Dockside Dave's and Snappers would probably be the two best on SPB that have a specific focus on seafood. Both have very fresh local fish. Snappers is more upscale. They have an early bird menu, etc, but don't let that dissuade you. I'm still a big fan of Dockside Dave's, and I actually prefer the SPB location over the Madeira Beach location. They still make the best grouper sandwich. A full half pound either beer battered, blackened, grilled, or breaded, for about $12.00. I always get the blackened grouper sandwich with provolone. The sweet pickles they serve on the side go so well with it. I also like their battered vegetable appetizer. It has onion rings, broccoli, mushrooms, etc. And their onion rings are some of the best ever. Really thick cut, heavy battered and sweet onion inside.
Also, a little up the road in Treasure Island is Middle Grounds Grill, which also has some creative fish dishes. It is also a little more upscale. And very fresh.