Difference in susceptibility to IPN virus among rainbow trout populations from three hatcheries in Japan.

Susceptibility of rainbow trout, Salmo gairdneri, to IPN virus was compared among those of three Japanese hatcheries in which inbreeding has been practiced for over 20 years. The fry from hatcheries K, F and N were tested totally 47 times, 36 times and 25 times, respectively for 6 years since 1979. As the results, susceptibility of rainbow trout to IPN virus was clearly different among the fry from the three hatcheries. The fry from hatchery K (rainbow trout strain RT-101) were always highly sensitive to IPN virus and the relationship between cumulative mortality and fish body weight was shown as a formula of linear regression; Y=113.0-209.4X (Y=cumulative mor-tality, X=fish body weight, correlation coefficient (r)=0.954). The fry from hatchery N were always less sensitive to IPN virus (≤25%) in cumulative mortality. The fry from hatchery F consisted of various ones ranging from highly sensitive to less sensitive.