Wild salmon is leaner than farmed salmon, which is fattier. Consequently, farmed salmon has tended to provide significantly higher amounts of the omega-3 fatty acids EPA and DHA per serving than wild salmon. However, farmed salmon must be fed fish oil in order for their meat to provide high levels of omega-3s (wild salmon get omega-3s from algae). With the demand for fish oil now outstripping supply, there is increasing use of vegetable oil in fish feed and levels of EPA and DHA in farmed fish are falling.
Farmed salmon will have higher, but still healthful, amounts of omega-6 fatty acids (mainly from vegetable oil), but less vitamin D than wild salmon.
Both types of salmon are low in mercury and tend to be low in PCBs (toxins which may increase the risk of cancer), although wild salmon may have even lower amounts of PCBs than farmed salmon. Of course, amounts of omega-3s and contaminants can be affected by many variables in both wild and farmed salmon, particularly the food which is fed to farmed salmon.
A standard serving of salmon provides about 2 to 5 times as much omega-3 as a regular fish oil capsule. Although fish oil in supplements is normally less contaminated than fish meat, the contamination levels in salmon are fairly low to begin with and generally not of great concern.
For more information about farmed and wild salmon, a list of other fish rich in EPA and DHA, as well as our test results and comparisons of EPA and DHA in dozens of fish/marine oil supplements, see the Fish Oil and Omega-3 Supplements Review (including Krill, Algae, Calamari, and Green-lipped Mussel Oil) >>
Also see how levels of omega-3s and contaminants vary across canned fish products in our Canned Tuna and Canned Salmon Review