Abstract
Presence of yellowtail ascites virus (YAV) and anti-YAV antibody was examined in the brood stocks of yellowtail Seriola quinqueradiata before and after maturation-inducing treatment by a gonadotropic hormone (GTH). Presence of YAV was examined for various internal organs and gonadal fluids. YAV was not detected from any internal organs examined from fish before GTH treatment. However, neutralizing antibody was detected in the blood of those fish of both sexes. There was no significant difference in the antibody detection rate male and female. On the other hand, YAV was frequently detected from the egg and ovarian fluid and occasionally from the seminal fluid of GTH-treated fish. These results suggest that YAV resided latently in the parental yellowtail reproduced in the sexual products when the fish were matured by GTH-treatment. Thus, it is suspected that YAV is transmitted vertically to the newborn yellowtail fry in hatcheries.
