Great Basin Naturalist


Two hundred woundfin minnows, Plagopterus argentissimus, from four sites along the Virgin River, Utah, were examined on two dates during summer 1985. The foreguts of 211 woundfin and variable numbers of other fishes from the Virgin River near Beaver Dam Wash, Arizona, and Mesquite, Nevada, were examined for cestodes on four dates throughout 1979. Seven parasites were found in P. argentissimus: Posthodiplostomum minimum (metacercariae), Diplostomum spathaceum (metacercariae), Bothriocephalus acheilognathi, Gyrodactylus sp., Lernaea cyprinacea, Trichodina sp., and Ichthyophythirius multifiliis. Fungal infections were noted on two fish during the study. Seventeen Virgin River roundtail chub, Gila robusta seminuda, were examined from two of the four sites in 1985 and 64 specimens from Beaver Dam Wash were examined in 1979. Gila robusta seminuda was infected with Posthodiplostomum minimum (metacercariae) and Bothriocephalus acheilognathi, the Asian fish tapeworm. This cestode probably gained entrance into the ichthyofauna of the Virgin River from red shiners, Notropis lutrensis, and has the potential of being very detrimental to the endemic and endangered fishes of the Virgin River. Parasite loads were correlated with water quality and habitat disturbance, with highest number and frequency occurring in "disturbed" sites. Low river flows and increased total dissolved solids appear to be associated with a higher parasite frequency and mean number in fishes of the Virgin River. These data represent the first known published records for parasites of the woundfin minnow and Virgin River roundtail chub.