Well, parasites are a factor of risk not only at freshwater fish, but at saltwater fish too. The most known sea fish parasite is probably Anisakis (anisakidosis). It is not by accident that the highest number or registered cases is in Japan (though as far as I know it is not too alarming). However, you can find it elsewhere too (
this document speaks abut clinical cases in France).
Most parasites live in the intestine, and start to move deeper into the tissue only certain time after the fish is killed. So if you spear a fish, dispatch it quickly, and eat fresh, there is relatively little chance you get a parasite. Another safe method is freezing it ASAP to -20°C.
Otherwise raw freshwater fish is being traditionally consumed in different countries (for example know as Eviche in Central America).
Here some tips for sushi consummation from
How to Determine if Sushi Fish Is Fresh - eHow.com
Quote:
- All fish, including seawater fish, may contain parasites. Although the risk is small, people at greater risk, including older people, small children and pregnant women, should be careful when eating raw fish. To kill the parasites, the fish needs to be frozen and then stored at -4 degrees F (-20 degrees C) for at least 24 hours. Your sushi fish should have been frozen this way, but if you are nervous, ask your sushi bar.
- Freshwater fish is riskier than saltwater fish, and salmon is thought to be particularly risky: It can be infected with tapeworms in addition to freshwater trematode parasites. Raw salmon is sometimes brined and vinegared when served raw, but this does not adequately kill any parasites.
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Some interesting links to the topic:
Why would someone eat raw fish? [Archive] - Sherdog Mixed Martial Arts Forums
Health and Consumer Protection - Scientific Committee on Veterinary Measures relating to Public Health - Outcome of discussions 05
High Prevalence of Seropositivity to a Major Allergen of Anisakis simplex, Ani s 1, in Dyspeptic Patients -- Toro et al. 11 (1): 115 -- Clinical and Vaccine Immunology
Health and Consumer Protection - Scientific Committee on Veterinary Measures relating to Public Health - Outcome of discussions 05
Fish Parasites
Seafood Safety
My friend, aquacultrure bilogist who I consulted it with, told me he would not be much more afraid consuming raw freshwater fish than sea fish. On the other hand is uses to consume such volumes of alcohol that would kill a horse, so couple of worms pose nor risk for him indeed. Finally, with this method, he survived several years in Central American and Amazonian jungles, and many missions to remote regions in Asia too.
