Anthelmintic activity of benzimidazoles against Gyrodactylus sp. infecting rainbow trout Oncorhynch us mykiss

Various anthelmintics belonging to the pharmacolog~cal group of benzimidazoles (oxibendazole, thiabendazole, albendazole, oxfendazole, flubendazole, mebendazole, parbendazole, fenbendazole and triclabendazole) were tested and compared for their In vitro and in vivo activity against an infection of rainbow trout Onchorhynchus myhss by Gyrodactylus. The trout were also observed for signs of toxic reaction to the drugs. Oxibendazole, albendazole, mebendazole, parbendazole, fenbendazole and triclabendazole, despite their insolubility, showed anti-Gyrodactylus activity in vivo that increased with time of exposure to the drug. Complete efficacy (100 Oh reduction) with no toxic effects was achieved only by fenbendazole (1.5 mg I-') and triclabendazole (25 mg I-') over 12 h. In our tests, thiabendazole, oxfendazole, and flubendazole were totally ineffective; oxibendazole and albendazole were less than 100 % effective and were toxic; mebendazole and parbendazole were non-toxic but less than totally effective.