WHIRLING DISEASE IN DISCUS ?
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.