Oily fish

# Overview
Oily fish, oil-rich fish or pelagic fish are those fish which have oils throughout the fillet and in the belly cavity around the gut, rather than only in the liver like white fish. Oily fish fillets may contain up to 30 percent oil, although this figure varies both within and between species. Oily fish generally swim in the pelagic zones of the oceans.
Oily fish are a good source of Vitamins A and D as well as being rich in omega 3 fatty acids. For this reason the consumption of oily fish has been identified as more beneficial to humans than white fish. Amongst other benefits, studies suggest that the omega 3 fatty acids in oily fish may help sufferers of depression, reduce the likelihood of heart disease and improve inflammatory conditions such as arthritis.

# Research

## Dementia
French research published in 2002 in the British Medical Journal followed 1,674 elderly residents of southern France for seven years, studying their consumption meat versus seafood and the presence of dementia symptoms. The conclusion was that people who ate fish at least once a week had a significantly lower risk of being diagnosed with dementia over a seven-year period, though the study was uncertain if fish consumption protected against dementia, or if dementia prevented the participants from consuming more fish.  Individuals with higher education also had a lower risk of dementia and higher consumption of fish, and the relationship between the three factors is uncertain.

## Cardiovascular health
Consuming oily fish twice per week may also help prevent sudden death due to myocardial infarction by preventing cardiac arrhythmia.  The eicosapentaenoic acid found in fish oils appears to dramatically reduce inflammation through conversion within the body to resolvins, with beneficial effects for the cardiovascular system and arthritis.

# Recommended consumption
In 1994, the UK Committee on Medical Aspects of Food and Nutrition Policy (COMA) recommended that people should eat at least two portions of fish per week, one of which should be oily fish.
In 2004 the UK Food Standards Agency published advice on the recommended minimum and maximum quantities of oily fish to be eaten per week, to balance the beneficial qualities of the Omega 3 fatty acids against the potential dangers of ingesting methylmercury (MeHg).
The EPAs Exposure Reference Dose (RfI) for MeHg is 0.1 micrograms per kg body weight per day. The corresponding limit of blood mercury is 5.8 micrograms per liter.
The recommendations on maximum consumption of oily fish were up to four portions (1 portion = 140g, or approx 4.9 ounces) a week for men, boys, and women past childbearing age, and up to two portions a week for women of childbearing age, including pregnant and breastfeeding women, and girls. There is no recommended limit on the consumption of white fish.
The United States Environmental Protection Agency (EPA)and the USDA current guidelines (as of 2007) sets a limit only on consumption of fatty fish with greater than one part per million of methylmercury. Specifically tilefish, king mackrel, shark and swordfish (and some fish caught in local waters). There are limits, however, for nursing/pregnant women and children under the age of 6. This population should completely avoid high MeHg fish (those listed above) and limit consumption of moderate and low MeHg fish to less than or equal to 12oz per week. Albacore tuna should be limited to 6 oz or less per week. (info available at: www.epa.gov/waterscience/fish/states.htm)

# Oils from fish or plants as a source of omega-3 fatty acids
Concerns about contamination, diet or supply have led to investigation of plant sources of omega-3 fatty acids, notably flax and hempseed oil.  Lactating women who supplemented their diet with flaxseed oil showed increases in blood and breastmilk concentration of alpha-linolenic acid and eicosapentaenoic acid but no changes to concentrations of docosahexaenoic acid.