Salmon is an oily fish and provides some of the daily recommended intake of omega-3 fatty acids. Eicosapentanoic acid, or EPA, and docosohexanoic acid, or DHA, are two of the most nutritionally-important fatty acids in the omega-3 group. Although many fish species contain dietary EPA and DHA, salmon is one of the richest sources, along with other common oily fish like mackerel, tuna and trout. On average, a serving of 100 grams (3.5 ounces) of any of these fish provides about a gram of omega-3 fatty acids altogether.
The term "salmon" encompasses a variety of salmon species. Atlantic salmon, according to Health.gov, contains the highest levels of EPA and DHA per 100 grams (3.5 ounces) at about 1.8 grams to 2.1 grams collectively, compared to other species like sockeye, chum, coho, pink or Chinook. Chum salmon has the least, at about 0.5 grams DHA and 0.3 grams EPA, followed by coho salmon with about 0.8 grams DHA and 0.4 grams EPA. Sockeye salmon has about 0.7 grams DHA and 0.5 grams EPA, and Chinook salmon is second-best at 0.7 grams DHA and 1.0 grams EPA.
Farmed or Wild
According to Health.gov, the difference between individual salmon species in terms of EPA and DHA content is greater than the difference between farmed and wild versions of the same species. According to their samples, a cooked serving of farmed Atlantic salmon of 100 grams (3.5 ounces) in weight, for example, contains about 1.5 grams of DHA and about 0.7 grams of EPA. In comparison, wild Atlantic salmon contains roughly the same amount of DHA and about 0.4 grams of EPA.
Fatty Acid Formation
The human body can form EPA and DHA from another type of omega-3 called alpha-linolenic acid, or ALA. The Linus Pauling Institute at Oregon State University says EPA and DHA are not considered essential fatty acids, as they can be made from ALA, whereas ALA is considered an essential fatty acid, as it cannot be synthesized, so has to be ingested.
The omega-3 fatty acids are polyunsaturated fatty acids. This means that their molecules contain two or more double bonds between carbon atoms. The reason they are called omega-3 is because, when you count three carbons down from the end of the molecule with the methyl group, the first double bond you come to is holding carbon 3 and carbon 4 together. The human body is unable to synthesize molecules with the double bond at this location, so this is why humans have to ingest omega-3 fatty acids in order to obtain their benefits.