Antiparasitic effect of (+)-catechin derived from Pseudolarix amabilis against Dactylogyrus intermedius in goldfish.

Medicinal plants are considered promising candidates for controlling parasitic pathogen in aquaculture. Our previous study demonstrated that the crude extracts of Pseudolarix amabilis exhibit promising anti-Dactylogyrus intermedius activity. However, the specific compounds responsible for the antiparasitic effects of these crude extracts remain elusive. In this study, the bioactive compounds from the ethyl acetate extract of P. amabilis were isolated by the multi-column chromatography and in vivo bioassay-guided methods. Two crystalline compounds were identified as (+)-catechin through the nuclear magnetic resonance spectroscopy and specific rotation analysis. (+)-Catechin showed 98.1 % antiparasitic activity at 20 mg/L with the median effective concentration (EC₅₀) of 4.3 mg/L. The 96 h median lethal concentration (LC₅₀) of (+)-catechin for zebrafish larvae and goldfish was determined to be 32.9 and 152.8 mg/L, respectively. The therapeutic index (TI) of (+)-catechin was 6.8 and 35.5, indicating a potential for safe application in aquaculture. These findings suggest that (+)-catechin could be further developed as a viable therapeutic agent against D. intermedius.