""Fish and fish oils are from organisms at the end of the food chain in the sea, and thus have high levels of the heavy metals.""

This may be true of some fish species, but not true with others. Some fishes, such as the pelagic variety are rich in oils. But, size and age (and of course where they roam and the species they eat) are big factors in what their oils are composed of and are contaminated with. If the oils comes from the liver (a heavy metal filter) than there are other issues to consider.