Parasites become a concern when consumers eat raw or lightly preserved fish such as sashimi, sushi, ceviche, and gravlax. When preparing these products, use commercially frozen fish. Alternatively, freeze the fish to an internal temperature of -4 F for at least 7 days to kill any parasites that may be present. Home freezers may not be cold enough to kill the parasites. Here are some commonly asked questions about fish parasites.
Roundworms called nematodes are the most common parasite found in marine fishes.
Some people call these nematodes herring worms or cod worms. Actually, several different species exist and it is hard to distinguish between them. 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.