This is interestingly sticky. Would anything be served by making a point of a quiet conversation with the manager regarding your objections to the fish? Kind of a non-accusatory statement that said fish slipped by their rigorous product inspection protocol?
It's no different than sending back a corked wine.
Only good things could come of it:
1. You get a new dish
2. The chef (at any decent place) immediately goes to the walk-in to give the ol' smell test to the rest of the product.
3. If the rest of it smells like Clorox they appreciate the fact that you tipped them off. Unless you ordered the Lutefisk, in which case that's on you.
The waitress certainly doesn't care. All she's going to do is go tell the chef what you said.
I think people think it'll be a bigger to-do than it actually ever is. You're not dining at Kenny Shopsin's, it'll be okay.