Study highlights ISKNV infections in aquarium fishes

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A study investigating outbreaks and risks of infectious spleen and kidney necrosis virus in farmed aquarium fishes has found that the pathogens are widespread.

Virologists from the Department of Aquatic Life Medicine at South Korea's Pukyong National University examined 10 different ornamental fish species that had been raised on fish farms in Korea and tested them for the presence of infectious spleen and kidney necrosis virus (ISKNV).

Their findings, which were published earlier this year in the journal Diseases of Aquatic Organisms, are based on a study that used two different types of Polymerase Chain Reaction (PCR) analysis to detect the viruses.

The results showed that every fish species examined was carrying the iridovirus - with the two types of PCR yielding widely different results.

"None of the 10 fish species analyzed were free of iridovirus as shown by 2-step PCR positive results, and 3 species yielded 1-step PCR positive results with associated mortality," the authors wrote.

"Cloned PCR amplicons of the adenosine triphosphatase (ATPase) and major capsid protein (MCP) genes in genomic DNA of iridovirus showed the same nucleotide sequences as that of infectious spleen and kidney necrosis virus (ISKNV) isolated from the mandarinfish Siniperca chuatsi.

"These results indicate the presence of ISKNV disease in various ornamental fish as new host species and that the disease is widespread throughout different Asian countries including Korea, Singapore and China."

The study claims that infections of ISKNV can either be clinical, with fish deaths reported, or asymptomatic, when fish appear externally healthy and do not die.

Only the 2-step PCR technique is capable of detecting fish that are carrying the viruses but not yet showing external symtoms.

The virus is contagious. During the experiment, the scientists experimentally infected Pearl gourami, Trichogaster leeri with virus from the Moonlight gourami, T. microlepis, which induced mortalities ranging from 70% to 20% in each species respectively.

For more information see the paper: Jeong JB, Kim HY, Jun LJ, Lyu JH, Park NG, Kim JK, Jeong HD. (2008) - Outbreaks and risks of infectious spleen and kidney necrosis virus disease in freshwater ornamental fishes. Dis Aquat Organ. 2008 Jan 24;78(3):209-15.