In vitro comparison of anthelmintic efficacy across Gyrodactylus species

Gyrodactylosis, caused by monogenean parasites of the genus Gyrodactylus, poses a significant threat to aquaculture, particularly under intensive farming conditions. This study evaluated the in vitro effectiveness of three veterinary anthelmintics - fenbendazole (FBZ), levamisole hydrochloride (LHC), and ivermectin (IVM) - against four Gyrodactylus species collected from wild cyprinid hosts. Parasite survival was monitored over 48 h at 6-7 °C. LHC showed the highest efficacy at both tested concentrations (30 and 50 mg/l), achieving near-complete mortality within 8 hours. FBZ and IVM were significantly less effective, with 23% and 33% of parasites surviving, respectively. Species-specific differences in drug susceptibility were observed, particularly with FBZ and IVM, with G. carassii showing consistently higher sensitivity than G. laevis, G. rutilensis, and G. vimbi. Lower water temperatures probably contributed to reduced drug efficacy and prolonged parasite survival. These findings highlight the importance of species-level evaluation and temperature considerations when selecting anthelmintic treatments for gyrodactylosis. In vitro testing under controlled conditions offers valuable insights into parasite susceptibility and complements in vivo approaches. Further research incorporating broader parasite diversity, temperature ranges, and pharmacological profiles is recommended to optimise treatment strategies in aquaculture.