A study of Myxobolus cerebralis in the Lostine River, Oregon : epizootiology, distribution and implications for resident and anadromous salmonids

Graduation date: 2001Myxobolus cerebralis, a myxozoan parasite that infects almost all species of wild\ud and cultured salmonids, was first identified in northeastern Oregon in the Lostine River in\ud 1986. Fish that are heavily infected with M. cerebralis develop whirling disease, which\ud was determined to be the cause of catastrophic declines in rainbow trout populations in\ud Montana and Colorado in 1996. There have been no reports of severe salmonid\ud population declines attributed to whirling disease in Oregon, although many populations\ud are at levels that warrant protective listing under the Endangered Species Act. This study\ud was undertaken to I) establish the distribution and seasonal prevalence of M. cerebralis\ud infection in the Lostine River, 2) investigate the epizootiological factors influencing the\ud occurrence of whirling disease in this river, 3) determine the potential impact of the\ud parasite on chinook salmon, and 4) evaluate the suitability of a non-lethal tissue sampling\ud protocol for the detection of M. cerebralis in juvenile and adult salmonids for use in\ud monitoring the effects and distribution of the parasite in protected salmonid populations.\ud Results of this study indicate that the parasite is present throughout the main stem of the\ud Lostine River during all seasons, and that rainbow and anadromous steelhead trout fry\ud emerging in the lower river are most likely to become infected and develop whirling\ud disease. Chinook salmon were shown to be relatively resistant to M. cerebralis at low\ud levels of exposure, but this effect was less evident when the parasite exposure increased.\ud The non-lethal sampling protocol was successful in detecting M. cerebralis in juvenile\ud salmonids but not in adults, where it is most needed. The information gathered during\ud these studies was then correlated with the life histories of resident and anadromous salmonids in the Lostine River to determine the potential impact of M. cerebralis On\ud salmonid populations in this region