I don't know your clientele at all, but here are a few ideas off the top of my head:
Shrimp, scallop and salmon or cod "Dynamite." (Cook off fresh overstocked fish and save for Dynamite). Dynamite is a huge favorite with anglo customers at sushi bars and is very easy to make.
"Caviar Cream Sauce," a fumet based veloute with Japanese caviar like tobiko or masago. I'd probably go with red masago and green wasabi tobiko.
Maple, pepper glaze. I use this all the time with grilled and smoked fish.
"Margarita style," marinated in a limeade plus tequila brine before grilling.
"Etouffe," you can add freshly (partially cooked) grilled fish to a prepared sauce in a gratin and run it under the broiler to finish.
"Puttanesca," it's an olive, caper tomato sauce you can handle like etouffe.
A mild curry sauce -- either a Thai green or a mild gold,
That old debbil hollandaise
"Vercurzana" or "Creole" presentation.
With etouffe, puttanesca, veracruzana and creole, curry, hollandaise you can just sauce the plate (or better, a big flat bowl) and put a freshly grilled piece of fish on top. That's a lighter, fresher presentation. I don't know your clientele, you do.
"Po-boy" sandwiches with fried fish, lettuce, etc., and remoulade
Fish tacos, either "Baja style" (fried, with cabbage and mayo) or "Acapulco style," grilled served with a little bit of chopped onion, cilantro, salsa and a lime squeeze. (You don't need beautiful fillets for this, you can use fragments effectively.)
"Meuniere" and "Piccatta" (these are basically butter sauces, prepared in the pan after the fish is sauteed
Aioli or mayo may be spread on top of cooked fish and browned under the salamander
A tomato concasse
A fish pasta arrabiata
Shrimp with grits (or polenta)
You can brine fish, drain, dry and hold dried in the reefer. Brining helps a lot with grilled fish.
A simple grill rub with kosher salt, smoked paprika, black pepper, lemon peel for all grilled fish. Smoked paprika really works with grilling. Finish with a lemon/butter baste.
Offer nearly all fish choices fried or grilled.
Think about these four choices for frying: Tempura; Your standard -- whatever that is. If it's corn meal; then Panko as a third choice. If it's bread crumb, offer Corn Meal. If you're using bread crumb, consider changing to panko.
Tempura plate; and/or "Fish Fry."
I doubt your clients would be interested in anything too haute -- like an "olive cream." But if you want, I got.
Depending on available space, I would strongly consider adding a small electric or gas smoker with good low temperature capability such as a Cookshack. Since you'll most likely smoke, reserve and reheat, the smoker need not be in the kitchen proper. From the little I've been able to gather about your op, I think smoked fish would go over very well. For instance, "Fresh Atlantic Salmon with a Maple-Pepper Glaze, smoked over maple wood, and serrved with a Scandinavian Sour-Cream, Horseradish, Dill Sauce."
Smoked fish and smoked fish products like pates are outstanding for packaged retail as well as on the menu. A complimentary smoked wall-eye "spread" (or "pate," whichever word you think would go over better) with some good bread would be a nice touch and pull future sales as well. Or, perhaps better as part of an "Appetzier plate" with hushpuppies, etc.
Finally, after considering everything you already have, everything that's been suggested, and everything you've thought of on your own -- do less. Simplify the menu to a a decent number of choices you can do really well. A menu with too many choices is a real kitchen killer, and an invitation to too long storage, too much holding and too much reheating. Concentrate on things which can be prepared freshly, and keep it simple.
Happy to answer any specific questions,