• Korean Journal of Fisheries and Aquatic Sciences
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• v.54 no.5
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• pp.596-616
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• 2021

A global increase in fish consumption has led to a rapid expansion of aquaculture production, which has been linked to enhancing the spread of infectious diseases. Viral diseases can cause high mortality in many cultured fish species, posing a serious threat to the aquaculture industry. Infectious hematopoietic necrosis virus (IHNV) is one of the primary threats to aquacultured salmonid species, causing huge economic losses. Since the first report in cultured sockeye salmon Oncorhynchus nerka during the 1950s in North America, IHNV has spread to other regions, including Europe, Asia, South America, and Africa by transportation of infected fish and eggs, causing disease and increasing mortality in a wide variety of salmonid species. Here, we review existing information relevant to IHNV: its phylogenetic characteristics, origin, infection history, virulence determinants, susceptible hosts, vectors, and vaccine development. This review also addresses a possible cross-species transmission of IHNV to a new host, olive flounder Paralichthys olivaceus, a cultured fish of economic importance in East Asian countries.

• Journal of fish pathology
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• v.34 no.1
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• pp.1-7
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• 2021

Red sea bream iridovirus (RSIV), belonging to the genus Megalocytivirus, is the predominant cause of mortality in marine fishes in Korea, including rock bream (Oplegnathus fasciatus). Rockfish (Sebastes schlegelii) are the host fish for RSIV, exhibiting no clinical signs or mortality. Cohabitation challenges, which mimicked natural transmission conditions, were performed to evaluate viral transmission between rock bream and rockfish, and to determine the pathogenicity and viral loads. In cohabitation challenge, artificially RSIV-infected rock bream were the viral donor, and healthy rockfish were the recipient. The results showed that although the donor rock bream had 95-100 % cumulative mortality (>10⁸ viral genome copies/mg of spleen 7-14 days after viral infection), the recipient rockfish did not die, even when the viral genome copies in the spleen were >10⁵ copies/mg. These results indicated asymptomatic infections. Notably, in a reverse-cohabitation challenge (artificially RSIV-infected rockfish as the viral donor and healthy rock bream as the recipient), RSIV horizontally infected from subclinical rockfish to rock bream (10⁷ viral genome copies/mg of spleen 21 days after cohabitation) with 10-20% cumulative mortality. These results suggest that an asymptomatic, infected rockfish can naturally transmit the RSIV without being sacrificed.

• Journal of fish pathology
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• v.36 no.2
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• pp.213-228
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• 2023

We evaluated the transcriptional response of interferon (IFN)-related genes in rock bream iridovirus (RBIV)-infected rock bream under high-, low-, or no-mortality conditions induced by different stocking water temperatures. Under the high susceptibility condition (group A, water temperature 26℃, 100% mortality), only the Mx gene was expressed early, with prolonged expression, and with heavy viral loads of approximately 10⁶~10⁷ major capsid protein gene copies/μL from 4 to 10 days post infection (dpi). However, IRF1, IRF3, IRF8, STAT1, ISG15, PKR, Viperin, GVIN1, IFI44, and ISG56 were activated at later time points (8 dpi) and then quickly decreased (10 dpi). For the low susceptibility condition, the water temperature was set at 23℃ for 7 days (group B) and then reduced to 17℃. Group B exhibited a 28% mortality rate, in which persistent and effective antiviral responses were observed for long periods of time. In particular, at 20 and 22 dpi, when virus replication was peaked at approximately 10⁷/μL, the expressions of most of the IFN-related genes (IRF1, IRF3, IRF8, Mx, STAT1, ISG15, PKR, Viperin, GVIN1, IFI44, and ISG56) were significantly higher in group B than in the control group. Moreover, prolonged and higher levels of IRF3 (at least 30 dpi), IRF8 (at least 30 dpi), ISG15 (at least 30 dpi), PKR (at least 28 dpi), Viperin (at least 30 dpi), and IFI44 (at least 30 dpi) were also observed in the recovery stage of infection. Under the no-susceptibility condition at 17℃ (0% mortality), significantly elevated levels of IRF3, Mx, ISG15, and PKR were observed mostly until 20 dpi. The findings indicate that RBIV infection can induce an efficient IFN-mediated antiviral immune response in low- and no-susceptibility conditions. The findings could be valuable for effective control of viral pathogens in fish.

