Here in the Great Lakes Region, you can get superior fish from a Lake Superior (ha ha, pun intended, and yes, I'm a Dad so I have licence to tell corny puns, in fact, it's my job!) But seriously, If wild trout make up the meal, and that fish is caught from any of the streams feeding the big lake, the flesh is light orange in color, and the flavor is robust and amazing. Salt helps temper the flavor. Stocked trout and salmon have a lighter flavor, and so require less seasoning, just a hint. Mebers of the perch and pike families are very mild, and almost sweet in flavor. Just the salt contained in butter is sufficient to flavor them.
IN my opinion, the stronger the fish flavor, the more salt is required to ballance it.
Another way to ballance fish flavor is by cooking it with other ingredients. Fresh speckled or rainbow trout (no larger that 12 inches please for best flavor), cooked in a foil packet along with butter, sliced potatoes, and sliced carrots is an extaordinary meal. Little or no salt is needed for that.
So, it just depends on what you are cooking, the kind of fish you are preparing, and how you prepare it.
Seeeeeeya; Goodweed of the North