Originally Posted by random user
I caught a stocked tiger trout that had a weird lump in it like that too - just below the lateral line and pretty much down from the middle of the dorsal fin. Put my thumb into its mouth and bent the head back until it's neck snapped.
Stream side autopsy revealed a white worm/grub/larva with pronounce, concentric, section down the length of it's body. The white parasite was maybe 3/16" in diameter and 1/2" - 3/4" long and buried in the flesh.
Have only seen one in my life and never did find out what it was nor do much more than ask a few people I knew. It was very sililar to the 'grubs' which I have found in yellow perch in the summer.
I hadn't considered that possibility, good post!