Untersuchung der Empfänglichkeit einer deutschen Regenbogenforellen-Linie (Oncorhynchus mykiss)gegenüber Myxobolus cerebralis, dem Erreger der Drehkrankheit der Salmoniden

Investigation into the susceptibility of a German wild rainbow
trout strain (Oncorhynchus mykiss) to Myxobolus cerebralis, the
causative agent of whirling disease in salmonids Whirling disease
is an important parasitic disease of salmonids that attains
increasing importance in Europe and in the USA. Previous studies
have shown that a hatchery rainbow trout strain from Germany (DtHo)
is relatively resistant to whirling disease compared to three other
German strains and one North American strain. The focus of this
work was to investigate the susceptibility of the German wild
rainbow trout strain DtWf to Myxobolus cerebralis and compare it
with an American rainbow trout strain (AmTl), known to be very
susceptible to the parasite. For the laboratory exposure, the trout
strains were divided into 5 groups, each with 30 to 40 fish. These
groups were infected with different doses of triactinomyxon-spores.
The Susceptibility to whirling disease was gauged using the
following two parameters, the incubation time and the percentage of
fish exhibiting clinical signs of the disease over a five month
period. Five months post exposure, 10 fish from each group were
randomly taken for histological evaluation and counting of the
spores. Each fish was processed separately. They were anesthetized;
the weight and the length of each fish were documented. The present
findings indicate that the German wild trout strain was less
susceptible to whirling disease than the American AmTl strain. In
the American strain, the disease had the shortest incubation time
and lead to the most severe clinical symptoms. In the laboratory
experiments, the American strain AmTl had the highest prevalence of
infection. The spore count and the patho-histological assessments
showed that the American strain was remarkably more susceptible to
the disease than the German wild trout strain. Indeed, the American
strain AmTl had 18 times more spores develop in their head than the
German strain DtWf, at a dosage comparable to that present natural
condition in North America. The investigation demonstrated that
German strain of rainbow trout DtWf possess significantly greater
resistance to whirling disease than the American strain AmTl.