Studies on proliferative kidney disease (PKD) in rainbow trout, Oncorhynchus mykiss
Proliferative kidney disease (PKD) is one of the most economically important diseases in commercial rainbow trout culture in Europe. It is recognised by the British Trout Association as the most significant problem affecting the industry in Britain, with annual losses in revenue in excess of £1.5 million, which represents a total loss to the industry of approaching 14%. The specific aims of this work were:- 1. To investigate aspects of the transmission and passage of infection to rainbow trout, with particular emphasis on the unknown alternate host and infective stage. 2. To determine environmental parameters which have an effect on the occurrence and severity of annual epizootics, and to see if early season conditions can be used to predict the arrival of the parasite and the time of each epizootic. 3. To test the efficacy of the antibiotic Fumagillin DCH in controlling the outbreak and severity of the disease on a commercial scale. 4. To examine the potential of biological methods of control, centering around a vaccination regime, in ameliorating the effects of the disease. Chapter 1 gave a general introduction to the problems posed by parasitic diseases in salmonid aquaculture and, more specifically, with important pathogens of the class Myxosporea. Chapter 2 dealt with the life cycle and transmission of PK'X'. A polyclonal antiserum to PK'X' was raised and used with fluorochrome techniques to label PK'X' cells within infected trout kidney. Screening oligochaetes with this diagnostic tool failed to show any evidence of infective stages to salmonids, as did random examination by light microscopy. Filtration experiments showed that the waterborne infective stage was capable of passage through 25μm mesh screens, but was at least partially held back on 10μm mesh. This suggested that, if an actinosporean, the infective stage is in the size range of an aurantiactinomyxon. Chapter 3 examined environmental factors which control the strong seasonal epidemiology characteristic of the disease. It was shown that the intensity of water temperature rises in spring promotes the early development of the disease.