Heterosporosis experiments begin in newly renovated MAISRC laboratory

Approximately 800 yellow perch will soon call MAISRC’s recently renovated Lab and Holding Facility home. The perch are part of a research project to determine how much of a threat to Minnesota’s lakes and fish the disease Heterosporosis presents.

This research, which will study how long it takes a fish to become infected, what role temperature plays, and how it is spreading, will inform a disease ecology and population model for estimating the impact of Heterosporosis on Minnesota wild fish populations. The project will:

1. Study how many spores of Heterosporis sutherlandae it takes to infect a fish, and how long it takes to develop a clinical infection. Fish likely have some natural defense to protect against the parasite, but it is unknown how effective they are. To test this, researchers will expose the perch to different concentrations of the parasite in the lab and monitor them for symptoms.

2. Determine whether water temperate has an impact on the virus. Anecdotal evidence is showing that the virus appears more often in the winter, when fish immune systems are weakened. The optimal temperature for perch growth is 22° Celsius (72° F), but lake temperatures can range from 0 – 26° C (32° – 79° F). It’s possible that when fish are stressed by suboptimal temperatures or lack of energy stores, their ability to protect against the infection decreases.

3. Establish how the parasite is spreading. Currently, researchers know of two ways that an otherwise healthy fish can become infected: eating an infected fish, or coming into contact with spores shed through the waste of an infected fish. To study this further, researchers will infect perch and measure how many spores are released through waste, as well as expose healthy fish to infected fish and measure the rate of new infections.

“Coarse data on infection rates and impacts of the disease already exist, but much more refined data on fish behavior such as their ability to swim, whether they are eating more or less, and whether their  reproduction could be affected will greatly improve the model,” said Megan Tomamichel, a graduate student working on the project. “It’s important that we predict how the harvestable biomass of perch could be impacted by Heterosporosis because these fish are so important for recreation and aquaculture in Minnesota, as well as important prey for species like walleye.”

Heterosporosis is caused by the microsporidian parasite Heterosporis sutherlandae, and is currently found in 45 lakes in the Great Lakes region. The microscopic spores of the parasite live inside the muscle cells of the fist. As the parasite replicates, it ultimately ruptures the cell and liquefies the muscle tissue. It was first reported in Leech Lake in 1990 and is known to affect 15 species of freshwater fish, including walleye, rendering them inedible.

“We may learn that Heterosporosis is peaking in Minnesota, that it will likely continue spreading, or that it is simply a low-level endemic disease,” added Dr. Paul Venturelli. “Knowing this will inform what kinds of management responses are needed.” 

Read the full April 2016 newsletter here.