MACROPARASITES OF GILA ORCUTTI AND PIMEPHALES PROMELAS (ACTINOPTERYGII: CYPRINIDAE) IN THE SANTA CLARA RIVER, VENTURA COUNTY, CALIFORNIA

Freshwater fishes in the southwestern United States live in some of the most highly modified habitats in the country. As a result, the relatively small number of native fish species has been impacted in many ways, including the introduction of nonnative fishes and their parasites. Both Gila orcutti and Pimephales promelas have been introduced to the Santa Clara Drainage, the former is native to adjacent drainages in southern California, while the latter was introduced from the eastern United States. Two hundred and fourteen G. orcutti (arroyo chub) and 18 P. promelas (fathead minnow) were collected and necropsied in June through September 2017 and May through September 2018. Eight macroparasite taxa were collected from these fishes, including 6 native and 2 nonnative parasites. Four taxa of parasites were shared between G. orcutti and P. promelas: Schyzocotyle acheilognathi (Asian fish tapeworm), diplostomid metacercariae, larval acuariid cysts, and Lernaea cyprinacea (anchor worm). This study also reports the first host-association records of G. orcutti with Gyrodactylus sp., S. acheilognathi, diplostomid metacercariae, Rhabdochona sp., Contracaecum sp., and larval acuariid cysts in the Santa Clara River. Additionally, it provides the first host-association records of P. promelas with larval acuariid cysts in the Santa Clara River. This study identifies new host-parasite associations that may be useful for future conservation efforts.