Disease dissolves game fish

Heterosporis is a disease infecting game fish and hurting resort owners who keep their own fisheries.

Graduate student Megan Tomamichel fillets fish to search for a virus, Heterosporis, in the University Veterinary Diagnostic Laboratory on Friday, October 2. The disease, while not known to be lethal to fish outright, infects their muscles and immune systems, preventing them from being sold by fisheries.

Alex Tuthill-Preus

Graduate student Megan Tomamichel fillets fish to search for a virus, Heterosporis, in the University Veterinary Diagnostic Laboratory on Friday, October 2. The disease, while not known to be lethal to fish outright, infects their muscles and immune systems, preventing them from being sold by fisheries.

Ryan Faircloth

Adisease dissolving the muscles of fish could be impacting commercial fishpond owners in the state, and University of Minnesota researchers are searching for a solution.
 
Scientists studying aquatic disease at the University are trying to figure out how heterosporis — a parasite that invades and liquefies fish muscles — travels across Minnesota lakes and impacts fish, particularly game fish meant for consumption.
 
When the parasite enters a fish, it plants itself in muscle cells and causes them to rupture, turning the muscle into liquid, according to the Minnesota Aquatic Invasive Species Research Center.
 
There are 26 known infected lakes in the state, with 15 species — like walleye and yellow perch — prone to the disease.
 
Though the parasite attacks fish, scientists don’t think it would hurt consumers.
 
“Humans aren’t known to be susceptible to it, but it’s definitely unsightly, and you wouldn’t [be able to eat it],” said Nick Phelps, co-principal investigator on the study and a University assistant professor in veterinary population medicine.
 
Phelps said heterosporis seems to impact yellow perch most, especially in the winter, which can hurt commercial pond owners who rely on having a variety of fish. 
 
“You have a resort owner that’s throwing away 30 to 40 percent of their fish because their customers don’t want to eat them,” he said. “That’s a big impact on the catchable biomass, not to mention the impact on the ecosystem.”
 
To model the disease’s impact, researchers are currently working on figuring out its prevalence in wild fish and how it spreads, Phelps said. In the future, researchers hope to control the parasite’s proliferation.
 
“If there is something unique about the environment here that makes it more suitable [for the disease], that’d be really important to know,” he said. 
 
Researchers plan to study in labs and out in the field in hopes of gathering enough data to map out the population of infected fish in the state, said Paul Venturelli, the study’s lead investigator and an assistant professor in the fisheries, wildlife and conservation biology department.
 
“The purpose of the field sampling for these two years is … to see how prevalent this disease is,” Venturelli said. “There’s some indication that the prevalence might vary with temperature.”
 
Though University Bass Fishing Team President Chris Burgan hasn’t encountered the parasite in his fishing practices, he said similar diseases can impact participants in fishing competitions.
 
“[Fish disease] just kind of lowers the population as a whole, so when there’s a big tournament, and you have, like, so many boats going out and looking for one specific species and that population is down, that makes it harder overall,” he said.
 
The disease has also impacted the state’s fishing economy, Phelps said.
 
“If you’re a fisherman, you’re going to pick two lakes to go to,” he said. “There’s a chance of taking home all your fish, or 60 percent of your fish. Which one would you go to?”
 
There are currently no disease control methods, Venturelli said, but he hopes his research will lead to those interventions.
 
“Once we have this modeling done and we understand the effects, then we can start to identify weaknesses,” Phelps said.