In recent memory people have been concerned about human introduced contaminates like mercury, PCB’s and pesticides in their seafood.

We just don’t think too often about the natural things in seafood that can make us ill — parasites and bacteria.

For example, if you prepare sushi yourself you should check your raw fresh unfrozen fish fillets.

Commercially processed fish fillets used in sushi are held over a light table to visually screen them for parasites. This method will only detect something a half inch deep or less. Some commercial seafood houses are starting to use ultra-sound technology.

There are two main kinds of parasites to watch out for in raw fish: liver flukes and nematodes. Flukes aren’t a big problem to find because they’re about the size of your thumbnail or larger.

Nematodes (worms) are more difficult to detect, since they can vary from three-quarters of an inch long and two diameters of a human hair in width or a bit larger.

Nematodes are translucent white in color and run perpendicular to the fish’s muscles, which is how they bore in. Also, check between the skin and flesh. The more experience you have examining fish the more you learn to tell what’s normal and what’s not. “When in doubt, throw it out.”

Reports indicate that there are only two dozen cases a year from fish parasite infestation in the U.S., usually due to people who prepare raw fish at home but don’t know what to look for.

“Between 1973 and 1987, shellfish accounted for 2.8 percent of the cases of food-borne illness reported to the Centers for Disease Control, and finfish accounted for 2.2 percent of the cases.

“These statistics may seem high at first glance, but they’re somewhat misleading. For example, 37 percent of the cases of seafood-borne illness in the U.S. between 1977 and 1981 were attributed to ciguatera, a toxin found only in tropical and subtropical fish.

An additional 37 percent of the cases during the same time period were attributed to scombroid poisoning, a toxin produced in the flesh of some species of fish when improperly stored at high temperatures.”

An example of a nematode parasite is “Anisakis simplex, called herring worm. Its primary hosts are dolphins, porpoises and sperm whales. In the larval stage, the stage that infects fish, the parasite is usually 18-36 mm long, 0.24-0.69 mm in width and whitish in color. Anisakis larvae are more prevalent in the Pacific than the Atlantic since the Pacific has a large population of whales, one of the final hosts of Anisakis.

“Humans are accidental hosts of Anisakis larvae. Anisakiasis, the illness, is associated with the presence of a marine mammal population and eating raw or undercooked fish (sushi, sashimi, lomi lomi, ceviche, sunomono, Dutch green herring, marinated and cold smoked fish).”

The prevalence of Anisakis infection increases with size and age of fish. Species that feed primarily on bottom organisms have a lower incidence of Anisakis contamination — while fish that predominantly feed on other fish generally have a high incidence of contamination.

The types of fish commonly infected with Anisakis larvae include: herring, Atlantic and Pacific cod, Pacific salmon, mackerel, Pollock, whiting, bonito, squid and Pacific rockfish.

The majority of Anisakis infections are acquired from dishes prepared at home with restaurants incriminated only rarely.

The first case of anisakiasis in the U.S. was reported in 1958. Since then there have been 30 to 50 documented cases in this country.

A recent study of sushi in restaurants in Oregon found that an appreciable amount of salmon sushi contains parasitic worms. Salmon was by far the worst; tuna was the safest with no worms found at all.

Think Global - Act Local.

Dr. “Skip” Lazauski can be seen on the television show “Eco-Bites”, which airs on Mediacom's channel 14 and Smartel's channel 4. To reach Dr. Lazauski for questions and comments, send e-mail to IchiOrca@yahoo.com. For more information, see his Web site, drskiponline.com