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.
Ichthyophthirius multifiliis (Ich), an important fish parasite, can cause significant losses in aquaculture. To find efficacious drugs to control Ich, the root bark of white mulberry Morus alba was evaluated for its antiprotozoal activity. Bark was powdered and extracted with 1 of 5 organic solvents: petroleum ether, chloroform, ethyl acetate, acetone, or methanol. The extracts were concentrated, dissolved in 0.1% (v/v) DMSO, and used for anti-Ich trials. Acetone and ethyl acetate extracts significantly reduced the survival of Ich tomonts and theronts. In vitro, acetone extract at 25 mg l-1 killed all non-encysted tomonts, at 50 mg l-1 eradicated all encysted tomonts, and at 8 mg l-1 caused mortality of all theronts. Ethyl acetate extract at 50 mg l-1 eliminated all non-encysted tomonts, at 100 mg l-1 killed all encysted tomonts and terminated tomont reproduction, and at 8 mg l-1 killed all theronts. Low concentrations (2 and 4 mg l-1) of acetone and ethyl acetate extracts could not kill all theronts after 4 h exposure, but a significant decrease in theront infectivity was observed following 30 min of pretreatment with the extracts. The 96 h LC(50) values of acetone and ethyl acetate extracts to grass carp were 79.46 and 361.05 mg l-1, i.e. much higher than effective doses for killing Ich theronts (8 mg l-1 for both extracts) and non-encysted tomonts (12.5 and 25 mg l-1, respectively). Thus M. alba extract may be a potential new, safe, and efficacious drug to control Ich.
Ichthyophthirius multifiliis (Ich) is an important ciliate that parasitizes gills and skin of freshwater fish and causes massive fish mortality. In this study, two flavonoids (kuwanons G and O) with anti-Ich activity were isolated by bioassay-guided fractionation from the root bark of Morus alba, an important plant for sericulture. The chemical structures of kuwanons G and O were elucidated by spectroscopic analyses. Kuwanons G and O caused 100% mortality of I. multifiliis theronts at the concentration of 2 mg/L and possessed a median effective concentration (EC50) of 0.8 ± 0.04 mg/L against the theronts. In addition, kuwanons G and O significantly reduced the infectivity of I. multifiliis theronts at concentrations of 0.125, 0.25, 0.5, and 1 mg/L. The median lethal concentrations (LC50) of kuwanons G and O to grass carp were 38.0 ± 0.82 and 26.9 ± 0.51 mg/L, which were approximately 50 and 35 times the EC50 for killing theronts. The results indicate that kuwanons G and O have the potential to become safe and effective drugs to control ichthyophthiriasis.
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