Tucked behind the new What's Up Dog, in a small service alley off of Pine (between Montgomery & Sansome), there's a walk-up place called Seafood Shack. Same owners as What's Up Dog. Serves fried seafood, including Fish & Chips and a Fried Fish Sandwich, among other things. I had the sandwich, and was pleasantly surprised, as the fish tasted fresher than I expected and was piping hot. Came with fries (crispy, salty, hot -- good fries, same as What's Up Dog's). The sandwich was generously stuffed with fish (I actually had to remove two pieces and eat them separately), tomatoes, sliced cucumbers and tartar sauce (not enough of the latter, but more is available at the counter). The menu mentioned that the bun was to be toasted, but I saw no evidence of that, and also the bun was a bit overwhelming in size, making the sandwich less tasty. I like the concept of a fried fish stand downtown, and I'd say they almost have it right, but the fish was a bit too bready (rather than battered) for my tastes, and they need to work on that bun. Price was $7.50, I think, for sandwich and fries.