Some fish, particularly fatty, cold water fish such as salmon, mackerel and herring are high in omega-3 fatty acids, a type of fat that helps make your blood less likely to form clots that may cause heart attacks. Anchovies, sardines and lake trout are other good sources of omega-3 fatty acids. Especially for those at risk of heart disease, the benefit of eating fish that's rich in omega-3 fatty acids outweighs potential risks.
Due to industrial pollution there are some risks for a build-up of contaminants in your body. The primary contaminant is mercury. Excess mercury accumulates in waterways and shows up in fish as the highly toxic methyl mercury. If you eat fish that contains methyl mercury, the toxin can accumulate and remain in your body for up to a year.
For most people, the amount of mercury ingested from fish is not a health concern. However, even small amounts of mercury may be harmful to developing fat uses, babies and young children.
Women who are pregnant or trying to conceive, nursing mothers and children age five and younger should avoid fish with the highest mercury levels: tile fish, swordfish, king mackerel and shark. They should limit fish intake to no more than twelve ounces a week of fish and shellfish that contains low levels of mercury. These choices include shrimp, salmon, pollock, canned light tuna and catfish. Albacore or "white” tuna is higher in mercury than canned light tuna, so limit albacore tuna to no more than six ounces a week.
Eating a variety of fish is recommended to reduce the potentially negative effects of environmental pollutants. When possible, select fish that are not farm raised. Farm-raised fish tend to have more fat and calories and slightly less protein. They also may have higher levels of contaminants due to toxins in their feed.
MEDICA.de; Source: Mayo Clinic