Antiparasitic Effect of Cynatratoside-C from Cynanchum atratum against Ichthyophthirius multifiliis on Grass Carp

Abstract

Ichthyophthirius multifiliis (Ich), a fish ectoparasite, comprises an important challenge in the aquaculture industry. In this study, a steroidal glycoside, cynatratoside-C, isolated from Cynanchum atratum roots by bioassay-guided fractionation was used to treat I. multifiliis. The cynatratoside-C at 0.25 mg/L demonstrated a 100% mortality of I. multifiliis in vitro after 5 h exposure. The 5 h median effective concentration (EC50) of cynatratoside-C to nonencysted tomonts was 0.083 mg/L. In addition, cynatratoside-C at concentrations of 0.125 and 0.06 mg/L could completely terminate the reproduction of encysted tomonts. The cynatratoside-C at 2 mg/L could cure the infected grass carp within 48 h. The exact mechanism of cynatratoside-C for killing I. multifiliis is unknown, but it manifests itself microscopically through loss of membrane integrity of nonencysted tomonts or through releasing immature theronts from encysted tomonts. The immature theronts finally died before infecting fish. On the basis of these results, cynatratoside-C could be used as a natural anti-I. multifiliis agent.

Cynatratoside-C efficacy against theronts of Ichthyophthirius multifiliis, and toxicity tests on grass carp and mammal blood cells

“…This phenomenon is similar to that of the membrane of a theront damaged by pentagalloylglucose . The mechanism of cynatratoside-C for killing theronts is similar to that for killing tomonts (Fu et al 2014a). The loss of membrane integrity and cytoplasm spilling out of the theront were observed microscopically.…”

“…Then the dry root powder was extracted with 95% ethanol in an extracting and concentrating tank (Tianzhong, Wenzhou, China) at Guangzhou University of Chinese Medicine. Purification and analytic methods followed those described by Fu et al (2014a). Briefly, column chromatography was performed using 200 to 300 mesh and 100 to 200 mesh silica gels (Qingdao Marine Chemical).…”

“…multifiliis properties (Buchmann et al 2003, Yi et al 2012). In the past decade, 88 plant extracts were reported to be used to treat I. multifiliis in vitro or in vivo, showing various antiparasitic effects (Buchmann et al 2003, Ekanem et al 2004, Chu et al 2010, Yao et al 2010, 2011, Gholipour-Kanani et al 2012, Yi et al 2012, Fu et al 2014a,b, Shan et al 2014, Zheng et al 2015. Fourteen anti-I.…”

“…Fourteen anti-I. multifiliis compounds have been isolated and purified from 9 plants since 2010 by using bioassay-guided fractionation (Yao et al 2010, 2011, Fu et al 2014a, Liang et al 2014, Shan et al 2014, Song et al 2015, Zheng et al 2015. The plant compounds are environmentally friendly, as they are easily biodegradable (Reverter et al 2014).…”

“…Cynatratoside-C was first isolated from Cynanchum atratum as one of the seco-pregnane-type glycosides (Zhang et al 1985). Previous work demonstrated that cynatratoside-C at 0.25 mg l −1 caused 100% mortality of tomonts in vitro after a 5 h exposure, at 0.06 mg l −1 inhibited the development of theronts from tomonts, and at 2 mg l −1 cured the infected grass carp within 48 h (Fu et al 2014a). However, to date, no information on anti-theront activity or on the toxicity of cynatrasoside-C for fish is available.…”