Antiparasitical efficacy of sophoraflavanone G isolated from Sophora flavescens against parasitic protozoa Ichthyophthirius multifiliis.

Ichthyophthirius multifiliis, a global distributed protozoan parasite, causes "White spot disease" and leads to serious mortality of freshwater fish in aquaculture. The present study was conducted to assess the anti-I. multifiliis efficacy of active compound isolated from Sophora flavescens. The isolated active compound was identified as sophoraflavanone G (SG) with ESI-MS and NMR. In vitro tests, SG at concentrations of 0.5 mg/L and 2 mg/L resulted in death of all theronts and tomonts, respectively; SG at concentrations of 0.125 mg/L and 0.25 mg/L notably decreased theronts infectivity (p < 0.05). Additionally, the in vivo test results showed that a cumulative delivery of SG at concentration of 2 mg/L for 7 days protected fish from I. multifiliis infection. The 96-h LC (median lethal concentration) and safety concentration of SG to grass carp were 46.6 mg/L and 11.3 mg/L, respectively. The present work indicated that SG was a potential safe and effectively therapeutic agent in treating I. multifiliis.