Cooperative Fish and Wildlife Research Units Program: Colorado
Education, Research and Technical Assistance for Managing Our Natural Resources

Myxobolus cerebralis, the parasite responsible for whirling disease, has caused widespread population collapses in wild rainbow trout (Oncorhynchus mykiss) populations throughout the intermountain west. Disease-resistant rainbow trout have been considered as a potential option for reintroducing rainbow trout populations in the presence of the disease and the German strain (GR) of rainbow trout is at least as resistant to whirling disease as the highly-resistant brown trout (Salmo trutta) under laboratory conditions. The GR strain has been crossed with the susceptible Colorado River rainbow (CRR) to produce rainbow trout that are resistant to whirling disease but retain traits necessary for survival in the wild. However, little is known about how these strains will survive and reproduce when stocked in streams and rivers. Our study has two objectives: one is to evaluate the success of ongoing resistant rainbow trout introductions in Colorado. We will assess survival, reproduction, and recruitment using mark-recapture and genetic methods. The second objective is to evaluate brown trout removal as a management option to promote the retention and survival of introduced whirling disease resistant rainbow trout. This study is designed to estimate the rate and magnitude of rainbow trout migration in areas with ambient levels of brown trout and in areas where brown trout numbers have been reduced. We are assessing rainbow and brown trout movement using Radio Frequency Identification (RFID) Passive Integrated Transponder (PIT) tags and 8 in-stream RFID antennas. We have marked 4000 rainbow trout which have been introduced into two areas of the Poudre River, CO. In one area brown trout were removed using electrofishing. We have about 1500 brown trout marked in each section. The study is designed to allow us to estimate the movement and survival of rainbow trout in each section.