Whirling Disease: A Northeastern Perspective     John H. Schachte and Christopher J. Petrie   New York State Department of Environmental Conservation, Fish Disease Control Unit, 8314 Fish Hatchery Road, Rome, NY 13440     During the early nineties whirling disease was found to be associated with mortalities of young of the year wild salmonids in the Rocky Mountain regions of Colorado. Shortly thereafter, the disappearance of year classes of wild rainbow trout in Montana waters were detected concurrently with the detection of Myxobolus cerebralis. In the fall of 1994, M. cerebralis was detected for the first time in rainbow trout in four New York state fish hatcheries. Extensive selected sensitive wild waters were subsequently investigated for the presence of the parasite.  Although M. cerebralis   was widespread, no clinical signs in any free ranging fish were observed. Further no population level effects have been observed to date.  In 1998, a fall spawning Montana strain was used in a companion exposure with the domestic Randolph, New York strain of rainbow trout. No differences in infection rates were observed in either strain based upon spores per gram of tissue from individual fish.   In 1999, a spring spawning Montana strain of rainbow trout was compared identically as in 1998 to the spring spawning wild Finger Lake, New York strain. No significant differences in infection were noted over the entire experimental exposure period. Stream sampling of the water supply at the experimental site for the presence and abundance of the oligochaete worm, Tubifex tubifex, revealed less than 1% of oligochaetes collected were T. tubifex. No triactinomyxons were recovered.   In 2000, we repeated the 1999 study to investigate the possibility of a strain growth rate relationship to infection severity, observed but not tested for the previous year. The Montana RT had a significantly higher rate of growth as compared to the New York strain of rainbow trout. The Montana strain also had a significantly higher spore load per gram of tissue as compared to the New York strain in one group of fish exposed at 100 d post hatch. Only one triactinomyxon was recovered in one 500 g sample collected during the hours of darkness.