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Oucible, Mohamed Amine (2007): Untersuchung der Empfänglichkeit einer deutschen Regenbogenforellen-Linie (Oncorhynchus mykiss)gegenüber Myxobolus cerebralis, dem Erreger der Drehkrankheit der Salmoniden. Dissertation, LMU München: Faculty of Veterinary Medicine
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Abstract

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.