The bacteria is dead, but their toxins can still be active. Bacteria-produced histamine, for instance, is not destroyed by heat, yet a number of deaths have been attributed to this bacterial toxin. That is why one must wash one's hand before handling fish. Shellfish from polluted waters may even infect people with hepatitis, salmonella or cholera. The key problem is that we simply cannot know for sure if certain fish are free of such contaminants due to the virtual fecklessness of government inspection.
All fish contain cholesterol and saturated fat.
Salmon has a very high fat content, while dole or haddock is much better and preferable in this respect. However, all fish lack fiber, have no complex carbohydrates, and may add too much protein to one's diet. For those trying to lose weight, certain fish are not an ideal food in that respect. The omega-3 oils are found in a more stable form in vegetables, fruits and beans, while these oils in fish are very unstable making for free radicals. The concern here is that with advancing age, levels of Ca in our bones decreases while the deposition of Ca in soft tissue increases.