Here is a dialogue I got from another list. I find it quite interesting
especially as I understand wild salmon is an endangered spieces in many
parts of the world:

>>I was under the impression that farmed salmon fish contains less
>>omega 3 fatty acids compared to their wild (not farmed) counterparts.
>>I checked the USDA Nutrient Database and discovered that the reverse
>>is true. For instance, 100 grams of raw wild Atlantic salmon contains
>>1.115 DHA (docosahexaenoic acid), while the farmed version contains
>>1.293.  Also, 100 grams of raw wild Coho salmon contains .656 DHA
>>while the farmed version contains .821. So, are we truly better off
>>eating the farmed version if we're after more DHA?

>It might depend on the time of year the wild salmon is caught. There
>is a substaintial seasonal variation in fatty acid content. The
>typical quoted value in the literature is that farmed fish have about
>1/3 the fatty acid content compared to their wild counterparts.
>Perhaps, the fish farmers have altered the feed to increase the fatty
>acid content?

>> As regards salmon as king (or queen) of omega 3's, the USDA Nutrient
>> Database reports that raw Atlantic mackerel contains more DHA (1.401
>>g) per 100 grams than either farmed or raw wild Atlantic salmon! So,
>>is Atlantic mackerel the true monarch?

>Mackerel is always the highest in tables of values.

>> Lastly, does anyone know why the USDA Nutrient Database does not
>>include EPA (eicosapentaenoic acid) values?

>I've found the USDA database to be spotty on some foods. Tuna, I know
>includes EPA. Oats on the other hand, is very sparse for fatty acids.