Abstract

Whirling disease, caused by the myxosporidian parasite Myxobolus (Myxosoma) cerebralis, can be a serious problem in both cultured and feral salmonid populations. In susceptible species of fish, the parasite has a selective tropism for neural and cartilaginous tissues which may result in abnormal swimming behavior, hyperpigmentation of the caudal peduncle and gross skeletal deformities. Recently, this protozoan parasite has gained considerable attention as the agent possibly responsible for complete year class losses of wild trout in the western United States. Concern about the possibility of contamination of healthy native populations through the stocking of infected fish has resulted in many states initiating investigations into the natural occurrence and distribution of the organism in trout populations. This study examined fish from private and state trout culture facilities, stocked trout populations, and native trout populations from Virginia, USA. Tissue samples of the three species of salmonids in Virginia (rainbow, brook and brown trout) from various locations were evaluated for mature spores using the modified plankton centrifuge method. Results of this study will help determine the range and effect of this parasite on wild and feral trout populations in the United States.

Acknowledgements

This work was partially supported by funds provided by the Commercial Fish and Shellfish Technology (CFAST) Program of Virginia Tech and the Virginia Trout Growers Association.