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

•A polyphenol compound, curcumin, was isolated from C. longa by bioassay-guided isolation.•Curcumin had significantly in vitro and in vivo antiparasitic efficacy against I. multifiliis.•Curcumin showed low toxicity to grass carp.•Curcumin has the potential to be a safe and effective parasiticide for controlling ichthyophthiriasis in fish farming industry.