Activity of two extracts of Cynanchum paniculatum against Ichthyophthirius multifiliis theronts and tomonts

SUMMARYThe 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.