Fifty-seven fish of three genera were taken from the Colorado River in west central Colorado and examined for external parasites. No external parasites were found on Ictalurus. Seven percent of the Hybognathus and 100 percent of the Catastomus were infected with a Hirudinean of the species Helobdella stagnalis.
Malek, Mitra and McCallister, Gary
"Incidence of the leech Helobdella stagnalis on the Colorado River in west central Colorado,"
Great Basin Naturalist: Vol. 44
, Article 20.
Available at: http://scholarsarchive.byu.edu/gbn/vol44/iss2/20