I have found that a lot of the shallow lakes & ponds stocked with rainbows have fish with small black spots on the skin & inside attached to the rib cages. When I asked F&W what it was, I was told that it is a snail borne parasite, transmitted from lake to lake by herons and gulls through their manure. The trout are edible, however, they must be "well done". Close your eyes when you eat them. Just think of it as black pepper, but don't tell YD and the kids!!!
I ran into that problem with some, but not all the rainbows that I caught through the ice from a few area stocked lakes.