• Journal of Microbiology and Biotechnology
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• v.25 no.10
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• pp.1761-1767
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• 2015

Sevenband grouper, Epinephelus septemfasciatus, is becoming an important aquaculture species in Korea. However, viral nervous necrosis disease is a large problem causing mass mortality in sevenband grouper aquaculture. Recombinant protein vaccines are one of the best methods to reduce these economic losses. However, the cell-based expression method mainly produces inclusion bodies and requires additional procedures. In this study, we expressed a recombinant viral coat protein of sevenband grouper nervous necrosis virus (NNV) using a cell-free protein synthesis system. The purified recombinant NNV coat protein (rNNV-CP) was injected into sevenband grouper at different doses followed by a NNV challenge. Nonimmunized fish in the first trial (20 μg/fish) began to die 5 days post-challenge and reached 70% cumulative mortality. In contrast, immunized fish also starting dying 5 days postchallenge but lower cumulative mortality (10%) was observed. Cumulative morality in the second trial with different doses (20, 4, and 0.8 μg/fish) was 10%, 40%, and 50%, respectively. These results suggest that rNNV-CP can effectively immunize sevenband grouper depending on the dose administered. This study provides a new approach to develop a recombinant vaccine against NNV infection for sevenband grouper.

• Journal of fish pathology
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• v.21 no.1
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• pp.13-20
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• 2008

This study evaluates the pathogenicity in striped beakperch, Oplegnathus fasciatus infected with red sea bream iridovirus (RSIV) at different water temperature (17°C, 20°C, 25°C and 27°C). When the fish group was infected with RSIV at 17°C and 20°C, cumulative mortality did not show any significant difference with control group. In contrast, the case at 25°C and 27°C, cumulative mortality reached more than 80%. However, RSIV was detected from all of the fish in each temperature. To confirm a relationship between temperature change and heat shock protein (HSP), partial HSP70 cDNA was isolated from striped beakperch.

• Journal of fish pathology
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• v.32 no.1
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• pp.29-35
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• 2019

A monitoring was performed to survey the mortalities that had occurred in the aquaculture farms of olive flounder (Paralichthys olivaceus) in South Korea from 2015 to 2017. The indirect inquiry for entire farms and the sample survey for selected farms were carried out. The aquatic organism disease inspectors, who have a national license for the diagnosis and prevention of aquatic organism diseases and a have close relationship with the farms, investigated the rates and causes of mortalities according to the standard manual. The mortality rate by sample survey of farms in 2015, 2016, and 2017 were 24.78% (Chunnam: 17.86%, Jeju: 28.69), 30.19% (Chunnam: 24.45%, Jeju: 32.65), and 21.59% (Chunnam: 10.57%, Jeju: 26.00%), respectively. The major cause of mortality was scuticociliatosis, and the mortality caused by viral hemorrhagic septicemia and emaciation disease (Jeju) were also high. Our results can contribute to effective establishment prevention of epidemics system and acquired status as a disease-cleansing country.

• Journal of fish pathology
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• v.34 no.1
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• pp.99-104
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• 2021

In this study, we investigated safety and efficacy of a low temperature immunization protocol with NNV in red spotted grouper, Epinephelus akaara and long tooth grouper, Epinephelus bruneus and seven band grouper, Hyporthodus septemfasciatus. Further, growth rate between immunized and naïve fish was evaluated during the experiment to check side effect of immunization. Three grouper species were immunized by immersion method with live NNV at 10^5.0 TCID₅₀/mL at 16.5℃ for 30 min and reared for 120 days at natural sea water temperature. To evaluate growth rate, total length and wet weight was measured 7 times after immunization. Immunized three grouper species were challenged by intramuscular inoculation with NNV at 10^4.2 TCID₅₀/100 µL/fish. Immunization at low temperature with live NNV did not show any clinical symptoms of infection, mortality and inhibition of growth. After challenge, cumulative mortality of naïve seven band grouper, red spotted grouper, long tooth grouper were 45, 10, 20 %, respectively. However no mortality was observed at immunized groupers. Thus, it was demonstrated that immunization at low temperature with live NNV are able to protect three different species of groupers without inhibition of growth.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.45 no.6
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• pp.606-611
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• 2012

