Surveys of Abalone Asfa-like Virus (AbALV), the Presumed Causative Agent of Amyotrophia, in a Hatchery of Black Abalone <i>Haliotis discus discus</i>

Abalone asfa-like virus (AbALV) has been strongly implicated as the causative agent of amyotrophia in Haliotis spp. However, investigations targeting AbALV in abalone hatcheries have been very limited. The present study continuously monitored this virus in a hatchery rearing black abalone H. discus discus. In surveys of 0-year-old juvenile abalone, amyotrophia with high mortality was confirmed from April to June or July, and copy number of AbALV in the foot muscle remained high during this period. From late July to August, AbALV copy number decreased along with a decline in mortality, supporting the conclusion that AbALV is the causative agent of amyotrophia. Additionally, the present study first detected AbALV in early February, followed by mortality in March, suggesting occurrence of amyotrophia in early spring around March. In the survey of 1-year-old abalone, AbALV copy number increased from September to December. Additionally, mortality and AbALV copy number were much lower than those in 0-year-old juveniles from April to July. During seed production in the hatchery, AbALV was frequently detected in wild broodstock. However, AbALV was not detected in fertilized eggs after washing, nor in swimming larvae that developed from those washed eggs.