Parasite community structure in Pimephales promelas (Pisces: Cyprinidae) from two converging streams.

Parasites of the fathead minnow, Pimephales promelas, were examined in fish collected from Elk Creek (40.88534 degrees N, 96.83366 degrees W) and West Oak Creek (40.90821 degrees N, 96.81432 degrees W), Lancaster County, Nebraska. These 2 streams are part of the Salt Valley watershed and flow together approximately 2 km downstream from the collection sites to form Oak Creek. This study examined the extent to which the 2 tributaries constitute a continuous habitat with respect to fish hosts. The parasite community included Trichodina sp., Myxobolus sp., Dactylogyrus simplex, D. bychowskyi, and D. pectenatus (all on gills); Gyrodactylus hoffmani (gill and body surface); Posthodiplostomum sp. (neascus, body cavity); and Uvulifer ambloplitis (encysted in skin). Among 46 fish from Elk Creek and 56 fish from West Oak Creek taken on 5 dates during April-July 1998, U. ambloplitis was found in Elk Creek fish at prevalences of 44-100% but in only 2 West Oak fish on 1 date. Prevalence and mean abundance of D. simplex also differed between the 2 sites. On the basis of these observations, fish populations in the 2 streams were considered to be distinct, with little or no fish movement between the tributaries.