The influence of immersing temperature for inoculation with IPNV and/or rearing temperature on mortality of rainbow trout fry postinfection.

The influence of immersing temperature for inoculation with IPNV and/or rearing temperatureon mortality of rainbow trout fry Salmo gairdneri postinfection was studied. An IPNV-Buhl strain which is the most dominant IPNV-serotype in Japan was used as a challenge virus and a highlysensitive strain to IPNV (RT-101 strain, 0.13g in B. W.) was used as an experimental fish in this study. The fry was immersed in 105.0 TCID50/ml of IPNV at 5, 10, 15 and 20°C for 1h and each group was shifted up or down to 5, 10, 15 and 20 and incubated for 28 days. As the results ob-tamed, rearing temperature influenced the cumulative mortality of rainbokw trout fry postinfection and the mortality pattern but immersing temperature for inoculation with IPNV did not. The IPNV-Buhl strain shows low or no cumulative mortaility at 5°C and as high a mortality as≥70% cumulative mortality at 10-20°C for the fish. At 20°C the death of fry started 3 days after inocula-tion in spite of the different immersing temperature and the mortality pattern was the acutest, namely 50% daily mortality appeared on the first or second day after the first death. Although the cumulative mortality at 10 and 15°C was about the same as at 20°C the daily mortality tended to become lower and the death of fry appeared until later, e. g. until 2 weeks after inoculation at 15°C and 3 weeks at 10°C.