Fish is high in omega-3 and Omega 3 has been proven to reduce incidence of heart problems, aid in decreasing cholesterol and may altogether help prevent strokes. It is high in protein, zinc and iron, and it's low on fat.
Besides reducing the risk of cardiovascular disease, fish rich in omega-3 fatty acids may reverse depression, slow the mental decline that can come with age and reduce the risk of rheumatoid arthritis and some cancers according to studies. There is evidence that infants born to mothers who received omega-3 fatty acids during pregnancy have better vision and brain development. Fish with high concentrations of omega-3s are the oily varieties, including salmon, herring, sardines and trout.
But let us hold our horses. Eating fish may not entirely be problem free. Some fish varieties have been found to contain high levels of mercury, polychlorinated bipenyls PCBs), and other toxic agents that can take away some of its health benefits. Fish highly tainted with Mercury is definitely toxic. Mercury is found in the air we breathe, is toxic to the brain, the heart and the nervous system.
Meantime, PCBs are cancer-causing chemicals which have been banned since 1976 but unfortunately can still be found in almost all forms of water systems.
But the risk of mercury and PCB contamination are not enough to prevent healthy adults from eating fish occasionally. So long as the following are observed per U.S. FDA and EPA:
1. Pregnant women, should eat a variety of fish and shellfish that are low in mercury at least twice a week, unless the fish is deep-fried (a serving size is 3 ounces of cooked fish or 4 ounces of uncooked fish). Pregnant women should limit their fish or seafood consumption to 12 ounces a week.
2. The American Heart Association recently added that healthy adults can eat 14 ounces of most fish a week without any danger.
3. Choose omega-3 fatty acids rich types of fish at the same time low in contaminants. The best sources are wild salmon, mackerel, mussels, oysters, anchovies, rainbow trout, herring and sardines.
4. Eat a wide variety of fish, especially if you eat more than two servings per week. Avoid large predatory fish that are packed with mercury in their bodies like swordfish, king mackerel and the like. Avoid farmed fish because they eat PCB laden fish feeds.
5. Per the Environmental Nutrition newsletter the following fish varieties have very high levels of mercury. Avoid altogether: king mackerel, sharks, swordfish, tile fish, and (high level 0-1 serving allowable per week) bluefish, lobster, marlin, red snapper, saltwater bass, freshwater trout, tuna (fresh), tuna, canned, white albacore; (medium levels of mercury 1 to 2 servings allowable per week) grouper, halibut, sablefish, sea trout.
6. Yes, prepare these (low levels of mercury 2 to 3 servings per week) cod, crab, blue haddock, herring, mahi mahi, ocean perch, tuna, canned light, whitefish and the best healthy fish grouping; (very low levels of mercury 3 to 4 servings per week) catfish, clams, crab, king flounder, oysters, salmon, farmed, salmon, canned or wild Alaskan, sardines, scallops, shrimps, sole, and the lowly tilapia.
7. Remove fish fat. PCBs accumulate in the fatty tissue of fish. Reduce exposure. Remove the belly and back fat before or after cooking. It's also a best to remove the skin before cooking because that's where a large portion of the toxins are.
8. Broiling, baking or grilling salmon or any other fish will cook off some of the PCBs in the fat.
9. Avoid taking large amounts of fish-based food supplements as they can usually interfere with blood clotting.
"The U.S. EPA allows 0.1 of mercury per kilogram body weight per day, a standard that is supported by the National Academy of Sciences, but applies only to recreationally caught fish. The FDA allows 0.4 micrograms of mercury per kilogram. The new UN - WHO recommendation would allow 0.2".
"Mercury from coal-burning power plants pollutes oceans and contaminates seafood. The FDA continues to fail to protect consumers by not adequately informing the public to avoid certain contaminated fish species, including canned tuna, which are especially risky for children and pregnant women".
Helpful sites for better appreciation of the topic: