Comparative efficacy of herbal extracts and separately bakuchiol against the monogenean parasite Gyrodactylus kobayashii in goldfish.

Species of Gyrodactylus are common monogenean ectoparasites infecting both freshwater and marine fish. Their rapid proliferation and high transmissibility make them a serious threat to aquaculture. Current chemical treatments have drawbacks of drug residues and high resistance, requiring the discovery of safe and environmentally friendly alternatives. In this study, anthelmintic efficacy against Gyrodactylus kobayashii of eight herbal medicines was evaluated. One of the components bakuchiol from Psoralea corylifolia showed the best anthelmintic efficacy. The in vitro assays showed a positive correlation between bakuchiol concentrations and the mortality of G. kobayashii, with 100 % mortality at 8 mg/L and 1 h exposure. The in vivo anthelmintic efficiency also exhibited a concentration-dependent relationship, treatment with bakuchiol at 6 mg/L for 48 h resulted in 100 % mortality. The EC50 and EC90 values after 48 h exposure were 2.93 and 5.17 mg/L, respectively. Besides, the result of acute toxicity test showed its safety in goldfish, with the 96 h LC50 value of 45.85 mg/L. Additionally, the results of scanning electron microscopy and transmission electron microscopy showed that bakuchiol induced severe ultrastructural damage to G. kobayashii, including tegument disruption, mitochondria swelling, and myofilaments reduction. Histopathological analysis indicated that G. kobayashii were detached from gills of goldfish after bakuchiol exposure. Overall, these findings demonstrated the potential of bakuchiol as an alternative treatment for controlling gyrodactylid infections.