For fish sauce definitely, assuming you also use the guts so you can get the enzymes. If you want to make with a protein source that doesn't have the enzymes present, like mushrooms, you can add them separately. Whole fish just fills the protein and protease slots with a single ingredient.

I've been wanting to make my own fish sauce for years at this point. I even found a huge crock to do it in. I've just never gotten it together to go to the fish market super early and source fish. What species do you use?

I've made a few batches of salmon garum that turned out nicely. Just make sure you use raw and not cooked, as the cooked fats will taste rancid. It tastes different than asian fish sauce or colatura but still of use in similar contexts.