Finding of whirling disease parasite in Provo River and Midway Hatchery
Fish Pathologists at the DWR Fisheries Experiment Station have reported the discovery of the whirling disease parasite in fish from the Provo River, as far down as the city of Orem. Rainbow trout at Deer Creek and Jordanelle Reservoirs have tested positive. Fish at both locations were lightly infected and no physical deformities or other clinical signs of disease have been seen. Investigators have sampled these waters and tested for whirling disease spores periodically since 1996. This first confirmed positive detection was in fish collected in the winter of 1999. A presumptive diagnosis was made in fish directly above Jordanelle Reservoir at the junction with the Weber-Provo Canal in 1997. The Provo River has been considered at high risk due to its connection with the Weber River drainage which has been contaminated for several years. Investigators feel the infection is a fairly recent downstream movement of the parasite. In August 2000, infected brown trout were detected in Snake Creek, a small tributary to the Provo River near Midway.
Since the presumptive identification of the whirling disease parasite in the Provo drainage as early as 1997, DWR was concerned about the potential threat to Midway hatchery. Several factors combined to make the hatchery particularly vulnerable such as its proximity to contaminated waterways, dirt raceways at the low end, presence of large numbers of avian predators, human trespass and possible introduction of wild fish. A scoping meeting took place at the hatchery in 1998 to identify the threats as well as short term and long term solutions. Although some measures were identified to reduce bird predation, the analysis was that there were no cheap or easy fixes to safeguard the hatchery. DWR hoped that Jordanelle reservoir would slow the downstream movement of the parasite to allow for funding sources and security plans to be implemented. Conventional testing for the parasite was increased to a semi-annual basis, using fish from the lowest part of the dirt systems at the locations deemed most vulnerable.
The discovery of the parasite in Jordanelle and Deer Creek reservoirs in February 2000 raised concerns even higher. After careful consideration, the response team decided to proceed with testing of Midway hatchery with both the conventional (pepsin-trypsin digest) method as well as an innovative molecular biology technique known as polymerase chain reaction (PCR) testing. While the use of this latter method was considered risky and it is not a Fish Health Section Blue Book standard method, we felt it was prudent because of the potential impact of stocking out undetectable carriers. No fish were scheduled for stocking out of Midway until May 2000, so there was a de facto quarantine of the facility.
On March 3, 60 fish were sampled for the digest testing and an additional 60 fish were sampled for PCR testing. PCR testing was performed by Pisces Molecular lab in Boulder Colorado. Thirty fish came from the upper concrete system and 30 from Pond 4 at the lowest portion of the dirt systems. All fish tested negative for the presence of myxospores, but 1/30 tested weakly positive from Pond 4 by the PCR method. Repeat testing a month later showed increasing numbers of positive fish in the lower dirt raceways. These results were brought before the Utah Fish Health Policy Board, which voted to stock the negative fish into Jordanelle and Deer Creek Reservoirs and to destroy all those fish from the lots in the dirt raceways which tested positive.
Longer-term plans are being derived to disinfect and secure the concrete raceways with bird covers and fencing in order to maintain production. Springs which supply the hatchery with water are being tested with sentinel fish and dye studies to make sure they are still safe and free of the parasite. Existing dirt raceways were drained and have been kept fish free. Stocking in many Utah streams was reduce for the year 2000.
Subsequent testing in the fall of 2000 has indicated that contaminated Provo River water may be mixing with the hatchery spring water at underground locations and allowing the whirling disease parasite to enter the water supply. Test wells are being drilled to see if deeper, uncontaminated water supplies can be found.
Outlook for fishing
There is no effective treatment for infected fish. Researchers are focusing much effort on finding ways to manage tiny tubifex worms, the intermediate host for the parasite, that are found on the bottom of most streams and reservoirs . The Division of Wildlife Resources has formed a response team to oversee further investigations to determine the extent and spread of the parasite and its impact of the sport fishery.
Biologists stress that fishing on Deer Creek and Jordanelle Reservoirs and on the Provo River system should remain good for the foreseeable future. Rainbow trout are stocked into both reservoirs at a large size that makes them less susceptible to whirling disease. Wild brown trout in the river are more resistant to the infection than rainbow and cutthroat trout. Anglers are urged to clean their waders and gear after fishing in the river and properly dispose of the remains of any harvested fish by placing them in garbage cans or complete burning. Whirling disease does not infect humans and fish can be safely consumed.
For more information, contact Don Wiley, regional aquatics manager at (801) 489-5678 or Dr. Chris Wilson at the Fisheries Experiment Station at (435) 752-1066 ext. 21.