About those contaminants; It is believed by many that the fatty portions of fish store most of the contaminants found in fish. Until relatively recently (within the last year or so), I believed the same thing. Careful research, and becoming friends with a biologist, who just happens to love fly fishing, has taught me more accurate accurate information. Some toxins, such as PCB's (a substance used in large electric transformers by the power companies) are indeed stored in the fatty tissues, including the dark areas such as directly under the dorsal fin and along the belly in tuna and salmonids. Mercury and other heavy metals, such as arsenic, lead, etc., are stored in the muscle tissue. And so, the toxic substances found in the water you will be fishing in will help determine prep techniques, and which fish are safe to eat, and what quantity is safe. As a general rule, the higher you go in the food chain, the greater is the accumulation of toxins. Muskies are the top predator in the Great Lakes and contain the highest amount of toxins; while less predatory fish such as whitefish, perch, and smelt are virtually free of toxins. I can eat as many perch as I desire, withing reason of course, and know that I am safe. But if I eat members of the pike family, or even many of the trout or salmon family, depending in what waters I catch them in, I need to watch my consumption. If I eat only deep water Lake Superior fish, I am eating very safe fish. But If I eat from many of the inland lakes, since they are generally more contaminated, the fish contain more toxins.
And remember, not all toxins are introduced by people. There are microbial nasties that will get you plenty sick if you don't cook yoru fish properly. Also, minerals such as mercury and lead occur naturally in many places and are absormed as methyl mercury and lead by plants, which are eaten by fish, which are eaten by larger fish, and thus, contamination is present in what appears to be a pristine body of water.
Check with your local fish and game experts. Adn do some careful study about fish contamination. There is more info on the WWW than you would believe. And if you are of a scientific background, then there are professional documents that you may be interested in reading as well.
Seeeeeeeya; Goodweed of the North