Whirling disease is a parasitic infection of trout and salmon. Fish become infected through contact with the fish infective form of Myxobolus cerebralis (MC), the whirling disease parasite. The Triactinomyxon or TAM enters the fish through mucous cells in the skin and injects its sporoplasm into the fish. The parasite develops within the fish and attacks cartilage causing deformities and damage to organs of equilibrium. This damage can cause the infected fish to whirl or spin when startled or while feeding, hence the name whirling disease. Damage from the parasite is most severe in juveniles, fish generally under 2-3" in length, whose skeletal structure consists largely of cartilage.
The effects of whirling disease on susceptible fish can include the darkening of the tail ("blacktail") and skeletal deformities of the spine and head. In severe infections WD can cause very high mortality rates amongst young fish; as high as 90% in some situations. However, anglers should be aware that this evidence is rarely visible in wild populations. Fish that are severely infected will die as juveniles, and the impact of a severe WD infection will manifest itself in declining populations and is verified only through laboratory testing.
The spread of whirling disease:
One of the major means by which whirling disease is spread is the movement of infected fish. Such movement can occur in wild populations and in association with fish culture and stocking activities. Once established in a natural system, the parasite can spread as infected fish move up or down stream and by passive downstream drift with the current. The parasites can be carried by predators that eat infected fish and then shed spores in their feces. They may also be transferred through mud on waders and boots or on boats, or other items moved between infected and uninfected waters. Whirling disease could also be spread through shipments of fish food infected with the parasite (in fact, it is believed that whirling disease first came to the United States in frozen food fish from Europe). Fish eggs do not become infected, so properly disinfected shipments of eggs should not contribute to the spread of disease.
What TU is doing:
When TU's Cold Water Conservation Fund (CCF) first issued "Whirling Disease in the United States" in 1999, the report included a series of priority research recommendations. Researchers from state and federal agencies and academic institutions have tackled many of the priorities identified in the report; Much of the current research on whirling disease has been funded by the US Fish and Wildlife Service through the National Partnership for the Management of Wild and Native Cold Water Fisheries. The Partnership funds were made available through a competitive grant program titled the Whirling Disease Initiative run by the Montana Water Center at Montana State University in Bozeman. Unfortunately, these funds were cut in 2008. In addition TU'S Whirling Disease Foundation and Cold Water Conservation Fund has raised both private and federal funds that have been used to support critical research in the area of whirling disease resistant trout and the organizing and hosting of the annual Whirling Disease symposia.
What is whirling disease? How is it detected in fish? How does it spread? Can it be controlled?