Fish oil
Fish oil is oil derived from the tissues of oily fish.
Fish oil is recommended for a healthy diet because it contains the omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), precursors to eicosanoids that reduce inflammation throughout the body
However, fish do not actually produce omega-3 fatty acids, but instead accumulate them from either consuming microalgae that produce these fatty acids,  as is the case with prey fish like herring and sardines, or, as is the case with fatty predatory fish, by eating prey fish that have accumulated omega-3 fatty acids from microalgae. Such fatty predatory fish like mackerel, lake trout, albacore tuna and salmon may be high in omega-3 fatty acids, but due to their position at the top of the food chain, these species can accumulate toxic substances (See biomagnification). For this reason, the FDA recommends limiting consumption of certain (predatory) fish species (e.g. albacore tuna) due to high levels of toxic contaminants such as mercury, dioxin, PCBs and chlordane.
Due to this limitation, many people have turned to fish oil supplements to get adequate omega-3 fatty acids.
Fish oil supplements have sometimes come under scrutiny in recent years. In early 2006, government agencies such as the Food Standards Agency in the UK and the Food Safety Authority of Ireland reported PCB levels that exceeded the strict new European maximum limits in several fish oil brands,
which required temporary withdrawal of these brands. To address the growing concern over contaminated fish oil supplements, the International Fish Oil Standards program, a voluntary review process, was created at University of Guelph.
Patented production purification processes do however exist in order to remove pollutants and dioxins from fish oil to levels far below the EU limits. This is called stripping technology.
Most of the fish oils used for Omega purposes are originating from Peru, Chile and Morocco because the Omega 3 levels in the fish caught in these areas are higher (around 30%) than in Scandinavian and other fish oils (around 20%). Fish oils are being used in the Omega 3 industry to produce nutraceuticals and pharmaceuticals. However the largest off-takers of the Omega 3 fish oils are still the feeding buyers with the big fish feed companies such as Ewos, Skretting and Biomar in the lead.

# Benefits of fish oil
Some experts believe that taking fish oil (in any form) can help regulate cholesterol in the body,Template:Who because fish oil has high levels of omega-3 fatty acids. The regulation occurs through effects of the EPA and DHA constituents on Peroxisome proliferator-activated receptor alpha (PPAR). Besides cholesterol regulation, benefits include anti-inflammatory properties and positive effects on body composition. However, the preferred source of Omega 3 should be from the fish's body, not the liver. The liver and liver products (such as cod liver oil) of fish and many animals (such as seals and whales) contain Omega-3, but also the active form of vitamin A. At high levels, this form of the vitamin can be dangerous. Early explorers to the land of the Inuit were given raw liver by the natives, which contained a toxic overdose of vitamin A for the white explorers; however, the same amount was harmless to the Inuit, who had no other source of Vitamin A except animal livers.
Studies
were conducted on prisoners in England where the inmates were fed seafood which contains Omega-3 Fatty acids.  The higher consumption of these fatty acids led to a drop in the assault rates. Another Finnish study found that prisoners who were convicted of violence had lower levels of omega3 fatty acids than prisoners convicted of nonviolent offenses. It was suggested that these kinds of fatty acids are responsible for the neuronal growth of the frontal cortex of the brain which, it is further alleged, is the seat of personal behavior.
The American Heart Association recommends the consumption of 1g of fish oil daily, preferably by eating fish, for patients with coronary heart disease.
The US National Institutes of Health lists three conditions for which fish oil and other omega-3 sources are most highly recommended: hypertriglyceridemia, secondary cardiovascular disease prevention and high blood pressure.   It then lists 27 other conditions for which there less evidence.  It also lists possible safety concerns: "Intake of 3 grams per day or greater of omega-3 fatty acids may increase the risk of bleeding, although there is little evidence of significant bleeding risk at lower doses. Very large intakes of fish oil/omega-3 fatty acids ("Eskimo" amounts) may increase the risk of hemorrhagic (bleeding) stroke."
According to a study from Louisiana State University in September 2005, fish oil may help protect the brain from cognitive problems associated with Alzheimer's disease.
Fish oil has also been shown to aid in the treatment of people suffering with depression.
For purchasing fish oil dietary supplements, it is highly recommended to seek a label certifying the product to be "molecularly distilled", USP Certified, and therefore free of mercury and other metal toxins.