Natural fish contains docosahexaenoic acid (DHA), which was shown to lower blood pressure by vasodilation at ion channels
on smooth muscle cells of blood vessels. But most fish oil pills contain DHA ethyl ester which doesn't activate those channels. In fact it competes for binding sites with the DHA from fish, preventing the healthy effect.
The article didn't say why most fish oil supplements have the ethel ester of DHA, or how putting fish oil inside of a gelatine capsule could cause this chemical change.
A couple of months ago, I bought a large bottle of fish-oil, but decided shortly after to eat fish instead, even though the expense hurts my budget. Now I've got a large amount of fish-oil that may never get used.
From what I've read, I'm convinced that natural food of all types are much better than taking vitamins, minerals, and processed food.