Determining heterosporis threats to inform prevention, management, and control

Project manager: Paul Venturelli

Funded by: Environment and Natural Resources Trust Fund, as recommended by the Legislative-Citizen Commission on Minnesota Resources

Description: Heterosporis was first discovered in Minnesota in 1990 and has since been detected in approximately 30 waterbodies and is considered a disease of emerging concern in Minnesota. This disease is caused by the parasite Heterosporis sutherlandae, which damages the skeletal muscle of susceptible fish and renders them unfit for human consumption, and can result in direct mortality. H. sutherlandae can infect up to 40% of the individuals in a wild population of game or bait fish and there is no known treatment.

The primary objective of this project is to provide an initial estimate of threat that heterosporosis poses to the harvestable biomass of yellow perch in Minnesota, and establish timelines for population-level impacts.

We will develop a population model of yellow perch and couple this model with a disease model that describes H. sutherlandae dynamics as well as a generic population model that describes the dynamics of other fish hosts. We will use the model to estimate the threat that heterosporosis poses to yellow perch harvest in Minnesota, and prioritize future empirical research for improving model predictions. The overall project (Phases 1 and 2) will generate advice related to heterosporosis spread prevention, monitoring, control, and management; and establish a framework for approaching other invasive species that are relevant to Minnesota.

Project start date: 2015

Project end date: 2017

Findings:

Heterosporosis was discovered in Leech Lake in 1990 and has since been detected in ~30 waterbodies and over a dozen species. Heterosporosis was identified as a high research priority by the 2014 MAISRC Research Needs Assessment because it can infect up to 40% of fish and we knew little about the disease or its population-level effects. Our objectives were to collect data to better understand this disease, and to estimate the threat that heterosporosis poses to perch harvest in a typical Minnesota lake. We collected perch and other fishes from Leech Lake seasonally from fall 2015 to winter 2017, and from Cass and Winnibigosish lakes in fall 2015 and 2016. Heterosporosis was rare among all species, seasons, and lakes. We detected the disease in only 9% of perch, and 20-30% of these fish had visible muscle damage. Heterosporosis did vary seasonally, and infected perch were not more susceptible to angling. In the lab, we found a 32%-34% infection rate when fish were fed infected tissue and a 2%-17% infection rate with passive transmission from co-habitating healthy and infected fish. We found no evidence of a relationship between growth or survival and infection. We used this and other information to develop a population model that suggested that heterosporosis can have short-term impacts on yellow perch harvest (e.g., in a naïve population or after a bad year), but that long-term impacts are unlikely. Sensitivity analysis indicated that disease associated parameters had little effect on overall harvest. Based on the results of this project, we do not consider heterosporosis to be a significant threat to Minnesota fish, but recommend further research to improve the model, because threats to aquaculture or laboratory fish may be higher.

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