From Site:
Unless that fish has been frozen first, it would be wise to pass.
That’s because a tiny tapeworm larva may lurk in the raw salmon flesh, just waiting for you to eat it so that it can take up residence in your digestive tract. Diphyllobothrium latum, carried by freshwater fish (including anadromous wild salmon, which spend their early lives in fresh water), is the largest human tapeworm. After the larva is ingested by a fish-eating mammal, it hooks onto the small intestine, where it grows to maturity, freeloading on its host for nutrients (it has a special affinity for Vitamin B12). Cooking fish or freezing it at minus-31 degrees Fahrenheit or colder for 15 hours will kill Diphyllobothrium larvae. Marinating will not. Freezing fish at slightly higher temperatures for longer periods will also kill the larvae but will likely diminish the quality of the fish.
While diphyllobothriasis is not life threatening, the tapeworm can grow up to 30 feet long and live for decades, sometimes causing anemia from B12 depletion. Most diphyllobothriasis cases are initially asymptomatic, so they often go undetected; people can live with a tapeworm for years without knowing they have one. Some make the unhappy discovery after passing a segment in their stool. Others learn of their cohort after seeking treatment for symptoms such as diarrhea, abdominal cramping, fatigue, and nausea.
[via: http://www.gourmet.com]
