Blood pressure is best treated holistically. Severe or poorly-managed stress could be the reason for it, and if so, blood pressure is merely a sign of the underlying condition. Always best to look for causes -- and treat as close to them as possible.
The trouble is, like most misfortunes of health, mental health disorders come to us across a spectrum. In some cases, they are merely troubling, and do not rise to the level of renouncing personal autonomy. In some cases, they are so extreme as to be all but unmanageable.
Eating fish confers net benefit. Maybe it's the omega-3, and maybe not. Maybe it's because of adding fish, and maybe it's because of displacing meat. Maybe it's all of these, and it's in spite of the contaminants that come along for the ride.