Traces of Mercury

• Most fish and shellfish, even freshwater species, contain traces of mercury, according to the U.S. Environmental Protection Agency. A recent study released by the U.S. Geological Survey stated that many lakes, rivers and streams in America are contaminated with mercury.
  
  

Harms

• Mercury is a heavy metal, and in large amounts it can harm the brain and body tissues, according to ABCNews.com. It can be especially harmful to pregnant women or young children.
  
  

Safe Fish

• It is generally safer to eat freshwater fish sold at the grocery store, which is usually grown in uncontaminated hatcheries. Saltwater fish is generally more dangerous because of mercury concentrations in seawater.
  
  

Safe Quantities

• The EPA recommends eating up to 12 oz. (or about two 6 oz. meals) of safe fish a week. Fish should not be altogether eliminated from your diet because it is high in protein and other nutrients and generally low in fat.
  
  

Unsafe Fish

• Recreationally caught freshwater and saltwater fish are more dangerous to eat regularly or in large quantities. Some fish that could pose a danger include large-mouth bass, pickerel, walleye, some catfish, shark, mackerel and tilefish.