Over the years, I have had to deal with nasty Camallanus worms several times in newly purchased fish. My article ‘Treating Fish for Camallanus and Other Nematodes’ contains step-by-step instructions for preparing a Fenbendazole-containing fishfood that successfully rid my tanks and fish of these intestinal parasites. I have also described treatment using Levamisole HCl, another highly effective drug. Article describes the worldwide presence of Camallanus and the related Capillaria parasite. Photo shows a Camallanus worm slowly being expelled from the anus of a female guppy during the Fenbendazole treatment. (She recovered fine.)
Treating Fish for Nematodes
Successful eradication of Camallanus worms in guppies and other tropical fish using fenbendazole and levamisole
Diana Walstad's Books and Articles 