There are many claims of the benefits of fish oils....and more and more science are recognizing them. There are some possible health down sides, but normally involve using high doses.

But, all commercial fish oils are not alike,   and they come from different species and locations and involve different grades, levels of oils, and different purifying, refining and processes.

I suspect oils from smaller northern marine pelagic species (mackerel and herring) may be the better ones....as they contain more of beneficial Omega 3 and have less toxic material (mercury, for example that is found in hih levels in larger, longer lived fish, like the big tunas).

Livers filter out and concentrate oil soluable toxins....so if the fish came from a contaminated source (including the fish's diet) I would be cautious, unless there was a valid purifying process involved).

Unfortunately, much of the information on which one is best on the web comes from a marketing source. Science,medical nutitional and university sources may supply the best information.