Abstract

Mortality of Cyclops bicuspidatus thomasi infected with the procercoid of Triaenophorus crassus was assessed and factors influencing the infectivity of the procercoid to the second intermediate host were evaluated. Over 80% of C. b. thomasi infected with T. crassus died after 28 days, and there was a bimodal pattern to cyclopid mortality. A decrease in the mean intensity over time indicated that this mortality was related to parasite numbers. The frequency of T. crassus in C. b. thomasi after 28 days fitted the negative binomial distribution. A higher proportion of lightly infected cyclopids at this time resulted from mortality of heavily infected hosts. Female cyclopids had larger procercoids than males, but the ratio of differentiated to undifferentiated procercoids did not vary between sexes. Procercoid size was smaller and the proportion of differentiated procercoids decreased with increasing intensities of infection. Exposure of laboratory-reared whitefish, Coregonus clupeaformis, and cisco, Coregonus artedii, to procercoids from crowded infections resulted in a low percent recovery of plerocercoids, while less crowded infections of procercoids produced a high percent recovery of plerocercoids in fish. The number of procercoids to which fish were exposed affected the percent recovery of plerocercoids.

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