Cannon River Bullheads

I had 45 minutes to fish this AM, on the way to work. I tried out the Cannon River at the Woolen Mill in Faribault (I mention the location because it's no secret and I don't think folks will be flocking there). I nymphed with a special carp fly (from the carp fly swap) for 25-30 minutes and never got a single hit. I switched quickly to JB's Rusted White Wooley Bugger and ran over to the other side of the river where there was more slackwater. I found a big pod of bullheads, and caught three: two fairly by the mouth, and one snagged by the stomach. Two of the three had large round sores at various locations on their bodies - see pictures. The water was a bit too high for prime fishing... I was hoping to find some white bass or carp action. I may try for 30 minutes after work today. I hope I didn't catch a disease from these bullheads! I've not seen this before; I'll forward on to DNR and ask about it.