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Parasite related to jellyfish found in Lake Onalaska, demonstrates 'biodiversity' of area

Parasite related to jellyfish found in Lake Onalaska, demonstrates 'biodiversity' of area

Eric Leis, fish biologist

Eric Leis, a fish biologist at the La Crosse Fish Health Center, and discovered the two new parasites while hunting for fish. 

A trip to collect fish from Lake Onalaska turned up two new species of parasites in Lake Onalaska, according to the La Crosse Fish Health Center.

The new species were accidentally discovered in 2017 when scientists were doing unrelated research on the waters.

The discovery was a feat because the infected fish, the pirate perch, are difficult to capture, living in shallow, weed-ridden waters.

The parasites are a relation to jellyfish and have similar stinging qualities but seem to cause no harm to the fish they infect. They depend on both the pirate perch and a river worm to reproduce and survive.

Parasites infecting fish

Two new species of parasites were found infecting the pirate perch, a fish found in Lake Onalaska that is elusive and hard to capture. The parasites only attach to the fish and pose no threat to humans.

This is a good example of the diversity our local ecosystem, and how much is still left to discover, according to fish biologist, Eric Leis, with the La Crosse Fish Health Center, and one of the researchers who found the parasites.

“It should be something that really notes the biodiversity present in the river,” Leis said, “that we can just find new species basically in our own backyard.”

Leis named the two parasites, one of them after a former school teacher, Susan Flock. He credits her with inspiring him to study nature when she taught science at Sacred Heart School in Cashton.

“She was just one of the best teachers I had at any level of my education,” said Leis. “I can remember being excited about her science class, and it’s the same feeling I have whenever we find something new.”

Liver of Pirate Perch

The liver of a pirate perch fish shows the life cycle of the two new parasites. The new species rely on the fish and a worm that lives on the bottom of the lake to reproduce and survive.

Discovering these new inhabitants has been particularly special, according to Leis, who has lived and worked in the area his whole life.

“I’ve been fishing on the river since I was little,” he said. “And it is really neat to find a new species in a place that you’ve lived basically your whole life.”

The parasites found are likely a native species, existing for millions of years, and pose no threat to the aquatic wildlife or ecosystem of the Mississippi Valley.

“They’re just along for the ride.”


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