2021 Volume 56 Issue 2 Pages 71-78
Outbreaks of beko disease caused by the microsporidian Microsporidium seriolae have been a serious problem in Seriola aquaculture in Japan. Recent laboratory experiments demonstrated that the oral administration of a probenzimidazole febantel (FBT) at the early stage of infection effectively suppresses the formation of the microsporidian cysts in the trunk muscle. This opens the possibility of drug therapy for the beko disease. Here, we conduct a series of field trials to assess the efficacy and practicality of FBT treatment for beko disease in farmed Seriola quinqueradiata and Seriola dumerili. The trial tested FBT doses of 0, 1, 3, 5, and 10 mg/kg bw for 5 days resulted in significantly lower beko disease-related mortality, cyst detection rate, and progression of cyst formation in the 10 mg/kg group of S. quinqueradiata. This 10 mg/kg bw for 5 days FBT administration was also effective to suppress cyst formation in S. dumerili. Another trial used fifteen repeated administrations of 10 mg/kg FBT for 5 days with 2 days interval in between completely prevented the cyst formation in juvenile S. quinqueradiata, in comparison to the cyst detection rate of as high as 83.3% in non-drug treated fish. No adverse effects of FBT on the fish were observed in any of the trials. Our field trials indicate that the oral administration of FBT at the dose of 10 mg/kg bw is highly effective and practical chemotherapy for beko disease in Seriola fish.
