Fish is a great source of many necessary nutrients, vitamins and essential fatty acids, and should be included in every balanced diet. Nevertheless, mercury level in fish has become an important issue when discussing children nutrition or food during pregnancyIts important to know which fish have the highest mercury content and which are safest to eat. As a general rule, smaller fish that are lower down in the food chain tend to have lower mercury levels. Whereas fish that feed on other smaller fish are usually top of the list in mercury content. Use this as a general indication and look below at our quick guide that includes the most common fish types.