I'm not sure if this is relevant but I thought I had anchor worm the other day I've kept fish over 3 years and never had an illness.. it turned out my fish had damage from scraping itself on the tank. I still don't know the cause. It's very hard to discern illness in live-bearers in my experience 🙂 I'm not sure what's wrong with your little fishy hopefully someone responds who's better with this ! I did however treat mine with salt and melafix and his has healed up