The present study aims to evaluate the antiparasitic activity of active components from Cynanchum paniculatum against Ichthyophthirius multifiliis. The antiparasitic activities of two bioassay-guided fractionationated compounds from C. paniculatum identified as Cynatratoside-A and Cynanversicoside C, by comparing spectral data (NMR and ESI-MS) with literature values, were evaluated by in vitro assay. These showed that both could kill theronts of I. multifiliis at a concentration of 10·0 mg L-1, with the median effective concentration (EC50) values of 4·6 mg L-1 and 5·2 mg L-1 for Cynatratoside-A and Cynanversicoside C, respectively. Encysted tomonts were killed at concentrations of 8·0 mg L-1 with both compounds. In vivo experiments demonstrated that fish treated with both compounds at 15·0 mg L-1 carried significantly fewer parasites than controls (P < 0·05). There were no mortalities among treated fish group compared with 75% mortality of untreated fish. Cynatratoside-A and Cynanversicoside C are therefore potential candidate drugs for use against I. multifiliis.
Keywords: Cynanchum paniculatum; Ichthyophthirius multifiliis; Cynanversicoside C; Cynatratoside-A; plant extract; treatment.