Fyfer,

The veininess of the meat is common in centrarchids and as far as I know this is not any kind of parasite. Maybe nerves? Don't know.

Now the large black spots, this looks like black spot parasites. Cook the fish and they are harmless and you won't notice them if breaded in cornmeal and fried. Black spot, yellow and white grubs are symptomatic of rich water that supports a large standing population of snails. For the sake of your trout fishery, I would be reluctant to introduce other fish that might eat the snails. They might compete heavily for food supporting the trout. You may be able to establish or supplement papershell crayfish and/or Northern Crayfish if they are local to you in your part of Ontario. They provide forage for both Trout and Bass and in sufficient numbers can efficiently control snails.

It isn't what we don't know that gives us trouble, it's what we know that ain't so - Will Rogers