Lost At Sea

You know fish is an excellent source of low-fat protein and is rich in omega-3 fatty acids. You're also aware that health advisories warn of toxic chemicals in fish, and environmental groups caution that many of the species we like to eat are facing depletion. As a consumer, how do you make educated decisions about the fish you buy?

Of the toxins in our waters monitored by the Environmental Protection Agency (EPA), mercury is the most widespread. A result of years of industrial pollution from coal-burning power plants, mercury, when stored in the body at elevated levels, can cause nervous-system damage, mental impairment, seizures, and cardiovascular problems.

Long-lived, larger species that feed on other fish are most likely to exceed the levels of mercury considered safe by the EPA. Shark, swordfish, king mackerel, and tilefish are the main culprits. Shellfish are generally low in mercury because they're at the base of the aquatic food chain and haven't had the time to accumulate high levels of the toxin.

Kathryn Mahaffey, PhD, director of the EPA's Division of Exposure Assessment, offers this general rule of thumb: "If a fish is small enough to fit in a pan whole, it's probably safe to eat. A fish that is 39 inches or more can pose a danger." When you see a part of a whole fish at the market, it's hard to tell how big the original fish was. Ask your fishmonger.

How you prepare the fish may also affect whether toxins remain in it. Contaminants, such as PCBs and many pesticides, are stored mostly in the fat of fish. You can reduce toxin levels by broiling, grilling, or baking your catch on a rack so the fat drips off. No matter the cooking method, the only way to reduce exposure to mercury contamination—systemic throughout fish tissue and muscle—is to avoid mercury-contaminated fish.

Increased demand has led some fisheries to use harvesting practices that catch more fish than our waters can sustainably produce—resulting in diminishing fish stocks and damage to the ecosystem. To ensure that your favorite seafood stays plentiful, Jennifer Dianto, program manager of the Monterey Bay Aquarium's Seafood Watch program, recommends asking your seafood supplier where the fish came from and how it was caught.

Although no clear-cut answers exist as to whether purchasing wild fish is more responsible than purchasing farmed, the following facts may be helpful. Farm-raised fish are often fed parts from wild fish, and the practice contributes to the extinction of wild fish. Also, farmed fish raised near natural bodies of water have been known to escape and then introduce disease to wild fish. On the other hand, farm-raised fish often live in enclosed tanks where keepers can monitor water pollution. And irresponsible harvesting of wild fish can contribute to the extinction of other species because they are caught accidentally in nets or traps and then thrown away.

The good news is that a provision in the recent USDA Farm Bill will make it mandatory by 2004 for fisheries to provide product labels that tell where a fish was caught and whether it was wild or farm raised. After all, the best way to make safe, environmentally sound choices about the fish you purchase is to know the risks, heed the warnings, and stay informed.

—Ana Schwartzman