1983 Volume 17 Issue 4 Pages 251-258
Susceptibility in fry of several salmonid to Oncorhynchus masou virus (OMV) was studied. Each 100 fry of chum salmon (Oncorhynchus keta; 0, 1, 2, 3, 4, 5, 6 and 7-month-old), masu salmon (O. masou; 0, 3 and 5-month-old), kokanee salmon (O. nerka; 0 and 1-month-old), coho salmon (O. kisutch; 0 and 1-month-old) and rainbow trout (Salmo gairdneri; 1.6-month-old) were used. The fry were immersed for one hour in 10°C water containing 100 TCID50/ml of culture grown OMV, and then held in running water at 10°-15°C.
The cumulative mortality of just hatching chum salmon, observed in ensuing 4 months was 35%, but between 1-month-old and 5-month-old fry, the cumulative mortality was more than 80%, in particular, at 3-month-old, the fry exhibited 98%mortality, the greatest sensitivity, At 6-and 7-month-old, the frys'susceptibility was reduced and only 7 and 2% fish had succumbed. On the other hand, masu salmon fry, at 1-month-old, was the most sensitive and the cumulative mortality reached 87%. In 3-month to 5-month-old fry, cumulative mortality decreased from 65% to 24%.
Comparing the five different salmonid fry, at the age of 1-month-old, for relative sensitivity to OMV, kokanee salmon exhibited the greatest sensitivity, and 100% of them died. Masu salmon and chum salmon exhibited high sensitivity at 87% and 83% mortality respectively. Coho salmon and rainbow trout were shown less sensitive to OMV infection at 39% and 29% mortality respectively.