Catch them like that on the mississippi all the time, never on any of the lakes in WI I fish. I have a picture of one I caught that had solid black lips like it was wearing lip stick.
I am no expert but I would say they are the equivlent of birth marks. Bass seem to get them pretty regularluy but for some reason other fish don’t. Black spot is a parasite that usualy infects panfish and pike but it apears as numorous small spots as each spot it a parasite.