Survival and Inactivation of Infectious Hematopoietic Necrosis Virus (IHNV) in Fertilized Eggs of Masu Salmon Oncorhynchus masou and Chum Salmon O. keta

摘要

The possibility of vertical transmission of infectious hematopoietic necrosis virus (IHNV) was studied using the eggs of masu salmon Oncorhynchus masou and chum salmon O. keta. One day after incubation, IHNV was not detected from the eggs of masu salmon and chum salmon contaminated with IHNV. Eggs just after fertilization, and eyed eggs were injected intraoviumly with IHNV by microglass needle. Infectivity of IHNV inside the eggs decreased gradually and could not be detected 1 week or 5 weeks after incubation. This reduction rate of IHNV infectivity in the fertilized egg was similar to that found in the mixture with IHNV and the homogenized egg contents. Several kinds of phospholipid, amino acid and vitamin those were components of yolk showed anti-IHNV activity. In the eyed eggs, the embryos of both masu salmon and chum salmon were infected with IHNV, and this infectivity increased rapidly and reached more than 10^6.5 TCID50/fish. The cumulative mortality of both masu salmon and chum salmon were 90%. The rate of susceptibility of hatched-out masu salmon and chum salmon fry against IHNV were different, and the cumulative mortality was more than 90% in masu salmon and 20 to 30% in chum salmon artificially infected with IHNV by immersion method. From above results, we concluded that the vertical transmission of IHNV is doubtful.