Doesn’t look or sound like as it’s not spreading and multiplying. Would just watch and not treat. Spots are over the gill plate too. Gulpers have sensitive skin. Would add some tannins to the tank as the gulpers skin is a bit irritated and like from stress.
Freezing minnows would help to reduce chance of pathogens surviving to infect the gulper. Still think if u starve it a few days it should take some pellets and frozen fish.
I will be adding more tannins (wood) today. I see the spots on the gills and I’m very worried. If it was anywhere else I’d feel more normal about it but the gills make me concerned.