| Summary: | A previously unknown microsporidian parasite that severely degrades muscle of yellow perch (Perca flavescens) from lakes in Minnesota, Wisconsin, and Lake Ontario was identified as belonging to the genus Heterosporis. This parasite is characterized by pyriform-shaped spores that are contained in sporophorocysts. In the wild, yellow perch, burbot (Lota lota), mottled sculpin (Cottus bairdi), trout-perch (Percopsis omiscomaycus), pumpkinseed (Lepomis gibbosus), northern pike (Esox lucius), walleye (Sander vitreus) and rock bass (Ambloplites rupestris) harbor Heterosporis naturally, but laboratory studies showed that 12 other fish species are susceptible to infection. In laboratory trials, smallmouth bass (Micropterus dolomieui) consumed significantly more fathead minnows infected with Heterosporis sp. than uninfected. Microscopically, Heterosporis sp. infection can be detected in the muscle of fish two weeks after exposure, and visually identified after seven weeks. To confirm infection, a PCR diagnostic assay was developed. Heterosporis spores are rendered noninfective by freezing, desiccation for 24 h, exposure to 2,200 mg/L bleach, and aging in air-exposed water for six months. This parasite can infect a wide range of fish species which can lead to devastating losses in commercial and sport fishing; however, there are preventative measures that may limit the spread of the parasite.
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