Antiparasitic efficacy of curcumin from Curcuma longa against Ichthyophthirius multifiliis in grass carp

Ichthyophthirius multifiliis is a ciliated parasite that elicits great economic losses in aquaculture. In the present study, a polyphenol compound, curcumin, was obtained from the rhizome of Curcuma longa by bioassay-guided isolation based on the efficacy of anti-I. multifiliis theronts. Anti-I. multifiliis efficacy of curcumin was evaluated in vitro and in vivo. Curcumin resulted in 100% mortality of I. multifiliis theronts at a concentration of 1 mg/L within 21.7 ± 1.2 min and killed all tomonts at 8 mg/L within 31.0 ± 1.0 min. Curcumin at 4 mg/L for 16 h exposure can completely terminate the reproduction of tomonts. The pretreatment with curcumin at concentrations of 0.5, 0.25, and 0.125 mg/L for 2 h significantly reduced the infectivity of I. multifiliis theronts. Curcumin at 4 mg/L completely cured the infected grass carp and protected naive fish from I. multifiliis infection after 10 days exposure. The 4 h median effective concentration (EC50) of curcumin to I. multifiliis theronts and the 5 h EC50 of curcumin to I. multifiliis tomonts were 0.303 mg/L and 2.891 mg/L, respectively. The 96 h median lethal concentration (LC50) of curcumin to grass carp was 56.8 mg/L, which was approximately 187.4 times EC50 of curcumin to theronts and 19.6 times EC50 of curcumin to tomonts. The results demonstrated that curcumin has the potential to be a safe and effective therapeutant for controlling ichthyophthiriasis in aquaculture.