I agree with Jack about risk versus thinking that it is certain. In addition there are some other factors.
First, "tapeworms" is the wrong name - at least for pratical concerns. The primary risk with parasites in fish are Anisakid nematodes. These occur in wild fish caught near shore - rock fish, sea bass, salmon.
These are quite different than the tapeworms that infest humans. Those are a totally different creature (different genus), and you can't get them from fish - you get them from contamination with human feces. There are very very rare tapeworms that can come from fish - I will dicuss that in the next post.
The Anisakids normally parasitize seals that eat fish. They are unable to parasitive humans, - when a human ingests Anisakid nematodes you get a bad stomache ache.
Blue water fish, such as tuna, do not get anisakids.
Farmed salmon, or other farmed fish do NOT carry anisakids. In order to get infested with anisakids the fish have to eat anisakid contaminated seal feces.
Anisakids are pretty common. For my cookbook project we wanted to photograph some so we went to the local branch of a large organic supermarket chain and took a careful look at the halibut fillets on sale. We spotted one with anisakids and bought it. Got some great photos.
Despite the fact that they are common, there are very few cases of anisakid related illness per year in the US - about 10 per year. Japan has many more, but still only about 2000 cases a year. Mostly this is from home prepared sushi. But even 2000 cases a year is quite rare considering that the population is 127 million people, many of whom eat raw fish on a daily basis.Here
is a popular article. Here is the FDA report
on Anisakids, and another FDA report on smoked fish
Anisakids are killed two ways - by heat, and by freezing.
There are very few good studies on heat - one study says 60C/140F for 1 minute, but does not give other time and temperature combinations. I do not trust information given with just one data point like that - I am looking for better data.
The other approach is freezing. A standard freezer is good enough - you do NOT need a blast freezer.
The US FDA recommends -4F / - 20C for 4 days. Or -31F/-35C for 15 hours.
EU regulation is -4F / - 20C for 24 hours.
Any household freezer can reach -4F/-20C.
I eat salmon mi-cuit even without freezing it. The risk is very low, but it is possible. However, if I was concerned I would simply freeze the fish overnight.
Edited by nathanm, 23 August 2008 - 10:47 AM.