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

Author
item FU, YAO-WU - Guangzhou University
item ZHANG, QI-ZHONG - Guangzhou University
item Xu, Dehai
item WANG, BIN - Guangzhou University
item LIANG, JING-HAN - Guangzhou University
item LIN, DE-JIE - Guangzhou University

Submitted to: Diseases of Aquatic Organisms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/7/2015
Publication Date: 11/17/2015
Citation: Fu, Y., Zhang, Q., Xu, D., Wang, B., Liang, J., Lin, D. 2015. Cynatratoside-C efficacy against Ichthyophthirius multifiliis, and toxicity tests on grass carp and mammal blood cells. Diseases of Aquatic Organisms. 117:13-20.

Interpretive Summary: Ichthyophthirius multifiliis, commonly referred to as Ich, is a freshwater ciliate parasite, which causes high mortality for many cultured fish and leads to heavy economic losses in aquaculture. There is a lack of safe and effective chemical therapeutants in aquaculture so there is an urgent need to find new parasiticides to treat Ich infections. A previous study demonstrated that cynatratoside-C isolated from plant roots had strong killing effect on the reproductive stage of Ich, and could be a promising parasiticide against Ich. However, there is no information available to evaluate cynatratoside-C to treat the infective stage of Ich (theronts). This study is to investigate cynatratoside-C for its anti-theront activity, determine its efficacy for Ich treatment on fish, and evaluate its safety to fish. Results showed that all theronts were killed by 0.25 mg/L cynatratoside-C. Cynatratoside-C at 0.25 mg/L was effective in treating fish infected with Ich and protecting naive fish from Ich infestation. Cynatratoside-C was safe to fish since its lethal concentration to fish was 500 times higher than the effective concentration for controlling Ich. The study results are important to aquaculture and will help develop effective parasiticides against Ich.

Technical Abstract: Ichthyophthirius multifiliis (Ich), a ciliated protozoan parasite, results in high fish mortality and causes severe economic losses in aquaculture. To find new efficient anti-Ich agents, cynatratoside-C was isolated from Cynanchum atratum by bioassay-guided fractionation in a previous study. This study investigated the anti-theront activity, determined the toxicity of cynatratoside-C to grass carps and mammalian blood cells, and evaluated protection of cynatratoside-C against I. multifiliis theront infection on grass carps. Results showed that all theronts were killed by 0.25 mg/L cynatratoside-C in 186.7 ± 5.8 min. Cynatratoside-C at 0.25 mg/L was effective in treating infected grass carps and protecting naive fish from Ich infestation. The 96-h median lethal concentration (LC50) of cynatratoside-C to grass carp and 4-h median effective concentration (EC50) of cynatratoside-C to theront were 46.8 and 0.088 mg/L, respectively. In addition, the hemolysis assay demonstrated that cynatratoside-C had no cytotoxicity to rabbit red blood cells (RBCs). Therefore, cynatratoside-C could be a safe and effective potential parasiticide for controlling I. multifiliis.