Well-known and respected Pennsylvania outdoors writer Darl Black said that a recent crappie fishing outing on Pymatuning Reservoir with his wife Marilyn stunk, but it wasn’t for the lack of catching any of the tasty panfish.
Instead, a nose-curling stench came from the rotting carcasses of untold thousands of carp, the fish dying as the result of the swift-moving and equally fast-acting koi herpes-virus. This virus was identified only in 2000 but has been encountered nearly worldwide – particularly in countries with extensive aquaculture industries such as India, China, and Israel where carp are raised for food.
Also heavily impacted are places with considerable ornamental fish businesses that raise the carps’ close cousin, the koi, the species after which the viral disease is named.
To date only carp and koi have been identified as susceptible to koi herpes-virus and no other member of the minnow family – to which these two species belong – has shown evidence of the disease.
As for visible symptoms, infected fish typically exhibit signs of infection that include severe gill lesions seen as gill mottling with red and white patches, bleeding gills, sunken eyes, and pale patches on the skin.
An infected fish may succumb to the disease in an eye-blink of a rush: within only one or two days. And some research says that an ornamental koi pond could be totally wiped out in a matter of just a few weeks.
However, both the Ohio Division of Wildlife and the Pennsylvania Fish and Boat Commission have been quick to quiet any fears that koi herpes-virus poses a risk to human health.
Matt Wolfe, fisheries biologist with the Wildlife Division’s District Three (Northeast Ohio) Office in Akron, said that diseased-dead carp were first noted around the Labor Day weekend at the 16,349-acre flood-control reservoir, built in the mid-1930s. The lake rests in both Ohio and Pennsylvania and which share joint fisheries management of the popular Northeast Ohio-northwest Pennsylvania angling destination.
No sick or dead carp were observed by Fish Commission staff in the eastern portion of the reservoir commonly referred to as the Pymatuning Sanctuary. The sanctuary is separated from the main lake by a narrow dam and small spillway. This is the fabled and popular tourism location where “the ducks walk on the fishes’ backs.”
Live carp were collected by Pennsylvania’s Fish and Boat Commission staff on September 12 who then shipped the fish to the University of Minnesota’s Aquatic Invasive Species Research Center for testing. The Center confirmed on September 21 that the fish had tested positive for the koi herpes-virus, said Commission spokesman Eric Levis.
Both Ohio and Pennsylvania fisheries experts say there is no way of knowing where the disease originated, though Pymatuning’s exceptionally large carp population made it an ideal candidate for koi herpes-virus to gain a foothold, Wolfe said.
“If you had to pick a lake where there’d be a high likelihood for the disease, Pymatuning would be it,” Wolfe said.
The Fish Commission’s addendum on the subject notes that the disease could have been found in some infected fish, been present in the bilge water of an angler’s boat, or perhaps it originated from a backyard pond or maybe the disease came with an aquarium fish that someone may have released into the lake.
But Wolfe did note that with the arrival of cooler weather the lake’s water temperature will decline as well, throttling back the incidence of the disease.
As for whether the koi herpes-virus will rear its ugly head, that is “hard to say”, though perhaps the disease’s impact template may match that of another fish virus, said Wolfe.
“Look at VHS (viral hemorrhagic septicemia) that hit Lake Erie; it ran rampant and eventually fish began developing an immunity to it,” Wolfe said.
However, the Fish Commission says it is entirely possible that Pymatuning may experience periodic outbreaks of koi herpes-virus. That situation has some history at Pymatuning which is still seeing residual outbreaks of “red spot disease,” a viral infection that has periodically plagued the lake’s renowned muskie population.
Even so, one concern remains that the some carp may not necessarily becomes victims of koi herpes-virus but possibly may become transmitters of the disease; a sort of Typhoid Mary for carp.
Added to that worry, Wolfe says, is that the disease “could jump ship and be bounced from one lake to another” via hitching a ride in the watery live well of an anglers’ boat or attached to the strands of hydruala - which has likewise infected Pymatuning - and then dropped in the waters of some other reservoir, lake or stream.
“Here at the Division when we retrieve one of our boats we thoroughly treat the hull and the trailer with disinfectant to kill any organism,” Wolfe said. “It’s a good and highly recommended practice for anyone to do.”
- Jeffrey L. Frischkorn