I do appreciate the distinction sorry yes; the fish primarily died for food and it's just a billy bonus that you get to play with the corpse.
The point I'm (badly) making is that fingering the corpse of an animal will not tell you
anything about how they lived their lives. Fish have their migration routes, their spawning habits, their place in the biosphere, their species and sub-species traits, the communities they belong to, their communicative methods within those shoals, electrolocation of food...all this can be learned from
studying live animals in their natural environment. A corpse is merely a simulacrum of life, not an insight into it.
What you've described sounds like killing a miracle all the better to look under the bonnet to see what kind of miracle you've killed. It's a special kind of human arrogance imo, that animals are used that way as though they were placed here for our morbid fascinations.
We've known for donkey's years "how a fish works" - but it's only as they oceans are emptying of fish that we're realising just how complex their existence really is. We now appreciate this just as the creatures slide, perhaps forever, out of view.
I'm not aware of any social taboos about animal dissection that have held back our knowledge of their physiology; we've had fishmongers for hundreds of years who could name every bone in a fish, what's more to find out?
Animal cruelty and animal testing is a modern social taboo, but in what way has that late 20th C movement slowed our knowledge of a species' physiology? It's not their physiology that's being tested nowadays, it's their response to mascara, air fresheners and agri-chemicals.