Variation in prevalence and intensity of infection of a trematode parasite in shorthead sculpin in Birch Creek, Idaho

Euryhelmis cotti (Simon, 1972) is an intestinal fluke with a complex life history with three hosts; in the metacercarial stage, E. cotti infects fish in the family Cottidae. Our objective was to determine the distribution, prevalence, and intensity of infection of E. cotti in shorthead sculpin (Cottus confusus Bailey and Bond, 1963) in Birch Creek, Idaho. We collected shorthead sculpin at five sites in Birch Creek with a backpack electrofisher and determined prevalence and intensity of infection on sculpin by counting metacercariae on the fins and body of each fish. We found shorthead sculpin with metacercariae at all sites. Prevalence of the parasite was lowest at the downstream sites (33.9% - 41.0%) and was higher at the upstream sites (> 83.2%). Mean intensity of infection on each fish ranged from 1.2 metacercariae per fish (S.E. = 0.08) at the site furthest downstream to 215.1 metacercariae per fish (S.E. = 19.06) at the site furthest upstream. High prevalence and intensity of infection in shorthead sculpin at upstream sites may have negative effects on fitness of the fish (e.g., reductions in growth, reproduction, survival, swimming performance) and warrants further research.