WHIRLING DISEASE IN DISCUS ?
By Fred Goodall
10-09-2000

Myxobolus cerebralis, better known as Whirling Disease is getting a lot of play on the net for possibly infecting "tropical fish", such as angels and Discus fish. No proof of that so far, laboratory results have not yet found a species that can live in the infectious stage ( TAMS for short or in full: triactinomyxons ) at "tropical" temps of 25 C to 30 C. ( 77 F to 86 F ). The bad news is that the "spores" of M. cerebralis can survive freezing and desiccation, (drying) and can survive for 15 to 20 years in stream beds. Good news is that it appears to be a "cold water" parasite true to its origins in Eurasia and not Asia proper as rumored on the web. Also not true is the net rumor that the "problem" came from Asia, it came to America from Europe with some brown trout in the 1950's.

M.cerebralis is classified as a "Myxozoan" a group of over 1,400 "known" parasites (not a bacteria or a virus) that infect fish. This group of parasites needs a secondary host other than fish to finish their life cycle. A completed study at UC Davis, California found that the M.cerebralis needs T. tubifex worms to "incubate" them before they can infect fish. The worms first ingest the spores, incubate them, then release the TAMS which then infect the fish. In short: Whirling Disease needs Tubifex worms of the species Tubifex tubifex to "hatch" the spores and "release" the fish infecting TAM stage. Once infected, the fish eventually start showing the classic "tail chasing" (whirling) behavior, the spinal, fin or head deformities classic for infected fish and may or may not show the "back tail". When the fish die, the "spores" release into the water waiting for worms to "eat" them and start the cycle over again.

The fish which are subject to infection are Trout, Salmon, and "White fish". Certain species show resistance of varying degrees for as yet unknown reasons. What is known is that the TAMS infect the fish through their skin and burrow into the soft cartilage before it hardens, causing the characteristic "deformities" of the skeleton, resultant pressure on the spinal column causing the "whirling" and in some fish the "black tail" markings. Current control is by way of reducing the TAM count and the exposure of "fingerlings" to the TAMS while the "fingerling's" cartilage is still soft. For cold water fish this means lowering the temp of the water below 9 C ( 48 F ). Filtering water through ultraviolet "filters" and using micron sized filter materials are new approaches for commercial food fish hatcheries currently being studied.

The results of the on going year 2000 studies will not be available until 2001, at which time this article will be updated. The reasons being ongoing studies that are looking into: the importation of possible Myxozoan infected live foods for ornamental fish, antibiotics effective against Whirling Disease, "gene tagging" of M. cerebralis species and of its host worms, development of resistant "hybrid" fish and worms, and the results of the "filtering" methods.