I found an article (Polish) that may shed some light onto the origins of this mysterious dish. The first two paragraphs in translation:
"If you were to show the Greeks fried hake or pollock filets, covered with grated carrots, braised until soft with onions and tomato concentrate, asking if they could recognize it as a Greek dish, they'd probably nod their heads in an affirmative manner. At such time it's good to know that this gesture has the opposite meaning in Greece as compared to us.
"Most likely, the original recipe was psari plaki - fish baked in a tray, covered in tomato sauce with vegetables. The vegetables are prepared separately. Onions and garlic are sauteed with olive oil, sometimes with the addition of carrots and celery, perhaps some olives, a spoonful of honey and always - a lot of tomatoes. This is braised briefly with the addition of white wine. The sauce is delicate, fragrant with the wine, herbs and full of vegetable chunks. The fish is gutted, rolled in olive oil, salt, pepper and lemon juice and prepared for baking by covering it with the vegetable sauce. It should not by any means be fileted, as it is detrimental to the flavour."
So as was to be expected, our national variation is probably at most a bastardized version of a Greek dish. But who cares, it still tastes great. ;) I just made my first batch and it was delicious, I highly recommend it if you have the opportunity. :)
The FDA recommends below, which is how every restuarant I have ever heard of does it as well.
A recent survey of U.S. gastroenterologists has confirmed that seafood-borne parasitic infections occur in the U.S. with sufficient frequency to make preventive controls necessary during the processing of parasite-containing species of fish that are intended for raw consumption...[]..Freezing and storing at -4°F (-20°C) or below for 7 days (total time), or freezing at -31°F (-35°C) or below until solid and storing at -31°F (-35°C) or below for 15 hours, or freezing at -31°F (-35°C) or below until solid and storing at -4°F (-20°C) or below for 24 hours is sufficient to kill parasites. FDA's Food Code recommends these freezing conditions to retailers who provide fish intended for raw consumpution
Best Answer
Yes, marinating, or letting sit with a rub (which is what you're doing) does help fish flavor.
However, for most fish, there's no point in marinating filets or steaks "for hours", since fish flesh is very porous and spices, acids, oils and other flavorings achieve maximum penetration in less than an hour. The exception to this is dense-fleshed fish, such as swordfish, tuna, and opah, which can be marinated for longer -- up to 8 hours. Also, if you're applying a rub to whole, skin-on fish, you do want to wait an hour for the spices to "soak in".
The other exception is salt. There are recipes where you want to salt fish, and let it sit and drain for between 2 and 8 hours to firm up the flesh or change the flavor.
The above is paraphrased and summarized from Jay Harlow's West Coast Fish, and confirmed by my own experience.