Epidemiological aspects of proliferative kidney disease amongst rainbow trout Salmo gairdneri Richardson in Northern Ireland

The epidemiology of PKD is described as it relates to one affected farm in Northern Ireland. From 1972–1976 stocking and management practices led to mortality of 10–15% amongst the 0+fish. 1+or older fish were never affected. In 1977 and 1978, however, delaying the stocking of the farm until July eliminated deaths in the 0+fish, and mortality in these 1977‐moved fish the subsequent year remained at an absolute minimum. Preliminary observations suggest that a means of controlling the disease has been found. Experimental work demonstrates that the resistance of 1 +or older fish is due to previous exposure and is not an age‐related immunity. Experimental work also suggests the presence of an incubation period of 6–7 weeks and that the peak time of infectivity is probably around May. None of the evidence detracts from the possibility that an infectious agent is involved although an attempt to transmit the disease failed.