If you want MEXICAN seafood, head to La Calle Doce on Skillman near Live Oak. (they have an Oak Cliff location, but this one gives you more options afterwards and is 5-10 from uptown/DTD. Great place.
Oceanaire for a true seafood restaurant is the right choice.
For an off the beaten path suggestion, try Kavala in North Oak Cliff. It's technically a mediterranean restaurant, but the chef came from Hatties and specializes in seafood. His seafood dishes are remarkable. I had a whole roasted branzini there last week that kicked all sorts of ***.
There will be a list of fresh stuff. You can get anything prepared however you like, simply grilled, blackened, broiled whatever. Among the regular, composed entrees, the most popular dish is probably the stuffed flounder. It's really good and good for people who aren't that excited about seared tuna and things like that.