The best I have found is the following:
"The house-permeating “fishy” aroma of cooked fish appears to involve a group of volatile molecules formed by fatty-acid fragments reacting with TMAO (trimethylamine oxide). "
However the answer is not clear to me, maybe because I forgot chemistry. TMAO exist in fish regardless of overcooking as do fatty acids.
Is it simply that heat/prolonged heat causes the fatty acids and TMAO to react creating the new compounds, thus decreasing heat/cooking time will causes less formation of these molecules?
The excerpt talks as though this smell is unavoidable, is this the case?