Meta-analysis of oily fish and fish oil supplements showed no benefits whatsoever. For those who aren’t aware of what a meta-analysis is, it’s when researchers take lots of studies and trials and take an overall view of all of them, rather than just reporting on a single study. A meta-analysis is therefore far more worthy of your attention than any individual study.
Basically, the fish oil/oily fish thing has all been a big con to get you to buy something that you never needed in the first place. The oceans and seas are being depleted rapidly of life and we do not need to be killing more of it to make supplements that serve no value to health whatsoever. So stop buying this stuff!