Mysterious Herpes Killing Carp in Canada

University of Guelph scientists helped determine that a strain of herpes was killing off carp in central Ontario lakes. But it remains unknown whether the Koi herpes virus (KHV), which caused a die-off of fish numbering in the tens of thousands, will spread. Guelph Lake has a large population of carp.

Grand River Conservation Authority is on the alert, and the Ontario Ministry of Natural Resources said there is no threat to human health from the virus.

"As to whether the carp die-off could hit the waters around Guelph, the short answer is, we can't predict that," said ministry spokesperson Rick Winston, explaining carp die-offs occur due to a number of factors, including spawning conditions and rapidly changing water temperatures. There was a similar die-off last year in the Kawartha Lakes area from the columnaris virus, but the species has made a strong recovery.

"We are not aware, on our properties, of any carp die-offs or anything like that this year," said Dave Schultz, GRCA manager of communications. "Obviously our aquatics people are paying close attention to this. It's part of their normal business. But until something happens, you just carry on."

U of G researchers identified KHV last year, and the finding was confirmed by federal laboratories. The virus is an infectious disease affecting carp, koi and goldfish. It is believed it was introduced into the wild carp population through the hobby-fish trade, perhaps through the release of infected koi or goldfish into streams or lakes, or the disposal of sick or dead hobby fish by flushing them down toilets.

Roselynn Stevenson is a professor of microbiology at U of G, and an expert in fish biology and fish immunology. She said there have been major problems with KHV in Europe, and wherever there is a sensitive population of carp there is a potential problem.

"The question always becomes, did it get brought from someplace, or have there been different and not so pathogenic strains, that have always been there at low levels?" she said. "You really only pick up on a pathogen when it has an effect. Changing conditions or stress on the fish can bring it out."

Setting goldfish free, she said, may seem like the compassionate thing to do, but they can be a carrier of disease, infecting sensitive fish in the wild.

The MNR recommends against flushing sick or dead goldfish or koi down the toilet, to prevent the spread of KHV. Instead, bury them or place them in the garbage.

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Mysterious Herpes Killing Carp in Canada