotations in KEGG were enriched for 124 pathways including the TNF signaling pathway, and the Toll-like receptor signaling pathway. The roles of DE genes involved in significant pathways and other processes were discussed. The 2,209 DE contigs that have yet to acquire proper annotation may represent candidate genes associated with infection in sturgeons and are expected to serve as immunogenetic resources for further study. To our best knowledge, this is the first transcriptome study on sturgeons under bacterial infection.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.50 no.5
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• pp.624-629
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• 2017

A rainbow trout Onchorhynchus mykiss farm located in Gangwon province, South Korea, experienced approximately 10% mortality in June 2017. Most diseased fish had a markedly distended, gas-filled stomach, and exhibited abnormal behavior at the water surface. In this study, we attempted to identify the cause of stomach distension syndrome in those rainbow trout. The stomach of most of the affected fish were full of unidentified gases and some exudate, and yeast was isolated from the stomach mucosa. Pure cultures of yeast were identified using a multilocus sequence typing scheme based on 18S rRNA, internal transcribed spacers, large subunit rRNA, and the gene encoding the largest subunit of RNA polymerase II (RPB1). The RPB1 gene sequences were compared with those of related species available in a database. The yeast was identified as Scheffersomyces coipomoensis (Candida coipomoensis) based on sequence analyses. This is the first study to reveal that Sch. coipomoensis is a potential causative agent of stomach distension syndrome in farmed rainbow trout. Our results will be helpful for future related studies, and indicate that farmers and stakeholders should observe this emerging disease closely.