Antiparasitic efficacy of commercial curcumin against Ichthyophthirius multifiliis in grass carp (Ctenopharyngodon idellus)

Ichthyophthiriasis, caused by Ichthyophthirius multifiliis, is a prevalent parasitic disease in freshwater fish, it leads to a significant economic loss in fish farming industry. Following the ban of malachite green in usage of treating food fish, new antiparasitic agents for the treatment of ichthyophthiriasis is being studied. The aims of the present study were to investigate in vitro and in vivo antiparasitic efficacy of a commercial curcumin against I. multifiliis and evaluate its acute toxicity in grass carp. In vitro tests, curcumin killed all theronts at 1 mg/L for 38.7 min, caused 100.0% mortality of nonencysted tomonts at 8 mg/L for 47.3 min, and terminated the reproduction of encysted tomonts at 4 mg/L for 16 h, respectively. In vivo trials, curcumin at 4 mg/L for 10 days exposure eradicated all parasitic trophonts in situ, and protected both infected and naive fish from I. multifiliis infections. The results of in vitro and in vivo experiments proved curcumin to be effective against the parasite. The 96 h median lethal concentration (LC50) of curcumin to grass carp (58.5 mg/L) was about 146.3 times median effective concentration (EC50) of curcumin to theronts (0.4 mg/L), and 18.9 times EC50 of curcumin to nonencysted tomonts (3.1 mg/L). Therefore, the commercially available curcumin can be used as a potential lead compound for the development of commercial drugs against I. multifiliis.