What makes overcooked fish smell?
Trimethylamine N-oxide (TMAO) is actually odorless, freshly caught fish doesn't smell fishy at all, however it breaks down to trimethylamine (TMA) which is responsible for that infamous rotting smell. 

As the the tissues containing TMAO is exposed to air, the usual suspects, the bacteria start breaking down the TMAO into TMA; thus causing the fishy smell...

I'm not aware of a mechanism of TMAO breaking down to TMA with heat, however TMA is a gas at room temperature and above. If the particular fish you're cooking is not so fresh, or loaded with  TMAO (thus TMA eventually)... With heat, the TMA trapped in the tissues of the fish might dissipate and result in "The house-permeating 'fishy'" smell.