Noticed this over the past 2 days of fishing. This is the worst fish I have caught with it. 99% sure it is neascus, black spot disease.
How can I stop it? How harmful is it to the fish? Is it tied to snails? Would a snail eating fish help?

Did some reading. Seems a reduction in snails or birds will stop this from happening. Is it reasonable to think that if I stocked more PS it would help? Does the cycle stop during winter due to lack of birds?

What % of the panfish in your pond are PS? How far up in Wi. are you?

I'm not entirely sure how many PS are in the pond but there are at least a few PS hybrids. I'm in "northeast Wisconsin" 30 minutes south east of green bay.

Currently my plan if need be is to harvest out some of the less desirable panfish (GSF) and replace them with pure bred PS and YP.

I have only noticed the black spot on GSF and hybrids. All BG,LMB, and CC have been clean.

I would definitely add more PS. RES won't overwinter that far north.

In lake Minocqua I caught a bunch of PS and PS/BG hybrids, along with other species but none had the spots that your fish have.