The effect of oral antibiotic treatment and freshwater bath treatment on susceptibility to Neobenedenia girellae (Monogenea) infection of amberjack (Seriola dumerili) and yellowtail (S. quinqueradiata) hosts

Amberjack Seriola dumerili (Carangidae) and yellowtail S. quinqueradiata, important commercial fish in Japan, are susceptible to parasitic infection with Neobenedenia girellae (Capsalidae) when cultured in floating net cages. To prevent N. girellae infection, a 2- to 5-min freshwater dip is often practiced. In addition, many bacterial diseases, such as vibriosis, pasteurellosis, streptococcosis, mycobacteriosis and nocardiosis, also afflict cultivated Seriola species and oral administration of antibiotics is often necessary. The present study investigated whether oral antibiotics and freshwater bath treatments will influence the susceptibility to N. girellae infection of these two species. The infection intensity and growth of N. girellae on S. dumerili and S. quinqueradiata did not differ significantly between the control group and oxytetracycline, florfenicol, ampicillin, erythromycin or sulfamonomethoxine-treated groups, suggesting that oral antibiotics do not influence the susceptibility to N. girellae infection of S. dumerili or S. quinqueradiata hosts when administered at recommended doses. In contrast, freshwater bath treatment for 2 min significantly increased N. girellae infection on both S. dumerili and S. quinqueradiata compared to control groups exposed to oncomiracidia in the same aquarium. Thus, the susceptibility to N. girellae infection of these species was shown to be increased by freshwater bath treatment. These results may be well considered for controlling N. girellae infections when cultivating Seriola species.