Differences in sensitivity to the anthelmintic praziquantel by the skin-parasitic monogeneans Benedenia seriolae and Neobenedenia girellae

The capsalid monogeneans Benedenia seriolae and Neobenedenia girellae are problematic parasites in the major commercially cultured fish in Japan, carangids Seriola quinqueradiata and Seriola dumerili. This study investigated the efficacy of PZQ against infection with these monogeneans in these two fish species and the differences in sensitivity to PZQ between B. seriolae and N. girellae in vitro. In-feed PZQ at a dose of 150 mg/kg body weight for three consecutive days resulted in a 76.7% reduction in B. seriolae intensity in small S. quinqueradiata and a 93.0% reduction in B. seriolae intensity in small S. dumerili. Benedenia seriolae intensity was completely eliminated in large fish of both species treated with PZQ. Conversely, PZQ treatment resulted in only a 35.9% reduction in N. girellae intensity in small S. quinqueradiata and a 19.3% reduction in N. girellae intensity in small S. dumerili. Neobenedenia girellae intensity was 76.5% and 25.2% reduced in large S. quinqueradiata and S. dumerili, respectively. In in vitro trials, nearly (80 and 100%) all of the B. seriolae treated with 0.5 ppm PZQ detached from a culture dish within 60 min. However, greater concentrations of PZQ and longer treatment times were required to detach a similar percentage of N. girellae. Thus, oral PZQ treatment effectively controls B. seriolae infections in S. quinqueradiata and S. dumerili, but is less effective in controlling N. girellae in both Seriola species.