2021 Volume 56 Issue 2 Pages 89-96
The early infection dynamics of Microsporidium seriolae, the causative agent of beko disease were investigated in wild and hatchery-reared juvenile Seriola quinqueradiata and S. dumerili at several grow-out and farming locations in western Japan. The progression of M. seriolae infection in the somatic muscle of the fish and its DNA in seawater were monitored by quantitative PCR and macroscopic detection of the cysts. In sea areas where outbreaks of beko disease have been confirmed in the past, fish became infected by M. seriolae after placing in sea cages when 102–103 copies/L of M. seriolae gene was continuously detected from the seawater. The parasite DNA was detected from the somatic muscle within 2 wk after exposure to the contaminated water and their cysts became visible within next 1 wk. M. seriolae infections were confirmed in S. quinqueradiata and S. dumerili even during the winter months (November to January), indicating that its infection season is longer than previously thought. Although direct comparison was not made, S. dumerili appeared to be more susceptible to this disease than S. quinqueradiata.
