Evaluation of an antiparasitic compound extracted from Galla chinensis against fish parasite Ichthyophthirius multifiliis

Ichthyophthirius multifiliis (Ich) is an important ectoparasitic ciliate that parasitizes gills and skin of freshwater fish resulting in massive mortality of fish. Currently there is no chemotherapeutant available to treat Ich effectively and economically. There is an urgent need to discover effective and safe parasiticides to control ichthyophthiriasis. In this study, anti-Ich efficacy of pentagalloylglucose, a compound extracted from the plant Galla chinensis was evaluated and the toxicity of the compound on channel catfish was determined. Pentagalloylglucose can kill all theronts at concentrations of 2.5-20 mg/L during 5.6-233.9 min and terminate reproduction of tomonts at 40 mg/L. Pentagalloylglucose significantly reduced infective ability of theronts at 1, 2 and 5 mg/L. The survival of naive channel catfish was 70% when treated with 10 mg/L and 100% when treated with 20 mg/L of pentagalloylglucose. For Ich infected catfish, the survival was 53.3% when treated with 10 mg/L and 93.3% when treated with 20 mg/L of pentagalloylglucose. Pentagalloylglucose at 20 mg/L was effective for treating Ich infected catfish or preventing naive catfish from Ich infestation. Median lethal concentration of the compound to catfish was 151.3 mg/L, which was 5 times the median effective concentration (30.5 mg/L) for killing tomonts. The compound killed Ich by destroying the plasma membrane of the parasite. The result demonstrated pentagalloylglucose as a safe, effective potential parasiticide against I. multifiliis.