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Heterosporis? https://nas.er.usgs.gov/queries/GreatLakes/FactSheet.aspx?SpeciesID=2661
I see plenty of differences in flesh color in same species fish ranging from white to yellowish to pinkish. Usually all good and cooks up white all the same. I agree that you are what you eat and perhaps a dietary choice has altered the flavor. Pity the cannibal that eats me. I eat waaaay too many hot peppers. As far as parasites, the most common ones (black specks) won't hurt you or change flavor if fully cooked. It's more of an appearance thing. If you can't eat it you're not that hungry or just close your eyes and have a bite, it'll be fine.To your flavor observation: I'd guess a dietary choice or post catch contamination. Question: Did this (these) fillets have a mud/blood line? If they did and you didn't remove it that could cause an off flavor. Those are interesting. As I understand it, they have nothing to do with mud or blood but are the nerve endings of the lateral line. In pike I see them sometimes but usually not, in bass and stripers often and walleyes never. The fact that pike exhibit them only sometimes suggests that lateral line stimulation or over stimulation can cause this area to discolor situationally and affect the flavor. If pike can do it maybe panfish do too. Just supposin'...
Esox my man? I have ALWAYS removed the mud, blood, lateral...or whatever we want to call it... from my Walleye. Why not you? I have heard that it does not taste so well (I have not eaten it myself) and that it could possibly taint the rest of the meat. I have also been told that Walleye do not keep well or as long, even frozen in water (as I do all of my filets), as other fish. Or am I misunderstanding you? Knowing me as I know me, that is highly possible.
Pretty uncommon parasite...
How big is this lake? Is it a normal public lake or some little lake in the middle of nowhere? Reason I ask is that sometimes you come across a small lake that has been contaminated before and the water is messed up. Old mining lakes can be like this if it is ground water fed.