DETECTION AND NEW-ZEALAND DISTRIBUTION OF MYXOBOLUS-CEREBRALIS, THE CAUSE OF WHIRLING DISEASE OF SALMONIDS

Whirling disease, caused by Myxobolus cerebralis, was diagnosed in rai nbow trout (Oncorhynchus mykiss) at Silverstream Fish Hatchery near Ch ristchurch in 1980. As a consequence, a nationwide survey for M. cereb ralis in salmonids was conducted by examination of 5307 wild and hatch ery fish. In addition, sentinel rainbow trout were used at six locatio ns to test for whirling disease. This survey and other studies reveale d M. cerebralis at locations in the Waimakariri, Rakaia, and Rangitata River catchments, and provide the first New Zealand records of M. cer ebralis in brook trout (Salvelinus fontinalis), chinook salmon (Oncorh ynchus tshawytscha), and sockeye salmon (O. nerka). This paper demonst rates use of sentinel rainbow trout in detecting low-level asymptomati c infection of M. cerebralis in chinook salmon.