Hi Jo, I asked a question about this in the Professional Support Panel a while back.

Oily fish is the best source of Omega 3. However you can also get it from:-
Nuts espacially wallnuts
Beans Especially soya beans
Flax seed
Leafy green vegetables
Canola oil

So if you include some of these (except the fish ) in your diet anyway, you should be getting enough without having to take artificial derivatives in supplements. HTH