The term "fish oil" is used to refer only to oils extracted from the muscle tissue of cold-water fish like salmon and sardines. Of course cod liver oil comes from fish too, and is there since technically also a fish oil yet it is not referred to as fish oil, but specifically as "cod liver oil". In this article we look into the essential fatty acid content of liver oils from a few species of fish.
The essential fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are needed for human health, but we can not synthesize them ourselves and so have to obtain them from our diet. What is the essential fatty acid content of oil from cod liver? According to US Department of Agriculture Nutrient Data Laboratory (USDA NDL) statistics one hundred grams of it contains 6.9 grams of EPA and 11.0 g of DHA. It is available in liquid form or as pills or capsules. However, codfish is an endangered species, and cod fisheries worldwide are experiencing pressure from overfishing.
You do not need to have your essential fatty acids from cod liver oil. Oil extracted from salmon liver, which is also commercially available, has a very favorable fatty acid profile, with 13.2 grams of EPA and 18.2 grams of DHA per 100 grams (USDA NDL). Another species of fish that is being studied for its potential as a source of essential fatty acids is the longnose skate Raja rhina , a seabottom-dwelling fish of which currently only the large flat pectoral fins or "wings" are used for human consumption. It is considered a bycatch, or unintentional byproduct of the Alaska and West coast fishing industry. A publication from the US Department of Agriculture shows that longnose skate liver oil contains 16 g EPA and 17.7 g DHA per 100 grams, a value comparable to that of salmon liver. For comparison, one hundred grams of chicken livers contain negligible amounts of these fatty acids.
A safe daily dose of any of these oils is closer to one to two teaspoons a day. One hundred grams of oil comes to about 7 tablespoons. That much fish liver oil would contain toxic amounts of vitamin A. Two teaspoons of cod, salmon or longnose skate liver oil would provide about one tenth of the amounts shown above for 100 grams, plus abundant amount of vitamins A and D. If you're ' d rather get just the essential omega-3 fatty acids without the vitamin A or D present in fish liver oils, you might prefer supplementation with fish oil instead. All liver oil contains cholesterol, which is only present in very small amounts (1 mg per gram or less) in fish oil.