In reply to MikeR:
You'll be pleased to hear the mackerel out of tescos also have plenty of parasites too (not the only fish to suffer this, and lets not go into shell fish - yes I know shell fish are not "real fish")
If you're squeamish, dont look it up on the internet. the majority we need to worry about live in the body cavities of fish, and tend to migrate to the flesh after death.... So a good reason to gut your fish asap.
If you just looked it up on the internet - deep fried and over cooked also helps kill off those in the flesh.
As for the poster who says transmission is low - most parasites the transmission probability is so low, its a miracle they still exist. Yet they do, in vast numbers....
Enjoy! I liked parasitology, but you've gotta have a strong stomach!