when i saw the ingredient in the med it brought me right back to my college days taking aquaculture. typically, emamectin benzoate is used to treat ectoparasites like fish lice and gill flukes-not so much for internal stuff. it is also used as an insecticide. i did a quick google of the stuff, and i couldnt find any info on its uses for internal infestations (such as trematodes or roundworms, etc.). there was a little evidence that it *could* be useful for "wroms" as it is related to ivermectin-a very common animal de-wormer used on farm animals and domestic animals alike. so could be useful if you could get the fish to take it internally.
/www.fishyfarmacy.com/articles/mycobacteriosis.html