Abstract
For the purpose of obtaining basic knowledge for screening IHN resistant stocks, infection experiments were performed by using a virulent strain of IHNV, TK8901 from 37 g diseased rainbow trout and several different brood and size groups of rainbow trout juveniles. In the infection experiments, 22 progenies, derived from individual pairing of rainbow trout, were inoculated with TK8901 by immersion method at the stages of 1, 8 and 25 g body weight. The results indicated that evident differences in mortality existed among the progenies. Cumulative mortalities of the virus infected fish ranged from 65%to 100% (87.4%in average) in 1 g groups, 33%to 90% (57.2%) in 8 g groups and 10%to 85% (57.0%) in 25 g groups.However, changes in susceptibility of fish with size differed among the progenies. These results suggest that challenge tests using different developmental stages of fish are necessary to estimate the susceptibility of rainbow trout to IHN for screening IHN-resistant strains.
