There’s nothing like the sight and smell of dead fish on a beach to ruin the cottage mood. Hundreds of common carp were found rotting on the shoreline of Lake Winnipeg’s cottage country, between Patricia Beach and Victoria Beach. Common carp are an invasive species in Canada that disrupt ecosystems by pulling up vegetation and stirring up mud, but seeing them wash up dead in large numbers is an alarming sight for Manitoba Fish and Wildlife officials who are investigating the possibility of a viral disease causing the mass fish death.
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Samples collected at the beginning of June are being analyzed for the presence of two viruses which are known to affect common carp. “We will not know the cause until the tissue analysis is completely, which will take approximately 2 weeks,” John Neufeld with MFW explained.
The team is on the lookout for koi herpes virus, which has been documented in Manitoba. A provincial factsheet about koi herpes virus notes that the disease affects common carp, koi, and goldifsh, but cannot be transmitted to humans. Infected carp are even safe to eat, if you can get past the symptoms of sunken eyes, blisters, and rotting gills.
The second virus the team is looking for, spring viraemia of carp, has not been reported in Manitoba. While it too is not harmful to humans, the Canadian Food Inspection Agency reports that the virus can spread to other finfish, including tench, northern pike, and pumpkinseed.
Koi herpes virus and spring viraemia can be spread by a method called horizontal transfer, says Sharon Clouthier, a research scientist at the National Aquatic Health Program under the Department of Fisheries and Oceans Canada. Horizontal transfer occurs when the virus is excreted through a fish’s feces, mucous layers, urine, and spawning products.
“If the die off coincides with spawning, normally the fish—particularly carp—are in close proximity with each other, and this becomes quite an effective mode of transmission.”
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“Generally die offs occur in native populations,” says Clouthier. Just like humans, if the fish haven’t been exposed to a virus in the past, they won’t have an immune response to protect them. If the test results indicate that a virus caused the die off, the immune systems of the carp in Lake Winnipeg could not have not been previously exposed to whatever virus they discover.
“You can never predict when a fish kill is going to occur in wild populations,” says Clouthier. But you can take proactive steps by tracking where viruses are found in the wild. The National Aquatic Health Program, which is co-delivered by Department of Fisheries and Oceans and Canadian Food Inspection Agency, conducts surveillance to identify where viruses occur in Canadian watersheds.
If you discover large numbers of dead fish washing up on your cottage property, the best thing to do is to take a step back and contact the appropriate provincial authority. While the Province of Manitoba has its Fish and Wildlife Branch, Ontario cottagers can contact the Ministry of Natural Resources and Forestry. It provides a detailed online overview on how to deal with a fish die off on your property.