West Coast fish pathogen found in Maryland stream
Organism previously seen in Pacific salmon and western trout turns up in Catoctin park fish
A fish pathogen previously seen in this country only in Pacific salmon and trout has turned up in a Maryland stream in yet another species of fish. The finding, by researchers with the U.S. Geological Survey, poses a potential new aquatic health threat in the Chesapeake Bay watershed.
Scientists surveying fish in Catoctin Mountain Park near Thurmont last year found the pathogen, Dermocystidium, in cysts on the bodies of Blue Ridge sculpin, a freshwater fish that favors rocky riffles in creeks and headwaters, according to Vicki Blazer, USGS research fish biologist and lead study author. The finding was published online Tuesday in the Journal of Aquatic Animal Health.
Dermocystidium is a single-celled parasitic organism that’s killed juvenile and adult Pacific salmon. While seen in numerous fish species in other parts of the world, it appeared to be limited here to West Coast rivers until recently, when it turned up in yellow perch in Ontario.
While usually seen on the outside of the sculpins’ bodies, the pathogen also has formed cysts in the gills and internal organs of infected fish, and sometimes lead to death. Blazer said it wasn’t clear if the Dermocystidium found had caused any die-offs, but the few fish found with it at Catoctin park were heavily infected, and populations scarce.
“In portions of the watershed where the infection was observed, sculpin numbers were lower than expected,” Blazer said in a press release announcing the study. “And a nearby stream lacked sculpin altogether, though they are typically common in the region.”
Populations of Blue Ridge sculpin are generally considered stable, according to the IUCN Red List of Threatened Species. They’re found in the Elk, Susquehanna, Bush, Patapsco, Patuxent, Potomac, Nanticoke, James, and Roanoke river drainages in Virginia, West Virginia, Maryland, Delaware, and Pennsylvania.
But Dermocystidium belong to a phylum of organisms considered an emerging threat to aquatic and terrestrial animals because they don’t limit themselves to infecting one species. Also, fish or animals with chronic, low-level infections can become carriers, spreading it to others.
“Sculpin can be found in many watersheds throughout the Chesapeake drainage and are an important part of the fish community,” said Blazer. “It is currently not known if other fish species may be affected, or if the pathogen will have significant effects on sculpin populations.”
USGS plans to work with the National Park Service, which manages the Catoctin park, and the Maryland Department of Natural Resources to monitor fish populations in the affected stream and others nearby.
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