Eating fish also has widely acknowledged health benefits. A recent report indicates eating fish frequently may cut chances of developing age-related macular degeneration. 
Currently, FDA suggests American to have two meals of fish and shellfish (12 ounces) a week, but limit albacore, or "white," tuna to one meal (6 ounces) per week because of its higher mercury levels. Elevated mercury levels have been linked to learning disabilities and developmental delays in children and to heart, nervous system and kidney damage in adults.
A study indicates some imports of canned tuna from South America have mercury levels higher than the federal limit. They tend to catch larger, more mature fish, which tend to have higher mercury levels: Calmex - 1.4 ppm, and Sardinar - 1.3 ppm. On the other hand, tuna from Asia had the lowest average levels of mercury. 
Fish oils and supplements also have side effects Low dose fish oil extracts are found to be beneficial to healthy, older or sick subjects, but long-term use of high dose fish oil may lead to harmful side effects. The most common side effects of fish oil supplements include fishy odor on the breath, stomach upset, gastrointestinal disturbances, and greasy stools.