Fish isn't supposed to be exposed to an acid for more than a few
minutes or the flesh will 'cook.'

I suppose that if you are spreading a liquid mixture on the fish
before cooking, it might be called a marinade.

The following is good on steelhead, salmon or a large fish.

1 clove garlic, minced
1 1/2 tablespoons fresh rosemary, chopped fine
1 lemon, zest of
1/2 lemon, juice of
1/4 teaspoon salt
1/2 teaspoon fresh ground pepper
1 tablespoon olive oil, plus additional oil for greasing pan.

Mix all into a paste and spread seasoning over the flesh of the fish.
Place fish skin side down on an oiled pan or perforated grill pan.

I have baked fish using this and I have put fish on the grill using
this. The fish flavor comes through but the