This study examined the effects of dietary glycoprotein extracted from Porphyra yezoensi on growth performance and resistance against the pathogenic bacteria Edwardsiella tarda in olive flounder. A porphyra-originated glycoprotein (P) was extracted using sequential processes of water and ethanol treatment. P extracts were added to a fish-meal-based diet at concentrations of 0.0, 0.5, and 1.0% (designated as Con, $P_{0.5}$, and $P_{1.0}$, respectively). Fish were fed one of the three experimental diets for 10 weeks. All fish groups exhibited over 96.7% survival during the experimental period. Results indicated that the fish fed diets containing P showed an increase in growth performance, including enhanced weight gain, specific growth rate, and feed efficiency. An increase in insulin-like growth factor (IGF-1) was observed in the fish fed the $P_{1.0}$ diet, as compared to those fed Con. At the end of the 10-week feeding trial, all fish were infected with E. tarda, and accumulated mortality was monitored for 8 days. Fish fed the Con diet exhibited increasing mortality from day 3 to the end of the challenge test, whereas the mortality of P-fed fish ceased at day 5. We suggest that supplementation with P-originated glycoprotein in aquafeed may increase growth performance and resistance against pathogenic bacteria in olive flounder juveniles.

• Journal of fish pathology
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• v.22 no.2
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• pp.97-105
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• 2009

Scuticociliates Miamiensis avidus (syn. Philasterides dicentrarchi) causes high mortality and bad growth in olive flounder Paralichthys olivaceus. Temperature is an important factor not only for growth of pathogens but also for host immune system in poikilothermal animal. In this study, temperature affecting ciliate growth and pathogenicity against olive flounder were examined. Doubling time for the ciliate growth was 61.82 hours at $5{^{\circ}C}$, 26.32 hours at $10{^{\circ}C}$, 21.14 hours at $15{^{\circ}C}$, 16.86 hours $20{^{\circ}C}$ and 16.21 hours at $25{^{\circ}C}$. Maximum ciliate numbers were similar at $10-20{^{\circ}C}$ at the range of $1.54-1.75{\times}10^{5}$/ ml. Duplicated intraperitoneal injections were conducted with the ciliates by the concentrations of $1{\times}10^{2}$, $1{\times}10^{6}$, $1{\times}10^{4}$and $1{\times}10^{5}$/ fish (average 8.34 cm, 4.33 g) then kept at $10{^{\circ}C}$, $15{^{\circ}C}$ and $20{^{\circ}C}$. Cumulative mortality was low at $10{^{\circ}C}$ and the mortality was increasing at higher water temperatures. In addition, cumulative mortality was higher at higher dose of infections. In conclusion, Scuticocilite M. avidus grew well at higher temperature (at $5{^{\circ}C}$, $10{^{\circ}C}$, $15{^{\circ}C}$ and $25{^{\circ}C}$) in vitro, and olive flounder mortality due to M. avidus was highly water temperature and dose dependent. The results of this study suggest that water temperature control may one of the essential factor to reduce mortality due to M. avidus infection.

• Journal of fish pathology
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• v.16 no.3
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• pp.153-159
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• 2003

The high mortality of cultured juvenile turbot, Scophthalmus maximus occurred in Gochang on June, 2003. The diseased fish was lethargic with reduced feed intake. Grossly, these fish showed pale body, abdominal extension and exophthalmia. The dominant internal gross features of diseased fish were severely enlarged spleen, pale gills and/ or liver. Diseased fish histologically showed basophilic enlarged cells in the kidney, spleen, gill, heart, stomach, intestine, liver, pancreas and adipose tissue. Transmission electron microscopy (TEM) reveled hexagonal virions in the cytoplasm of necrotic cells. The viral particles lead a central electron-dense core and an electron translucent zone, and were 136-159 nm in diameter. These results suggest that the virus belonging to the iridoviridae was responsible for the mortality of cultured juvenile turbot.