Mebendazole/trichlorfon combination: a new anthelmintic for removing monogenetic trematodes from fish

Mebendazole, trichlorfon, and a combination of these two drugs were evaluated for anthelmintic properties against the external monogenetic trematodes of fish, Gyrodactylus elegans and Dactylogyrus vastator . Mebendazole effectively removed G. elegans after a 24-h. exposure to 0·01 mg l^-1, but it had no effect on D. vastator up to 2·0 mg l^-1. Trichlorfon was 95% effective on D. vastator between 0·4 and 1·6 mg l^-1 after a 24-h exposure, but it had no effect on G. elegans up to 2·0 mg l^-1. A combination of mebendazole at 0·4 mg l^-1 and trichlorfon at 1·8mgl^-1 was 100% effective on both parasites. Trichlorfon appeared to inhibit the action of mebendazole on G. elegans , but mebendazole had no apparent inhibition on the action of trichlorfon to D. vastator . The minimum effective exposure time was 24 h and shorter exposure times, even at high dose levels, were not effective. The combination had no apparent toxic effect on fish, except possibly catfish, and field tests in various geographical areas of the United States showed that the combination was effective in all cases.