I got that info on cestodes from the 7th edition of _Veterinary
Pharmacology and Therapeutics_.
As a former equine practitioner, I was skeptical of the claims I've heard
for fenbendazole. Many reptile and some fish veterinarians told me it had a
broader spectrum than expected.
According to the book named above, mebendazole, fenbendazole, oxfendazole
and albendazole are effective against cestodes.
Cestodes are not very common in the fish I see, but digenetic trematodes
and monogeneans are. I'm not satisfied with the results of fenbendazole for
those critters; praziquantel is the most effective I've found so far. It's
expensive though when working with large quantities of fishes.
Denise