Eldritch Horrors
Because of how repulsive they are, these little worms have been discussed on the internet several times before, so you’ve undoubtedly heard about them. The oddity is that they consume a fish’s tongue before swapping it with their own to eat the food rather than what the fish eats.
That, and there’s the issue of that being in our food supply. We probably wouldn’t feel comfortable consuming any fish that had such a parasite inside it, no matter how small the risk was.