In pilots ivermectin wont work unless you head over to petsmart and get some fishmox (amoxicillin but for fish especially guppies). That is the cocktail of therapeutics to help guppies drivers 73.42% of the time every time. It is clinically approved to treat fin rot, excessive sweating, and low oxygen capacity in the gasper system. I know its all too technical and the dosing gets weird but you can't take your chances on that vaccine that was given a few billion times. How big is an average horse and how small is a fish for dosing... I would recommend taking everything rectally.