I’m not a food scientist, but I think this is what is going on:
Meat, when it was alive, puttered along at relatively high temperatures. The pathogens that thrive on it prefer similar temperatures, the enzymes in it, that can keep working after death, are optimized for that temperature.
Cool it down and decay slows down. Room temperature helps a bit, but meat will also stink if left out.
Fish are not only, in general, not warm when they are alive, but their environment is generally a lot cooler, so pathogens and enzymes will be working overdrive when it’s sitting around at room temperature, which to fish-flesh is hot.
Fish-flesh also seems has a higher water content than meat, allowing more microbial activity, even after cooking.
The muscle and bone tissue of fish and other animals that live their entire lives in water is generally not as dense or powerful as land dwelling animals. That’s because of gravity which needs to be resisted daily on dry land while in an aquatic environment you just float… kind of like how astronauts experience muscle loss and bone density reduction while in orbit.
Fish meat is pretty weak so to speak; it easily over cooks and is quite soft. You can tear it apart with your fingers like a Kleenex. You can grab the corner of a steak on the grill with tongs and pick the whole thing up, but try that with a fish fillet and you’ll usually just pull pieces off. So, that not-so-dense tissue with weak collagen connections simply breaks down easier and faster when bacteria get after it.
Fish are wet (surprise I know) and the surface of their bodies is prone to a VAST array of microorganisms partly held in check by a layer of slime they exude that behaves much like the outer layers of our skin. given a bit of warmth and the cessation of that layer of defense, those microorganisms go hog wild in a hurry. couple that with the increased exposed surface area from trimmings and you have a perfect storm for bacterial growth.
When I worked at OfficeMax, I had a regular customer who apparently had this condition. She happened to run a wholesale seafood business and I assumed that she was coming to the store in her work clothes in the evening. Then one evening she came all dressed up and she still had that odor.
Edit: She never seemed self-conscious about it and I got used to since I knew what to the expect when she came. My co-workers upon helping her for the first time may have mentioned it, but we never talked about after that.
Saltwater fish cells contain a lot of the precursor to the odorant molecule, and humans are remarkably sensitive to the presence of TMA. So the question might be more of ‘why are we so sensitive to the odor of TMA as opposed to the odor of putrescine or cadaverine?’ rather than ‘why do fish stink so fast?’. Is it actually established that the fish is decomposing faster, or just that we are more tolerant of the decomposition of terrestrial meat?
If I were to guess, I would guess that fish unlike other meat consumed by humans spend their life in low oxygen environments. Oxygen (air) causes fast deterioration to an organism’s makeup not adapted to oxygen.
The basic metabolic processes of fish operate on the same chemistry as terrestrial animals, with sugars and oxygen. There’s little reason why the inside of a fish should react differently to the inside of a cow when it comes to oxygen, as oxygen is bad in excess for our insides as well.
Not saying it’s not oxygen, just that your analysis seems oversimplified.