Some brands are certified mercury free, tested throughly and are molecully distilled. So not only are the oils taken from fish in lower mercury areas (and lower mercury fish) but the oils are put through this process to clear any possible remaining mercury and then tested to make sure.

A little bit different than eating the entire fish (flesh and all). I am sure there are some oils better than others. There are brands that are well trusted in this area and the ones I know of are "blue ice" and "nordic naturals".

I have taken nordic natural ultimate omega and had NO reactions at all. Normally I can get reactions easily. I cannot even have algae products without symptoms.