I think you need to make sure your hook is set when you're fishing for something.
By that I mean, next time you find a dish you especially like, ask your server what makes it soo good. Say you can taste the xyz ingreds, but what is the elusive flavor that brings it together, is it cream or cream cheese, or what herbs does the chef use or inquire about the parts you can't quite define. IT's a hinting game, since they probably won't share the recipe.
Not sure what defines a crab/ blue crab "crust". Is it like a crab stuffing or a crab cake. Perhaps that is too much, and it was not as thick.
Today's Oceanaire menu offers Barramundi with spicy blue crab and thai chili butter or swordfish with chipotle carrots and black lentils. I love restaurants that offer menu creativity. Regrettably, I seldom can afford the luxury.
Further, clicking on Oceanaire's menus in other cities, they may be a chain, but do not offer the same dishes each resto. One place offers mahi mahi w/ blue crab and thai chili butter today.
I googled mahi mahi / crab crust, and I like the looks of this topping. even though it's not precisely what you ask.
Crab Topped Mahi Mahi with a Lemon Sauce over Brussels Sprouts
I tried google several combos. Including Google Images I think the best I found was g/ Images/ Fish with crab crust or Swordfish with crab crust.
Once you see something that looks similar to the dish you were served, click on the pic and review the recipe. even if the fish turns out to be cod or something else, it's the crab crust you are aiming for.