Whirling disease detected in South Carolina trout for first time

The S.C. Department of Natural Resources’ Wildlife and Freshwater Fisheries Division, working with the Southeastern Fish Disease Cooperative at Auburn University, has documented the presence of whirling disease for the first time in four streams sampled recently in Pickens and Greenville counties.

This represents the first positive diagnosis of the whirling disease pathogen in South Carolina trout streams.

For more information on whirling disease in South Carolina, visit https://www.dnr.sc.gov/whirling.html.

First detected in the United States in 1958, whirling disease is found in more than 20 states, including North Carolina and Georgia. Whirling disease can cause 90 percent or greater mortality of young rainbow trout and can have serious impacts to wild and hatchery trout populations. The disease is caused by the microscopic parasite Myxobulus cerebralis, which damages cartilage and skeletal tissue in trout, causing diseased fish to swim in a “whirling” motion.

“While whirling disease is not harmful to humans, this disease has caused high trout mortalities in hatchery systems and in wild trout, particularly in Western streams,” said Ross Self, S.C. Department of Natural Resources (SCDNR) chief of freshwater fisheries. “There is no practical way to eliminate this pathogen. While the pathogen is now documented in South Carolina, it is positive news that it has not been observed to cause the classic disease symptoms here or seen to cause observable population declines. It appears rare that this pathogen manifests as full-on whirling disease in Southern Appalachian freestone streams, like we have in South Carolina.”

A recent fish health inspection at Walhalla State Fish Hatchery in Oconee County was negative for whirling disease and other new exotic pathogens.

SCDNR has conducted surveillance for exotic trout pathogens in wild trout populations and at Walhalla State Fish Hatchery for decades. Much of this work was conducted in partnership with the U.S. Fish and Wildlife Service’s Wild Fish Health Project, operated out of their fish disease lab in Warm Springs, Ga. Since 2015, SCDNR has increased surveillance for whirling disease and other exotic pathogens in trout due to recent documented outbreaks of whirling disease and two species of parasitic gill lice in nearby states. At this point, no parasitic gill lice have been documented in South Carolina trout.

Self said SCDNR fisheries biologists will be collecting additional trout samples for disease analysis in the upcoming 2022 Summer/Fall survey season.

Anglers are reminded to NOT stock or move trout around between bodies of water or release or dispose of them anywhere other than the location where they were caught. Anglers are also reminded to always disinfect waders and properly clean all equipment before leaving an area when fishing. Thoroughly dry equipment in the sun if possible before reuse. If anglers are traveling directly to other waters, they are asked to clean equipment with a 10 percent solution of chlorine bleach or use another set of equipment.

For more information on whirling disease, visit the U.S. Department of Agriculture’s web site at https://www.invasivespeciesinfo.gov/aquatic/pathogens-and-diseases/whirling-disease.