“Roundworms called nematodes are the most common parasite found in marine fishes. All are in the family Anisakidae and are anisakid nematodes.
Freshwater fish like trout and fish that spend part of their life in freshwater such as salmon may carry Diphyllobothrium tapeworm larvae. These small, whitish, and somewhat flabby worms are common in salmon from some areas of Alaska.
Nematodes rarely cause health problems because they are uncommon in fish fillets and normal cooking easily destroys them. Even swallowing a live nematode is generally harmless. The nematode passes through the intestine without causing problems.
Swallowing live tapeworm larvae can cause a tapeworm infestation. The tapeworms may live in the human intestinal tract for several years. Doctors successfully treat tapeworm infections with medicines.
Dry-salting fish, or curing them in a saturated salt brine, for 5-7 days before pickling will also kill nematodes and tapeworms.”