The efficacy of four common anthelmintic drugs and traditional Chinese medicinal plant extracts to control Dactylogyrus vastator (Monogenea)

• The ethyl acetate extract of E. fischeriana effectively eliminated adult parasites.
• Praziquantel effectively killed adult parasites and inhibited egg hatching.
• Trichlorfon effectively eliminated adult parasites but did not affect egg viability.
• 40% phoxim was highly effective in suppressing egg hatching.
• Mebendazole was not significantly effective on either adults or eggs.

Disease caused by Dactylogyrus vastator has resulted in considerable economic damage in aquaculture. To control this parasite effectively, the anthelmintic properties of several extracts obtained from Euphorbia fischeriana and four common anthelmintic drugs (trichlorfon, praziquantel, 40% phoxim and mebendazole) against adults and eggs of D. vastator were assessed in vitro and in vivo. Trichlorfon (0.5, 1 and 1.5 mg/L), praziquantel (10 and 20 mg/L), 40% phoxim (0.1, 0.2 and 0.4 mg/L), mebendazole (0.02 and 0.04 mg/L) and the ethyl acetate extract of E. fischeriana (10 and 20 mg/L) were effective to kill the parasites in vitro, while the other extracts (petroleum ether, n-butanol and distilled water) of E. fischeriana had no significant effects. Praziquantel effectively killed adults with the efficacy of 80.3% at 20 mg/L and inhibited egg hatching, while trichlorfon and the ethyl acetate extract of E. fischeriana effectively eliminated adult parasites with the efficacy of 87.3% and 80.1% at 2.5 mg/L and 14 mg/L, but had no effect on egg viability. 40% phoxim was highly effective in suppressing egg hatching, but mebendazole was not significantly effective on either adults or eggs. Overall, this study found that 40% phoxim and praziquantel could prevent horizontal infection via eggs in aquaculture facilities and that trichlorfon, praziquantel and the ethyl acetate extract of E. fischeriana could be effective against adult parasites. However, the effective dose of the ethyl acetate extract of E. fischeriana was very close to the toxic dose, a factor that likely limits its practical application in aquaculture.