Farmed fish have lower omega 3 essential fatty acids

I have always proposed that farmed fish have lower levels of omega 3 essential fatty acids. I.e. wild fish are better for you than farmed fish. This is because I have the belief that the omega 3's found in fish come from their food. Don't know why I believe that, suspect either logical deduction or I read it someplace that has been lost in the mists of time.

Anyway glancing through a 1990 journal and found:

The ratio of n-3 to n-6 polyunsaturates was significantly lower in cultured than in wild fish

This was across the three fish they measured trout, eel and salmon. So my gut feel has been validated. Therefore we need to be asking our suppliers of fish oils - are they farmed fish? Because if they are the oil you are taking is likely to have less omega 3's than stated on the bottle. Also we need to ask if our salmon and other fish are wild ( and sustainably harvested).   

Reference: T van Vliet and MB Katan Lower ratio of n-3 to n-6 fatty acids in cultured than in wild fish. American Journal of Clinical Nutrition, Vol 51, 1-2