I found the following post on a food-related forum (here):
Farmed fish do have omega 3 in them. They have a chunk of omega 6 too so while they do have omega 3, they're not ideal for normalizing the ratio. However there is a case in which sardine flesh is being sold after the omega 3 has been extracted to make sardine oil. A good rule of thumb is that the saturated fat should be about a quarter or less of of the total fat if the tin doesn't specifically say that it has omega 3. If saturated fat is a higher percentage of the sardine, the omega 3 has been removed. Also be wary of fish canned in oil. Bad news!
Why should we be wary of fish canned in oil?